Citation
Experimental and Numerical Study of Moisture Movement in Sealed Attics

Material Information

Title:
Experimental and Numerical Study of Moisture Movement in Sealed Attics
Creator:
Viswanathan, Aravind
Place of Publication:
[Gainesville, Fla.]
Florida
Publisher:
University of Florida
Publication Date:
Language:
english
Physical Description:
1 online resource (116 p.)

Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Civil Engineering
Civil and Coastal Engineering
Committee Chair:
PREVATT,DAVID
Committee Co-Chair:
GURLEY,KURTIS R
Committee Members:
MILLER,WILLIAM A

Subjects

Subjects / Keywords:
experimental-analysis -- moisture-movement -- numerical-analysis -- open-cell-spray-polyurethane-foam -- sealed-attics -- wood-durability
Civil and Coastal Engineering -- Dissertations, Academic -- UF
Genre:
bibliography ( marcgt )
theses ( marcgt )
government publication (state, provincial, terriorial, dependent) ( marcgt )
born-digital ( sobekcm )
Electronic Thesis or Dissertation
Civil Engineering thesis, M.S.

Notes

Abstract:
Sealed attics have spray polyurethane foam insulation to the underside of the wood roof sheathing. Due to differences in the moisture buffering properties and drying rates between the wood sheathing and the insulation, moisture laden air can condense and accumulate at the sheathing-to-insulation interface. High humidity in Florida sealed attics provides conducive conditions for moisture condensation. Poor workmanship of sealing the attic could cause air leakage into the attic which can potentially remove the excessive humidity. However, high air leakage can affect the indoor air comfort and compromise the energy efficiency of the home. This research seeks to study the effect of air leakage on the moisture content in the roof sheathing of sealed attics and the indoor air comfort. Four Florida homes with sealed attic construction were experimentally analyzed to quantify the roof sheathing moisture content and a numerical analysis was performed to predict the moisture content by varying the air leakage rates and occupant habits. Experimental analysis revealed that all four houses had little moisture accumulation at the wood sheathing and were safe from moisture problems. One of the four houses was retrofit with spray foam insulation and had the highest air leakage from the attic, three times greater than the other three houses. The excessive air leakage affected the thermal comfort of the house. Using the field-measured data, a numerical model was developed to study the effect of several parameters on the heat and moisture movement in the attic. The parameters are 1) building geometry, 2) building envelope air leakage, 3) duct leakage and 4) occupant habits. 1000 probabilistic variations of inputs were simulated to create a bandwidth of predicted attic temperature, humidity and roof sheathing moisture content. Field measurements from the four houses fall within this bandwidth. Once the inputs were made deterministic, the simulated bandwidth closely matched the field measurements showing the good predictive capacity of the toolkit. The research shows that outdoor to attic air leakage and building geometry has the least effect on the moisture movement in a sealed attic. Occupant habits and duct leakage have the highest effect on the roof sheathing moisture content. However, outdoor to attic air leakage greatly affects the indoor air comfort, hence the attic should be sealed with least air leakage to increase the indoor thermal air comfort. ( en )
General Note:
In the series University of Florida Digital Collections.
General Note:
Includes vita.
Bibliography:
Includes bibliographical references.
Source of Description:
Description based on online resource; title from PDF title page.
Source of Description:
This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Thesis:
Thesis (M.S.)--University of Florida, 2017.
Local:
Adviser: PREVATT,DAVID.
Local:
Co-adviser: GURLEY,KURTIS R.
Statement of Responsibility:
by Aravind Viswanathan.

Record Information

Source Institution:
UFRGP
Rights Management:
Applicable rights reserved.
Classification:
LD1780 2017 ( lcc )

Downloads

This item has the following downloads:


Full Text

PAGE 1

1 EXPERIMENTAL AND NUMERICAL STUDY OF MOISTURE MOVEMENT IN SEALED ATTICS By ARAVIND VISWANATHAN A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2017

PAGE 2

2 2017 Aravind Viswanathan

PAGE 3

3 To my parents, for their endless love, support and encouragement

PAGE 4

4 ACKNOWLEDGMENTS Viswanathan and Viswanathan Srinivasan. My parents have been my fiercest admirers and critics sculpting my way of lif e. Since I stepped into the US, one person has shaped my career path and character, given me q uality education, high level mentorship and a powerful work experience. I would like to sincerely thank my advis o r and committee head, Dr. David O. Prevatt. I th ank my committee members, Dr. Kurtis R. Gurley and Dr. William A. Miller for their extended support and mentorship for my thesis. I would like to thank all my school teachers to have instilled quality education and critical thinking skills in me. I thank G od, for providing me a wonderful and healthy life. I thank all my colleagues in the Prevatt research group for having helped me to achieve this personal milestone especially Arpit Bhusar, Mitali Talele, Anshul Shah, Anant Jain I thank my friends Vaishali Vijaykumar, Shriraam Ravindran, Trishanth Katepali, Vignesh Ravi for being my second family 9000 miles away from home. My brother Akshay Viswanathan has been a moral support for me and my parents while I have been away from home and I thank him for all the memories and good will throughout my life. Additionally, this research was supported by the Florida Building Commission and the Florida Roofing and Sheet Metal Contractors Association. I thank the sponsors for their interest and funding in this research. The conclusions of this thesis do not necessarily represent those of the sponsors.

PAGE 5

5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ ............... 4 LIST OF TABLES ................................ ................................ ................................ ........................... 8 LIST OF FIGURES ................................ ................................ ................................ ......................... 9 LIST OF ABBREVIATIONS ................................ ................................ ................................ ........ 13 ABSTRACT ................................ ................................ ................................ ................................ ... 14 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .................. 16 Knowledge Gaps in Sealed Attic Constructions ................................ ................................ ..... 16 Research Overview ................................ ................................ ................................ ................. 18 Layout of Thesis ................................ ................................ ................................ ..................... 19 2 REVIEW OF LITERATURE ................................ ................................ ................................ 21 Vented and Unvented Attics in Single Family Residential Houses ................................ ....... 21 Climate Zones in the USA ................................ ................................ ................................ ...... 23 Building America (BA) Climate Zone Map ................................ ................................ .... 23 International Energy Conservation Cod e (IECC) Climate Zone Map ............................ 24 Properties of Construction Materials ................................ ................................ ...................... 25 Polyurethane Foam Insulation ................................ ................................ ......................... 26 Wood as an Engineering Material ................................ ................................ ................... 27 Moisture Movement in Unvented Attics ................................ ................................ ................ 27 Parameters Affecting Moisture Movement ................................ ................................ ..... 27 Previous Experimental Testing of Unvented Attics ................................ ........................ 29 Previous Numerical Testing of Unvented Attics ................................ ............................. 31 Air Leakage in Residential Houses ................................ ................................ ......................... 32 Fan Pressurization Tests ................................ ................................ ................................ .. 34 Duct blast er equipment ................................ ................................ ............................. 34 Blower door equipment ................................ ................................ ............................ 35 Calculation of Air Leakage Areas ................................ ................................ ................... 36 Selection of Parameters Affecting Heat and Moisture Movement ................................ ......... 37 Building Envelope Air Leakage ................................ ................................ ...................... 38 Attic Duct Leakage ................................ ................................ ................................ .......... 41 Indoor Heat and Moisture Generation ................................ ................................ ............. 43 Thermostat Set Points and Mechanical Ventilation ................................ ........................ 45 3 EXPERIMENTAL TEST ON FLORIDA SEALED ATTIC HOUSES ................................ 46

PAGE 6

6 Selection of Field Houses ................................ ................................ ................................ ....... 46 Description of Field Hou ses ................................ ................................ ................................ ... 47 House 1 West Palm Beach ................................ ................................ ........................... 47 House 2 Venice ................................ ................................ ................................ ............. 49 House 3 O rlando ................................ ................................ ................................ ........... 50 House 4 Gainesville ................................ ................................ ................................ ...... 52 Field Data Acquisition ................................ ................................ ................................ ............ 53 House Owner Questionnaire ................................ ................................ ............................ 53 Air Leakage Test ................................ ................................ ................................ ............. 56 Duct blaster test ................................ ................................ ................................ ........ 56 Blo wer door test ................................ ................................ ................................ ....... 57 Guarded duct blaster test ................................ ................................ .......................... 58 Guarded blower door test ................................ ................................ ......................... 59 Attic Instrumentation ................................ ................................ ................................ ....... 60 4 RESULTS OF EXPERIMENTAL TESTING ................................ ................................ ........ 64 Air Leakage Test Results ................................ ................................ ................................ ........ 64 Heat and Moisture Flow in Selected Florida Sealed Attic Houses ................................ ......... 66 Heat Movement in Selected Florida Sealed Attic Houses ................................ ............... 67 Relationship between Temperature, Humidity and Moisture ................................ .......... 69 Moisture Content in Roof Sheathing ................................ ................................ ............... 74 Effect of Hurricane Matthew on Heat and Moisture Flow in House 1 ........................... 76 Indoor Air Thermal Comfort ................................ ................................ ................................ .. 78 5 PROBABILISTIC RISK ASSESSMENT TOOLKIT ................................ ............................ 80 Description of Software Packages ................................ ................................ .......................... 80 Building Energy Optimization Software (BEopt) ................................ ........................... 80 Energy Plus Modelling Software ................................ ................................ ..................... 81 WUFI 1D Modelling Software ................................ ................................ ........................ 83 Probabilistic and Deterministic Simulations ................................ ................................ .......... 84 Generation of Indoor Heat and Moisture Tool ................................ ................................ 86 Probabilistic Simulations ................................ ................................ ................................ 89 Attic temperature and relative humidity ................................ ................................ ... 90 Roof sheathing moisture content ................................ ................................ .............. 92 Correlation of Simulated Moisture Contents with Probabilistic Inputs .......................... 95 Deterministic Simulations ................................ ................................ ............................... 96 Attic temperature and relative humidity ................................ ................................ ... 96 Roof sheathing moisture content ................................ ................................ .............. 98 Parametric WUFI simulations with varying attic air leakage rates .......................... 99 Parametric WUFI simulations with varying insulation R value ............................ 101 6 CALIBRATION OF THE PRAT WITH MEASURED DATA ................................ ........... 103 Scatter Plot s of Measured and Simulated Data ................................ ................................ ..... 104 Error in Prediction ................................ ................................ ................................ ................ 105

PAGE 7

7 7 CONCLUSIONS ................................ ................................ ................................ .................. 108 Future Scope ................................ ................................ ................................ ......................... 110 Applications ................................ ................................ ................................ .......................... 111 LIST OF REFERENCES ................................ ................................ ................................ ............. 112 BIOG RAPHICAL SKETCH ................................ ................................ ................................ ....... 116

PAGE 8

8 LIST OF TABLES Table page 1 1 Insulation R value Requirement, Florida Building Code ................................ .................. 17 2 1 Climate zone of selected field houses ................................ ................................ ................ 25 3 1 Characteristics of field houses ................................ ................................ ........................... 47 3 2 Material properties of superstructur e in all four houses ................................ .................... 55 3 3 Instruments scanned by Campbell CR1000 micro logger ................................ ................. 61 3 4 Location of temperature, relative humidity and moisture sensors ................................ ..... 62 4 1 Envelope Air Leakage Results ................................ ................................ ........................... 64 4 2 Duct leakage results ................................ ................................ ................................ ........... 66 4 3 Percentage time house conditions were outside of ASHRAE comfort zone ..................... 79 5 1 Inputs for PRAT ................................ ................................ ................................ ................. 84 5 2 Simula ted house and field house characteristics ................................ ................................ 85 5 3 Type of inputs used for PRAT simulations ................................ ................................ ........ 86 5 4 Details of probabilistic and dete rministic inputs for PRAT simulations ........................... 88 5 5 Probabilistic inputs for PRAT ................................ ................................ ............................ 89 5 6 WUFI parametric simulations ................................ ................................ ............................ 99

PAGE 9

9 LIST OF FIGURES Figure page 1 1 Climate zones in Florida as defined in International Energy Conservation Code 2012 .... 17 2 1 Vented and unvented attics. ................................ ................................ ............................... 22 2 2 Air and heat movement in a sealed attic house.. ................................ ................................ 23 2 3 US climate zone map based on Buildi ng America climate map ................................ ........ 24 2 4 US climate zone map based on International Energy Conservation Code. ....................... 25 2 5 Open cell and closed cel l insulation in microscopic level ................................ ................ 26 2 6 Moisture movement onto the roof ridge ................................ ................................ ............ 28 2 7 Attic relative humidity for a summer week in Charleston, South Carolina ....................... 30 2 8 Relationship of relative humidity and moisture content of wood ................................ ...... 31 2 9 Effects of air leakage on various parameters ................................ ................................ ..... 33 2 1 0 Duct blaster test equipment. ................................ ................................ ............................... 35 2 11 Blower door equipment ................................ ................................ ................................ ...... 35 2 12 Intermediate air flow rate combined with high vapor pressure gradient can cause RH exceeding 100% ................................ ................................ ................................ ................. 39 2 13 Theoretical heat and moisture movement in an air le akage pa th causing condensation ... 40 2 14 Simulated indoor moisture and ASHRAE Sta ndard 160 for varying occupants ............... 44 3 1 Selected field hous es in Florida climate zones 1 and 2 ................................ ..................... 46 3 2 Front view of house 1 in West Palm Beach, FL. ................................ ............................... 48 3 3 Sealed attic of house 1 ocSPF in sulation under the sheathing and ductwork .................. 48 3 4 Front view of house 2 in Venice, FL. ................................ ................................ ................ 49 3 5 Sealed attic of house 2 showing ocSPF under sheathing and ductwork in the attic .......... 50 3 6 Front view of house 3 in Orlando, FL. Photo courtesy of author. ................................ ..... 51 3 7 Sealed at tic of house 3 showing ocSPF under roof sheathing and ductwork running through the attic ................................ ................................ ................................ ................. 51

PAGE 10

10 3 8 Front view of house 4 in Gainesville, FL ................................ ................................ .......... 52 3 9 Sealed attic of house 4 showing ocSPF below the roof sheathing and ductwork running through the attic ................................ ................................ ................................ .... 53 3 10 House owner questionnaire for house 4 in Gainesville showing salient features of the house documented for use in numerical toolkit ................................ ................................ 54 3 11 Total duct leakage test to measure the duct leakage into the conditioned space and the attic. ................................ ................................ ................................ .............................. 56 3 12 Building envelope air leakage test to measure the air leakage into the conditioned space ................................ ................................ ................................ ................................ ... 57 3 13 Guarded duct blaster test to measure the air leakage f rom ducts into the attic. ................. 58 3 14 Guarded blower door test to measure the air leakage from attic to the outside ................. 59 3 15 Location o f temperature, relative humidity and moisture sensors in each of the four houses ................................ ................................ ................................ ................................ 62 3 16 Cross section of sealed attic showing placement of thermistors, relative humidity sensors and moisture p ins in demonstration homes ................................ ........................... 63 3 17 Temperature, relative humidity and moisture pins installed at the interface of the wood sheathing and the spray polyurethane foam insulation. ................................ ........... 63 4 1 Total building envelope leakage results for test houses. ................................ .................... 65 4 2 Total duct leakage results for test houses. ................................ ................................ ......... 65 4 3 Daily averaged temperatures measured from various locations in house 2 and house 4. ................................ ................................ ................................ ................................ ......... 67 4 4 Measured attic and indoor temperatures. ................................ ................................ ........... 68 4 5 Diurnal variation in measured temperatures for a weekly period in summer. ................... 69 4 6 Measured attic air temperature and humidity for house 2 and house 4. ............................ 70 4 7 Measured sheathing temperature and humid ity for house 2. ................................ ............ 71 4 8 Weekly attic and indoor temperature for house 2 in Venice and house 4 in Gainesville. ................................ ................................ ................................ ........................ 72 4 9 Measured sheathing temperature and humidity for house 4. ................................ ............. 73 4 10 Measured roof sheat hing moisture content for a summer week from house 1in West Palm Beach. ................................ ................................ ................................ ....................... 74

PAGE 11

11 4 11 Roof sheathing moisture content in four houses, June 2016 to June 2017. ....................... 75 4 12 Hurricane Matthew tracking al ong the east coast of Florida. ................................ ............ 76 4 13 Time history of moisture content, temperature and relative humidity for house 1 in West Palm Be ach for October 3 rd to October 10 th 2016. ................................ .................. 77 4 14 Indoor thermal comfort zone. ................................ ................................ ............................ 78 4 15 Comparison of measured indoor climate and ASHRAE Standard 55 thermal comfort zone. ................................ ................................ ................................ ................................ ... 79 5 1 Generic house model ................................ ................................ ................................ .......... 85 5 2 Interior latent heat generation for house 2 and house 4 from the GIHM tool ................... 87 5 3 Interior sensible heat generation for house 2 and house 4 from the GIHM tool ............... 87 5 4 PRAT simulations ................................ ................................ ................................ .............. 90 5 5 PRAT simulations and field measurements ................................ ................................ ....... 91 5 6 Generic roof section model in WUFI. ................................ ................................ ................ 93 5 7 PRAT simulated roof sheathing moisture content. ................................ ............................ 93 5 8 PRAT simulations and field measurements of roof sheathing moisture content .............. 94 5 9 Correlation coefficient of input parameter on peak moisture content ............................... 95 5 10 1000 PRAT simulated attic temperature and house 2 measured attic temperature ........... 96 5 11 1000 PRAT simulated attic temperature and house 4 measured attic temperature ........... 97 5 12 1000 PRAT simulated attic RH and house 2 m easured attic RH ................................ ...... 97 5 13 1000 PRAT simulated attic RH and house 4 measured attic RH ................................ ...... 97 5 14 Actual roof models in WUFI ................................ ................................ ............................. 98 5 15 PRAT simulated moisture content using actual outdoor temperature compared to house 4 measured moisture content ................................ ................................ ................... 98 5 16 PRAT simulated moisture content using actual outdoor temperature compared to house 4 measured moisture content ................................ ................................ ................... 99 5 17 Parametric simulations performed for a deterministic roof model. ................................ 100 5 18 WUFI simulations for house 2 and house 4 with different R value of insulation ........... 102

PAGE 12

12 6 1 Comparison of 24 hour average of measured and simulated para meters for house 2. .... 104 6 2 Comparison of 24 hour average of measured and simulated parameters for house 4. .... 105 6 3 C oefficient of v ariation of root mean squared error for house 2 and house 4 in summer and winter ................................ ................................ ................................ ........... 106 6 4 N ormal mean bias error for house 2 and house 4 in Summer and Winter. ...................... 107

PAGE 13

13 LIST OF ABBREVIATIONS ACH Air changes per hour ASHRAE American Society of Heating, Refrigerating and Air Conditioning Engineers BEopt Building Energy Optimization Software ccSPF closed cell Spray Polyurethane Foam CFM cubic foot per minute CV RMSE Coefficient of Variation of Root Mean Squared Error CZ climate zone FBC Florida Building Commission FECC Florida Energy Conservation Code FRSA Florida Roofing and Sheet M etal Contractors Association GIHM Generation of Indoor Heat and Moistu re Tool HVAC Heating, Ventilation and Air Conditioning IECC International Energy Conservation Code LBNL Lawrence Berkley National Laboratory NMBE Normal Mean Bias Error ocSPF open cell Spray Polyurethane Foam OSB oriented strand board PRAT Pr obabilistic Risk Assessment Toolkit RECS Residential Energy Consumption Survey RH relative humidity T temperature WUFI Wrme Und Feuchte Instationr

PAGE 14

14 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science EXPERIMENTAL AND NUMERICAL STUDY OF MOISTURE MOVEMENT IN SEALED ATTICS By Aravind Viswanathan August 2017 Chair: David O. Prevatt Major: Civil Engineering Sealed attics h ave spray polyurethane foam insulation to the underside of the wood roof sheathing. Due to d ifferences in the moisture buffering properties and drying rates between the wood sheathing and the insulation, moisture laden air can condense and accumulate a t th e sheathing to insulation interface High humidity in Florida sealed attics provide s conducive conditions for moisture condensation. Poor workmanship of sealing the attic could cause air leakage into the attic which can potentially remove the excessive hum idity. However, high air leakage can affect the indoor air comfort and compromise the energy efficiency of the home This research seeks to study the effect of air leakage on the moisture content in the roof sheathing of sealed attics and the indoor air c omfort. Four Florida homes with sealed attic construction were experimentally analyzed to quantify the roof sheathing moisture content and a numerical anal ysis was performed to predict the moisture content by varying the air leakage rates and occupant habi ts. Experimental analysis revealed that all four houses had little moisture accumulation at the wood sheathing and were safe from moisture problems. One of the four houses was retrofit with spray foam insulation and had the highest air leakage from the at tic,

PAGE 15

15 three times greater than the other three houses. The excessive air leakage affected the thermal comfort of the house. Using the field measured data, a numerical model was developed to study the effect of several parameters on the heat and moisture mo vem ent in the attic. The parameters are 1) building geometry, 2) building envelope air leakage, 3) duct leakage and 4) occupant habits. 1000 probabilistic variations of inputs were simulated to create a bandwidth of predicted attic temperature, humidity an d roof sheathing moisture content. Field measurements from the four houses fall within this bandwidth. Once the inputs were made deterministic, the simulated bandwidth closely matched the field measurements showing the good predictive capacity of the toolk it. The research shows that outdoor to attic air leakage an d building geometry has the least effect on the moisture movement in a sealed attic Occupant habits and duct leakage ha ve the highest effect on the roof sheathing moisture content. However, outdoo r to attic air leakage greatly affects the indoor air comfort, hence the attic should be sealed with least air leakage to increase the indoor thermal air comfort.

PAGE 16

16 CHAPTER 1 INTRODUCTION Knowledge Gaps in Sealed Attic Constructions The International Energy Conservation Code (IECC), the International Residential Code (IRC), the ASHRAE 90.1 and other state and local codes are directing the construction industry towards a more energy efficient and sustainable future. Single family residential homes are built w ith new techniques and improved materials to conserve energy. One such technique is sealing the attic space from the outside environment by removing the attic vents such as ridge and soffit vents. By sealing the attic, the conditioned air leaking from the ductworks placed inside an attic is entrapped leading to a semi conditioned attic space. In typical ventilated or vented attics, the attic floor is insulated by a thermal barrier to reduce heat leaking from the living space into the attic. In sealed attics this insulation layer is moved to the roof line. Spray applied polyurethane foam insulation is most commonly used as the insulation underneath the wood roof sheathing. Florida has two climate zo nes 1 and 2 as defined by the International Energy Conser vatory Code ( F igure 1 1 ) The two climate zones have hot humid climate. Baechler (2015) defines the hot humid climate as a region that receives more than 20 inches (50 cm) of annual precipitation and where one or both of the following occur: A 67F (19.5C) or higher wet bulb temperature for 3,000 or more hours during the warmest six c onsecutive months of the year; 73F (23C) or higher wet bulb temperature for 1,500 o r more hours during the warmest six consecutive months of the year. The Florida Building Code provides prescriptive and whole building performance guidelines for attic insulation for both climate zones ; it does not distinguish requirements between the at tic floor and the roof deck Table 1 1.

PAGE 17

17 Figure 1 1 Climate zones in Florida as d efined in International Energy Conservation Code 2012 Table 1 1 Insulation R value Requirement, Florida Building Code FBC Attic Floor A Prescriptive Req. Attic Floor B Pe rformance Req. Roof Deck C Sealed Attic Req. CZ 1 CZ 2 CZ 1 CZ 2 CZ 1 CZ 2 2001 R 30 R 30 R 19 R 19 NA NA 2004 R 30 R 30 R 19 R 19 NA NA 2007 R 30 R 30 R 19 R 19 NA NA 2010 R 30 R 30 R 19 R 19 NA NA 2012 R 30 R 30 R 19 R 19 NA NA 2014 R 30 R 38 R 19 R 19 R 0 / R 5 R 0 / R 5 A. Prescriptive Requirement for attic floor. B. Performance Requirement for attic floor, subject to R405.2.1 of FECC, 2014, R405.2.1 ceiling Insulation. C. Impermeable spray foam has no R value requirement abo ve the deck. R 5 is required above the deck for permeable spray foam insulation applied to the underside of the sheathing (see R806.5 requirement, 2014). Table 1 1 displays the changes in R value requirement s for attic floor and roof deck insulation in s everal editions of the Florida Building Code from 2001 through 2014 R value represents the thermal insulating capacity of a material. The h igher the R value, the higher is its insulating capacity. Open cell s pray polyurethane foam is an air permeable ins ulation and did not have any prescription or performance requirements prior to 2014 in the Florida Building Code.

PAGE 18

18 In the 2014 version of the Florida Building Code an R 5 rigid insulation layer is required above deck when air permeable (spray foam) insulat ion is directly applied under the roof deck for condensation control. (Section R806.5) Builders typically try t o achieve either the R 19 or the R 30 insulation requirements by apply ing spray foam to the underside of the roof deck either 5 in thick or 7 in. thick layers respectively of ocSPF Poor workmanship can lead to attic air leakage s crossing t he plane of the attic floor or the plane of the two roof decks. Attic a ir leakage is an important factor affecting moisture movement in an attic. Air leakage combined with lower temperatures can produce favourable conditions for condensation to occur at the roof sheathing to insulation interface. Condensation at the sheathing to insulation interface can lead to mold formation and deterioration of the wood shea thing. These moisture induced problems occur generally when the moisture content in wood exceeds 20% and is deemed risky at 30% Bergman (2010) Research Overview Sealed attic constructions have been studied previously to understand the condensation potential (Rudd et al. (1998) Miller et al. (2013) Ueno et al. (2015) Prevatt et al. (2016) ) The risk due to condensation is higher in Florida because of high humidity in the attic. Moisture move ment in sealed attic construction depend s on the roof type, insulation thickness, occupant behavior, air leakage parameters and exterior climate. T he number of occupants affect s the interior latent heat generation and moisture generation rates. These two p arameters greatly affect the moisture movement within the house and ultimately into the attic. While it is important to analyze the behavior of these parameters in occupied field houses, it is a daunting task to obtain the necessary information from every single house A risk assessment toolkit is necessary to capture the sensitivity of the different parameters on the moisture movement in an attic. This research combines field measured experimental results with

PAGE 19

19 a numerical toolkit to predict the moisture r isk in semi conditioned sealed attics and to quantify the correlation between different parameters affecting the moisture movement in a sealed attic. A Probabilistic Risk Assessment Toolkit (PRAT) developed by Oak Ridge National Laboratory is used in conju nction with field measured data to estimate the roof sheathing moisture contents in residential sealed attic constructions of Florida. The PRAT toolkit can predict the roof sheathing moisture contents given a set of input parameters like building geometry, air leakage parameters and occupant habits. The toolkit uses a generic model and probabilistically varied inputs to predict the roof sheathing moisture content for any house in climate zone 2A. For predicting the moisture contents in the four Florida hous es, field measurements (Prevatt et al. (2016) ) are used as input parameters to the toolkit. Field measurements include building envelope air leakage parameters, heat and moisture flow in the attic and occupant habits. This research deter mined that the roof sheathing of the four Florida houses were safe from moisture condensation. Poor workmanship in spray foam retrofitted attics can cause high attic air leakage leading to reduction in indoor air comfort. The numerical toolkit coupled with field measurements can predict the existing moisture contents in the roof sheathing with good accuracy. Layout of Thesis The remainder of this thesis is organized as follows. Chapter 2 describes the literature review performed on the behavior of sealed a ttics and previous analytical and experimental studies on the moisture flow in sealed attics. Chapter 3 describes the experimental testing conducted on sealed attic houses in Florida Chapter 4 presents the results of the experimental testing performed on the four Florida houses. Chapter 5 discusses the structure and working of the Probabilistic Risk Assessment Toolkit. Chapter 5 also compares the field measured and

PAGE 20

20 PRAT simulated indoor and attic temperature and humidity as well as the roof sheathing moist ure content. Chapter 6 presents the statistical analysis performed to measure the prediction accuracy of the PRAT. Chapter 7 is a summary of the major findings and conclusions from the project, including the limitations of the model and critical areas need ing further research.

PAGE 21

21 CHAPTER 2 REVIEW OF LITERATURE Vented and Unvented Attics in Single Family Residential Houses Light wooden framed structures (LWFS) are common in Europe and the United States. Constructional ease and do it yourself attitude of the Americans ha s led to the popularity of the LWFS. Over 77% of the single family residential houses in southern US are slab on grade LWFS, U.S. Census Bureau (2011) Typical residential houses have conditioned li ving spaces and unconditioned spaces such as attics and crawlspaces. Attics are enclosed spaces located above the ceiling and typically they fall outside the thermal insulation envelope and the conditioned space of the house. In modern residential constru ction, t he thermal comfort within the living (or occupied) space is maintained by the Heating Ventilating and Air Conditioning (HVAC) system The HVAC supplies conditioned air through a series of ducts to the conditioned space. A nother series of return a ir ducts recycles air from the conditioned space back to the HVAC In many houses these ducts are conveniently placed within the attic of the house Often the HVAC system is placed inside the attic or garage to maximize available space within the conditi oned space of the house Conventional attic construction provides a continuous air flow throu ridge and gable vents, F igure 2 1 Conventional attics are referred to herein as unconditioned, vented attics; an d, it is not part of the buildings thermal envelope. In contrast, a non ventilated, semi conditioned ( unvented ) attic is made part of the thermal envelope. The attic space is encapsulated by spraying polyurethane foam under the roof sheathing and any duct leakage of conditioned air is exploited to semi condition the attic, F igure 2 1 putting ducts in conditioned or semi conditioned space is typically one of the most energy savings features, with the po tential to be one of the most cost effective.

PAGE 22

22 Figure 2 1 Vented and unvented attics. Gray shaded area represents conditioned building enclosures Air and heat movement plays a key role in affecting the moisture movement in an attic. Air movement predom inantly occurs due to large openings like doors and windows. The outdoor climate plays a major role in influencing the indoor conditioned space temperatures. Air can also leak through gaps in doors and windows, constructional defects and small unintended o penings. This air movement is often termed as background air leakage. Heat can move through three different mechanisms from the building envelope to the outdoor environment or vice versa: conduction, convection and radiation. Conduction is the transfer of heat through a material. Convection is the movement of heat carried by fluids, which occurs primarily by winds or buoyance Hot air tends to move upward due to less density and denser cold air tends to move downwards. Radiation is the main source of heat t ransfer in the outdoor environment caused by solar radiation. The air and heat flow in a typical sealed attic house is shown in Fig ure 2 2

PAGE 23

23 Figure 2 2 Air and heat movement in a sealed attic house Brown color represents wooden members and yellow represents spray polyurethane foam insulation. Climate Zones in the USA The United States of America is a vast country with varying landscapes along the northern hemisphere of the world. It is important to know the local climate in a particular re gion of the country to study the heat and moisture movement in buildings. Hence a brief study on the climate zones of the USA was performed to identify the climate characteristics of residential houses in Florida. Building America (BA) Climate Zone Map In collaboration with Building Science Corporation, developed a climate zone map of the US for the Building America program. The map developed, divided US into eight regions. Since most states fall within multiple climate zones, a county wise guide was prepared (Briggs et al 2015). This program was developed to provide more climate and building information to builders.

PAGE 24

24 Florida falls under the hot humid climate zone. Baechler (2015) defines the hot humid climate as a region that receives more than 20 inches (50 cm) of annual precipitation and where one or both of the following occur: A 67F (19.5C) or higher wet bulb temperatur e for 3,000 or more hours during the warmest six consecutive months of the year; or 73F (23C) or higher wet bulb temperature for 1,500 or more hours during the warmest six consecutive months of the year. Figure 2 3 US c limate z one m ap based on Building America climate m ap Source : Building Energy Codes Program (2009) International Energy Conservation Code (IECC) Climate Zone Map In ea Laboratory (PNNL) prepared a climate map of USA based on analysis from 4775 weather sites. This map divided USA into 8 zones (1 to 8) based on temperature and 3 regions (moist dry and marine) based on moisture as shown in Figure 2 4 This new map was setup along county boundaries to help builders easily determine the climate zones. This map was adopted first by the 2004 IECC Supplement and it appeared in the ASHRAE 90.1 in 200 4. ASHRAE 90.1 is used by builders for commercial purposes while various state governments have adopted the IECC 2009

PAGE 25

25 code for low rise residential structures. IECC 2009 provides information about several building envelope requirements such as R value, fen estration factor for different climate zones. Florida has two IECC climate zones, 1A and 2A. Figure 2 4 US c limate zone m ap based on International Energy Conservation Code Source : Baechler (2015) Table 2 1 Climate zone of selected field h ouses House Location County BA Climate Zone IECC Climate Zone West Palm Beach Palm Beach FL Hot Humid 2A Venice Sarasota FL Hot Humid 2A Orlando Orange FL Hot Humid 2A Gainesville Alachua FL Hot Humid 2A Properties of Construction Materials This study involves quantifying the moisture content in the roof sheathing of residential sealed attics. The physical interaction of moisture laden air with the wood sheathing and the insulation layer create s a favorable condition for moisture condensation to occur. It is important

PAGE 26

26 to study the material properties of wood and spray foam to identify the parameters affecting the condensation potential. Polyurethane Foam Insulation Spray applied polyurethane ins ulation is of two types. i) open cell spray polyurethane foam (ocSPF) and closed cell spray polyurethane foam insulation (ccSPF). Polyurethane foams consist of two components, an A side and a B side. Both the components are mixed on site before spray appli cation. The A side is a mixture of 50% methylene diphenyl diisocyanate and 50% polymeric methylene diphenyl diisocyanate, two chemicals which are highly reactive when mixed with water or each other. When both the components are mixed, an exothermic reactio n produces low conductivity gases or water, making the B side a blowing agent. The exothermic reaction causes bubbles to form, and the curing of such bubbles determines the density of the foam. Water blown foams have low densities and are open cell foams. They are permeable to vapor transmission and are non structural, but h ave high resistance to air flow. The differences in material properties of ocSPF and ccSPF is defined in Ecologic (2009) The d ensity of ocSPF ranges from 0.5 to 1.2 lb per cubic foot, with R values ranging from R 3.6/inch to R 4.5/inch. The two leading manufacturers of ocSPF are Sealection500 and Icynene. When applied, this foam instantly expands more than 100 times its original size. The density of ccSPF ranges from 1.7 to 2.2 lb per cubic foot, with R values ran ging from R 5/inch to R 7/inch. Figure 2 5 Open cell and c losed cell insulation in microscopic level (Foam 2014)

PAGE 27

27 Open cell spray polyurethane foam is vapor permeable, having a vapor permeance of about 19 perms for a 3 in thickness o f foam. In comparison closed cell spray polyurethane foam insulation is impermeable and has a permeance of about 0.5 Perm for a 3 in thickness of foam, Kumaran (2006) Wood as an Engineering Material Evaluating mois ture content in wood is important to calculate the structural capacity and durability. Moisture is held in wood in two ways; as free water in cell cavities and as bound water in capillaries of cell walls. The bound water content affects the structural perf ormance. The initial moisture content in wood members used for construction in southeastern USA is around 11%, Bergman (2010) Typically, moisture content levels greater than 20% have been found to cause decay and deteriorat ion of wood, Bergman (2010) Long time exposure to rain water leaking into th e roof can cause even further damaging moisture contents, exceeding 30% and can accelerate the decay process. The moisture content in wood is generally calculated by Eq. 2 1: ( 2 1 ) Moisture Movement in Unvented Attics Parameters Affecting Moisture Movement Temperature and humidity inside and outside the thermal building envelope affects the moisture movement insi de a house. The indoor temperature is controlled by the HVAC systems climate, the average peak temperatures in Summer can rise above 80 F. The outdoor relative humidity levels are inversely related to the outdoor temperatures. During peak temperatures at

PAGE 28

28 the daytime, the relative humidity levels are the lowest but the moisture carrying capacity of the air increases The indoor humidity is affected by five factor s: 1. Interior moisture generation 2. House ventilation 3. Air infiltration 4. HVAC scheduling 5. Moisture sorption or desorption in materials Pallin (2014) identified several parameters affecting the moisture movement in unvented attic constructions. Building geometry, occupant behavior, interior latent heat and moisture generation, exterior cl imate as well as leakage areas from i) living space to exterior, ii) attic space to exterior and iii) attic floor were determined to be the most affecting parameters. Lstiburek (2016) conducted field studies to examine the moisture content at different lo cations in a roof and observed higher moisture content at the ridge (highest point in roof) The reason behind this observation is termed as the ping pong effect by Lstiburek (2016). T he water molecules tend to shift towards the ridge due to the buoyancy e ffect Moist air is more buoyant than dry air. It is interesting to note that the research house used for the study had a dehumidifier in the semi conditioned sealed attic. Lstiburek concluded the study with high recommendations of using a dehumidifier in an ocSPF sealed attic in the hot humid climates of USA. Figure 2 6 Moisture movement onto the roof ridge, Lstiburek (2016)

PAGE 29

29 Previous Experimenta l Testing of Unvented Attics Rudd (1999) studied the effects of moving the insulation from the ceiling to the roof plane, producing unvented semi conditioned attics. Based on computer simulations, he observed that the higher attic relative humidity at nighttime drives the moisture into the wood and the solar radiation pushes moisture back into the attic during the day. Lstiburek (2006) recommended climate zone specific construction methods for unvented attics. For all climate zones, Lstiburek suggested the use of a thermal barrier and air barrier separating the insulation from the interior of the house. Rudd found out that the peak temperatures in the wood sheathing in an unvented attic is about 17 F greater than the sheathing peak temperatures in a vented attic. Parker et al. (2002) performed analytical studies to determine the impact of roofing systems on the energy consumption of the house. Parker studied seven roof systems both vented and unvented with a combination of dark colored shingles and reflective shingles. Sealed attics with R 19 insulation at the underside of the sheathing and dark shingles had energy savings of 6 11% in cooling energy use over vented attics wit h dark shingles. Energy savings of about 20% in cooling energy use was observed with the use of reflective shingles. Shreyans (2011) conducted field evaluations before and after installing ccSPF insulation under the roof sheathing in a vented attic home. He observed a 5% reducti on in energy consumption and 20 o F reduction in peak summer attic temperatures. Shreyans used WUFI 1D to simulate the l ong term moisture content of the sheathing and observed a potential for accumulation of moisture greater than 20% in ccSPF retrofitted attics susceptible to air leaks and roof leaks. The peak moisture content in the simulated unvented roof assembly was lo wer than the peak moisture contents in a vented roof assembly. For a Florida sealed attic with ocSPF insulation under the roof deck, (Colon 2011) studied the hygrothermal behavior of an ocSPF unvented attic house in Florida for a whole year.

PAGE 30

30 Colon observed diurnal relative humidity (RH) fluctuations in the attic and seasonal variation of moisture in the attic. An increase in the moisture content levels was observed during the winter months of October through Februa ry, however within the 20% threshold for mold growth. Miller et al. (2013) measured the heat and moisture flow in an unoccupied research house with different roof configurations. The control attic had an R 38 insulation layer at the ceiling level. Two sea led attics with R 22 ocSPF and R 22 ccSPF under the roof deck were analyzed in the study. The vented attics had less than 60% relative humidity during the day time for seven contiguous days in summer. However, the sealed attics had 100% relative humidity o n two of the measured seven days during the day time. The relative humidity had an inverse trend to that of a vented attic and remained above 60% throughout the seven days. Figure 2 7 Attic relative humidity for a summer week in Charleston, South Carol ina (Miller et al. 2013) Boardman et al. (2017) compared the relative humidity of wood and the moisture c ontent in wood from various studies and observed that moisture contents over 20% occur when the relative humidity of the wood is near saturation levels.

PAGE 31

31 Figure 2 8 Relationship of relative humidity and moisture content of wood, Boardma n et al. (2017) Grin et al. (2013) studied the effect of rainwater intrusion through roof leaks on the moisture durability of unvented attics. Using WUFI and field studies, the report concluded that roof systems with ocSPF allowing less than 1% of the annual rainfall total leakage were safe against moistur e accumulation and roof decay. Previous Numerical T esting of Unvented Attics Pallin et al. (2013) investigated four unvented and four vented houses in mixed humid climate of Knoxville, Tennessee and found that homes with unvented attics had reduced energy consumptions and despite high interior moisture levels, there was no sign of material degradation in the attic. Pallin suspected that his numerical models devoid of air l eakage parameters could not accurately represent field house characteristics and recommended the inclusion of air leakage testing for future studies. Boudreaux et al. (2014) performed building energy simulations and hygrothermal analysis on one of the unvented attic homes from Pallin study and determined that size of air leakage ar eas and indoor moisture generation rates affected the moisture performance of unvented attics by producing moisture contents greater than the 20% threshold for mold formation and decay. Boudreaux also discussed the variables affecting the indoor air comfor t of

PAGE 32

32 unvented attic homes. Indoor moisture generation rates and attic to outside air leakage were found to be the deterministic variables using Energy Plus simulations. Straube et al. (2002) studied several parameters affecting the moisture performance of unvente d attics. Using WUFI simulations, Straube determined that outdoor climate and interior humidity levels affected the condensation potential at the roof sheathing. Straube concluded that code specific ocSPF and ccSPF insulations produced moisture levels belo w 20% at the roof sheathing. Miller et al. (2016) compared thermal and hygrothermal performance of an attic unvented with R 2 0 closed cell spray foam, an attic unvented with R 20 open cell spray foam to a conventionally vented attic with R 38 insulation in the ceiling level in a hot, humid climate of Charleston, South Carolina The v ented attic showed less moisture movement in t he sheathing than those unvented with either open or closed cell spray foam. Miller concluded that the use of permeable spray foam in a hot humid climate inadvertently allows moisture buildup at the sheathing. The moisture transfers back to the attic air as solar irradiance bears do wn on the roof. The heat transfer from the attic to the conditioned space was twice as m uch as that measured for the ventilated attic. Lstiburek (2015) came to similar conclusions that a moisture accumulation potential is imminent in ocSPF unvented attics in hot humid climates. Lstiburek recommended the use of a dehumidifier in the attic if ocSPF was used to seal the attic. Air Leakage in Residential Houses Air leakage in residential str uctures is caused by gaps between materials such as gaps in doors, windows, and roof to wall connections. Commonly this air leakage is referred to as background leakage. The air leaking into the house (infiltration) and leaking out of the house

PAGE 33

33 (exfiltrati on) can cause various problems as shown in F i gure 2 9 This thesis focusses on the effects of air leakage on the indoor climate and the moisture durability of the roof section. Studies suggest air duct leakage account s for as mu ch as 25% of total house energy loss, and in many cases, has a greater impact on energy use than air infiltration. Leaks can cause conditioned air to be dumped directly outside or in the attic or crawlspace rather than delivered to the building. The impact on a building will depend on the size of the air duct leak, its location and whether the leak is connected to the outside. Figure 2 9 Effects of air leakage on various p arameters

PAGE 34

34 Fan Pressurization Tests Blower door and duct blaster equipment is us ed to measure house air leakage and duct leakage characteristics Both systems use the same physical principles to measure the air flow parameters. A powerful fan is used to blow air in or out of the space in question. In technical terms, this is referred to as pressurization and depressurization. By these mechanisms, the air flow through the gaps and cracks in the tested space is measured by a pressure gauge mounted along with the blower fans. By mechanically pressurization and de pressurization of a build ing and measuring the resulting air flow rates at given indoor outdoor static pressure differences, the air flow parameters of a building envelope are determined. Duct b laster e quipment The duct blaster test equipment shown in F igure 2 10 consists of a d uct blaster fan, a DG 70 0 digital pressure g auge and a flexible duct. The DG 700 gauge has two separate measurement channels which allow simultaneous monitor and display of the duct system pressure and the airflow through the Duc t Blaster fan during the duct airtightness test. The Duct Blaster fan is controlled by a variable fan speed controller. The 12 fee t long flexible extension duct is used to connect the Duct Blaster fan to the duct system of the building. The round transi tion piece connects the flexible extension duct to either the fan exhaust flange for pressurization testing or the fan inlet flange for depressurization testing. A square transition piece is used to connect the flexible extension duct directly to the air h andler cabinet. The extension duct allows the Duct Blaster fan air flow to be easily directed to the duct system. A duct blaster equipment is used to measure the air leakage from the ductwork system into the living space or the attic space. The duct blast er fan is used to pressurize and depressurize the ductwork system and the flow from the fan is quantified to identify the amount of air leakage occurring through the ductwork.

PAGE 35

35 Figure 2 10 Duct blaster test equipment Source: http://www.energyconservatory.com/sites/default/files/documents/mod_3 4_dg700_ _new_flow_rings_ _cr_ _tpt_ _no_fr_switch_manual_ce_ 0.pdf Blowe r door e quipment The blower door test equipment shown in F igure 2 11 consists of a blower fan, an adjustable door frame, a temporary covering, and a DG 700 digital pressure gauge. The adjustable door frame fitted with the temporary covering is mounted onto an external door in the house. The blower fan and the DG 700 pressure gauge is mounted onto the frame to conduct the pressurization and depressurization testing. The pressure gauge is connected to the blower fan by pressure tubing to measure the blower fan pressure as well as the air flow. Figure 2 11 Blower door equipment

PAGE 36

36 Calculation of Air L eakage A reas From the air flow parameters measured, ASTM Standard E 779 is used to calculate the effective leakage area which is a measure of the leakage opening in a building envelope. The following terminology is obtained from ASTM Standard E 779: 1. Air leakage: The movement of air through the building envelope, which is driven by either or both positive and negative pres sure differences across the envelope. 2. Air leakage rate (Q) : The volume of air movement per unit time across the building envelope including airflow through joints, cracks or a combination of mechanical pressurization and de pressurization, natural wind pre ssures, or air temperature differentials between the interior and exterior of the building envelope. 3. Building Envelope: The boundary or barrier separating different environmental conditions within a building and from the outside environment. 4. Effective leak age area ( A L ) : The area of a hole, with a discharge coefficient of 1, which, when subjected to a standardized pressure difference of 4 Pa, leaks the same volume of air as the test building. 5. Pressure exponent (n): The pressure exponent, n is a parameter wh ich depends on the characteristic shape of the leakage orifice in the fan testing. 6. Air Leakage Coefficient (C): The air leakage coefficient, C is a parameter which depends on the characteristic size of the leakage orifice in the fan testing. From the fan p ressurization testing, the air flow is measured in cubic feet per minute at 50 Pascals (CFM 50) pressure difference and is converted to air changes per hour at 50 Pascals (ACH 50). CFM50 and ACH50 are widely used by building engineers to quantify the leaka ge levels of a building envelope. To convert the air flow rate (Q) to air l eakage area (A L ) equations Eq. 2 2 through Eq. 2 5 are used. ( 2 2 ) ( 2 3 ) ( 2 4 )

PAGE 37

37 ( 2 5 ) The variables in the above equations are defined below: Selection of Parameters Affecting Heat and Moisture Movement Based on the literature review performed, seven input variables were hypothesized to have the most impact on the heat and moisture movement in a sealed attic house: 1. Attic to outdoor air leakage area 2. Indoor to outdoor air leakage area 3. Attic floor leakage area 4. Attic duct leakage rate 5. Indoor moisture generation rate 6. Indoor heat generation rate 7. Thermostat set poi nts The attic to outdoor air leakage, indoor to outdoor air leakage and the attic floor leakage are termed collectively as the building envelope air leakage. Moisture movement occurs through water vapor diffusion and air leaks through the building envelop e. The vapor diffusion is determined by the partial pressure differential between the inflowing air and the sheathing as

PAGE 38

38 well as the vapor permeance of the material. The differences in the partial pressure of the attic air and the roof sheathing and the ai r pressure difference causes moisture to flow from areas of higher concentration to lower concentration. The pressure differential caused by duct leakage as well as the conditioned air leaking from the ducts affect the moisture movement in a sealed attic. Several researchers (Miller et al. 2013, Colon (2011) ) have also proposed that solar driven moisture in the sheathing can move into the attic air and increase the moisture levels. Boudreaux et al. 2013 investigated the moisture pathways in an unvented atti c house and found out that the moisture content in the sheathing was not affected by the solar driven moisture transfer. Building Envelope Air Leakage The attic to outdoor air leakage is an effect of poor workmanship. Poorly constructing the roof (gaps i n sheathing, underlayment) or poorly sealing the attic (insulation levels below code level) causes air movement between the attic space and the outdoor environment. Air leakage typically occurs through i) a direct path which results in energy efficiency pr oblems or ii) an indirect path which results in moisture problems. Water vapor diffusion and air convection are the main parameters causing moisture movement. Air can rapidly move between different zones of temperature and pressure thereby causing moisture and energy movement into building materials. Air convection causes increase or decrease in the temperature surrounding the air leak. When the partial pressure of the inflowing air reaches saturating levels, the moisture moves into the wood sheathing which has a lower partial pressure. L ow air flow rate in an indirect airflow path also aids the condensation process by inhibiting the energy exchange between the sheathing and the inflowing air. The humidity of the inflow air cannot reach beyond 100% instead, a condensation plane is formed where the water vapor condenses at the first surface whose temperature is below the dew point temperature. In hot and humid climates, the air flow is generally considered to be from the outdoor environment into the attic due to elevated outdoor

PAGE 39

39 temperature. If the air flow rate of the inflowing air is sufficiently high, the temperature and moisture of the inflowing air approaches the same level of temperature and moisture in the sheathing. Hence, an intermediate air flow rate will not have sufficient energy to increase the sheathing temperature beyond dew point resulting in condensation. Higher vapor pressure gradient between the sheathing and the inflowing air can drive more moisture into the air flow path influencing the crit ical moisture contents. This theoretical condensation plane based on the hygrothermal conditions of the sheathing and the inflow air is shown in F i gure 2 12 Figure 2 12 Intermediate air flow rate combined with high vapor pr essure gradient can cause RH exceeding 100% (Boudreaux et al. 2014) The theory of the condensation plane is elaborated in Ojanen et al. 1996 and Boudreaux et al. 2014. It is important to understand that temperature and moisture movement occurs at diffe rent rates. The movement from a higher to a lower temperature or moisture level is dependent on the conditions of the inflowing air. Based on the air flow rate, changes in temperature and moisture could occur in a number of ways finally reaching an equilib rium state.

PAGE 40

40 For low air flow rates, the energy exchange between the air and the sheathing is minimized, thereby keeping the sheathing temperatures above dew point leaving no potential for condensation. As the air flow increases, the sheathing temperature and moisture reach the temperature and moisture of the inflowing air. Saturating levels of humidity and vapor pressure differentials drive the moisture laden air to condense at the wood sheathing. A theoretical explanation is provided in Boudreaux et al. 2 014. Figure 2 13 Theoretical heat and moisture movement in an air leakage path causing condensation, (Boudreaux et al. 2014) Building envelope air leakages increase the air flow into the sealed attic. Even if the air leakage rates do not cause condens ation problems, they affect the thermal air quality of the conditione d space and the energy efficiency of the whole building. By encapsulating the attic into the thermal envelope, the duct leakages are contained. However, the HVAC system has to

PAGE 41

41 operate for a longer time to condition the whole thermal envelope. This additional run time brings in conditioned air into the attic thereby removing any excessive moisture. Attic Duct Leakage Duct leakage into vented attics is a major source of energy penalties. The conditioned air leaking from the supply ducts can easily escape to the building exterior through the attic vents. The conditioned air leak disrupts the HVAC performance, resulting in increased running time to compensate for the conditioned air leak. Duct leakage inhibits the continuous air flow within the building envelope disrupting the pressure balance between the building envelope and the outdoor environment. The pressure differential can lead to air infiltration or exfiltration which affects the moveme nt of temperature, humidity and moisture throughout the building envelope. The changes occurring in the building envelope ultimately lead to poor indoor air quality, occupant comfort and energy efficiency. Several studies point out that the energy penalty occurring due to high duct leakage can be countered by sealing the attic space. When the ducts are placed in a sealed attic, the duct leakage is contained within the thermal envelope of the building thereby reducing the energy losses. Parker et al. (2002) analyzed the cooling energy demand for two identical houses in Florida; one with a traditional vented attic and one with a sealed attic. Parker found that the sealed attic house had a 6% 11% reduction in the cooling energy when compared to the vented at tic house. Pallin et al. (2013) performed building energy simulations to quantify the relationship between duct leakage and energy savings from a sealed attic. Pallin performed numerical analysis by varying the duct leakage from 4% to 20% and found that t he duct leakage of 20% increased the energy consumption by 10%. A supply duct air leak into the attic brings in conditioned air into the attic space. Sealed attics in hot climates have saturating levels of humidity in the attic air. The vapor pressure

PAGE 42

42 dif ferential drives the moisture from the attic air into the spray foam insulation and eventually into the wood sheathing. The conditioned air from the duct leak has different temperature and humidity levels thereby mixing with the humid attic air and reduces the attic air relative humidity thus, inhibiting the attic air from reaching saturating levels of humidity Hence, the supply duct leakage into sealed attic space helps in removing excessive moisture in the attic. Air leakage through the return vents br ings in hot and humid air from the attic into the air handler system and vice versa The interior and exterior surfaces of the conditioned duct system have lower temperature the attic air. Due to higher humidity and temperature below the dew point of the a ir, condensation can occur at the surface of the ductwork system. Overall, the duct leakage in to sealed attics unintentionally supplies conditioned air into the attic potentially reducing the excessive moisture from the attic. However, increased duct leak age can cause high air infiltration or exfiltration between the thermal envelope and the outdoor environment leading to reduction in air quality and occupant comfort. The increased HVAC run time causes energy losses as well as reduction in the l ifespan of the HVAC equipment. Lstiburek (2014) explains that in the past, the duct systems were leakier, thereby providing unintentional conditioning to the attic. However, with stringent rules on building energy efficiency, the duct systems are well insulated and h ave minimal duct leakage. Due to the increased concern for energy efficiency, the side benefit of having a leaky duct to semi condition an attic has disappeared. Duct leakage can be measured in the field by performing a duct blaster test. For numerical an alysis, the Lawrence Berkeley National Laboratory (LBNL) residential database was used. LBNL (2015) provides whole house air leakage data and duct leakage data for houses specific to a climate zone.

PAGE 43

43 Indoor Heat and Moisture Generation Energy efficiency of a building envelope and occupant comfort depend on the movement of heat within the building envelope and the outdoor environment. As the building codes are moving towards an energy efficient future, insulation systems and space conditioning equipment have evolved to keep out unwanted air, heat and moisture flow to and from the thermal envelope of the building. The indoor air temperature is a factor of the heat gain and the cooling load of a building. Heat gain is the summation of all the heat flows inside the thermal envelope : solar radiation, number of occupants, lights and appliances in the building. Cooling load is the rate at which the space conditioning system removes the heat gains from the thermal envelope. Sensible heat is the amount of energy requ ired to alter the air temperature of a material. Solar heat gain through radiation and conduction, air infiltration, heat from appliances and equipment contribute to the sensible heat. Latent heat is the amount of energy released when a material changes it s physical state (liquid to gas or vice versa). Air infiltration and occupant activity like cooking and bath contribute to the latent heat. Latent heat affects the humidity levels in the air thus, directly influencing the indoor thermal air quality. HVAC systems are sized accordingly to remove both the sensible and latent heat from the thermal envelope. However, oversized or undersized HVAC systems cannot remove the sensible and latent heat to maintain the temperature and humidity at equilibrium. The exces s latent and sensible heat reach the upper levels of the conditioned space and flow through leaks in the attic floor. Sealed attics do not have insulation at the ceiling level and allow the passage of the latent and sensible heat onto the attic. The vapor pressure of the humid attic air is higher than the vapor pressure of the spray foam and the sheathing during the nighttime and can condense at the first cold surface in its path. Spray foam is air permeable and vapor permeable allows the moist air to

PAGE 44

44 reach the sheathing. Cold nighttime temperatures in winter cools the wood sheathing below the dew point of the attic air and condensation occurs at the sheathing to insulation interface. Since the indoor latent and sensible heat affect the moisture movement and the occupant comfort through different mechanisms, it is difficult to model these parameters which change with time. Boudreaux et al. (2016) and other ORNL researchers have developed a numerical model using Energy Plus to simulate the indoor sensible and heat. The numerical model known as the Generation of Indoor Heat and Moisture (GIHM) tool considers several factors like occupant habits, air infiltration, solar heat gain and HVAC sizing to predict the indoor sensible and latent heat. The simulated values well represent the ideal conditions prescribed in ASHRAE Standard 160 as shown in Figure 2 14. Figure 2 14 Simulated indoor moisture and ASHRAE Standard 160 for varying occupants (Boudreaux et al. 2014)

PAGE 45

45 Thermostat Set Points and Mechanical Ventilat ion Occupant controlled thermostat set points and mechanical ventilation could affect the moisture movement by either supplying or removing air inside the thermal envelope The thermostat set point controls the air temperature and the sensible heat but not the latent heat. The thermostat set point is programmed to remove almost all the sensible heat but only a fraction of the latent heat. This means the humidity inside the thermal envelope still remains at an uncomfortable level for the occupants. Sealed at tics allow lesser sensible heat movement into the house than a vented attic. This causes the HVA C to run for shorter periods which in turn affects the energy efficiency of the house. Bailes (2014) measured the indoor humidity and temperature of a vented attic house for a one month period to determine the relationship between thermostat setti ngs and the moisture movement. During a 5 day interval within the measured days, Bailes changed the thermostat fan and off to maintain the temperature setting. When the fan is on, the HVAC coil becomes cold and allows surrounding warm air to condense. When the fan is off, the condensed vapor turns back into vapor and is expelled out. However, the fan runs continuously over the condensed coil and pushes the excessive moisture into the house. The added air flow i nto the house along with the sustained latent heat can increase the humidity levels inside the conditioned space. During the five days of continuous airflow from the mechanical systems the mean humidity levels increased by 10%. In more airtight residential houses humidity levels could reach saturation especially if the HVAC system is oversized.

PAGE 46

46 CHAPTER 3 EXPERIMENTAL TEST ON FLORIDA SEALED AT TIC HOUSES Selection of Field Houses We test ed the behavior of sealed attic systems in the field with respect to occupancy in four single family residential houses in Florida. The Florida Roofing and Sheet Metal Contractors Association (FRSA) assisted in f inding house owners interested in the research. Prevatt et al. (2016) conducted p reliminary surveys and identified house characteristics like number of occupants, type of roof cover and sheathing, type and thickness of insulation for eig ht houses with sealed attics. From surveyed houses, four houses with open cell spray polyurethane foam insulation in the attic w ere selected for the field test. All house owners were involved directly or closely with the construction industry hence all se lected houses had excellent roofing and no problems associated with rain water intrusion Figure 3 1 Selected field houses in Florida climate z ones 1 and 2 The four selected homes are located in West Palm Beach, Venice, Orlando and Gainesville. Furth er in this thesis, the houses will be referred to as House 1, House 2, House 3 and House 4. House 1 in Palm Beach county borders the ASHRAE defined climate zones 1A &

PAGE 47

47 2A; other three houses fall within climate zone 2A. Retired couples are the house owners for all four houses. House 4 is a retirement home occupied only during the winter period. Description of Field Houses Table 3 1 Characteristics of field h ouses Characteristic House 1 House 2 House 3 House 4 Location West Palm Beach Venice Orlando Gainesv ille Attic Sealed ocSPF Sealed ocSPF Sealed ocSPF Sealed ocSPF Type of roof Standing seam metal Concrete barrel tile Asphalt shingle Asphalt shingle Conditioned Area 2,043 sq. ft. 3,592 sq. ft. 2,348 sq. ft. 3,055 sq. ft. Conditioned Volume 29,670 cubi c ft. 42,183 cubic ft. 22,115 cubic ft. 29,022 cubic ft. Attic Volume 6,800 cubic ft. 7,692 cubic ft. 5,106 cubic ft. 14,002 cubic ft. HVAC System AC with Elec Furnace Air Handler in attic Ducts in attic Heat Pump Air Handler in closet Ducts in attic Hea t Pump HVAC outside No Duct in tested attic Heat Pump Air Handler in closet Supply Ducts in attic Roof deck insulation (hft 2 F/Btu) R 15: R 21: R 15: R 27: ocSPF Code minimum R value/ Active FECC* R 19: 2010 FECC R 19: 2010 FECC R 19: 2002 FECC R 19: FECC 2007 *FECC code performance requirement for attic floor insulation. No requirement in place for insulation under the wood sheathing. House 1 West Palm Beach House 1 built in 1962 is located in West Palm Beach, FL. The single story house has a hip roof structure with metal roof cover and plywood roof deck The attic was ventilated at the time of construction and was retrofitted in 2010 with 4 in. of open cell polyurethane insulation sprayed under the plywood roof sheathing making the attic a sealed attic. No insulation layer is provided at the ceiling level. The house has two occupants and the HVAC ductwork runs through the sealed attic. The roof was built with excellent workmanship ruling out the possibility of r ain water intrusion. West Palm Beach in Palm Beach County falls within ASHRAE Climate Zone

PAGE 48

48 2 A, defined as hot humid by ASHRAE 169 ( 2006 ) and the International Energy Conservation Code and the Florida Building Code. Figure 3 2 Front view of h ouse 1 in West Palm Beach FL Photo courtesy of author. Figure 3 3 Sealed a ttic of h ouse 1 ocSPF insulation under the sheathing and ductwork Photo courtesy of author.

PAGE 49

49 House 2 Venice House 2 built in 2012 is located in Venice FL. The two story house has a hip roof structure with concrete tile cover and OSB roof sheathing panels. The attic was sealed at the time of construction with 5 .5 in. of open cell polyurethane insulation sprayed under the OSB roof sheathing No insulation is provided at the ceiling level. The house had two occupants and the HVAC ductwork runs through the sealed attic. The homeowner was the builder of the house and built the house with excellent workmanship in the attic and the roof, thus ruling out the possibility of rain water intru sion. Venice in Sarasota County falls within ASHRAE Climate Zone 2A, defined as hot humid by ASHRAE 169 ( 2006 ) and the International Energy Conservation Code and the Florida Building Code. Figure 3 4 Front view of h ouse 2 in Venice, FL Photo courtesy of author.

PAGE 50

50 Figure 3 5 Sealed attic o f h ouse 2 showing ocSPF under sheathing and ductwork in the attic Photo courtesy of author. House 3 Orlando House 3 built in 2002 is located in Orlando, FL. The two story house has a combination of hip and gabl e roof structure s with asphalt shingle cover and plywood roof sheathing panels. The attic was sealed at the time of construction with 4 in. of open cell polyurethane insulation sprayed under the plywood roof sheathing. The house had two occupants and the H VAC ductwork runs through the second floor sealed attic. However, the main attic was not accessible nad it contained the duct system. An attic over a portion of the first floor was instrumented but this attic contained no duct work., The house was built wi th excellent workmanship in the attic and the roof, thus ruling out the possibility of rain water intrusion. Venice in Orange County falls within ASHRAE Climate Zone 2A, defined as hot humid by ASHRAE 169 ( 2006 ) and the International Energy Conservation Co de and the Florida Building Code.

PAGE 51

51 Figure 3 6 Front v iew of h ouse 3 in Orlando FL Photo courtesy of author. Figure 3 7 Sealed attic of h ouse 3 showing ocSPF under roof sheathing. No ductworks are located in the attic Photo courtesy of author.

PAGE 52

52 House 4 Gainesville House 4 was built in 2007 and is located in Gainesville FL. The single story house has a hip roof structure with asphalt shingle cover and plywood roof sheathing panels. The attic was sealed at the time of construction with 7 in. o f open cell polyurethane insulation sprayed under the plywood roof sheathing. The house had two occupants and the HVAC ductwork runs through the sealed attic. The house was built with excellent workmanship in the attic and the roof, thus ruling out the pos sibility of rain water intrusion. Gainesville in Alachua County falls within ASHRAE Climate Zone 2A, defined as hot humid by ASHRAE 169 ( 2006 ) and the International Energy Conservation Code and the Florida Building Code. This house is occupied only during the winter months (November February) and is colloquially known as a winter bird house. Of the four houses analyzed in this research, House 4 had the highest insulation thickness at the roof sheathing level. Figure 3 8 Front v iew o f h ouse 4 in Gaine sville, FL Photo courtesy of author.

PAGE 53

53 Figure 3 9 Sealed attic of h ouse 4 showing ocSPF below the roof sheathing and ductwork running through the attic Photo courtesy of author. Field Data Acquisition At each of the selected houses three main tasks w ere performed by the research team. A questionnaire was completed by the homeowner to collect information about the house such as building geometry, construction materials and occupant habits. Air leakage tests were performed to quantify building envelope and duct leakages. The attic, living space and the outside of the house was instrumented with temperature and humidity sensors to study the heat and moisture flows in the building envelope. A detailed analysis of the tasks performed at each of the four hou ses is summarized in the upcoming sections. More details about the field testing is presented in Prevatt et al. (2016) House Owner Questionnaire An Internal R eview Board at ORNL develop ed a survey for the homeowners participating in the field study. The survey provided general information about the study regarding why the study is being conducted, who is involved in the study, length of time the

PAGE 54

54 study lasts, potential issues with house damage, and how the data will be used and reported. A ll homeowners signed the survey. Prevatt et al. (2016) documented the dimensions of each single family residence, including the dimensions of all rooms in the conditioned space of the houses. In addition, the students recorded the slop e and style of the roofs, the roof structure, size of the attic and the type and thicknesses and locations of the spray foam insulation. The exterior wall cladding and details, number and dimensions of exterior windows and foundation were recorded for late r use in numerical model development. Homeowners were asked when the attic was sealed and by what Florida contractor. The survey included questions about the heating, ventilation and air conditioning (HVAC) system and duct work in the attic. The insulation was installed during initial construction in three of the four houses, and it was added during re trofitting of the fourth house. Prevatt et al. (2016) contains results of the questionnaires for all four homeowners. provides a succinct s ummary of features for each home. Figure 3 10 House owner questionnaire for h ouse 4 in Gainesville showing salient features of the house documented for use in numerical toolkit

PAGE 55

55 Table 3 2 Material p roperties of s uperstructure in all four ho uses Compon ent House 1 West Palm Beach House 2 Venice House 3 Orlando House 4 Gainesville Roof Cladding Standing seam metal Barrel Concrete tile Asphalt shingle Asphalt shingle Pitch 3/12 at perimeter 6/12 at ridge 6/12 4/12 6/12 Structure Hip Hip Gable and Hip Hip Underlayment 30# felt paper WR Grace Peal & Stick 2(15# felt paper) 30# felt paper Sheathing Plywood OSB (5/8 in) Plywood(5/8 in) Plywood(5/8 in) Framing 2 by 4 Truss at 2 by 4 Truss at 2 by 4 Truss Y ear Constructed 1962 2012 2002 2007 Year Attic Sealed 2010 2012 2002 2007 Roof deck insulation (hft2 F/Btu) R R R R ocSPF Attic floor insulation (hft2 F/Btu) Gypsum board R 0.45 Gypsum board R 0.45 G ypsum board R 0.45 Gypsum board R 0.45 Conditioned Area 2,043 ft 2 3,592 ft 2 2,348 ft 2 3,055 ft 2 Conditioned Volume 29,670 ft 3 42,183 ft 3 22,115 ft 3 29,022 ft 3 Attic Volume 6,800 ft 3 7,692 ft 3 5,106 ft 3 14,002 ft 3 HVAC Duct Sizes in Attics Main: 24 in Branch: 6 & 8 in Main: 24 in Branch: 6 & 8 in 1 st Floor Attic no ducts; 2 nd Floor attic had ducts Main 18 in Branch: 6 & 8 in Air Conditioner 2 (2RT Lennox) NA NA Carrier (3RT) Goodman (2RT) Heat Pump NA 2 (2 RT TRANE) Lennox (3RT) NA Dehumidifier NA In second floor NA In bath

PAGE 56

56 Air Leakage Test The air leakage tests performed in each house were: 1. Duct Blaster Test To determine the total duct leakage, 2. Guarded Duct Blaster Test To determine the duct leakage to the unvented attic, 3. Blower Door Test T o determin e the airtightness of the house, and 4. Guarded Blower Door Test To determine the attic leakage to the outdoor ambient Duct blaster t est The total duct leakage test is used to measure the duct leakage rate in the entire duct system when the duct system is subjected to a uniform test pressure. This test measures duct leakage to the outside of the building The air flow through the duct blaster fan required to pressurize the duct system to the test pressure is the measured total duct leakage rate. From the measured duct leakage rates and the conversion methods elaborated in Eq. 2 2 to Eq. 2 5, the duct leakage areas for the house is computed. The pressure in the duct system was varied by order of 25, 30, 35, 40, 45, and 50 Pascals Each test run acc ounted for 10 minutes. Figure 3 11 Total duct leakage test to measure the duct leakage into the conditioned space and the attic. The duct blaster fan is connected to the HVAC return vent

PAGE 57

57 Blower door t est To determine the airtightness of the buil ding envelope, the home is left in usual condition (with attic hatch and garage door closed). The blower door fan is used to pressurize and depressurize the house. This test determines the total leakage out of the building envelope due to constructional le aks through gaps in doors and windows, gaps in the roof to wall and wall to ceiling connections. The blower door fan was fitted to an external door and all doors and windows were closed. The house was pressurized and depressurized by the blower door fan. Based on the air flow rates measured from the blower door fan and equations Eq. 2 2 to Eq. 2 5, the effective air leakage areas of the building envelope are computed The pressurization test was conducted by pressurizing the attic and the duct system in t he order of 25, 30, 35, 40, 45, and 50 Pascals. Each test run accounted for 10 minutes. Figure 3 12 Building envelope air leakage test to measure the air leakage into the conditioned space. The blower door fan is connected to an external door.

PAGE 58

58 Gua rded duct b laster t est To determine the duct leakage into the attic, one duct blaster fan was connected to the return of t he duct system and a blower door br ought the home to the same pressur e as the ducts. This negates any airflow between the duct system and the interior of the home, thus the measured leakage is only t he duct leakage to the attic. The pressurization test was conducted by pressurizing the attic and the duct system in the order of 10, 15, 20, 25, 30 Pascals. To perform a multi point depres surization test, the home was depressurized by one blower door fan, while the duct system was depressurized by using the duct blaster fan. The pressure in the duct system was varied by order of 10, 15, 20, 25, 30 Pascals. The duct leakage into the attic sp ace was com puted using the TECLOG 1 software. Figure 3 13 Guarded duct blaster test to measure the air leakage from ducts into the attic The blower door fan is connected to an external door to pressurize the house and a duct blaster fan is connecte d to the return vent of the HVAC system. 1 TECLOG is a data logging program for Windows based computers. TECLOG allows real time tracking of fan flow and pressure measurements an d can automate pressure equalization for multiple fan pressurization systems. http://energyconservatory.com/products/product/teclog/?categories=6

PAGE 59

59 Guarded b lower d oor t est The guarded blower door test was conducted to determine the attic leakage to the outside of the house. This test was conducted by fitting a blower door to an exterior door and two duct blas ters to the attic. Two duct blasters were used since one duct blaster fan was not sufficient to pressurize the attic to the required test pressure This configuration negates any leakage between the attic and the home since they are both at the same pressu re. Therefore, the flow through the duct blaster fans is a measure of the leakage in the attic to the outside. When the blower door fan and the duct blaster fans were operated by utilizing the TECLOG software, the blower door fan was used to pressurize the conditioned space. The duct blaster fans were used to pressurize the attic. The blower door fan maintained the test pressure inside the house, the air blown through the duct blaster escaped through the leaks to the outside of the attic. The test pressures were in the order of 30, 35, 40, 45, 50 Pascals. The same test was carried out for depressurization testing as well. The test pressures were the same and both tests took about 20 minutes to complete in total. Figure 3 14 Guarded blower door test to measure the air leakage from attic to the outside. The blower door fan is connected to an external door to pressurize the house and a duct blaster fan is connected to the attic hatch to pressurize the attic.

PAGE 60

60 Attic Instrumentation Each house has 16 sen sors installed in the attic to measure the temperature, RH and moisture content at various locations. All houses had a similar layout of sensors as shown in F igure 3 15 for consistency interpreting data among the 4 houses. These measu red parameters are available in engineered units. The moisture content of wood is measured in the form of electrical resistance and is converted into % MC using an algorithm developed by ORNL and benchmarked against data from Garrahan (1989), Carli, TenWol de and Munson (2007) and Huber Engineering (2013). Campbell Scientific model CR1000 m icro loggers were setup for remote acquisition and recording of field data. The loggers are equipped with 4 MB of memo ry, rechargeable battery, a 115 V ac to 24 V dc transf ormer, cellular modem and associated cables. The micro loggers take measurements of all sensors ( T able 3 3 ) every 30 seconds and reduce analog signals to engineering units. Averages of the reduced data are written electronically to an open file (internal on logger) every 15 min. Averages are calculated over the 15 min interval and are not running averages; they are reset after each 15 min interval. The electronic format is comma delimited for direct access by spread sheet programs. Software running on a server at ORNL is configured to remotely collect data at scheduled intervals from all micro loggers via cellular connection. Data are stored in server archive which has routine backup for data protection. Absolute hu midity probes and moisture pins w ere installed on the adjacent roof decks to analyze the in situ performance of the attics Absolute humidity sensors were fabricated using the technique described by Straube, Onysko and Schumacher (2002). A thermistor and r elative humidity probe were packaged together in a vapor permeable and liquid water repellent cover fabricated from commercially available weather resistive barriers designed to allow passage of water vapor but not liquid water. Thermistor and humidity sen sors were calibrated by the

PAGE 61

6 1 manufacturer. ORNL Metrology made checks for a couple of the absolute humidity probes. The probes met the manufactures specification for the temperature response of +/ 0.2C. Humidity sensors were checked at 25, 50, 75 and 90 % RH. The error in RH ranged from 2% of reading at 25% RH and 15C to 6.5% of reading at 90% RH and 26C. Data is mea sured every 30 seconds and is reduced as raw data averages over 15 minute, 60 minute, and 24 hour intervals. Post processing of the raw dat a yields weekly or annual records containing data averages over 15 minute and 60 minute intervals for all four houses. 60 minute averaged data is analyzed in thesis. Table 3 3 Instruments scanned by Campbell CR1000 m icro l ogger Program Variable Sensor Lo cation Type of Sensor Therm1 North roof sheathing near ridge* Honeywell 192 103LET Therm2 North roof sheathing at mid span of roof* Honeywell 192 103LET Therm3 South roof sheathing at midpoint of roof* Honeywell 192 103LET Therm4 Attic ambient air Hone ywell 192 103LET Therm5 House ambient air Honeywell 192 103LET Therm6 Outside ambient Honeywell 192 103LET RH1 North roof sheathing near ridge* Honeywell HIH 003 Humidity RH2 North roof sheathing at mid span of roof* Honeywell HIH 003 Humidity RH3 Sou th roof sheathing at midpoint of roof* Honeywell HIH 003 Humidity RH4 Attic ambient air Honeywell HIH 003 Humidity RH5 House ambient air Honeywell HIH 003 Humidity RH6 Outside ambient Honeywell HIH 003 Humidity MP1 North roof sheathing adjacent rafter near ridge Moisture Pin MP2 North roof sheathing center of cavity near ridge Moisture Pin MP3 North roof sheathing adjacent rafter at mid span of roof Moisture Pin MP4 North roof sheathing center of cavity at mid span of roof Moisture Pin *Sensor cente red between roof rafters.

PAGE 62

62 The sensors were placed in the same pattern for each home to provide consistent comparisons among the attics under field study. F igure 3 16 shows the placement of sensors Absolute humidity probes were install ed for measuring the outdoor, the indoor and the attic ambient temperature and relative humidity. Absolute probes were also placed on the underside of the roof sheathing about mid span from eave to ridge. An absolute probe was also placed on the sheathing at the north side of the roof ridge, F igure 3 16 Table 3 4 Location of temperature, relative humidity and moisture sensors Type of Sensor Location of Sensor A MP and T/RH at center of cavity; MP near joist 14 ft, 6 in away from r idge on north B MP and T/RH at center of cavity; MP near joist 10 in away from ridge on north C T/RH at center of cavity 14 ft, 6 in away from ridge on south D T/RH outside the building envelope Under eave on east wall Figure 3 15 Location of temperature, relative humidity and moisture sensors in each of the four houses. The plan shown is for h ouse 4 in Gainesville Prevatt et al. (2017)

PAGE 63

63 Figure 3 16 Cross s ection of sealed attic showing placement of thermistors, relative humidity sensors and moisture pins in demonstration homes For each home, one set of moisture p ins were nailed into the underside of the sheathing adjacent to the absolute probes centered between rafters for the north pitch locations shown in F igure 3 17 In addition, a second set of pins were installed to the underside of sheathing about 1 in from the rafter The p ins near the roof rafter were in the same rafter cavity as those centered in a rafter cavity. Figure 3 17 Temperature, relative humidity and moisture pins installed at the interface of the wood sheathing and the spray polyurethane foa m insulation.

PAGE 64

64 CHAPTER 4 RESULTS OF EXPERIMENTAL TESTING Air Leakage Test Results The envelope of House 2 was the most air tight of all four houses; its Air Change per Hour value in 50% (ACH50) was 2.2, compared to 5.2 for House 4, 6.7 for House 1 and 8.6 for Hou se 3. House 1 was poorly sealed and had the largest air leakage from the attic, 2,510 CFM as compared to all other houses that has air leakage of less than 700 cfm. However, the total duct leakage in House 2 in cfm per square foot of footprint was roughly the same as in the other three houses. For House 2 the duct leakage to the attic could not be determined directly, so we instead measured the duct leakage to the conditioned space and subtracted this from the total duct leakage yielding duct leakage to the attic. To determine the duct leakage into the conditioned space, we connected one duct blaster to the return vent and one duct blaster to the attic access and performed the test. Table 4 1 Envelope air l eakage r esults Parameter House 1 House 2 House 3 Ho use 4 West Palm Beach Venice Orlando Gainesville Envelope Air Leakage CFM at 50 Pa Total Air Leakage 4298 1820 4143 3718 Attic Air Leakage 2510 656 506 187 Living Space Air Leakage 1794 1164 3624 3531 Envelope Air Leakage Ratio % Attic Air Leakag e 58% 36% 12% 5% Living Space Air Leakage 42% 64% 87% 95% Envelope Air Leakage ACH at 50 Pa Total Air Leakage 6.7 2.2 8.6 5.2 Attic Space Air Leakage 22.1 5.12 5.7 Living Space Air Leakage 3.62 1.65 9.6

PAGE 65

65 Figure 4 1 Total b uilding e nvelope l e akage results for test houses Figure 4 2 Total d uct leakage results for test houses

PAGE 66

66 Table 4 2 Duct l eakage r esults Parameter House 1 House 2 House 3 House 4 West Palm Beach Venice Orlando Gainesville Duct Leakage CFM at 25 Pa Total Duct L eakage 115 579 608 655 Attic Duct Leakage 73 116 Living Space Duct Leakage 42 464 608 Duct Leakage Ratio % Attic Duct Leakage 64% 20% 0% Living Space Duct Leakage 36% 80% 100% Duct Leakage CFM/ft Total Duct Leakage 0.11 0.16 0.26 0.21 F our houses with open cell spray polyurethane foam insulated sealed attics were selected for this research study. The cause and effect of parameters affecting the moisture movement in sealed attics are studied. From previous literature, air leakage and duct leakage are considered as two important parameters for moisture movement. House 1 in West Palm Beach had an attic leakage of 22.7 ACH making the attic essentially function like a vented attic. House 3 in Orlando had no ductwork in the sealed attic. Hence, House 2 and House 4 are selected as best representing the sealed attic houses in Florida. House 2 has a concrete tile roof with OSB sheathing and House 4 had asphalt shingle roof cover with plywood decking. Heat and Moisture Flow in Selected Florida Seale d Attic Houses Each of the four houses in Florida were instrumented with temperature, relative humidity and moisture sensors to monitor the heat and moisture flows from the sealed attic to the conditioned space of the house. The temperature and humidity in a confined space affect the moisture movement and penetration into building materials.

PAGE 67

67 Heat Movement in Selected Florida Sealed Attic Houses To monitor the temperatures t hermistors were installed at six locations in each of the four sealed attic houses. The ambient temperatures of the outdoor environment, the attic space and the indoor conditioned space were measured along with the roof sheathing temperatures at the roof ridge, the north midpoint of the roof and the south midpoint of the roof. Literature review of sealed attics has generally led to an observation that the temperature and humidity in the attic is coupled well with the temperature and humidity of the indoor space irrespective of the leakage occurring at the ceiling level, Less et al. (2016) Transforming a ventilated attic into a semi conditioned space cause s the temperatures in the sealed attics of House 2 and House 4 to closely follow the indoor temperatures, Figure 4 3 For House 4, the occupi ed period of the house can be observed when there are most fluctuations in the indoor temperature i.e. between the summer months of November and March, the house was occupied. Figure 4 3 Daily averaged t emperatures measured from various locations i n h ouse 2 and h ouse 4. Figure shows good correlation between attic and indoor temperature.

PAGE 68

68 The close relationship between the attic temperature and the indoor temperature can be clearly seen in F i gure 4 4 The outside temperature drives th e variations in the indoor temperatures. The temperatures at the roof sheathing are consistent with the outside temperature. The sheathing facing south has higher temperatures than the north facing roof. House 4 located in Gainesville has lower outside tem perature in the winter months when compared to House 2. This is a potential reason for higher moisture contents in House 4. Both House 2 and House 4 have well insulated and sealed attics which lead to excellent correlation between the attic and the indoor temperatures. Figure 4 4 Measured attic and indoor t emperatures Attic temperature and i ndoor temperatures are well correlated. The outdoor air temperature fluctuates diurnally, i.e. the temperature hits a maximum around the solar noon when the solar irradiance is at the peak and the temperature hits a minimum during the early morning hours (about 5 A M) The outdoor air temperature directly influences the attic air temperature and the indoor air temper atures and the temperature in the

PAGE 69

69 roof sheathing. The temperatures at the interface of the sheathing and the ocSPF insulation are much higher than the attic temperatures. This is because the foam insulation traps the heat within the material and lack of air movement slows down the heat movement. The sheat hing temperatures during peak irradiance are close to 50 o F higher than the outdoor temperature and about 80 o F higher than the indoor conditioned space temperature. The diurnal variation in temperatures for a typical summer week is plotted below in F igure 4 5 Figure 4 5 Diurnal variation in measured temperatures for a weekly period in summer. Relationship between Temperature, Humidity and Moisture The attic temperature and humidity produces a partial pressure of wat er vapor that controls the behavior of moisture movement in the attic and the roof sheathing. Attic humidity over 80% for prolonged periods can induce more moisture movement and lead to potential moisture accumulation in the attic, Miller et al. (2013) and (2013) Salonvaara et al. (2013). The time history and means of attic air temperature and relative humidity is plotted for House 2 and

PAGE 70

70 House 4 in F i gure 4 6 Hous e 2 has relatively smaller diurnal swings of temperature and humidity. The humidity in the attic is controlled by means of a dehumidifier and hence the humidity does not climb above 80%, meaning no conditions for moisture movement. House 4 has large diurna l swings in attic humidity and reaches over 80% for a long period during December June. Alarming humidity values of over 90% and close to saturating humidity occur during this period allowing favorable conditions for moisture accumulation. Figure 4 6 Measured attic air t emperature and h umidity for h ouse 2 and h ouse 4. Blue trace and green trace shows air temperature plotted on the left y axis. Grey trace and green trace shows the air relative humidity plotted on the right y axis The dew point tempera ture is the temperature at which the air cools to saturation point allowing for the water to condense. When the temperature of the sheathing reaches the dew point, condensation of the water vapor occurs at the sheathing to insulation interface. In winter, the cold outdoor environment cools the sheathing at a faster rate. The higher partial pressure of water vapor (high humidity ) in the attic drives the moisture from the attic air through the spray foam insulation and into the wood sheathing. When hotter air from the attic reaches the cold

PAGE 71

71 sheathing, the air condenses over the wood sheathing. If the temperature of the sheathing is below or close to the dew point temperatures, the moisture laden air condenses over the wood sheathing. This moisture dries at a slower rate than the temperature differential across the materials and hence if the attic air is saturated with humidity and the temperature at the sheathing is below the dew point, the condensing moisture can accumulate at the sheathing to insulation inte rface. This effect can be analyzed by plotting the sheathing temperatures and humidity along with the dew point temperatures. Figure 4 7 Measured sheathing t emperature and h umidity for h ouse 2. Sheathing temperatures (black) reach dew point (red) duri ng the winter months for a small time period The relationship between sheathing temperature, humidity and dew point for House 2 located in Venice is shown in Figure 4 7 During the winter months of November to March, the

PAGE 72

72 sheathing tempe ratures is as low as the dew point temperature during the night time when the outside air is the coldest. However, the relative humidity of the sheathing as well as the attic is controlled by the HVAC and does not reach above 80 % at any point of the analys is period. For House 4 located in Gainesville, the extreme minimum outdoor air temperature is about 10 o F lesser than that of the other Florida houses during the winter period. This causes a dip in the attic temperature as shown in F i gure 4 8 Figure 4 8 Weekly at tic and indoor temperature for house 2 in Venice and ho use 4 in Gainesville Gainesville has a colder climate than Venice. The homeowner of House 4 in Gainesville occupies the house only during the winter period and sets th e thermostat to 80 o F during the summer months. The thermostat setting causes high humidity ranges over 80% and near saturation levels in the sealed attic. Salonvaara et al. (2013) had analyzed sealed attics with open cell polyurethane foam insulation in Florida and observed that humidity ranges over 80% in the attic caused moisture accumulation in the sheathing to insulation interface. This effect of higher attic h umidity causing risk of moisture

PAGE 73

73 accumulation is analyzed in this study. The sheathing temperature, humidity and dew point temperature are plotted in F i gure 4 9 Figure 4 9 Measured sheathing temperature a nd humidity for h ouse 4. Sh eathing temperatures (black) reach dew point (red) during the winter months for a small time period The sheathing temperatures reach the dew point temperatures during the winter months of November to March. The sheathing relative humidity is above 80% and reaches over 95% for a short time, especially around January months. This period of two weeks show the highest moisture content in the roof sheathing, with the moisture levels reaching up to 20% as shown in F igure 4 9 This behavior confirms the relationship posed by Boardman et al. (2017) However, the effect has to be analyzed further to understand this anomaly in the moisture content values. This could be due to occupant activity since the house is typically occupied only during the

PAGE 74

74 winter period. However, the moisture contents reached a safer level during the first week of February 2 017. Moisture Content in Roof Sheathing Each of the four Florida sealed attic houses were instrumented with moisture pins at the wood sheathing at four locations which would quantify the moisture content values in pe rcentage. An example case of time histor y for a recorded week of moisture content is presented in the figure below F igure 4 10 A time history of sheathing temperature and humidity is presented for the same week to show the relationship between these parameters. Figure 4 10 Measured roof sheathing moisture content for a summer week from h ouse 1in West Palm Beach. Diurnal variation of moisture content is due to the diurnal variation in temperature and humidity. For ease of analysis, the peak moisture content values from the two pins along the ridge were combined as a single value and the same process is repeated for the midpoint of the roof. These observations are presented below. It is interesting to see that for three of the four houses, there is no significant variation i n the moisture content between the ridge and the midpoint.

PAGE 75

75 Figure 4 11 Roof s heathing m oisture c ontent in four h ouses, June 2016 to June 2017 For House 2 in Venice, the moisture content in the ridge was higher than the moisture content in the midpo int during the winter period. This could be explained because of the excellent workmanship in House 2. When an attic is well sealed with spray foam insulation and there is no possible source for rain water shedding, the moisture in the roof sheathing is dr iven by water vapor diffusion and pressure differential between the outside environment and the attic.

PAGE 76

76 The buoyancy of the saturated water molecules tends to shift the moisture upwards towards the ridge of the moisture content. This effect is explained in a clear manner in Lstiburek (2016) Effect of Hurricane Matthew on Heat and Moisture Flow in House 1 In early October 2016, Hurricane Matthew tracke d along the eastern seaboard of Florida. House 1, situated in West Palm Beach was the closest to the path of the hurricane. The measured data is used to visualize the hygrothermal behavior of the attic during the hurricane. Cloud cover and precipitation ( F igure 4 12 ) temperature levels shown for three consecutive and earlier days, F igure 4 12 In addition, the relative humidity measured in the attic does not show the same trends observed for the three earlier days seeing clearer sky. Figure 4 12 Hurricane Matthew tracking along the east coast of Florida. Image of cloud cover over West Palm Beach on October 7th. Source: National Weather Service The diurnal va riation of the moisture content of the roof sheathing also differed from that observed for the three earlier days. Cloud cover shaded the roof during the storm, the roof was wet from precipitation but the moisture content did not raise or drop during the a fternoon

PAGE 77

77 hours as observed for the three earlier days of data. The differences in trends are due to the presence (3 days prior to storm) and absence (during storm) of solar radiation. Figure 4 13 Time history of moisture content, temperature and relati ve hu midity for h ouse 1 in West Palm Beach for October 3rd to October 10th, 2016. Hurricane Matthew tracked along the east coast of Florida. The above observation led to the conclusion that the moisture in the attic originates primarily from inside the h ouse, due to occupant activities but can also emanate from air leakage crossing the outdoor to attic boundary. During evening hours, the night sky radiation cools the roof deck below the outdoor ambient temperature and unwanted moisture in the attic diffus es by the gradient in vapor pressure through the spray foam and enters the wood sheathing. Hence, the moisture content in the wood deck is higher at night. During daytime, the solar radiation drives

PAGE 78

78 the moisture from the wood sheathing back into the attic air, which causes a rise in attic relative reaches peak values. The effect of the solar driven moisture diffusion was clearly documented during sunny days and the phe nomenon was absent during rainy days or when thick cloud cover blocked the irradiance. The weather effect of Hurricane Matthew on House 1 caused less moisture from the sheathing to be driven into the attic air as compared to days having solar irradiance be aring down on the roof. Indoor Air Thermal Comfort ASHRAE Standard 55 defines an indoor thermal comfort zone a range of ambient house temperatures and humidity ratios resulting in indoor conditions comfortable to occupants. Figure 4 14 Indoor therma l comfort zone Source : ASHRAE Standard 55 (2013) The green shaded area in Figure 4 15 represents this comfort zone. This thermal comfort zone produces optimum climate conditions for best occupant comfort. The zone comprises of temperature and humidity f or both heating and cooling seasons. We compare field measured

PAGE 79

79 indoor climates with ASHRAE comfort zone to determine the occupant comfort levels in the sealed attic houses. House 1 is a retrofit home and has a large attic to outside leakage area. House 2, 3, 4 had spray foam installed at the time of construction and have smaller attic to outside leakage area. We have identified an inverse trend between attic air leakage and indoor air comfort. Table 4 3 Percentage t ime h ouse conditions were ou tside of ASHR AE comfort z one House House 1 West Palm Beach House 2 Venice House 3 Orlando House 4 Gainesville Retrofit with ocSPF? YES NO NO NO % of hours outside comfort z one 36% 3.9% 13.6% 11.1% Attic air leakage (cfm) 2510 656 506 187 Figure 4 15 Comparison of measured indoor climate and ASHRAE Standard 55 thermal comfort zone The percentage inside each subplot shows the percentage of hours the indoor conditioned space falls within the ASHRAE Standard 55 thermal comfort zone.

PAGE 80

80 CHAPTER 5 PROBABILISTIC RISK ASSESSMEN T TOOLKIT The Probabilistic Risk Assessment Toolkit ( PRAT ) is a probabilistic indoor climate and sheathing moisture content assessment toolkit. This toolkit utilizes three software packages Building Energy Optimization (BEopt), Energy Plus ( ENERGY PLUS ) and WUFI 1D. ENERGY PLUS is a whole building computer tool developed by the Department of Energy (DOE) focused on modelling the energy consumption in residential and commercial structures by simulating interzonal air and moisture flow along with temperatur e and humidity conditions. BEopt is used as a front end graphical use interface (GUI) for Energy Plus. WUFI is a hygrothermal modelling software used to analyze the heat and moisture movement through building materials. Description of Software Packages Bui lding Energy Optimization Software (BEopt) For accurate numerical prediction of the heat and moisture flow in a sealed attic, it is important to replicate the materials and the physical conditions in the field. To account for the numerous materials used i n residential construction, a more sophisticated software, Building Energy optimization (BEopt) is used. BEopt was also developed by the DOE to serve as a front end graphical user interface (GUI) for ENERGY PLUS Based on previous research, the following v ariables are used as input for the ENERGY PLUS model. 1. Leakage area of attic to outside 2. Leakage area of living space to outside 3. Leakage area of living space to attic 4. Attic duct leakage 5. Interior moisture generation rate 6. Interior heat generation 7. Thermostat s et points

PAGE 81

81 These inputs are specific to each house and characterize the sealed attic behavior in climate zones 1 and 2. When defining the house geometry, the materials are defined as surfaces of two types, heat storage surfaces and heat transfer surfaces. Ceilings, floors, exterior walls and roofs separate two zones of varying temperatures. Hence these members are defined as heat transfer surfaces. Partition walls are within the same zone having constant temperatures and are defined as heat storage walls. T o accommodate for the air leakage through the building envelope, holes are assumed leakage is introduced at the supply duct in the attic. This information along with the occupanc y conditions are important in determining the indoor moisture generation and latent heat generation rates. As per the inputs specified, BEopt generates a visual representation of the whole building envelope. Energy Plus Modelling Software Once the .idf fil e is fed into ENERGY PLUS we have to identify and specify the key variables for which ENERGY PLUS would create simulated results. ENERGY PLUS utilizes two modules the Air Flow network (AFN) and the Effective Moisture Penetration Depth (EMPD) to incorpor ate the interzonal air flow and moisture movement. Gu, 2007 discusses the AFN module. It simulates air, heat and moisture movement between zones caused due to interzonal pressure difference. Holes are defined at each outward facing wall to account for livi ng space to attic leakage. The attic roofs and walls also have holes to represent the attic to outside leakage. A hole in the attic floor characterizes the living space to attic leakage. Duct leakage in the attic is modelled as a forced air system with sup ply and return leakages. EMPD module is used to induce moisture buffering properties of construction materials. Moisture penetrates into the building envelope materials due to short term humidity fluctuations and long

PAGE 82

82 term humidity fluctuations. Christense n et al 2013 states that the indoor humidity is affected by five factors: 1. Interior moisture generation 2. House ventilation 3. Air infiltration 4. HVAC scheduling 5. Moisture sorption or desorption in materials ENERGY PLUS considers a non isoth ermal behavior of the materials. As water vapor is absorbed into the material, the heat of sorption drops and the surface temperature increases. This in turn lowers the relative humidity, which decreases the equilibrium moisture content in the wood. Hence the wood would absorb less moisture from the attic air. This means that the moisture buffering capacity of the materials is reduced due to the inverse relationship between temperature and equilibrium moisture content. The higher the moisture content in the wood the higher must be the relative humidity for absorption to continue. ENERGY PLUS simulations will be performed by varying the key input variables. A test matrix will be created which will contain minimum, maximum and average values of the key input variables used for sim ulating T and RH. The field measured variables for the four houses will fall within this range. ENERGY PLUS simulations produce air flow rates between zones and temperature and RH values for each zone. By comparing the indoor climate (T & RH) with the comf ort zone defined in ASHRAE Standard 55, the range of variables which satisfy the comfort zone can be formulated. Boudreaux et al 2014 found out that the key variables affecting indoor comfort zone are leakage from attic to outside, living space to outside and duct leakage. Simulations closely matching the behavior of the four field houses will be analyzed to produce air leakage rates from the attic to the outside environment. This will be used as an input for the WUFI 1D model.

PAGE 83

83 WUFI 1D Modelling Software WUFI 1D is a hygrothemal modelling software which is used to simulate the moisture content in and moisture flows through materials. A roof section will be designed for each house, giving all dimensions and material properties. An air leakage path will be developed to model the air leakage between the attic and the outside environment. A direct leakage path can be defined to model the energy losses. This leakage will be throughout the section of the roof. For the effect of moisture accumulation, the air lea kage path is more of an indirect path, at the interface of the insulation and the wood sheathing. The air leakage is introduced as a point source leak in WUFI 1D. This minute leakage path has potential to induce condensation effect s which in turn might cause moisture to accumulate at the interface. Critical moisture contents of more than 20% are considered to cause molds, fung i and decay or wood. Moisture contents greater than 30% can cause structural failure of building members (ASHRAE Fundamentals 2013). The air flow rates play an important role in the accumulation of moisture. High outdoor air flow leakage through the attic cause s the attic temperature and moisture to be like the outside air producing lesser condensation effect. Very low air flow rates will not have sufficient vapor pressure to allow the moisture to condense. Boudreaux et al. 2014 concluded that medium air fl ow rates between the attic and the outside environment causes more condensation effect leading to moisture contents greater than 20% for a period of three months in a year (January March 2011). WUFI simulations are performed for all four houses by varyi ng the internal moisture generation rates, the attic to outside leakage, and the living space to outside leakage and the duct leakage. Correlation coefficient of the inputs and the outputs will be computed. A range of these input variables which produce sa fe moisture contents in the wood roof sheathing will be formulated to produce moisture durable sealed attic constructions.

PAGE 84

84 Table 5 1 Inputs for PRAT Building Energy Optimization BEopt Energy Plus WUFI 1D House location and climate throughout the resear ch period House geometry and material properties Building occupancy conditions (number of people, fans, lights, how many meals cooked per day, number of baths per day etc.) Measured thermostat temperatures HVAC schedules Effective Leakage Areas (ELA) for leakages from attic to outside, living space to outside, living space to attic. Attic duct leakage Interior moisture generation rate Interior heat generation Thermostat set points Roof section details Air leakage rates from ENERGY PLUS Outdoor Climate Probabilistic and Deterministic Simulations In Phase I, students from the University of Florida and an ORNL summer intern recorded pertinent characteristics of each single family residence. Information included dimensions of all rooms in the conditioned s pace, slope and style of the roofs, the roof structure, size of the attic and the type and dimensions of the spray foam insulation. In addition, the students documented building envelope dimensions and materials for the exterior wall cladding, exterior win dows and foundation and roof. The ORNL intern used the field measured house characteristics and the BEopt (v 2.6.0.1) program to develop into numerical models, F igure 5 1 The analytical models include the house physical characteristics of mechanical ventilation, space conditioning and associated conditioning schedules, lighting, water heating and appliances. The spray foam insulation was installed during initial construction in three of the four houses, and it was added

PAGE 85

85 during retrofitti ng of the fourth home. Questionnaire data for all four homeowners were reported by Prevatt et al. (2016). The BeOpt models illustrated in F igure 5 1 are used to generate input files for Energy Plus, which, in turn will be used in the PRA T software package. A generic house model was developed to represent the sealed attic houses in Florida. The details of the generic house model and the selected two Florida sealed attic houses are shown in T a ble 5 2 Table 5 2 Simulate d house and f ield h ouse c haracteristics House Generic House Model House 2 Venice House 4 Gainesville Story 2 story 2 story 1 story Plan Area 2,400 sq.ft. 3,592 sq.ft. 3,055 sq.ft. Roof Structure Hip Hip Hip Roof Cover Asphalt Shingle Concr ete S tile Asphalt Shingle Roof Sheathing Plywood (5/8 in) OSB (5/8 in) Plywood (5/8 in) Roof Deck Insulation R 38 10 in. ocSPF R 21 5.5 in. ocSPF R 27 7 in. ocSPF Conditioned Volume 19000 ft 3 42,183 ft 3 29,022 ft 3 Attic Volume 4000 ft 3 7,692 ft 3 14,002 ft 3 # of Occupants 1 6 2 2 Figure 5 1 Generic house model (top). house 2 model (left bottom) and h ouse 4 model (right bottom)

PAGE 86

86 Table 5 3 Type of inputs used for PRAT s imulations Inputs Simulation 1 Simulation 2 Simulation 3 Probabilistic Inp uts Probabilistic + Deterministic Probabilistic + Deterministic House Model Generic model Generic model Specific House Model Exterior Temperature Texas (climate zone 2A) Florida (climate zone 2A) Florida (climate zone 2A) Indoor Moisture and Heat Probab ilistic data Probabilistic data Probabilistic data Attic Duct Leakage Area Generic house leakage Field measured leakage Probabilistic data Attic to Outside Leakage Area Generic House Leakage Field measured leakage Field measured leakage Interior to Out side Leakage Area Generic House Leakage Field measured leakage Field measured leakage Attic to Interior Leakage Area ORNL measured leakage from 12 houses ORNL measured leakage from 12 houses ORNL measured leakage from 12 houses Thermostat Set Point Climate zone 2A Homeowner Survey Homeowner Survey Mechanical Ventilation ASHRAE Standard 62.2 ASHRAE Standard 62.2 ASHRAE Standard 62.2 Simulation Set 3 same as set 2, except for specific house models Generation of Indoor Heat and Moisture Tool ORNL h as developed a sophisticated tool known as the Generation of Indoor Heat and Moisture (GIHM) tool to simulate residential generation of moisture and heat. The GIHM tool uses statistical data for residential user behaviors together with moisture and heat pr oduction rates from occupant activities and appliances inside homes to predict the indoor heat and moisture rates. Since the amount of moisture generated in homes is building and climate dependent, the tool also uses the type of building (multi or single family) and location as inputs. The tool is a probabilistic instrument that simulates hourly variations of moisture and heat generation in homes using a stochastic approach. So, for each climate zone, an output set of hourly profiles captures the range and distribution of moisture and heat generation in real homes.

PAGE 87

87 F i gure 5 2 shows the probability distribution of average daily moisture production simulated by the tool for House 2 and House 4 as a function of occupants compared with th e deterministic ASHRAE 160 standard. The indoor sensible heat generation was based directly on the indoor latent heat (moisture) generation. Figure 5 2 Inte rior latent heat generation for house 2 and h ouse 4 from the GIHM tool To estimate the sensibl e heat generation a multiplier of 2.7 was used with the simulated latent load. This is based on an estimation of the latent/sensible total load split from the appliances, miscellaneous electric loads, and occupants from the Building America research benchm ark. (Boudreaux et al. 2016). Figure 5 3 Interior sensible heat generation f or h ouse 2 and h ouse 4 from the GIHM tool

PAGE 88

88 Table 5 4 Details of p robabilistic and deterministic inputs for PRAT s imulations Parameter Simulation 1 Simulation 2 All Houses House 2 Venice House 4 Gainesville House Model Generic 2400 sq.ft., 2 story, box house, gable roof Generic 2400 sq.ft., 2 story, box house, gable roof Generic 2400 sq.ft., 2 story, box house, gable roof Specific 3592 sq.ft., 2 story, hi p roof Specific 3055 sq.ft., 2 story, hip roof # of Occupants 1 6 2 2 Indoor Heat & Moisture GIHM Tool (varied FFA, # occupants) GIHM Tool (3592 sq.ft. FFA, 2 occupants) GIHM Tool (3055 sq.ft. FFA, 2 occupants) Attic Duct Leakage Area LBNL Residential Diagnostics Database Duct Leakage 0.002 [kg/s] balanced supply and return leakage LBNL Residential Diagnostics Database Duct Leakage Attic to Outside Leakage Area LBNL Table 5 in.A Literature Review of Sealed and Insulated Atticsin. 0.0058 [m 2 ] x 4 for each face (2 gable + 2 roof) 0.0017 [m 2 ] x 4 for each face (2 gable + 2 roof ) Interior to Outside Leakage Area LBNL Residential Diagnostics Database Duc t Leakage 0.0052 [m 2 ] x 8 for each face (N,S,E,W walls for each story) 0.0158 [m 2 ] x 8 for each face (N,S,E,W walls for each story) Attic to Interior Leakage Area ORNL Measured Data from Field Sites ORNL Measured Data from Field Sites ORNL Measured Data from Field Sites Thermostat Set Point 2009 Residential Energy Conservation Survey (RECS) microdata 76F during day 75F during night Homeowner Survey 75F dur ing heating season 80F during cooling season Homeowner Survey Mechanical Ventilation 0 if ACH@50 is above IECC 2015 Code, calculated using ASHRAE 62.2 if ACH@50 is below Code 0.037 [m 3 /s] Based on ASHRAE 62.2 and that homes ACH@50 = 2.2 < 5 0 [m 3 /s] Based on ASHRAE 62.2 and that homes ACH@50 = 5.2 > 5 Simulation Set 3 same as set 2, except for specific house models

PAGE 89

89 Probabilistic Simulations In preparation for the field study, ORNL used BEopt t o model a generic single family two story home specific to climate zone 2A. A base Energy Plus input file (.idf file) was created and, on command, Energy Plus varied the base inputs stochastically to produce a statistical database of simulations for evalua ting the probability of moisture accumulation in the roof sheathing. We have used the numerical results for this preliminary prototype model to identify key variables affecting the moisture performance of sealed attics. The key input variables used in the simulations and th e test matrix follow in Table 5 5 LBNL 2 database is used to determine the air leakage areas for a generic house in climate zone 2A. The indoor moisture is developed from ol. Another important parameter affecting the PRAT outputs is thermostat set points. The thermostat set points for both heating and cooling seasons are obtained from the 2009 Residential Energy Conservation Survey 3 Table 5 5 Probabilistic inputs for PRAT Input Parameter Low Medium High Attic Floor Leakage Area (in2) Attic to Outside Leakage Area (in2) Indoor to Outside Leakage Area (in2) Duct Leakage Rate (kg/s) Indoor Moisture Generation Rate (lb/hr) Indoor Heat Generation Rate (kWh/day) Temperature Hea ting Set Point (oC) Temperature Cooling Set Point (oC) 14.59 11.64 7.29 0.0003 5.68 11.94 14.4 15.6 23.44 59.53 52.07 0.0055 19.31 20.55 20.26 22.50 34.50 329.08 245.64 0.021 50.10 28.58 26.7 29.4 2 LBNL LBNL (2015). "La wrence Berkeley National Laboratory Residential Diagnostics Database." from http://resdb.lbl.gov/ The LBNL database contains whole house air leakage data from 147,000 houses. Climate zone specific data is available for building envelope as well as duct leakage results. 3 Residential Energy Conservation Survey RECS (2015). "Residential Energy Consum ption Survey ". from http://www.eia.gov/consumption/residential/ The RECS Household Survey is a U.S. Department of Energy, Energy Information Administration, research program that collects inform ation from households regarding uses of energy, behaviors and housing characteristics that affect present and long term uses of energy, and the size of household energy bills.

PAGE 90

90 Attic t emperature and relative h umidity 1000 variations o f the seven input parameters were made within the ranges specified in Table 5 5 and fed into BEopt and Energy Plus to perform building energy simulations to predict the attic temperature and relative humidity for a two year period. All 1 000 PRAT simulations are made with a generic house model and probabilistic inputs. The simulated attic temperature and relative humidity is shown below. The 1000 variations can be seen clearly. Figure 5 4 PRAT simul ations: a) attic temperature and b ) relative humidity

PAGE 91

91 Figure 5 5 PRAT simulat ions and field measurements: a) attic temperature and b) relative humidity measured attic temperature and relative h umidity of the selected two Florida house s fall within the blue band in F igure 5 5 The field measured attic temperatures fall near the upper limit of the

PAGE 92

92 PRAT simulated bandwidth and the field measured attic relative humidity fall near the lower limit of the PRAT simulated bandwidth. Roof sheathing m oisture c ontent To compare the actual field measured moisture contents to the simulated moisture contents, the parameters affecting the moisture movement in the field should be considered in the WUFI 1D model roof section. Several parameters like outside temperature, attic temperature, wind speed, radiation of the roof, air leakage paths and material properties affect the moisture movement. The generic models have a concrete tile roof, a weat hering membrane, OSB wood sheathing and 5.5in. of open cell spray polyurethane foam insulation. A small air layer separates the concrete tile and the weathering membrane. The generic house models do not consider any roof leak, air leakage paths from the at tics or varying insulation thickness. The sections are modelled to represent a generic climate zone 2A house having hot and humid climate, with attic temperature simulated from Energy Plus and generic rainfall patterns. However, two models are developed to account for the airflow occurring at the sheathing to insulation interface. Air flow can occur at the sheathing to insulation interface if the thickness of the insulation layer is less and the joists and rafters are not completely covered by the insulatio n. If the insulation layer is thick enough, no air can pass through the interface. Two cases of air flow within the roof section was considered to determine the actual behavior of the roof section in the field. Air flow at the interface between the sheathi ng and spray foam insulation No Air flow at the interface between the sheathing and spray foam insulation

PAGE 93

93 Figure 5 6 Generic roof s ection m odel in WUFI. Figure 5 7 PRAT simulated roof sheathing moisture content. Air flow is considered at the sheathing to insulation interface (top) and no air flow is considered at the sheathing to insulation interface (bottom)

PAGE 94

94 The air flow at the sheathing to insulation interface makes a significant difference in the peak moistur e content levels as shown in F i gure 5 7 It is imperative to find out which case better matches with the field houses to better predict the moisture content. A comparison of the measured moisture contents and simulated mo isture contents are presented below. Figure 5 8 PRAT simulations and field measurements of roof sheathing moisture content : a) with air flow at the insulation cavity for house 2, b) with air flow at the insulation cavity for house 4, c) without air flow at the insulation cavity for house 2, d) without air flow at the insulation cavity for house 4.

PAGE 95

95 From F i gure 5 8 it can be seen that the PRAT simulated moisture contents can match the field measured moisture contents in the roof sh eathing with better accuracy for House 2 and House 4. The difference is an airflow layer at the insulation cavity. The continuous air flow inhibits the water vapor to condense and hence House 2 with the air layer had a 5% reduction in peak moisture conten t when compared to House 4 without the air layer. Correlation of Simulated Moisture Contents with Probabilistic Inputs A correlation analysis was performed f or the PRAT simulations using a generic house model and probabilistic inputs, to determine the cor relation coefficient between input parameters and the peak simulated moisture contents. This simulation set has 1000 variations of all input variables to produce 1000 time histories of moisture contents for a 24 month period. The results of the analysis ar e shown below. Figure 5 9 Correlation coefficient of input parameter on peak moisture content The results show that the interior heat and moisture generation as well as the thermostat cooling set points are positively correlated with the roof sheathin g moisture contents. These

PAGE 96

96 values are indicative that for a generic house model, the occupancy conditions influence the moisture movement in the attic when compared to the building geometry. The duct leakage and thermostat heating set points have a negativ e correlation with the roof sheathing moisture content. The duct leakage into the attic actively serves as a dehumidifier and removes the excess moisture from the attic thereby inhibiting the moisture moveme nt from the attic into the roof. Deterministic Si mulations A second set of simulations was performed using the PRAT generic house model and field measured deterministic air leakage and thermostat inputs. The details of the deterministic inputs are presented in T a ble 5 4 Attic t emperature and r elative h umidity Simulated attic temperatures for House 2 are lower than the measured temperatures in the winter season. House 4 has a better match throughout the year for the simulated and measured data. The 1000 variations of PRAT have a reduced band and superimpose with one another as shown below. Hence the average of the 1000 simulations is used as the input for the WUFI model to predict the moisture content in the roof sheathing. Figure 5 10 1000 PRAT s imulated attic te mperature and h ouse 2 measured attic temperature

PAGE 97

97 Figure 5 11 1000 PRAT s imulated attic temperature and h ouse 4 measured attic temperature Figure 5 12 1000 PRAT simulat ed attic RH and h ouse 2 measured attic RH Figure 5 13 10 00 PRAT simulated attic RH and h ouse 4 measured attic RH

PAGE 98

98 Roof sheathing m oisture c ontent For the roof sheathing moisture content, the actual roof model was used instead of a generic model. By using the actual roof model and Energy Plus simulated attic temperature and relat ive humidity, the moisture contents were expected to have variations between them but closely matching the field measurements. Due to time constraint, 1000 WUFI simulations could not be completed. Instead, simulations were performed with v ariations in the air leakage rate and roof sheathing insulation levels and using field measured temperature conditions. Figure 5 14 Actual roof models in WUFI for a) h ouse 2 with air flow at sheathing to i nsulation interface and b) h ouse 4 without air flow at sheathing to insulation interface Figure 5 15 PRAT simulated moisture content using actual outdoor temperature compared to h ouse 4 measured moisture content

PAGE 99

99 Figure 5 16 PRAT simulated moisture content using actual outdo or temperature c ompared to h ouse 4 measured moisture content Field measured temperature and relative humidity of the attic space and the outdoor environment are used as inputs to the WUFI models shown in Figure 5 13. The ocSPF insulation levels as well as the m aterial pr operties were identical to the field houses Air leakage in the attic varies with time due to differences in wind, temperature and HVAC operation. The varying air leakage could not be incorporated into the WUFI models and clearly affected the moisture move ment. The diurnal variation or the hourly variations in the field measurements was missing in the simulated data. Overall, the mean monthly trends of the measured data were observed in the simulated data but the toolkit could not predict the anomalous mois ture spike in House 4. Parametric WUFI simulations with varying attic a ir leakage r ates Table 5 6 WUFI parametric s imulations Case Number Outdoor Temperature Attic Temperature Air Leakage 1 WUFI inbuilt Energy Plus Probabilistic Simulations LBNL Proba bilistic Data 2 WUFI inbuilt Energy Plus deterministic simulations No air leakage 3 Field measured Field measured No air leakage 4 Field measured Field measured 1 ACH mixing with attic air 5 Field measured Field measured 1 ACH mixing with outside ai r

PAGE 100

100 Table 5 6 shows five parametric WUFI simulations performed by varying the outdoor temperature, attic temperature and the attic air leakage WUFI simulations (Case 5) performed using field measured outdoor temperature and attic temperature along with an air leak into the outside environment matched well with the fie ld measured data. Simulations (Case 2, Case 3) performed with no air leak had very low moisture content (< 5%) throughout the summer. By supplying an air leak of 1 ACH from the attic to the ou tdoor (Case 4) increased the moisture content but not to the level of the field measured data (orange trace in Figure 5 16). Finally, the field measured moisture contents could closely be simulated by using field measured outdoor and attic temperature boun dary conditions as well as an air leak flowing from the outdoor into the attic (Case 5). WUFI simulations also could not predict the extreme moisture content spikes that occurred during the occupied period of House 4. Figure 5 17 Parametric simulations performed for a deterministic roof model. WUFI inputs are shown in Table 5 6

PAGE 101

101 In summer, the partial pressure of the outdoor air is higher than the partial pressure of the attic air. This allows air to flow from the outside into the attic. It is understan dable because, both attics do not have a supply vent pumping air into the attic and typically the attic hatch is closed. So due to the wind blowing onto to the roof system, the leaks allow air to flow into the attic. During the winter, the attic is warmer than the outdoor environment. The attic air with higher partial pressure diffuses into the permeable spray foam insulation. Wood has greater resistance to vapor permeance and temperature less than the dew point of the attic air making the sheathing the fi rst condensing surface for the attic air. These trends are replicated in the WUFI results but the diurnal variation of the moisture content is absent. This is due to the fact that the WUFI model used a constant value of attic air leakage while in reality t his changes every hour. Further analysis is required to accurately model the field conditions. Parametric WUFI s imulations with v arying insulation R v alue A parametric analysis was performed by keeping all input parameters to the WUFI model constant and by varying the R value of the spray foam insulation layer. For this analysis, field measured outdoor temperature and attic temperature are used as inputs to the WUFI model along with an air leakage rate of 1ACH from the outside to the attic. The comparison i n question might not reflect the true world behavior. By changing the insulation levels under the roof deck, the temperature and humidity of the attic space changes. However, for this comparison the temperature and humidity were the same for all four vari ations in insulation. The results of th e WU FI analysis is presented in Figure 5 1 8 The analysis shows that R 38 insulation being more resistant to vapor flow, reduces the partial pressure of the foam thus reducing moisture movement from the attic to the o utdoor. A small portion of the moisture laden air reaches the cold wood sheathing and condenses at the sheathing to insulation interface. However, none of

PAGE 102

102 the levels of insulations produce dangerous moisture contents closer to 20% in a normal working condi tion. Figure 5 18 WUFI simulations for house 2 and h ouse 4 with different R value of insulation

PAGE 103

103 CHAPTER 6 CALIBRATION OF THE PRAT WITH MEASURED DATA The Probabilistic Risk Assessment Toolkit (PRAT) was created with the aim of predicting roof sheath ing moisture content in sealed attics by varying seven input parameters. For the first set of PRAT simulations, the inputs were probabilistically varied and the resulting attic temperature, attic relative humidity and the roof sheathing moisture content we re benchmarked against field measured data. The correlation coefficient for the input variables and the roof sheathing moisture content determined the most affecting input parameters. For the second set of PRAT simulations, field measured thermostat set po ints, air leakage areas, duct leakage areas were used as deterministic inputs for the PRAT. Indoor heat generation, indoor moisture generation and attic floor leakage values were probabilistically varied. The predictive power of the Probabilistic Risk Asse ssment Toolkit (PRAT for the deterministic simulations are discussed in this chapter. For a visual comparison, the hourly values of measured data are plotted along the x axis and simulated data along the y axis. Data points with good prediction fall along a 45 o centerline. A band is created on either side of the centerline (+/ 5 o F for attic temperature, +/ 5% for attic relative humidity and +/2% for roof sheathing moisture content) to account for errors caused in measurement, prediction and analysis. Data points falling within the bandwidth are considered to have good correlation. To quantify the deviation or the spread of data, the mean, median and standard deviation of the measured and simulated parameters are computed. A probability density function is fitted to the histogram to visualize the variation in distribution of data The best matching probability density function fit has the least log likelihood and better represents the variations in the dataset. Finally, the coefficient of variation of root m ean squared error and normal mean bias error are computed and compared against ASHRAE Guideline 14.

PAGE 104

104 Scatter Plots of Measured and Simulated Data To visually compare the prediction accuracy on a 24 hour average data a scatter plot is used where the daily d ata points with good prediction accuracy fall along a 45 o centerline. Previous research (Salonvaara et al. 2013, Boudreaux et al. 2014, Lstiburek et al. 2015, Prevatt et al. 2017) show that prediction of temperature and moisture becomes difficult due to th e complexity of building materials and how heat and moisture move through the building envelope. Hence, a band is created on either side of the centerline (+/ 5 o F for attic temperature, +/ 5% for attic relative humidity and +/2% for roof sheathing moistu re content) to account for errors caused in measurement, prediction and analysis. The prediction accuracy for attic temperature, attic relative humidity and roof sheathing moisture content for House 2 in Venice is given below. Figure 6 1 Comparison of 24 hour average of measured and simulated parameters for h ouse 2 Data points inside red band indicate good prediction power of the PRAT For House 2 in Venice, the attic temperatures were well predicted while the relative humidity was consistently over p redicted. The roof sheathing moisture contents had good

PAGE 105

105 prediction in a general sense but had 100% correlation in the winter. Figure 6 2 Comparison of 24 hour average of measure d and simulated parameters for h ouse 4. Data points inside red band indica te good prediction power of the PRAT For House 4 in Gainesville, the attic temperatures were well predicted while the relative humidity was consistently over predicted in the summer and under predicted in the winter. The house is occupied only in the win ter months during when the attic humidity climb over 80%. The above plot shows a 24 hour average of the parameters. The roof sheathing moisture contents had good prediction summer but the model could not predict the peak moisture contents in House 4. Error in Prediction The error in prediction or the prediction accuracy is useful to quantify the predictive capacity of the PRAT toolkit. The coefficient of variation of the root mean squared error and the normal mean bias error are used to quantify the error i n prediction. ASHRAE Guideline 14 says that the root mean squared error is a measure of variability in the data. For every hour, the error, or the difference in the paired data points is calculated and squared. The sum of all the squares is divided by the number of hours to produce the mean squared error (MSE). A square root of the

PAGE 106

106 result yields the root mean squared error (RMSE). The coefficient of variation of the root mean squared error (CV RMSE) is calculated by dividing the RMSE by the mean of the meas ured data. Hence, CV RMSE is a measure of the average deviations in the dataset and values under 30% are acceptable for model validation (ASHRAE Guideline 14). The normal mean bias error (NMBE) gives a measure of the overall bias in data. Bias in data occu rs if a certain parameter consistently affects the outputs. NMBE values under 10% are accepted for model validation (ASHRAE Guideline 14). Figure 6 3 C oefficient of variation of root mean squared error for h ouse 2 and h ouse 4 in s ummer and w inter. Red line shows ASHRAE Guideline 14 limit of 30% The CV RMSE values for House 2 fall within the 30% limit both in the summer and winter. For House 4, the relative humidity in winter exceeds the 30% limit but the yearly prediction ranges fall within the 30% li mit.

PAGE 107

107 Figure 6 4 N ormal mean bias error for h ouse 2 and h ouse 4 in Summer and Winter. Red line shows ASHRAE Guideline 14 limit of 10% The NMBE exceed the ASHRAE limit 10% only for attic relative humidity. The main reasons for the model to fail in prediction of humidity are: 1) moisture buffering properties of the numerical model and the actual field house materials are different, 2) latent and sensible heat can be guessed for an average household; it is very difficult to match the actua l field conditions.

PAGE 108

108 CHAPTER 7 CONCLUSIONS A combined numerical and field study was conducted to collect field data, benchmark the data against numerical tools and document the effects of air leakage and the diffusion of water vapor on the moisture flow occurring in sealed semi conditioned attics Prevatt et al. (2016) and Prevatt et al. (2017) Field s ite selection s w ere base d on homes setup with unventilated, semi conditioned attics, the type of roof system, placement of the HVAC and the occupation of the homeowner. Homeowners who are builders or who are closely related to construction were given workmanship was better managed by the homeowner, which would hopefully eliminate the effects of poor roof and attic workmanship that could cause water leakage and confound the study The main conclusions of this thesis are: No moisture accumulation (moist ure contents over 20%) is seen in the roof sheathing of the Florida homes monitored for a full year. Building envelope air leakage affects the indoor thermal air comfort and energy use of the home Air leakage for the interior to the attic and from the exterior to the attic provide sources of moisture that can accumulate in the sheathing of the attic and cause high humidity in the attic and conditioned space during periods of peak irradiance rying inputs can be used to represent sealed attic houses in Florida The PRAT toolkit can predict the existing moisture contents and can be used to predict moisture contents with extreme input conditions Analysis of field data showed that all the four hom es with sealed attics had measured moisture accumulations in the roof sheathing that yielded less than 20% moisture content over the duration of the one year field study. House 4 located in Gainesville had a spike in moisture content during January 2017 th at reached levels of about 20% for a two week period. The reason for this spike is unknown but presumed due to some occupancy habit because the house is

PAGE 109

109 occupied only during the winter months. However, the moisture content did drop to safer levels by the s tart of February 2017. The moisture in the attic originates primarily from inside the house, due to occupant activities but can also emanate from air leakage crossing the outdoor to attic boundary. During evening hours, the night sky radiation cools the r oof deck below the outdoor ambient temperature and unwanted moisture in the attic diffuses by the gradient in vapor pressure through the spray foam and enters the wood sheathing. Hence, the moisture content in the wood deck is higher at night. During dayti me, the solar radiation drives the moisture from the wood sheathing content drops around solar noon and the attic humidity reaches peak values. The effect of the solar driven moisture diffusion was clearly documented during sunny days and the phenomenon was absent during rainy days or when thick cloud cover blocked the irradiance. The weather effect of Hurricane Matthew on House 1 caused less moisture from the sheathing to be driven into the attic air as compared to days having solar irradiance bearing down on the roof. The measured attic leakage rates for House 1 located in West Palm Beach were excessively high which essentially made the attic perform as a conv entionally ventilated attic. Therefore, attic ventilation removed any excessive moisture. However, the air leakage caused the indoor climate to fall outside the comfort zone prescribed by ASHRAE 55. About 36% of the time the indoor temperature and relative humidity was outside the thermal comfort zone. The other three houses had lower levels of attic leakage and better maintained comfort conditions. The PRAT toolkit was further formulated and benchmarked against the year of measured field data. Initial eff orts using fixed rates of air leakage crossing the boundary of the conditioned space and using the actual house geometry yielded poor agreement with the field measurements.

PAGE 110

110 Assessments showed that air leakage was a predominant parameter in better predictin g the temperature and humidity of the conditioned space and the attic space. The team opted to use a more generic model based on a more robust set of empirical data (RECS 2015) for a multiplicity of homes representing climate zone CZ 2A. As a result, the g eneric model successfully benchmarked the field data and was therefore used to predict the moisture content of the sheathing in the Probabilistic Risk Assessment Toolkit (PRAT). The toolkit varied seven input parameters to predict the moisture content in t he roof sheathing; leakage areas from 1) the attic to the outside, 2) indoor space to the outside and 3) indoor space to the attic as well as 4) the attic duct leakage, 5) interior heat generation, 6) interior moisture generation and 7) thermostat set poin ts. A correlation analysis was performed to quantify the effect of each of the seven parameters on the peak moisture content in the roof sheathing. The indoor heat and moisture generation rates along with the duct leakage into the attic play a major role in affecting the moisture flows in a sealed attic. The duct leakage brings in conditioned air into the attic and helps mitigate the high humidity in hot and humid climates. thermostat temperature. House 4 in Gainesville is unoccupied during the summer and the homeowner sets the thermostat to 80F. High indoor temperature coupled with high outdoor temperatures causes near saturated levels of humidity in the attic air. However, the 7 in. of ocSPF (R 27) insulation drops the partial pressure gradient for attic air to the foam and impedes moisture from condensing on the sheathing. Future Scope The Probabilistic Risk Assessment Toolkit (PRAT) was developed to predict the heat an d moisture flows in a sealed attic for a hot and humid climate. The sealed attics analyzed using the

PAGE 111

111 WUFI tool considered well constructed roofs with no rain water shedding into the attics. The roof was subjected to normal functioning. A future scope would be to induce a rain water leak onto the sheathing and predict the moisture contents for a prolonged period to observe the effect of water intrusion on the moisture durability of sealed attics. Applications The PRAT toolkit can be utilized to predict moist ure performance of sealed attics in various climate zones of the USA. By varying the input parameters to the toolkit, the results could be generated for a custom house configuration. The tool can be utilized by the building code authorities to predict dang erous moisture contents for varying input condition s.

PAGE 112

112 LIST OF REFERENCES Circle NE Atlanta, GA 30329. www.ashrae.org. ASHRAE Standard 55, 2013. in.Thermal Environmental Conditions for Human Occupancy,in. 1791 Tullie Circle NE Atlanta, GA 30329. www.ashrae.org. ASTM Standard E779, 2010, "Standard Test Method for Determination of Air Leakage Rate by Fan Pressurization," ASTM International, West Conshohocken, PA, 2003, DO I: 05/16/2011, www.astm.org. Baechler, M. C., Gilbride, T. L., Cole, P. C., Hefty, M. G., and Ruiz, K. (2015). "Building America Best Practice Series Volume 7.3: Guide to Determining Climate Regions by County." Building America Best Practices Series B. A merica, ed., 45. Bailes, A. (2014). "This Thermostat Setting Can Cost You Money and Make You Sick." [Blog post], Retrieved from: http://www.energyvanguard.com/blog/76674/This Thermostat Setting Can Cost You Money and Make You Sick Energy Vanguard Date Ac cessed: 06/29/2017 BECP (2009). "Energy Code Climate Zones." Building Energy Codes Research Center. Boardman, C. R., Glass, S. V., and Lebow, P. K. (2017). "Simple and accurate temperature correction for moisture pin calibrations in oriented strand board." Building and Environment 112, 250 260. Envelopes of Buildings, XIII, proceed ings of ASHRAE THERM XII, Clearwater, FL., Dec. 2016. Boudreaux, P. R., Pallin, S. B., Hun, D. E., Kehrer, M., Jackson, R. K., & Desjarlais, A. O. (2016). Protocol to Evaluate the Moisture Durability of Energy Efficient Walls. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Building Technologies Research and Integration Center (BTRIC). Boudreaux, P., Pallin, S., & Jackson, R. (2013). Moisture Performance of Sealed Attics in the Mixed Humid Climate. Retrieved from Springfield, VA: http:/ /info.ornl.gov/sites/publications/files/Pub46670.pdf Bureau, U. C. (2011). Historical Census of Housing Tables. Retrieved from https://www.census.gov/hhes/www/housing/census/historic/units.html. Chasar,D., Sherwin, J., vonSchramm, V., Chandra, S. 2010. by Whole Building XI International Conference.

PAGE 113

113 Christensen, C., & National Renewable Energy Laboratory (U.S.). (2006). BEopt software for buildi ng energy optimization features and capabilities. In Nrel/Tp 550 39929 (pp. 16 p.). Retrieved from http://purl.access.gpo.gov/GPO/LPS89821 Colon, C. (2011). New Construction Builders Challenge: Sealed Attics and High Efficiency HVAC in Central Florida. Re trieved from Cocoa, FL: http://www.fsec.ucf.edu/en/publications/pdf/FSEC PF 454 11.pdf Conservatory, T. E. (n.d.). Minneapolis Duct Blaster Operations Manual. Retrieved from https://buildingsfieldtest.nrel.gov/sites/default/files/pdfs/duct_blaster_manual_ series_b_ _dg700_0.pdf Crawley, D. B., Pedersen, C. O., Lawrie, L. K., & Winkelmann, F. C. (2000). Energy Plus: Energy Simulation Program. ASHRAE Journal, 42(4), 49. EcoLogic Energy Solutions 2009. "The Science of Spray Foam Insulation" http://www.ecologic es.com/pdf/scienceofsprayfoam.pdf Foam, A. S. (2014). "Closed Cell vs Open Cell Foam." < http://www.aplussprayfoam.com/?page_id=84 >. (05/20/2017). Florida Energy Conservation Code, 5th Edition, 2014 Web site: http://floridabuilding2.iccsafe.org/app/book/toc/2014/Florida/Energy%20Conservation% 20Code/index.html Grin, A., Smegal, J., & Lstiburek, J. (2013). Application of Spray Foam Insulation Under Plywood and OSB Roof Sheathing. Building America Report 1312. Karagiozis, A., Knzel, H., & Holm, A. (2001). WUFI ORNL/IBP a North American hygrothermal model. Paper presented at the Eighth Building Science and Technology. Kumaran, M. K. 2008. "A Thermal and Moisture Property Database for Common Building and Insulating Materials," American Society of Heating, Ventilation and Air Conditioning Engineers (ASHRAE), RP 1018. LBNL (2015). "Lawrence Berkeley National Laboratory Residential Diagnostics Database." from http://resdb.lbl.gov/ Date retrieved: 12 June, 2 017 Less, B., Walker, I., & Levinson, R. (2016). A Literature Review of Sealed and Insulated Attics Thermal, Moisture and Energy Performance. Lstiburek, J. (2006). Understanding Attic Ventilation. Retrieved from https://buildingscience.com/documents/diges ts/bsd 102 understanding attic ventilation Lstiburek, J. (2015). Venting Vapor. Retrieved from https://buildingscience.com/documents/insights/bsi 088 venting vapor

PAGE 114

114 Corpor ation. https://buildingscience.com/documents/building science insights/bsi 016 ping pong water and chemical engineer?utm_source=Building+Science+Corporation+List&utm_campaign=c7470a2abe BSC+Newsletter+Issue+%2392&utm_medium=email&utm_term=0_194890bc8c c747 0a2abe 63894017 Markose, S. M., & Alentorn, A. (2005). The generalized extreme value (GEV) distribution, implied tail index and option pricing. Masters, F. J., & Gurley, K. R. Draft Final Report for Project Entitled: Impact of Spray Foam Insulation on Dur ability of Plywood and OSB Roof Decks Performance Period: 1/6/2014 6/15/2014. Miller, W., Desjarlais, A., & LaFrance, M. (2013). Roof and Attic Design Guidelines for New and Retrofit Construction of Homes in Hot and Cold Climates. Paper presented at the ASHRAE 2013. Miller, W. A., Railkar, S., Shiao, M. C., & Desjarlais, A. O. (2016). Sealed A ttics Exposed to Two Years of Weathering in a Hot and Humid Climate. Minneapolis Duct Blaster Operations Manual (Series B systems). (August 2012). Retrieved from http://www.energyconservatory.com/sites/default/files/documents/mod_3 4_dg700_ _new_flow_rings_ _cr_ _tpt_ _no_fr_switch_manual_ce_0.pdf Pallin, S. B., Boudreaux, P. R., & Roderick, J. (2014). I ndoor Climate and Moisture Durability Performances of Houses with Unvented Attic Roof Constructions in a Mixed Humid Climate. Retrieved from Oakridge, TN: http://info.ornl.gov/sites/publications/files/Pub52510.pdf Parker, D. S., Sonne, J. K., & Sherwin, J. R. (2002, August 2002). Comparative Evaluation of the Impact of Roofing Systems on Residential Cooling Energy Demand in Florida. Paper presented at the ACEEE Summer Study, Washington. Prevatt, D. O., Miller, W. A., Boudreaux, P. R., Jackson, R., Gehl, A., Atchley, J., . Talele, M. (2016). Commissioning a Field Study of Four Semi Conditioned and Non Ventilated Attics in Florida. (UF#00125306). Florida Building Commission Tallahassee, 25. Prevatt, D. O., Viswanathan, A., Miller, W. A., Boudreaux, P., Pa llin, S., and Jackson, R. (2017). "Analytical Assessment of Field Data to Predict Moisture Buildup in Roof Sheathing of Sealed Attics." Florida Building Commission, Tallahassee, 25. RECS (2015). "Residential Energy Consumption Survey ". from http://www.eia .gov/consumption/residential/. Date retrieved: 12 June, 2017

PAGE 115

115 Rose, W. B. (1995). Attic construction with sheathing applied insulation (0001 2505). Framed Attics in Cool Marine Climates. ASHRAE Thermal Performance of the Exterior Envelopes of Whole Building XI International Conference. Rudd, A., Lstiburek, J., & Kohta, U. (1999). Unvented Cathedralized Attics. Retrieved from https://buildingscience.com/documents/reports/rr 9904 unvented cathedralized attics where we ve been and where we re going/view Rudd, A. F., & Lstiburek, J. W. (1998). Vented and sealed attics in hot climates. ASHRAE Transactions, 104, 1199. Salonvaara, M., Karagiozis, A., & Desjarlais, A. (2013). Moisture p erformance of sealed attics in climate zones 1 to 4. Shreyans, S. (2011). Thermal Performance of Foam Retrofitted Vented Residential Attic. (MS Civil Engin eering Thesis), University of Florida. Straube, J., Onysko, D., & Schumacher, C. (2002). Methodology and design of field experiments for monitoring the hygrothermal performance of wood frame enclosures. Journal of Thermal Envelope and Building Science, 26(2), 123 151. ld and Hot http://tinyurl.com/qaf267v Walker, I.S. 1998. Technical Background for Default Values used for Forced Air Systems in Proposed ASHRAE standard 152P. ASHRAE Trans. Vol.104 Pa rt 1. (presented at ASHRAE TC 6.3 Symposium, January 1998. LBNL 40588.

PAGE 116

116 BIOGRAPHICAL SKETCH Mr. Aravind Viswanathan hails from Chenna degree in c ivil e ngineering from Anna University in 2015. During his un dergraduate studies, he worked primarily on the interaction of wind with steel structures. After graduating, he jo ined the D epartment of Civil and Coastal Engineering at the University of Florida in 2015 to pursue a m e completed a m thesis in 2017 under th e gu idance of Dr. David Prevatt; as a part of the Wind Hazard Damage Assessment Group at UF.