|Table of Contents|
Front Cover 1
Front Cover 2
Table of Contents
List of figures and tables
National solar data program reports
2. Summary and conclusions
3. System description
4. Performance evaluation techniques
5. Performance assessment
Appendix A. Definitions of performance factors and solar terms
Appendix B. Solar energy system performance equations
Back Cover 1
Back Cover 2
Solar Energy System
HULLCO CONSTRUCTION COMPANY
SINGLE FAMILY RESIDENCE Prescott, Arizona
May, 1978 through April, 1979
U.S. Department of Energy
National Solar Heating and
Cooling Demonstration Program
National Solar Data Program
This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Department of Energy, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibwty for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights.
This report has been reproduced directly from the best available copy.
Available from the National Technical Information Service, U. S. Department of Commerce, Springfield, Virginia 22161.
Price: Paper Copy $5.25
SOLAR/1043-79/14 Distribution Category UC-59
SOLAR ENERGY SYSTEM PERFORMANCE EVALUATION
MAY 1978 THROUGH APRIL 1979
MICHAEL W. WESTON, PRINCIPAL AUTHOR
V. S. SOHONI, MANAGER OF PERFORMANCE ANALYSIS
LARRY J. MURPHY, IBM PROGRAM MANAGER
150 SPARKMAN DRIVE
HUNTSVILLE, ALABAMA 35805
PREPARED FOR THE
DEPARTMENT OF ENERGY
OFFICE OF ASSISTANT
CONSERVATION AND SOLAR APPLICATIONS
UNDER CONTRACT EG-77-C-01-4049
H. JACKSON HALE, PROGRAM MANAGER
TABLE OF CONTENTS
Section Title Page
I F 0R L'IOR. .. ................ ....1
3 SYSTEM UESCRIPTION .. ........ ........5
4 PERFORMANCE EVALUATIONi TECHNIQUES. .........11
4.1 Instrumentation and Data Acquisition . . 12 4.2 Energy Balance Technique. ............12
5 PERFORMANCE ASSESSMENT. .. .............19
6 REFERENCES. .. ....................47
APPENDIX A DEFINITION OF PERFORMANCE FACTORS AND
SOLAR TERMS. ........ ............A-1
APPENDIX B SOLAR ENERGY SYSTEM PERFORMANCE EQUATIONS . . B-1
LIST OF FIGURES AND TABLES
FIGURE TITLE PAGE
1-1 Hullco Construction Solar Energy System . . . . 2
3-1 Hullco Construction Company Solar Energy System
Schematic . . . . . . . . . . . 6
3-2 Interior View of Greenhouse . . . . . . . 7
3-3 System with Summer Shading in Position . . . . 8
3-4 Wood Stove . . . . . . . . . . . 9
5-1 Average Monthly Solar Collection Efficiency . . . 25
5-2 System Performance Unoccupied Building . . . . 27
5-3 Average Monthly Storage Temperatures . . . . . 28
5-4 Average Monthly Greenhouse Wall and Building
Temperatures . . . . . . . . . . . 29
5-5 Greenhouse Wall Temperatures April 18, 1979 . . . 31
5-6 Average Monthly Comfort Index Values . . . . . 35
5-7 Zone 1 Comfort Index . . . . . . . . . 37
5-8 Zone 2 Comfort Index . . . . . . . . . 38
5-9 Average Monthly Relative Humidity Levels . . . . 39
5-10 Interior Daily Average Relative Humidity and
Greenhouse Fan Operating Energy . . . . . . 41
5-11 Daily Minimum and Maximum Storage Temperatures and Comfort Index . . . . . . . . . . 42
5-12 System Performance December 5-6,, 1978 . . . . 44
5-13 Interior View of Living Room Area . . . . . . 46
TABLE TITLE PAGE
4-1 Hullco Construction System Sensor Locations . . . 13
5-1 Weather Conditions . . . . . . . . . 20
5-2 Comparison to Design Performance Heating Season . . 21
5-3 System Thermal Performance Summary Heating Season . 23
5-4 Energy Savings . . . . . . . . . . 33
5-5 Comfort Levels . . . . . . . . . . 34
NATIONAL SOLAR DATA PROGRAM REPORTS Reports prepared for the National Solar Data Program are numbered under a specific format. For example, this report for the Kulico Construction systen project site is designated as SOLAR/1043-79/14. The elements of this designation are explained in the following illustration.
Prepared for the____ Report Type
National Solar Designation
Demonstration Site Year
0 Demonstration Site Number:
Each Project site has its own discrete number 1000 through 1999 for residential sites and 2000 through 2999 for commercial sites.
* Report Type Designation:
This number identifies the type of report, e.g.,
Monthly Performance Reports are designated by the numbers 01
(for January) through 12 (for December).
Solar Energy System Performance Evaluations are designated
by the number 14.
Solar Project Descriptions are designated by the number 50.
Solar Project Cost Reports are designated by the number 60. These reports are disseminated through the U. S. Department of Energy, Technical Information Center, P. 0. Box 62, Oak Ridge, Tennessee 37830.
The National Program for Solar Heating and Cooling is being conducted by the Department of Energy under the Solar Heating and Cooling Demonstration Act of 1974. The overall goal of this activity is to accelerate the establishment of a viable solar energy industry and to stimulate its growth in order to achieve a substantial reduction in nonrenewable energy resource consumption through widespread applications of solar heating and cooling technology.
Information gathered through the Demonstration Program is disseminated in a series of site-specific reports. These reports are issued as appropriate, and may include such topics as:
0 Solar Project Description
0 Design/Construction Report
0 Project Costs
0 Maintenance and Reliability
0 Operational Experience
0 Monthly Performance
0 System Performance Evaluation
The International Business Machines Corporation is contributing to the overall goal of the Demonstration Act by monitoring, analyzing, and reporting the thermal performance of solar energy systems through analysis of measurements obtained by the National Solar Data Program.
The System Performance Evaluation Report is a product of the National Solar Data Program. Reports are issued periodically to document the results of analysis of specific solar energy system operational performance. This report includes system description, operational characteristics and capabilities, and an evaluation of actual versus expected performance. The Monthly Performance Report, which is the basis for the System Performance Evaluation Report, is published on a regular basis. Each parameter presented in these reports as characteristic of system
performance represents over 8,000 discrete measurements obtained each month by the National Solar Data Network.
All reports issued by the National Solar Data Program for the Hullco Construction solar energy system are listed in Section 6, References.
This Solar Energy System Performance Evaluation Report presents the results of a thermal performance analysis of the Hullco Construction passive solar space heating system. Analysis covers operation of the system from May 1978 through April 1979. The Hullco Construction solar energy system provides space heating to a single-family residence (Figure 1-1) located in Prescott Arizona, using an attached greenhouse as the primary solar energy collection area. A more detailed system description is contained in Section 3.0. Analysis of the system thermal performance was accomplished using measurements and a system energy balance technique described in Section 4. Section 2 presents a summary of the results and conclusions obtained, while Section 5 presents a detailed assessment of the system thermal performance.
Figure 1-1. HULLCO CONSTRUCTION SOLAR ENERGY SYSTEM
2. SUMMARY AND CONCLUSIONS
This system Performance Evaluation Report provides an operational summary of the solar energy system at the Hullco Construction site, a single family residence located in Prescott, Arizona. This analysis is conducted by evaluation of measured system performance and by comparison of measured weather data with long-term average climatic conditions. The performance of major subsystems is also presented.
Features of this report include: a system description, a review of actual system performance during the report period, analysis of performance based on evaluation of meteorological load and operational conditions, and an overall discussion of results.
The Hullco Construction passive solar space heating system satisfied 75 percent of the building energy requirement during the winter of 19781979. Wood, as another renewable energy form, provided much of the remainder of the energy requirement. Although this performance level is slightly below design performance specifications, the differences in design and actual performance can be accounted for by both the severe winter weather conditions encountered and by facets of owner interaction with operation of the system. Comfort levels inside the building were acceptable over most of the year, although some comfort-related problems were encountered with summer overheating and winter interior humidity levels. However, practical solutions to the comfort difficulties have been identified so that the problems can be reduced during the next year of system operation. Since most of the difficulties encountered were related to system operation or control, it is important that the home owner have a good awareness of appropriate system control operations. The important aspects of system control awareness, along with a detailed discussion of the performance and comfort encountered, are presented in Section 5.
Digitized by the Internet Archive in 2012 with funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation
3. SYSTEM DESCRIPTION
The Hullco Construction solar energy system Cl]* is a passive space heating system for a single-family residence located in Prescott, Arizona. The 1,056 square foot, south-facing building, illustrated in the drawings of Figure 3-1, is a combination greenhouse and direct gain passive system. Incident solar energy enters the building through approximately 400 square feet of double-glazed prefabricated Kalwall panels. Two sliding glass doors between the greenhouse and the house, along with a window in the bathroom, admit incident solar energy directly into the master bedroom, living room, and bath areas of the house. Collected solar energy which is not used to satisfy the immediate building space heating demand is stored directly in the massive walls and floors of the building or indirectly in the 670 cubic feet of 3 to 5 inch diameter rock storage located under the floor of the north half of the building. Stored energy is released by low-temperature radiation and convection to satisfy the building space heating demand during periods of time when incident solar energy is not available.
Direct storage of collected solar energy is provided by the walls and floor of the building. The brick floor and the black painted north wall of the greenhouse (Figure 3-2) provide solar energy storage for the greenhouse. The 12-inch thick, sand-filled concrete block greenhouse north wall acts as a Trombe wall, storing collected energy from the greenhouse during the day and releasing the collected energy by radiation to the south part of the building at night. The 4-inch thickbuilding concrete slab floor acts as direct solar storage, particularly in the living room and master bedroom areas where the floor is covered with Mexican tile masonry. Additional storage is provided by the 8-inch thick, solid grouted, concrete exterior insulated building walls on the north, east, and west perimeter of the building.
Indirect storage of collected solar energy is provided by the 670 cubic feet of rock storage located under the north side of the building and by the 4-inch thick carpeted concrete slab floor poured on top of the rock.
Numbers in brackets denote reference numbers in Section 6.
BEDROOM BEDROOM KITCHEN
MASTER BATH LIVING ZON
PLAN VIEW ) SOUTH
FLOOR USED AS G ,STORAGE
WALL_//ROCK BED STORAG' SECTION VIEW ) Figure 3-1. HULLCO CONSTRUCTION COMPANY SOLAR ENERGY SYSTEM SCHEMATIC
Solar energy collected in the greenhouse is transferred to the rock bed from vents at the top of the greenhouse through under-floor ducts by two one-third horsepower blowers located at the east and west ends of the greenhouse shown in Figure 3-2. After transferring energy to the rocks,
Figure 3-2. INTERIOR VIEW OF GREENHOUSE
the air returns to the greenhouse through the house from floor vents located at the north side of the building. The greenhouse fans operate when temperatures near the top of the greenhouse reach approximately 90*F. Energy stored in the rock is released through the carpeted concrete floor to the house.
Summer overheating protection is provided by venting of the greenhouse and by both natural and artificial shading of the greenhouse glazing. Natural shading of the greenhouse is accomplished by the use of an
existing tree to the southeast of the structure. However, the tree, a Juniper, does shade the greenhouse some during the mornings during the heating season. Additional greenhouse shading can be provided by a redwood snow fence placed over the glazing (Figure 3-3). Draperies covering the
Figure 3-3. SYSTEM WITH SUMMER SHADING IN POSITION
sliding glass doors on the north wall of the greenhouse can be closed to prevent incident sunlight from entering the building. Ni-ghttime venting of the building can be used to cool the energy storage masses, thus allowing the building to be cooled during the day as energy generated inside the building is absorbed by the walls and floor. Daytime venting of the greenhouse is accomplished using a thermostatically controlled powered fan located at the top of the greenhouse to draw air through the house and out at the top of the greenhouse.
Low building heating loads are maintained by the use of good energy conservation construction techniques. The north, east, and west walls are insulated on the outside of the concrete blocks with two inches of
styrofoam to yield a total wall R-value of 11. Nine inches of fiberglass batt insulation is used in the roof to yield a roof R-value of 32. The entire perimeter of the concrete slab floor is insulated. A minimum of window area is used on the north, west, and east walls. The building is bermed four feet into the earth on the north and west sides.
Auxiliary energy for space heating can be supplied by either electric radiant heat panels or by the wood-burning stove located in the living room (Figure 3-4). The stove uses outside air for combustion. The
Figure 3-4. WOOD STOVE
ceiling-mounted electric radiant heat panels located in each room are controlled by individual room thermostats.
The predicted annual solar contribution to the building load is 80 percent. Design monthly building heating loads, including the greenhouse load, are approximately 11,000 Btu per heating degree-day.
A non-instrumented thermosyphoning hot water system is used to provide domestic hot water preheating. The collector panel for the hot water system is located immediately behind the center panel of the greenhouse, with the preheat tank located in the greenhouse immediately above the collector. Hot water is preheated in the tank, and passes on demand to the hot water heater where it is raised to operating temperature.
4. PERFORMANCE EVALUATION TECHNIQUES
The thermal performance of the Hullco Construction solar energy system is evaluated using data from monitoring instrumentation located at the site. Performance factors which represent the thermal performance of the system are computed using this measurement data. Definition of the performance factors used follows the general outlines of the intergovernmental agency report, "Thermal Data Requirements and Performance Evaluation Procedures for the National Solar Heating and Cooling Demonstration Program," . The analysis technique used is outlined in another report, "Performance Evaluation Reporting for Passive Systems," . This section addresses the application of the passive system thermal performance evaluation technique to the Hullco Construction system along with a description of the measurements used to monitor the system performance.
4.1 Instrumentation and Data Acquisition
Measurement data is provided for analysis using the IBM-developed Central Data Processing System (CDPS), . Data from sensors is sampled approximately once each five minutes by a microprocessor controlled device 'located at the site and recorded on cassette tape. Approximately once per day a processor at the CDPS automatically accesses the site located microprocessor via telephone to collect the data stored on tape. This data is further processed by another computer to provide the measurement data in a form compatible with both visual and automated data analysis procedures. The measurement data is scanned by an analyst, either in tabular or plot form, on a frequent basis in order to detect significant changes in solar energy system or instrumentation/data acquisition system operation. The measurement data is also available to software which provides for the computation of the performance factors discussed in the remainder of the report.
System thermal performance at the Hullco Construction site is monitored using 70 different measurements of conditions at the site. The monitoring measurements sampled at the site are summarized in Table 4-1. The measurement identification number used in Table 4-1 follows the system defined in Reference . The prefix I is used for insulation measurements, T for temperature measurements, EP for electrical power, W for air or liquid flow, V for wind velocity, and D for switches or wind direction. Units used for the measurements are Btu/ft 2_ hr for insulation,
*F for temperature, kilowatts for electric power, feet per minute for air flow, miles per hour for wind speed and degrees for wind direction.
4.2 Energy Balance Technique
The basis for the analysis technique is an energy balance concept developed for use in the National Solar Data Network. All significant sources of energy entering and leaving the system, along with the change in energy inside the system, are accounted for. The details of the derivation of
TABLE 4-1. HULLCO CONSTRUCTION SYSTEM SENSOR LOCATIONS
I001 Incident solar energy normal to the plane of the
TOOl Outside ambient temperature.
EPIOO,EP1OI Power used by the greenhouse to rock storage blower
TlOO,TlOl Temperatures in the greenhouse at the entry to the
ducts to the rock storage.
WlOO,WIOl Air flow rate through the greenhouse to rock storage ducts.
RH600 Interior relative humidity, measured in the living
RH601 Outside relative humidity.
D002 Thermal switch used to indicate wood stove operation.
T200,T201,T202 Rock bed temperatures at three locations on the
T203,T204,T205 northeast side of the building: three sensors are
T206,T207,T208 located two inches from the top of the slab, three
sensors are located in the rock 11 inches from the slab top, and the remaining three sensors are located 20 inches down from the top of the slab. T209,T210,T211 Rock bed temperature sensors located on the northT212,T213,T214 west side of the house at 2, 11, and 20 inches down
T215,T216,T217 from the top of the slab.
DO01 Wind direction.
VO01 Wind speed.
EP400,EP401 Measurements of the power used by the radiant elecEP402,EP403 tric heaters used for auxiliary heating.
T218,T219,T220 Measurements of the greenhouse floor temperature
T224,T225,T226 near the surface, above the vapor barrier, and
below the vapor barrier on the east and west sides of the greenhouse.
TABLE 4-1. (Continued)
T221,T222,T223 Measurements of floor surface temperature, below
T227,T228,T229 slab temperature and earth temperature in the living
T245,T246,T247 room and the master bedroom.
T230,T231 ,T232 Temperatures in the wall between the house and
greenhouse near both surfaces and in the center of the wall.
T233,T234 Temperatures near the inside and outside surfaces
of the east building wall.
T235,T236 Temperatures near the inside and outside surfaces
of the north building wall.
T237,T238 Temperatures near the inside and outside surfaces
of the west building wall.
T239,T240 Temperatures near the inside and outside surfaces
of the west greenhouse wall.
T241,T242,T243, Air temperatures at the outlets of the rock storT244 age on the north side of the house.
T600,T601,T602 Ambient air temperatures inside the building in
T603,T604 bedroom 1, bedroom 2, the master bedroom, the bath
and hall, and the living room.
the technique used are presented in References  and . The equations used are listed in Appendix B of this report.
The space heating load used in this report and in References [61  is the building load minus the other sources of energy generated inside the building which would cause a reduction in the equipment load of an active solar energy system or a conventional heating system. As such there may be periods of time when significant amounts of energy are supplied to the building from renewable energy sources other than solar energy. Consequently there may exist periods of time when the reported load appears small in relation to the building load since the reported load is actually an equivalent equipment demand.
Using the energy balance concept, the solar energy used is found as the difference between the space heating load and the auxiliary energy supplied to the building. Both the load and the solar energy used represent the energy requirements of the building being analyzed and include the energy which is lost back through the S*olar glazing area. All other primary performance factors, including energy savings, are computed with respect to these load and solar energy used values (Appendix B.) following the guidelines of Reference . However, the energy savings, particularly when used for comparison with another solar energy system, can be misleading if a comparison is made between a passive system analyzed by this technique and an active system. Consequently, other energy savings comparisons must be made.
The building savings, or the energy savings for the system as built, are presented first. The building savings is the difference between the energy required to maintain the measured building interior environment and the auxiliary energy used. As such, the building savings represents the difference between the homeowner's utility bills with and without the use of incident solar energy.
The second savings is the comparison savings. The comparison savings represents the difference between the energy which would be required to maintain the measured interior environmental conditions in a comparison
building and the auxiliary energy used by the system. The comparison building is a building which has thermal characteristics identical to the passive system on all exterior surfaces except the glazed south wall area. For the comparison building load determination, the solar glazing is replaced by a wall with thermal characteristics similar to the other passive system building walls. Thus, the comparison savings represent the savings realized by comparison to a building with the same energy conservation characteristics which does not make use of incident solar energy for heating. In effect, the comparison savings is the building savings reduced by the high losses through the glazed south area on a passive system.
The third savings, the comparison set point savings, is the energy savings compared to the energy requirements of the comparison building under conditions when the temperature inside the comparison building is controlled to a set point. This would be the case if a conventional heating system was used for control of the building environment. To determine the comparison set point savings, a two degree range of building temperature, from 68'F to 70'F, is used as the set point. When the building temperature is below the lower set point temperature of 680F, the comparison set point savings is reduced by the additional energy which would be required to maintain the lower set point temperature in the comparison building. Although this energy would not decrease the actual savings, it is applied as a penalty to the comparison savings for convenience, rather than creating a new performance factor. When the building temperature is above the upper set point temperature of 70'F, the assumption is made that the additional energy used to maintain the higher temperature is excess energy. Consequently, the comparison set point savings are reduced by this excess energy unless all or part of this excess energy was derived from a renewable energy source such as wood. If the excess heating energy requirements could be satisfied totally from the other renewable energy sources, then no reduction in the solar comparison set point savings is made. Otherwise, the savings are reduced by the difference between the excess energy and the other source of renewable energy (wood).
Presentation of the three values of energy saved allows the reader to observe the effect of more constrained operation of the passive space heating system through successively more severe constraints. It should be noted that both the comparison savings and the comparison set point savings for a well designed and well built passive system will be relatively low. However, if the use of auxiliary energy is also low, then the relatively low magnitude of the savings reflect only the energy conservation features of the system. For a building where the glazing is an integral part of the building (i.e., a direct gain system) the comparison savings most adequately describe the energy savings realized. However, as the glazing and area of collection becomes more isolated from the living space, the building savings become more meaningful. A greenhouse is in between -- that is, it is a livable part of the building when greenhouse temperatures are high, but less usable when temperatures are lower. Consequently, both the building savings and the comparison savings have periods of applicability for the greenhouse system. No attempt is made in this report to quantify the energy savings resulting from the application of energy conserving construction techniques. That is, the energy savings presented in the report are savings resulting only from the use of the incident solar energy.
More complete definitions of the performance factors used for system analysis are presented in Appendix A. The equations used to generate these performance factors for the Hullco Construction system are presented in Appendix B.
5. PERFORMANCE ASSESSMENT
During the winter of 1978 1979, the solar space heating system satisfied 75 percent of the building heating load and 100 percent of the subsystem space heating demand. The actual performance was slightly below the design performance specifications due to the unusually severe winter weather. However, significant amounts of energy were saved, even as compared to a more conventional style of building construction. Comfort levels were within an acceptable range over most of the year. High building temperatures encountered during the summer months could have been prevented by more appropriate use of system controls. A problem with excess interior humidity has existed, but also can be corrected by appropriate use of system controls.
Climatic conditions in the Prescott area during the time period covered by this analysis, as shown in Table 5-1, were such that both winter heating and summer cooling loads were more severe than in a typical year. While summer outside ambient air temperatures were near the longterm average, the amount of solar energy incident on the greenhouse glazing was 10 to 15 percent higher than the long-term average, particularly during the late spring and early summer months. Both the outside ambient temperature and the available solar energy were much less than normal during the winter, particularly during the month of January, contributing to the more severe heating requirements encountered. Average measured monthly values of wind speed were near three miles per hour for each month. However, during all seasons except the fall, average daily wind speed frequently exceeded 5 miles per hour and occasionally exceeded 10 miles per hour. Outside relative humidity averaged slightly over 50 percent for the year. However, the average values during both spring and summer were relatively low, while late fall and early winter values were quite high, averaging near 70 percent.
Design predictions of the system thermal performance, shown in Table 5-2 along with actual system thermal performance, were made using a degreeday technique. Assumptions made in the design performance calculations included:
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As can be- seen from d comptrison of the design and actual solar fractions of the building heating load shown in Table 5-2, the heating season performance fell well below the design estimates. However, since the outside air temperature was cooler than the design temperature and the inside air temperature was maintained considerably above the design temperature of 650F, then the actual building heating loads shown in Table 5-2 were considerably higher than the design values. The higher building loads, along with the lower than average available solar energy caused the majority of the differences in the design and actual solar fractions. However, even after the differences in temperature are accounted for, the actual load remained higher than the design load. This was due to differences between the design infiltration rate of one-half air change per hour and the actual infiltration rate which averaged one to one and one-half air changes per hour. The building appears to be tightly weatherized, thus justifying a design infiltration rate of onehalf air change per hour. The higher actual outside air infiltration rate appears to have been caused not by building design, but by the way tbe system was operated. Relative humidity levels inside the building were high enough during the winter to cause some discomfort to the occupants arid to cause some mildew to occur inside the building. In an attempt to reduce the interior humidity level, the occupants would frequently open the bu~ildIng windows a small amount to allow the dry outside air to enter the house during daytime hours. As a consequence of the slightly open windows, the average infiltration rate was higher than the design rate. The causes of the high interior relative humidity will be discussed
in later paragraphs.
A month-by-month summary of the Hullco Construction passive solar space heating system thermal performance is shown in Table 5-3. As discussed earlier, the building loads were considerably higher than expected. However, nearly 100 percent of the building heating load was satisfied by renewable energy forms -wood and sunlight. Since the internal heat 22
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During the winter, the wood stove was used on many days to maintain comfortable conditions inside the building. A total of 13.51 million Btu of useful thermal energy was derived from use of the wood stove during the winter. According to the occupants, approximately one and one-half cords of wood were used during the winter. Assuming a heat content of 30 million Btu per cord of wood, then the wood stove operation provided energy at an average efficiency level of 30 percent. The wood stove was used primarily to maintain a lower bound to the building temperature and interior comfort level. Thus, the majority of the wood stove use occurred at night through early morning hours and during cloudy days.
Other energy used to satisfy the building load was derived from electric lights, appliances, etc., including the greenhouse fans, and from the body heat of the occupants. This internal heat gain over the winter is estimated to be 5.67 million Btu.
For reporting purposes, the reported load is an equivalent equipment demand. As illustrated in Table 5-3, this space heating equipment demand is the difference between the building load and the sum of the wood and internal energy gains. This demand is the amount of energy which would be required to maintain the measured building environmental conditions. Almost 100 percent of this space heating subsystem demand was satisfied by collected solar energy. Only 0.04 million Btu (11 kwh) of auxiliary electric fuel was used over the entire heating season.
The primary collection of incident solar energy at the Hullco Construction site occurs in the greenhouse. Energy collected in the form of warmed air, walls, or floors is transferred to the remainder of the house by both active (fans) and passive or natural means. The efficiency of this collection is illustrated in the plot of average monthly collection efficiency presented in Figure 5-1. As can be seen from the plot, the
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efficiency reaches a maximum near the coolest part of the year (mid-winter) and drops off rapidly in the fall and spring when shading and venting to control overheating reduce the efficiency of energy collection. Of particular interest is the plot of the two months (March and April) of 1978, as compared to the corresponding period of 1979. During the spring of 1978 the house was unoccupied. The house was occupied in late May of 1978. Consequently, minimum overheating control in the form of manual shading and venting was accomplished. As a result, higher collection efficiencies were observed during the two months of 1978. It should be noted that the value of collection efficiency does not directly compare to the collection efficiencies presented for active solar energy systems, since the thermal losses through the passive system glazing are a part of the building load instead of a part of the collection efficiency.
Storage of collected solar energy at the Hullco Construction site is provided by building floors, walls, and the under floor rock bed. The storage provided several days reserve heating on a number of occasions throughout the winter while also aiding in moderation of daily temperature variations within the conditioned space, as illustrated by the plot in Figure 5-2 showing average building and storage temperatures during a two-day winter period when the building was unoccupied. The effect of the greenhouse fan operation on building temperature is apparent during both days as a change in the rate of change of building temperature with time. Of the three areas of storage (wall, floor, rocks) the wall between the house and greenhouse, a primary absorbing area for incoming solar radiation, was the primary solar storage media. Referring to the plot of monthly average storage temperatures presented in Fi*gure 5-3, it can be seen that the wall is generally five or more degrees warmer than the floor or the rocks, thus indicating that the wall is the primary storage media. It should also be noted that the floor provided good secondary storage, since its temperature was consistently near or above 70'F. As shown in Figure 5-4, the greenhouse wall was consistently maintained at a higher temperature than the building average temperature, thus providing energy to the house.
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The thickness of the wall also provides a time lag to the energy availabilit,, to the house. From mid-morning through late afternoon, when solar energy is available through the sliding glass doors in direct gain form, the inside of the greenhouse wall is at its lowest temperature. However, at some time after sunset, the inside of the greenhouse wall reaches its maximum temperature, and continues to remain at a higher temperature than the outside of the wall, thus providing a time lag in the energy availability to the house.
The under floor rock storage appears to have provided little benefit to the system thermal performance. In terms of storing energy and releasing it for later use, the rocks were seldom warm enough to provide useful heating to the building. Only in November did the average rock temperature even approach the direct gain floor average temperature. Consequently, the rock storage served principally as a thermal buffer to the outside environment, and not as an effective thermal storage area. Near the end of December the greenhouse fans were disabled and remained off until February 10. Consequently, during this period and after the greenhouse fans were enabled, the rock storage was rather ineffective fruf, a thermal standpoint, since the rock temperature was lower than the
As discussed in section 3, the control thermostats for the greenhouse fans were set such that operation of the greenhouse fans occurred when
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greenhouse temperatures exceeded 90'F. The thermostats are manually adjustable. If the thermostats had been set at a lower level, i.e., 80'F, then fan operation would have occurred over longer periods, causing more energy to be transferred from the greenhouse to the rock beds. Further discussion of the effects of the greenhouse fans on comfort is contained in later paragraphs.
Energy savings realized by the system throughout the heating season, as presented in Table 5-4, were substantial, even as compared to more conventional construction (comparison and comparison set point savings). Operation of the greenhouse fans consumed only 1.07 million Btu of electrical energy. Total energy savings for the heating season were 16,798 kwh for the building, 9,506 kwh as compared to a building of similar design but with an insulated non-glazed south wall with thermal properties similar to the other building walls, and 6,747 kwh as compared to the conventional building where temperatures were controlled to a setpoint. Of particular interest is the month of October, where the comparison set point savings are zero, while other savings are greater than zero. This is due to the building temperature being eight degrees higher than the upper set point.
Comfort conditions inside the building were marginally acceptable to the occupants during most of the year. Average monthly differences between Zone I and Zone 2 comfort indices, shown in Table 5-5, were generally less than two degrees, indicating good north-south energy transfer within the building. During late December through early February, however, a more significant difference (Figure 5-6) in the two comfort levels was noticed since the greenhouse fans were disabled over the entire month, resulting in cooler rock bed temperatures. Summer comfort levels were somewhat high, primarily due to the effect of the wall between the house and the greenhouse. Even though both the greenhouse and house were vented some during the summer, incident sunlight still caused considerable heating of the wall, as shown in the plot of storage temperatures presented in Figure 5-3. Consequently, the massive wall retained a substantial amount of collected solar energy and caused the
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building, particularly on the south side, to be significantly warmer than prevailing ambient conditions.
The comfort index used in this analysis is the operative temperature, which is defined as the average of the space dry bulb and mean radiant temperatures. For this analysis, the space mean radiant temperature is defined as the average surface temperature of all radiating surfaces bordering the space, except the wood stove, since a surface temperature measurement of the wood stove is not currently available. The building is divided into two comfort zones. Zone 1 is the south part of the building, while Zone 2 is the north part of the building. While relative humidity does play an important part in the perception of comfort, it is not presently included in the comfort index. The effects of humidity on comfort will, however, be discussed in later paragraphs.
An indication of the variation of conditions inside the building is shown in Figures 5-7 and 5-8 where, in addition to the average monthly values of the comfort index, the average of the daily maximum and minimum values is shown. The difference in the average variations is generally five degrees or less for both zones. Minimums in Zone I seldom were less than 70'F due to both the warming effect of the wood stove and the efficient radiant and convective energy transfer from the greenhouse wall. However, minimums of the Zone 2 comfort index were frequently below 70'F, especially when the greenhouse fans were not operating (late December through early February). This is due to relatively inefficient fan-off energy transfer from the greenhouse to the north side of the building, particularly to the two north side bedrooms.
The greenhouse to rock storage fans were disabled by the occupants during late December and remained off until February 10. This was due to the occupants' perception that operation of the fars was causing an increase in interior relative humidity and a consequent decrease ill their comfort. Examination of the monthly average values of both exterior and interior relative humidity, shown in Figure 5-9, reveals a considerable increase in interior relative humidity during November. This
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increase would appear to be caused by the corresponding increase in outside relative humidity. However, even though the outside relative humidity level increased substantially during November, the outside ambient temperature decreased to a monthly average of 42'F so that tile absolute humidity of the outside air actually decreased. The decreased outside absolute humidity was equivalent to an interior relative humidity of approximately 20 to 25 percent at a temperature of 70"F.
Further examination of Figure 5-9 shows that there was a decrease in interior relative humidity noted during the month of January when the greenhouse fans were disabled, thus indicating a possible correlation between the greenhouse fan operation and interior relative humidity. Proof of this effect is contained in the plots presented in Fi ure 5-10, where daily values of interior relative humidity and greenhouse fan operating energy are plotted. As can be seen from the plots, definite increases in interior relative humidity are noted when the greenhouse fans operate. Also, during both the period before January and tile period after January, a slight increase in the relative humidity with time is apparent. The increase in relative humidity during the greenhouse fan operation could be due to either high humidity in the greenhouse air from plant transpiration and watering of the plants, or due to water in the rock bins, although the most probable cause is high humidity in the greenhouse air.
Further effects of the greenhouse fan operation can be seen in the plots presented in Figure 5-11, illustrating the daily maximum and minimum of both the average storage temperature and the comfort index for both building zones. The greenhouse to rock bed fans were disabled from December 26 through February 9. During this period, minimum values of the comfort index remained near minimum values seen in other periods due to the use of the wood stove. However, maximum values, particularly near the end of the fan-off period, were considerably higher than previously noted. Also, as seen in the storage temperatures, another effect of disabling the fans was to reduce the system storage capacity, thus reducing the levels of energy, and consequently temperatures in storage,
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since the north floor rock storacqe was no longer being charged. This reduction of storage capacity is also reflected in the higher day-to-day variation of maximum comfort index values, since less effective energy storage mass was available to temper the effects of changing daily weather conditions.
Insight into the ,ysterr performance during a day is provided by the plots presented in Figure 5-12. During the 2-day period illustrated (December 5-6, 1978), considerably more solar energy was available during the first day than the second day. Building hourly average temperatures were maintained within a range of 69.5'F to 76*F on December 5, while storage temperatures, particularly in the greenhouse wall, varied considerably. Building average temperatures on December 6 were slightly cooler until late in the afternoon, when wood stove operation was noted. Until the wood sto've operation began on December 6, building temperatures decayed slowly due to both the small amount of available solar energy and the energy released from storage. The direct gain floor began to become more effective as an energy storage mass as it dropped slightly in temperature and energy level on the 6th. Relative humidity effects, as previously discussed, were noted on December 5 corresponding to the period of operation of the greenhouse fans. However, a considerable decrease in interior relative humidity was noted on December 6, when wood stove operation began, indicating the increased infiltration of outside air (low moisture content) necessary to provide combustion air for the wood.
The two major difficulties encountered during the year, as previously discussed, were comfort related difficulties. Both problems could have been alleviated by changes to the method of operation of the system. The overheating in the summer could have been better controlled by both proper venting of the building and appropriate use of greenhouse shading devices. The high interior relative humidity was reduced some by winter building venting, but at the expense of increased building load. The relative humidity increases could have been eliminated by controlling the air flow such that it would pass through the rock bins but not return through the building.
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Figure 5-12 SYSTEM PERFORMANCE-DECEMBER 5-6, 1979 44
Control of the conditions inside a passively-heated building is an extremely important aspect of the system operation. In general, the controls applied in the form of venting and shading must be somewhat anticipatory in nature that is, the occupants must begin to change system control strategies in advance of seasonal weather changes (spring and fall). This was not done at the Hullco Construction site for the summer of 1978, primarily because the building was unoccupied during the spring. A more appropriate control strategy is to begin in the spring to try to keep the thermal storage masses at as low a temperature as possible by venting the house to the cool spring air and by applying shading controls early in the season. If the storage masses can enter the summer cooling season at a lower temperature, then they can be much more effective in reducing high daytime temperature levels by absorbing more energy during the day. Also, venting of the greenhouse should begin as early as possible to try to maintain lower temperatures in the greenhouse. With the occupants aware that this type of control is necessary then the summer of 1979 should yield significantly lower system temperatures.
In the same vein, control strategies for winter operation should be entered as early in the fall as possible, thus providing a "fully charged" system for heating season operation. This was accomplished in 1978 due to two factors. First, high temperatures were maintained inside the house due to greenhouse operation and improper use of system venting. Second, the redwood snow fence used to provide partial greenhouse shading was not used until late in the summer; thus, the system and its storage masses were "fully charged" in anticipation of winter heating demands.
Another factor contributing to potential overheating is the placement of furniture and rugs in the direct gain areas of both the living room and the master bedroom. During the spring of 1979, furniture and rugs were placed over the rrexican tile floor in both rooms, as shown in Figure 5-13. Consequently, energy entering through the sliding glass doors was absorbed in material with little thermal storage capacity, causing the material
Figure 5-13. INTERIOR VIEW OF LIVING ROOM AREA
(furniture, rugs, etc.) and the surrounding air to warm rapidly and contribute to larger daily temperature variations within these rooms.
The high relative humidity inside the house during the winter can be eliminated by removing the cause; that is, by causing the air from the rock beds to return to the greenhouse without entering the house. Since the rock beds are continuous from east to west, then the rock bed can be charged by only one greenhouse fan. By closing the floor vents on the north side of the building, the return air to the greenhouse will be ducted through the other side greenhouse fan ducts. Thus, the humid air will pass only through the rocks and not through the house. If the operating fan control thermostat is set lower (near 800F), then significant greenhouse overheating should not occur.
From the discussions of the preceding paragraphs, it can be seen that owner interaction with the system is quite important, particularly in the area of maintaining appropriate comfort conditions. Although the appropriate system controls are not complex and do not require significant effort, the homeowner must be made aware of the type of controls he has over his system, and how he should anticipate seasonal weather changes in their application. Without this owner awareness, the best designed and built passive heating system can produce an environment that is only
marginally comfortable at best.
1. "The Hull Residence: A Passive Solar Hybrid System", proceedings
of the 2nd National Passive Solar Conference, March 16-18, 1978,
2. "Thermal Data Requirements and Performance Evaluation Procedures
for the National Solar Heating and Cooling Demonstration Program",
NBSIR 76-1137, Washington: National Bureau of Standards, August,
3. *"Performance Evaluation Reporting for Passive Systems", April 17,
4. *U. S. Department of Energy, "National Solar Data Network," prepared
under Contract Number EG-77-C-01-4049, by IBM Corporation, December,
5. A Thermal Performance Analysis Technique for Passive Solar Space
Heating Systems" proceedings of the 3rd National Passive Solar
Conference, January 11-13, 1979, San Jose, California.
6. *"Monthly Performance Report, Hullco Construction", March 1978,
7. *"Monthly Performance Report, Hullco Construction", April 1978
8. *"Monthly Performance Report, Hullco Construction", May 1978,
Copies of these r'eorts may be obtained from Technical Information
Center, P. O. Box 6. Oak Ridge, Tennessee 37830
9. *"Monthly Performance Report, Hullco Construction", June 1978,
10. *"Monthly Performance Report, Hullco Construction", August 1978,
11. *"Monthly Performance Report, Hullco Construction", September 1978,
12. *"Monthly Performance Report, Hullco Construction", October 1978,
13. *"Monthly Performance Report, Hullco Construction", November 1978,
14. *"Monthly Performance Report, Hullco Construction", December 1978,
15. *"Monthly Performance Report, Hullco Construction", January 1979,
16. *"Monthly Performance Report, Hullco Construction", February 1979,
17. *"Monthly Performance Report, Hullco Construction", March 1979,
18. *"Monthly performance Report, Hullco Construction", April 1979,
19. *"User's Guide to the Monthly Performance Report of the National Solar
Data Program," February 28, 19,78, SOLAR/0004-78/18.
Copies of these reports may be obtained from Technical Information
Center, P. 0. Box 62, Oak Ridge, Tennessee 37830
DEFINITION OF PERFORMANCE FACTORS AND SOLAR TERMS
This section contains the definitions of performance factors used in the Hulico Construction monthly reports (References  ). Those performance factors used to describe the thermal performance of solar energy systems are described in Reference .
The overall system performance is characterized by monthly summnations and averages of appropriate daily and hourly performance factors.
INCIDENT SOLAR ENERGY (SEA) is the total insolation available
on the gross collector array area. This is the area of the collector energy-receiving aperture, including the framework, which
is an integral part of the collector structure.
COLLECTED SOLAR ENERGY (SECA) is the thermal energy removed
from the collector array by the heat transfer medium.
0 AVERAGE AMBIENT TEMPERATURE (TA) is the average temperature of
the outdoor environment at the site.
AVERAGE BUILDING TEMPERATURE_(TB) is the average temperature in
the controlled space of the building which the system serves.
ECSS SOLAR CONVERSION EFFICIENCY (CSCEF) is the ratio of the
solar energy delivered to the load subsystems to the total energy
incident on the collector array.
ECSS OPERATING ENERGY (CSOPE) is the electrical operating energy
required to support the ECSS heat transfer loops.
0 TOTAL ENERGY CONSUMED (TECSM) is the sum of the collected solar
energy, the total system operating energy, the total fossil fuel energy, and the total electrical fuel energy. This performance
factor represents the total energy demands of the system from all
0 SYSTEM PERFORMANCE FACTOR (SYSPF) is the ratio of the total system
load to the equivalent fossil energy required to support the system
for the month. The equivalent energy, as used in this context, is
the sum of the actual fossil fuel (1/0.3) times the electrical
requirements (for operating energy and fuel). This multiplication factor results from the estimation that, on the average, the efficiency of extracting fossil fuels from the ground, converting to
electricity, and transmitting the electrical energy to the site is
0 LOAD is the amount of energy required for the month for each of the
0 SOLAR FRACTION is the percentage of the load demand during the
month for each subsystem which was supported by solar energy.
0 SOLAR ENERGY USED is the total amount of solar energy supplied
each subsystem for the month.
0 AUXILIARY THERMAL USED is the amount of energy supplied, during
the month, to the major components of each subsystem in the form of thermal energy in a heat transfer medium. This term also includes the converted electrical fuel energy supplied to the subsystem.
6 AUXILIARY ELECTRICAL FUEL is the total amount of electrical energy
supplied directly to each subsystem during the month.
ELECTRICAL ENERGY SAVINGS is the estimated difference between the electrical energy requirements of an alternative conventional system (carrying the full load) and the actual electrical energy
required by each subsystem.
SPACE HEATING SUBSYSTEM
The space heating subsystem is characterized by an accounting of the energy flow into and from the subsystem. In addition, the savings in energy attributable to the use of solar energy are presented.
9 SPACE HEATING LOAD (HL) is the energy demand on the space heating
subsystem, generally less than the building heating load.
0 SOLAR FRACTION OF LOAD (HSFR) is the percentage of the space heating demand satisfied by solar energy.
0 SOLAR ENERGY USED (HSE) is the amount of solar energy used by the
space heating subsystem.
0 AUXILIARY THERMAL USED (HAT) is the amount of energy supplied to
the major components of the subsystem in the form of thermal energy in a heat transfer fluid or its equivalent. This term includes the converted electrical and fossil fuel energy supplied to the subsystem.
0 AUXILIARY ELECTRICAL FUEL (HAE) is the amount of electrical energy
supplied directly to the subsystem.
0 ELECTRICAL ENERGY SAVINGS (HSVE) is the estimated difference between
the electrical energy requirements of an alternative conventional system (carrying the full load) and the actual electrical energy
required by the subsystem.
0 BUILDING TEMPERATUE(B is the average heated space dry bulb
AMBIENT TEMPERATURE (TA) is the average ambient dry bulb temperature at the site.
ENV IRONMENTAL SUMMARY
The environmental summary is a collection of the weather data which is
generally instrumented at each site in the program. It is tabulated in this
data report for two purposes -- as a measure of the conditions prevalent
during the operation of the system at the site, and as an historical record
of weather data for the vicinity of the site.
0 TOTAL INSOLATION (S)is accumulated total solar energy incident
upon the gross collector array measured at the site.
0 AMBIENT TEMPERATUE(A is the average temperature of the environment at the site.
0 WIND DIRECTION (WDIR)-is the average direction of the prevailing
WIND SPEED (WIND) is the average wind speed measured at the site.
DAYTIME AMBIENT TEMPERATURE (TDA).is the temperature during the
period from three hours before solar noon to three hours after
0 RELATIVE HUMIDITY (RELH) is the average outside relative humidity.
PASSIVE SPACE HEATING
In addition to the characterization of the space heating subsystem previously mentioned, several other parameters are reported for passive space heating systems.
0 CHANGE IN STORED ENERGY (STECH) is the change in energy level of
all components of the solar energy storage mass.
0 DIRECT SOLAR UTILIZATION EFFICIENCY (CSCEF) is the ratio of the
solar energy used to the incident solar energy.
PASSIVE SYSTEM ENVIRONMENT
In addition to the environmental summary performance factors presented earlier, additional performance factors describing the interior environment of a passive space heating system are presented.
0 BUILDING COMFORT ZONE 1 (COM1) is an index relating to the comfort conditions on the south side of the building. The index
is formed as an average of the average dry bulb and mean radiant
temperatures inside the zone.
0 BUILDING COMFORT ZONE 2 (COM2) is an index relating to the comfort
conditions on the north side of the building and is defined similarly to the other comfort index.
BUILDING TEMPERATURE MIDNIGHT (TMID) is the average building interior temperature at midnight local solar time.
0 BUILDING TEMPERATURE 6 A.M. (T6AM) is the average building interior
temperature at 6 A.M. local solar time.
e BUILDING TEMPERATURE NOON (TNOON) is the average building
interior temperature at local solar noon.
e BUILDING TEMPERATURE 6 P.M. (T6PM) is the average building
interior temperature at 6 P.M. local solar time.
e INTERIOR RELATIVE HUMIDITY (RELHIN) is the average relative
humidity inside the building.
AVERAGE STORAGE TEMPERATURE (TST) is the mass weighted average
temperature of all solar storage masses.
HULLCO SITE SPECIAL REPORT
For the Hullco Construction Site, the average temperatures of all significant storage masses are presented.
0 ROCK STORAGE AVERAGE TEMPERATURE (TSTROCK) is the average temperature of the north side bed as measured by the twelve sensors
in the rock bed.
TROMBE WALL AVERAGE TEMPERATURE (TSTWALL) is the average temperature of the wall between the greenhouse and the house.
e DIRECT GAIN FLOOR AVERAGE TEMPERATURE (TSTFLOOR) is the average
temperature of the concrete building slab floor near the south
side of the building.
SOLAR ENERGY SYSTEM PERFORMANCE EQUATIONS
Solar energy system performance is evaluated by performing energy balance calculation's on the system and its major subsystems. These calculations are based on physical measurement data taken from each subsystem every 320 seconds. This data is then numerically combined to determine the hourly, daily, and monthly performance of the system. This appendix describes the general computational methods and the specific energy balance equations used for this evaluation.
Data samples from the system measurements are numerically integrated to provide discrete approximations of the continuous functions which characterize the system's dynamic behavior. This numerical integration is performed by summation of the product of the measured rate of the appropriate performance parameters and the sampling interval over the total time period of interest.
There are several general forms of numerical integration equations which are applied to each site. These general forms are exemplified as follows: The total solar energy available to the collector array is given by
SOLAR ENERGY AVAILABLE = (1/60) x Z [1001 x AREA] x AT
where I001 is the solar radiation measurement provided by the pyranometer in Btu/ft 2_ hr, AREA is the area of the collector array in square feet, AT is the sampling interval in minutes, and the factor (1/60) is included to correct the solar radiation "rate" to the proper units of time.
Similarly, the energy flow within a system is given typically by
COLLECTED SOLAR ENERGY [WlOO x CP x RHO x (T150 -TlOO)] x AT
where W100 is the flow rate of the heat transfer fluid in gal/min, CP and RHO are the specific heat and density, and T100 and T150 are the temperatures of the fluid before and after passing through the heat exchanging component. Frequently this temperature difference is referred to as simply TDIOO. The product WOO x RHO Is often combined and represented as MlOO.
For electrical power, a general example is
ECSS OPERATING ENERGY = 3413/60) x r (EP100] X AT
where EPIOO is the power required by electrical equipment in kilowatts and the two factors (1/60) and 3413 correct the data to Btu/min.
These equations are comparable to those specified in "Thermal Data Requirements and Performance Evaluation Procedures for the National Solar Heating and Cooling Demonstration Program" . This document was prepared by an inter-agency committee of the government, and presents guidelines for thermal performance evaluation.
Performance factors are computed for each hour of the day, Each numerical integration process, therefore, is performed over a period of one hour. Since long-term performance data is desired, it is necessary to build these hourly performance factors to daily values. This is accomplished, for energy parameters, by summing the 24 hourly values. For temperatures, the hourly values are averaged. Certain special factors, such as efficiencies, require appropriate handling to properly weight each hourly sample for the daily value computation. Similar procedures are required to convert daily values to monthly values.
All energies are expressed in Btu's, while temperatures are expressed as degrees Fahrenheit. Efficiencies are expressed as dimentionless ratios.
Location and definition of the measurements used are contained in Table 4-1 of Section 4.
EQUATIONS USED IN MONTHLY REPORT
AVERAGE AMBIENT TEMPERATURE
TA = (1/60) x E TOOl X AT
DAYTIME AVERAGE AMBIENT TEMPERATURE
TDA = (1/360) x z TOOl x AT
FOR + 3 HOURS FROM SOLAR NOON
AVERAGE BUILDING TEMPERATURE
TB = (1/300) x z (T600 + T601 + T602 + T603 + T604) X AT
TIME OF DAY BUILDING TEMPERATURES (ONCE PER DAY)
TMID = TB
AT 12 HOURS FROM LOCAL SOLAR NOON
T6AM = TB
AT 6 HOURS BEFORE LOCAL SOLAR NOON
TNOON = TB
AT LOCAL SOLAR NOON
T6PM = TB
AT 6 HOURS PAST LOCAL SOLAR NOON
INCIDENT SOLAR ENERGY PER SQUARE FOOT
SE = (1/60) x E I001 X AT
AVERAGE ROCK STORAGE TEMPERATURE
TSTROCK = (1/1080) x E (T200 + T201 + T202 + T203 + T204 + T205 + T206 + T207 + T208 + T209 + T210 + T211 + T212 + T213 + T214 + T215 + T216 + T217) X A~T
AVERAGE FLOOR STORAGE TEMPERATURE
TSTFLOOR = (1/600) x1E (T218 + T219 + T221 + T222 + T224 + T225 + T227 + T228 + T245 + T246) X AT
EQUATIONS USED IN MONTHLY REPORT (Continued)
AVERAGE GREENHOUSE WALL STORAGE TEMPERATURE
TSTWALL = (1/180) x E (T230 + T231 + T232) x AT
NORTH SIDE HEAT LOSS
HLN = (1/60) x E [NOAREA x UWALL x (T235 T234) +
NGLASS x UGLASS x 0.5 x ((T600 + T601) TOOl)] X AT
SOUTH SIDE HEAT LOSS
HLS = (1/60) x E [SOAREA x USOUTH x (0.5 x (T100 + T101) TOOl)] x AT
EAST SIDE HEAT LOSS
HLE = (1/60) x E [GHAREA x UWALL x (T239 T240) + EAAREA x UWALL x (R233 T234) + EGLASS x UGLASS x (T604 TOOl)] x AT
WEST SIDE HEAT LOSS
HLW = (1/60) x E [GHAREA x UWALL x (T239 T240) + WEAREA x UWALL x (T237 T238)] x At
FLOOR HEAT LOSS
HLF = (1/60) x E [FLAREA x UFLOOR x (TB 0.2 x (T220 + T223 + T226 + T229 + T247))] x AT
ROOF HEAT LOSS
HLC = (1/60) x E [ROAREA x UROOF x (TB TOOI)] x AT
INFILTRATION HEAT LOSS
NCHANGE = (1/60) x E [ICI + IC2 x (TB TA) + IC3 x V001] x At
IN AIR CHANGES PER HOUR
EQUATIONS USED IN MONTHLY REPORT (Continued)
HLI = NCHANGE x VOLUME x [H(TB) H(TA)] x RHO
IN BTU WHERE H IS AIR ENTHALPY FUNCTION AND RHO IS
ECSS OPERATING ENERGY
CSOPE = (3413/60) x E (EP100 + EPlOl) x AT
WOOD STOVE ENERGY
HFIRE = (1/60) x E FIRERATE x AT
IF THE WOOD STOVE IS OPERATING
AUXILIARY ELECTRIC AND THERMAL ENERGIES
HAE = (3413/240) x z (EP400 + EP401 + EP402 + EP403) x AT
HAT = HAE
WIND DIRECTION AND VELOCITY (WDIR AND WIND)
WNS = (1/60) x E VOOl x COSINE (DOOl) x AT
WEW = (1/60) x z VOOl x SINE (DOOl) x AT
WDIR = INVERSE TANGENT (WEW/WNS)
WIND = (1/60) x E VOOl x AT
ZONE 1 COMFORT INDEX
COMI = (1/60) x E 0.5 x [(T602 + T603 + T604)/3 +
(T221 + T227 + T232)/3] X AT
ZONE 2 COMFORT INDEX
COM2 = (1/60) x E 0.5 x (T600 + T601) x AT
INTERIOR RELATIVE HUMIDITY
RELHIN = (1/60) x E RH600 x AT
EXTERIOR RELATIVE HUMIDITY
RELH = (1/60) x E RH601 x AT
SOLAR ENERGY TO SPACE HEATING SUBSYSTEM (BTU)
HSE = STEO x STORSFR
AUXILIARY THERMAL ENERGY TO SPACE HEATING SUBSYSTEM (BTU)
HAT = STEO x [1 STORSFR] + HAE x HPCOMPF
WHERE HPCOMPF = HEAT PUMP COMPRESSOR EFFICIENCY (ASSUMED TO BE 0.7)
INCIDENT SOLAR ENERGY ON COLLECTOR ARRAY (BTU)
SEA = CLAREA x SE
COLLECTED SOLAR ENERGY (BTU/FT2)
SEC = SECA/CLAREA
COLLECTOR ARRAY EFFICIENCY
CAREF = SECA/SEA
CHANGE IN STORED ENERGY (BTU)
STECH = STECH1 STECH1
WHERE THE SUBSCRIPT p REFERS TO A PRIOR REFERENCE VALUE STORAGE EFFICIENCY
STEFF = (STECH + STEO)/STEI
SOLAR ENERGY TO LOAD SUBSYSTEMS (BTU)
SEL = CSEO
ECSS SOLAR CONVERSION EFFICIENCY
CSCEF = SEL/SEA
SPACE HEATING SUBSYSTEM SOLAR FRACTION (PERCENT)
HSFR = 100 x HSE/HL
SPACE HEATING SUBSYSTEM ELECTRICAL ENERGY SAVINGS (BTU)
HSVE = CONV HOPE
WHERE CONV IS THE ELECTRICAL ENERGY REQUIRED FOR THE
EQUATIONS FOR MONTHLY REPORT (Continued)
UNDER = UA x (68 TB)
IF TB IS LESS THAN 68 FIRE = MINIMUM OF HFIRE AND OVER
SETHSVE = COMHSVE UNDER (OVER FIRE)
TOTAL ENERGY CONSUMED
TECSM = HSE + CSOPE + HAE + HFIRE
AVERAGE SOLAR STORAGE TEMPERATURE
TST = RiF x TSTROCK + R2F x TSTFLOOR + R3F x TSTWALL
CHANGE IN LEVEL OF STORED SOLAR ENERGY
STECH = TMROCK x (TSTROCK TSTROCK ) + TMFLOOR x (TSTFLOOR
TSTFLOOR ) + TMWALL x (TSTWALL TSTWALL ) COLLECTED SOLAR ENERGY
SECA = HSE + STECH
COLLECTED SOLAR ENERGY PER UNIT COLLECTION AREA
SEC = SECA/CLAREA
ECSS SOLAR UTILIZATION EFFICIENCY
CSCEF = SEL/SEA
*U.S. GOVERNMENT PRINTING OFFICE: 1980-640-189/4221. Region 4.
UNIVERSITY OF FLORIDA
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