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1 TOWARDS NET ZERO ENERGY: BUILDING ENVELOPE DESIGN STRATEGIES FOR SINGLE FAMILY HOME S IN HOT DRY REGIONS BY: AHMED ABDULLATIF ALYAHYA O F FLORIDA IN PARTIAL FULFILLMENT O F THE REQUIREMENTS F OR THE DEGREE O F MASTER O F SCIENCE IN ARCHITECTURAL STUDIES WITH A CONCENTRATION IN SUSTAINABLE DESIGN UNIVERSITY OF FLORIDA 2017 CHAIR: DR. NAWARI NAWARI CO CHAIR: DR. ROBERT J. RIES
2 2017 Ahmed A. Alyahya
3 T o my parents Abdullatif and Bahia Alyahya To my family To my friends
4 ACKNOWLEDGMENTS First, I would like to thank God for making me able to do this research and for all graces that he gave me. Second, I would like to thank my parents for a ll their support and prayers for whole my life especially during the distressful moments of my study and without them, I would not be able to do what I did. Third, I would like to express my sincere appreciation to my Committee Chair Dr. Nawari Nawari then my Committee Co chair Dr. Robert J. Ries for all their guidance and assisting that they provided to me. Forth, to all my family and friends who encouraged and helped me to achieve my goals. Lastly, to the University of Florida and all my teachers who hav e taught and supported of Sustainable Design program.
5 TABLE OF CONTENT S P age ACKNOWLEDGMENTS 4 TABLE OF CONTENTS 5 LIST OF TABLES 7 LIST OF FIGURES 8 ABSTRACT 1 0 CHAPTER 1 INTRODUCTION 11 O bjectives 2 LITERATURE REVIEW 13 Climate .. 13 Building Envelope 14 Wall Systems 16 Reinforced Concrete 16 Precast Concrete 17 Reinforced Masonry 18 Roof System 19 Insulation System 21 Fenestration System 27 The Envelope Design Strategies 29 Orientation 29 Courtyard 30 Net Zero Energy 31 3 CASE STUDIES 34
6 Vali Homes Prototype I 34 38 4 METHODOLOGY 42 5 DESIGN PROPOSAL 44 The Design General Information 6 DISCUSSION AN D RESULTS 53 Design strategies 53 The House Layout Wall System Roof System Fenestration System Energy Simulation Analysis of The Design Proposal Energy Simulation Analysis of a Conventional Design 2 The Design Proposal and the Conventional Design Comparison 7 CONCLUSIONS 69 REFERENCES
7 LIST OF TABLES Table 1: Thermal resistance properties of some building materials 1 9 Table 2: Insulation materials 2 2 Table 3: R value table 2 4 Table 4: G eneral information of Vali homes prototype I 3 4 Table 5. PHV and STV building envelope materials 3 9 Ta ble 6. PHV and STV U values (W/m2K) 3 9 Table 7: U value and R 5 8 Table 8 : Photovoltaics energy generation with 20 o 6 6 Table 9 : Photovoltaics energy g eneration with 0 6 6 Table 10: Photovoltaics energy generation for the conventional house 6 8
8 LIST OF FIGURE S Figure 1: Koppen Climate Classification System 4 Figure 2: Reinfor ced concrete wall 7 Figure 3: Reinforced masonry wall 8 Figure 4: 6 Figure 5: Effects of WWR on energy consumption a nd solar heat gain 8 Figure 6: Vali homes prototype I perspective 6 Figure 7: Vali homes prototype I Plan and sections 7 Figure 8: PHV and STV perspective and layout 8 Figure 9: PHV and STV wall section 40 Figure 10: PHV and STV energy consumption 40 Figure 11: Energy generated by PV 40 Figure 12 13: Indoor and outdoor perspectives of PHV 4 5 Figure 14 16: The maps of Saudi Arabia, Riyadh and the site 5 Figure 17: Average temperatures and precipitation 6 Figure 18: Average temperatures and preci pitation 4 6 Figure 19: Average cloudy, sunny, and precipitation days for each month 7 Figure 20 21: first and second floors 8 Figure 22: s roof) 9 Figure 23: 9 Figure 24: Perspectives of the house 50
9 Figure 25: The eastern facade of the house 51 Fig ure 26: The western facade of the house 51 Figure 27: The southern facade of the house 52 Figure 28: The northern facade of the house 52 Figure 29: Air movement through t he courtyard 4 Figure 30: Wind rose for Riyadh, Saudi Arabia (Revit analysis) 4 Figure 31: Walls section 6 Figure 32: 7 Figure 33: The window frame 8 Figure 34: The total energy consumption 60 Figure 35: The monthly energy consumption 60 Figure 36: The monthly pea k demand 61 Figure 37: The total energy consumption 62 Figure 38: The monthly energy consumption 62 Figure 39: Total energy consumption with only low efficient wal l system 63 Figure 40: 63 Figure 41: Total energy consumption with a clear single pane glazing 4 Figure 42: The design proposal and the conventional desig n comparison 5 Figure 43: Photovoltaics energy generation comparison 7 Figure 44: 8
10 ABSTRACT Global warming and climate change are both serv ing as warning signs as they gradually begin to capture the attention of people at large. Many actions have been, and continue to be taken by governments and organizations to preserve the planet, which is impactful and needed. But conservation efforts are not exclusive to governments and large institutions individuals can contribute in multiple ways that will have ripple effects, one being the choice to build sustainable, net zero energy homes. To build a net zero energy home, many strategies should be tak en into consideration. One of the most effective factors in reducing the home energy consumption, to then achieve a net zero energy home especially in hot dry regions, is the optimization of the building envelope performance. This paper discussed several b uilding envelope design strategies that are suitable for homes in hot dry regions and tested them. All those strategies were applied to a design proposal for a house in Riyadh, Saudi Arabia, which is a hot dry region, and were analyzed by some of the Autod esk energy simulation programs. Further, the same analyses were projected onto an identical house to the design proposal, but with a conventional, low efficient building envelope. The results showed that the house with the high efficient building envelope had 4 8 % less energy consumption than the one that has the low efficiency envelope. This paper will provide a high efficient building envelope design for the hot dry regions which may potentially help architects and decision makers to build net zero energy homes.
11 CHAPTER 1 INTRODUCTION Should individuals sit comfortably with their arms crossed neglecting the environment rather the duty of every single person that can realize the weight of the current negative activities on the environment. Individuals can make a huge change toward having a sustainable environment. One of the most significant aspects that individuals can contribute to saving the environ ment, and their money as well, is by making their homes sustainable, especially in regards to energy consumption. According to the United States Environmental Protection Agency EPA report, 2,039.32 million metric tons of carbon dioxide emissions in 2014 we re from the combustion of fossil fuels to generate electricity (Inventory of U.S. Greenhouse Gas Emissions and Sinks, 2016). Moreover, the statistics of U.S. Energy Information Administration, the EIA, show that the total energy consumption of the resident ial sector in 2015 was 20,693 trillion Btu (Energy Consumption by Sector, 2016). Thus, 21.21% of the total energy consumption is from the residential sector. All these statistics illustrate that supplying buildings, especially the residential buildings, wi th electricity that is generated by fossil fuels causes significant, adverse impacts on the environment. Therefore, for this reason, net zero energy buildings are a powerful alternative for conserving the environment. The crux to achieving a net zero energ the solar pa nels generate the remaining energy needed for the building.
12 The research concentrates on the wall, roof, fenestration and insulation systems design, also some factors that affect the building en velope such as orientation and inclusion of a courtyard. Then, how all these factors contribute to a decrease in energy demand to, in turn produce from the renewable energy the same amount that a house needs. The entirety of this process will make the building a net zero energy building. This research is used in many methods to illustrate that the high efficiency building envelope can make a family home in hot dry regions a net zero energy home. Using simulation software that estimates the energy demand of a building and other software will help to make the study mor e realistic; Autodesk Green Building Studio and Insight 360 for Revit are examples of these methods. Further, a key method is to learn and build off of previous case studies. The types of case studies that are used in the research are about homes that are in the hot dry regions. In general, this research will illustrate to what extent does the building envelope of a single family home in hot dry regions contribute to the achievement of net zero energy. Objectives Achieving the optimum building envelope desi gn for hot dry regions that can decrease a 4 0%. Successfully designing a net zero energy home. Creating a home with a both high efficient building envelope and visual appeal.
13 CHAPTER 2 LITERATURE REVIEW A wide variety of research has been done revolving around my area of interest. Every one of these sources focuses on an aspect of my study so that they will be very beneficial as a base for my research. Climate The most critical function of the bui lding envelope is that it separates the interior environment of the building from the exterior environment. Consequently, the climate in which the building is located determines the features of the building envelope design. Building envelope design strate gies in cold areas differ from those in hot or tropical areas; thus, every element of the building envelope from the array of materials, to the fenestration design, and the insulation are dependent on a region's climate classification. The Koppen Climate C lassification System organizes the world climate based on many factors including temperature, humidity, precipitation, atmospheric pressure, wind and others The following research will focus on the building envelope design strategies in hot dry (desert) r egions which is BWh based on Koppen Climate Classification System as shown in Figure 1. This climate zone is characterized by precipitation of less than 10 in. (250 mm) per year, less vegetation and high day to day shifts in temperature. The desert climate BWh mostly located in central Australia, northern and central Africa, Arab peninsula and parts of southwestern United States. The hot dry regions are one of these areas that have a great opportunity to achieve the net zero energy because the buildings t here are exposed to the sun for most of the year, so they can utilize the solar light and heat to generate a tremendous amount of energy. Of course, there
14 are some challenges in the hot dry regions like the very high temperature in the summer and the lack of vegetation, but with high efficient building envelope design, these challenges or issues will be solved. Figure 1 : Koppen Climate Classification System (Adapted from Peel et al., 2007). Building Envelope the skeleton of the structure, or the monolithic load other words, the building envelope acts as the separator between the internal and the external environment of a building. T he building envelope contains opaque components and fenestration systems. Opaque components are walls, roofs, ground slabs, basement walls, and opaque doors; the fenestration systems combine windows, ventilators, skylights, and glazed doors. There are
15 two main functions of the building envelope, th e first is that it serves as a barrier to protect occupants and the interior of the building from weather conditions, noise, pollution etc. The second function is aesthetic, in that building envelopes set the tone for impression and style via the design and look of the facades. features are responsible for the heat gain and loss, and the amount of wind that is allowed to enter the building. To expound, there are external and internal thermal loads that a well built envelope design should control of the heat transference through it. The external loads are mainly from solar heat that transfers through windows, the envelope surface s, and unwanted air infiltration in the building. The internal loads include the heat that comes from the artificial lighting systems, equipment, and body heat. The basic design strategies for designing high performance building envelopes include: Determin ing the orientation of the building and the massing form design depending on solar position. Maximizing the shading device to reduce the external thermal loads. Providing natural ventilation to decrease cooling loads that a building needs and to improve th e air quality. Maximizing the natural light to be a substitutional of the artificial light. Optimizing the building envelope insulation system. (Aksamija, 2013)
16 Wall Systems The wall system consists of all the vertical opaque components of the building e nvelope. All of the materials, thermal insulation, thickness, wall assembly and finishes of the wall can be designed based on the climate of where the building is located and whether it needs heating or cooling. The ASCE Standard 11 Guideline for Structura l Condition Assessment of Existing load bearing. The load bearing wall system is a wall that carries any extra vertical load in addition to its own weight; the non load bearing wall is that which does not support any vertical loads apart from its own weight. The components for both load bearing and non load bearing wall systems can be identical (American, 2014). Reinforced Concrete The reinforced concrete wall consists of concrete and rods, bars, or mesh of steel inside it to strengthen the wall. This wall system has an astounding ability to carry loads and is common in all types of construction. The thermal insulation can be incorporated with this system to improve its thermal resistance. Th e components of the reinforced concrete wall may include: Concrete Rods, bars, or mesh of reinforcement steel Insulation Vapor retarder Interior finish such as wood or metal furring and gypsum wallboard or plaster Exterior finish like molded formwork, exposed aggregate, or coating applications (American, 2014)
17 Figure 2 : Reinforced concrete wall (Adapted from ICF Concrete Wall Systems) Precast Concrete The precast concrete is composed of prefabricated panels that cast and curd in factory, a nd from there are transported to a construction site and lifted into place. The profile of the panels can be in several designs such as single or double tee, or solid or hollow core slab panels. Precast concrete components may include: Concrete. Reinforcem ent steel Embedded steel plates or shapes for connection purposes Insulation
18 Vapor retarder Interior and exterior finishes. (American, 2014) Reinforced Masonry Reinforced masonry is any type of brick or concrete that is strengthened with reinforced st eel to increase vertical and lateral load resisting ability. Reinforcement can be accomplished many ways. One example is by hollow or between wythes of solid masonry units. The components of this type of reinforced masonry wall may include: Interior and exterior masonry wythes Metal wall ties or horizontal joint reinforcement Flashings, weeps, or lintels Insulation Steel reinforcement Grout Bar placement accessories Interior finishes Exterio r finishes (American, 2014) Figure 3 : Reinforced masonry wall (Adapted from COSC 253 Study Guide, 2015 )
19 Selecting materials of a wall system is a fundamental aspect of obtaining a high efficiency building envelope for an appropriate climate. Each materia l has physical properties that determine the level of its thermal resistance (R value). Table 1 displays the thermal resistance (R value) of some building materials that are used for opaque building envelopes (Aksamija, 2013). Table 1: Thermal resistance properties of some building materials (Aksamija, 2013). Material R value (h ft 2 o F/Btu) Brick 0.10 0.40 per inch CMU, 8 in. (200 mm) 1.11 2.0 CMU, 12 in. (300 mm) 1.23 3.7 Concrete (sand and gravel aggregate) 0.05 0.14 per inch Concrete (limestone aggregate) 0.09 0.18 per inch Concrete with lightweight aggregate 0.11 0.78 per inch Roof S ystem role in heat gain in the hot dry regions. In these reg ions, the roof should be well insulated to reduce heat gains. There are many approved strategies that can improve the efficiency of the roof system. One of these strategies involves the efficacy of light color in reducing heat gain. Suehrcke, Peterson and Selby have shown in their study that light and dark colored roof surfaces have a large disparity in heat gain. The equations in this paper illustrate accurate results of the
20 imates. The study shows that in north Australia a light colored roof has 30% lower heat gain than a dark colored roof (Suehrcke, Peterson and Selby, 2008). Another study by Prado and Ferreira discussed the only materials among those that were measured that had reached surface temperatures lower (Prado and Ferreira, 2005). Another strategy that can cause a significant reduction of indoor temperatures is the application of a roof pond cooling system. Kharrufa and Adil made an experiment for a room in Baghdad, Iraq, which is a hot dry region, and t hey measured the temperature inside the room in summer in three stages. The first measurement was in normal conditions without the pond, then another measurement with the pond on the top of the roof and without mechanical ventilation, and finally with mech anical ventilation. The results showed a noticeable enhancement in the indoor temperature of the room by around 11.0 F degrees cooler in the room with the pool than the room without, and 12.0 cooler with a ventilated one. The measurements were taken duri ng the peak time at 3:00pm when the outside temperature is the hottest (Kharrufa and Adil, 2008). Sharifi and Yamagata did a more comprehensive study and discussed 19 different roof pond systems. These roof ponds were taken from different regions and clima te zones. Ponds with movable insulations, shaded ponds, open roof ponds, ventilated roof ponds, energy roof and walkable roof ponds are examples of some of the roof pond systems that are discussed in this paper. Regardless of the advantages of the roof pon d and its effect of reducing the cooling load of the building, there are some disadvantages that were provided in their study. Some of these
21 disadvantages are, that roof ponds are not suitable for roofs that are built according to lightweight construction standards because the weight of the ponds need building structures that resist the extra weight of the ponds, and in case of leaking, this pond system could cause a severe Yamagata, 2015). Insulation System The insulation of the building envelope is one of the most efficient factors that contribute to the decrease of cooling loads of houses in hot dry regions. The type of insulation material used depends on the market avail ability, climate, and the required level of insulation that a building needs. The insulation materials are the most effective element of the envelope that can increase the thermal resistance (R value). Al Sanea and his colleagues did a study of the three m ost common insulation materials and installed them in two different masonry materials which are hollow concrete block and hollow red clay block. One of the important results that they found value of wall under optimum conditions becomes more d ominated by insulation Sanea, Zedan, Al Mujahid and Al Suhaibani, 2016). The study did not show enough variety of insulation materials and their properties; however, Table 2 by U.S. Department of Energy shows the most available insulation materials and some information on how they are installed, where their installation is applicable, and their advantages. Also, Table 3 displays the R value of some of these materials.
22 Table 2: Insulation materials types (adapted from U.S. Department of Energy). Type Insulation Material s Where Applicabl e Installation Method(s) Advantages Blanket: batts and rolls slag) wool walls, including foundation walls ceilings Fitted between studs joists, and beams. Do it yourself. Suited for standard stud and joist spacing that is relatively free from obstructions. Relatively inexpensive. Concrete block insulation and insulating concrete blocks Foam board, to be placed on outside of wall (usuall y new construction) or inside of wall (existing homes): Some manufacturers incorporate foam beads or air into the concrete mix to increase R values walls, including foundation walls, for new construction or major renovations (insulating concrete blocks) Require specialized skills Insulating concrete blocks are sometimes stacked without mortar (dry stacked) and surface bonded. Insulating cores increases wall R value. Insulating ou tside of concrete block wall places mass inside conditioned space, which can moderate indoor temperatures. Autoclaved aerated concrete and autoclaved cellular concrete masonry units have 10 times the insulating value of conventional concrete. Foam board o r rigid foam walls, including foundation walls ceilings Interior applications: must be covered with 1/2 inch gypsum board or other building code approved High insulating value for relatively little thickness. Can block thermal short circuits when installed
23 slope roofs materia l for fire safety. Exterior applications: must be covered with weatherproof facing. continuously over frames or joists. Insulating concrete forms (ICFs) foam blocks walls, including foundation walls for new construction Installed as part of the building structure. Insulation is literally built into the home's walls, creating high thermal resistance. Loose fill and blown in llulose slag) wool existing wall or open new wall cavities attic floors to reach places Blown into place using special equipment, sometimes poured in. Good for adding insulation to existing finished areas, irregularly shaped areas, and around obstructions. Reflective system faced kraft paper, plastic film, polyethylene bubbles, or cardboard walls, ceilings, and floors Foils, films, or papers fitted between wood frame studs, joists, rafters, and beams. Do it yourself. Suitable for framing at standard spacing. Bubble form suitable if framing is irregular or if obstructions are present. Most effective at preventing downward heat flow, effectiveness depends on spacing.
24 Rigid fi brous or fiber insulation slag) wool unconditioned spaces requiring insulation that can withstand high temperatures HVAC contractors fabricate the insulation into ducts either at their shops or at the j ob sites. Can withstand high temperatures. Sprayed foam and foamed in place existing wall cavities attic floors Applied using small spray containers or in larger quantities as a pressure sprayed (foamed in place) product. Good for adding insulation to existing finished areas, irregularly shaped areas, and around obstructions. Structural insulated panels (SIPs) liquid foam insulation core insulation walls, ceilings, floors, and roofs for new construction Construction workers fit SIPs together to form walls and roof of a house. SIP built houses provide superior and uniform insulation compared to more traditional construction met hods; they also take less time to build. Table 3: R value table (adapted from Colorado energy, 2016 ). Material R/Inch hrft 2 F/Btu Fiberglass Batts 3.14 4.30 Fiberglass Blown (wall) 3.70 4.30 Rock Wool Batt 3.14 4.00 Rock Wool Blown (wall) 3.10 4. 00 Cellulose Blown (wall) 3.80 3.90 Vermiculite 2.13 Autoclaved Aerated Concrete 1.05 Urea Terpolymer Foam 4.48 Rigid Fiberglass (> 4lb/ft3) 4.00
25 Expanded Polystyrene (beadboard) 4.00 Extruded Polystyrene 5.00 Polyurethane (foamed in place) 6.25 P olyisocyanurate (foil faced) 5.0 5.6 An important aspect in achieving better insulation performance is the number and location of insulation layers. The study that has been done by Al Sanea and Zedan compared between different wall configurations and the effect of the number and location of the insulation layers in the wall. All investigated walls had the same thermal mass, which is 308 mm. Additionally, they had the same materials, which were 15 mm thick cement plaster on each side enclosing the wall asse mbly, either 100 or 200 mm thick, heavy weight hollow concrete blocks (HWHCB), and molded polystyrene for the insulation layers. The climate condition used in this study was that of Riyadh, Saudi Arabia which is a hot dry region. Figure 4 displays the wall arrangement of each wall. The results showed that the best thermal performance was achieved by wall W3 which had three layers of insulation, each 26 mm thick, then wall W2c that had two layers of insulation with 39 mm thickness in each one, placed on the outside and in the middle of the wall. The least thermal performance was wall W1 that had one 78 mm insulation layer placed inside. (Al Sanea and Zedan, 2011).
26 Figure 4 : (Adapted from Al S anea and Zedan, 2011 )
27 Fenestration system load bearing element that is installed doors, curtain walls, louvers, skylight and clerestories. Energy consumption is highly influenced by fenestration systems throughout infrastructure. When constructing a fenestration system, the elements that should be most considered are, the heat transfer coefficient (U value), solar h eat gain coefficient (SHGC), light to solar gain (LSG), and visible light transmittance(VLT). To expound, the U value is the rate of the heat transmission through the fenestration materials and it is expressed in units of Btu/hr ft 2 o F. Materials with lowe r U value are more insulated and energy efficient. The SHGC quantifies how much solar heat passes into the building through the glass. The measurement ra te of SHGC is from 0 to 1, with zero indicating 100% of solar heat is blocked, and one meaning the glas s allows 100% of the solar heat to pass through. The LSG is the ratio between SHGC and visible light transmittance(VLT). A higher number of LSG means the glass transmits more light with less amounts of heat (U.S. Department of Energy). Ajla Aksamija mentio which is the window to wall ratio (WWR); in other words, it is the ratio of glazing area to opaque component area (Aksamija, 2013). She showed the relationship between WWR and the energy c onsumption and solar heat gain for north oriented office spaces in different locations throughout the United States. Figure 5 displays the charts in the hot dry area, or BWh as measured by the Koppen Climate Classification System, which was specifically in Phoenix, Arizona. The charts show that in the BWh regions, having a smaller WWR is more advantageous
28 because windows increase the solar heat gain, resulting in more cooling loads required for the building Figure 5: Effects of WWR on energy consumption and solar heat gain (Adapted from Aksamija, 2013 )
29 Design Strategies Orientation Another critical design strategy with various ramifications on the building envelope is building orientation. The amount of solar radiation that the build ing envelope receives changes orientation of the building is a leading factor in the decrease or increase of the amount of solar radiation that horizontal and ve rtical walls, as well as the inclined roof, can gain. In most climate zones, in winter and to minimize it in summer. The walls that are exposed to the highest solar r adiation in summer are the ones located in the east and west facades, where they get the lowest solar radiation in winter as well. The southern walls, especially in the northern hemisphere, receive the highest solar intensity in winter and in summer they i ntake low solar radiation (Givoni, 1998). One of the most informative studies about building orientation was done by Faizi, N oorani, Ghaedi and Mahdavinejad named the Case Study of Maskan Mehr Complexes in Tehran, Iran. It focused on four features of the building which are building orientation, overall size, form of building, and translucent layers and the thermal inertia of layers. Then, the study analyzed four different types of buildings in Maskan Mehr complexes, gathering data on shadows and overshadow ing, solar radiation, lighting access simulation, and thermal simulation and analysis. These analyses show varied results between the four residential building types (Faizi, Noorani, Ghaedi and Mahdavinejad, 2011). Many Other studies have also discussed th e optimum orientation of the building such as Morrissey, Moore and Horne (2011), Givoni (1998) and Aksamija (2013). These studies show that choosing the right orientation of a building reduces a
30 considerable amount of energy consumption, especially in very extreme climates like in the desert regions. Each of these studies suggest that in hot be oriented to the east west axis to maximize the northern and southern facade area (Morrissey, Moore and Horne, 2011) (Givoni 1998) (Aksamija, 2013). Courtyard A very practical facet of design is building form, especially when dealing with hot dry climates. In the they state that the courtyard shape has a large effect on heating and cooling the building in the hot and dry climate. The geometric shape of the courtyard significantly impacts the shadows produced on the building envelope and the amount of solar radiation that a building receives. This study aims to show simulations of different shapes dry region. The determination of building form (courtyard building) alter natives and the determination of the building envelope were the only factors that these studies addressed. The results of this study illustrated that by increasing the floor area of the courtyard, the cooling and heating loads of the building gradually inc rease. Many details in this study reveal how a small change in the design can make a substantial difference. This study is an example of the efficacy of the courtyard design for reducing Another study done by Muhaisen (2006) assessed the shading performance of courtyard forms in order to provide the maximum amounts of shadow in summer and sunlit areas in winter. The study examined various locatio ns, one being Cairo, Egypt which is a hot dry region. Many aspects of the courtyard design were discussed in this study. Firstly, the percentage of the shaded internal wall surface area of the courtyard which reduces gradually whenever the courtyard
31 become s shallower; however, in winter, when a courtyard is less deep, a more sunlit area will be obtained. Second, the orientation of the courtyard and the results show that in a hot dry climate, the optimum orientation to ensure an efficient performance in both summer and winter is that which places the courtyard between the northeast southwest axis and the north south axis. Finally, the most appropriate courtyard height and number of stories that can be obtained in a hot dry region in both seasons was found to be two stories (Muhaisen, 2006). Net Zero Energy The definition of net zero energy as Hootman (2012) defined in his book Net Zero Energy ormance, whereby it produces as much or more renewable energy as it Laboratory (NREL) has classified the net zero energy building to four systems. The ranking from A class which provides electricity to the building that is generated by renewable energy from sources located within the footprint of the building such as photovoltaics or wind turbine that mounted on the roof or integrated with the building facade, throug h D class which purchases renewable energy to operate the building (Hootman, 2012). Arid hot regions get a magnificent amount of sunlight for most of the year since the sky is always clear. Thus, solar power is a significant opportunity in this climate zo ne. solar power can be produced either by converting the sunlight to electricity by the photovoltaic cells or by converting the heat of the sun to energy as seen in solar solar thermal collectors. Solar power is not a recent innovation, it has been used si nce the 7th Century B.C. when people used to concentrate the sunlight by holding a magnifying
32 glass above a small piece of wood for making fire (Maehlum, 2013). However, the idea of converting the sunlight to electricity started in 1839 by the French physi cist Edmund Becquerel. The actual first photovoltaic cell was created in 1954 by David Chapin, Calvin Fuller and Gerald Pearson (Maehlum, 2013). Nowadays, there is much variety in reaping the benefits of solar power. One common way to optimize solar power is through the use of photovoltaic cell, or what is called a solar panel. The cell gets its name from the conversion process of light (photons) to electricity (voltage), and thus is referred to as photovoltaic PV. There are many types of photovoltaics such as the flat plate one which is made from silicon, the thin film solar cells, and some PV that made from different materials than silicon. The flat plate is the traditional PV, but nowadays, it is the most efficient one. Another type of PV is the thin film solar cells that is the second generation of the PV. The thin film solar cells made from amorphous silicon such as cadmium telluride. This type of PV is a flexible, so it is used in many places such as the building elevations, rooftop shingles and tiles, and the glazing for skylights. The third generation of the PV is made from different materials than silicon like solar inks, solar dyes and conductive plastics (National renewable energy laboratory). Furthermore, another technique to get the benefit from t he solar power is by converting the heat of the sun to energy. The most popular way to achieve this is by using the solar thermal thermal energy through a solar thermal collectors are powerful in any solar energy system. They absorb the solar radiation
33 then, convert it to heat energy and transfer it through a working fluid such as air, water or a refrigerant, for several helpful purposes (Kumar, Baredar and Qureshi, 2015). Moreover, one of the most recent technologies in the solar power utilizations is the photovoltaic thermoelectric hybrid power generation system. The idea of the PV TEG hybr id system is to utilize the wasted thermal energy of concentrated photovoltaic system by attaching the thermoelectric generator to the back side of the photovoltaic module (Lamba and Kaushik, 2016). Studies show that the PV TEG generates more power than th e photovoltaic system alone. The efficiency of PV TEG is around 23% which is more than photovoltaic which has an efficiency of about 19%, so the PV TEG efficiency is 25% more than that of the PV cells. (Zhu, Deng, Wang, Shen and Gulfam, 2016).
34 CHAPTER 3 CASE STUDY Vali Homes Prototype I Architects and developers created this standard plan prototype house to fit in any place within Phoenix, Arizona. The goals of designing this prototype house are to create a high quality and sustainable net zero energy hou se at a low to mid price that is affordable to many people, and to make the design a standard that can be replicated in any lot within Phoenix. The home is a net positive energy which means it generate energy by PV more than the house need. The photovoltai c system generates 3.6 kW while the house uses about 6000 kWh of electricity per year. The photovoltaic system is grid connected, so no energy storage needed. More than just being a net positive energy home, it surpassed LEED Platinum certification and pro vided a blower test rating of .68 ACH50 (Living Future). Table 4: G eneral information of Vali homes prototype I (adapted from Living Future). General Information P roject Team Location: Phoenix, Arizona Owner: Vali Homes, LLC Project Area: 6,500 sf Own er Representative: Austin Trautman Gross Building Area: 1,500 sf Architect: coLAB Studio LLC Building Footprint: 1,500 sf Project Director/Manager: Austin Trautman Start of Construction: May 2013 Contractor: 180 Degrees, Inc. Start of Occupancy: December 2013 Mechanical: Vali Homes, LLC
35 Owner Occupied: Yes Electrical: Woodward Engineering, Inc. Occupancy Type: Residential Plumbing, Lighting and Interior Design: coLAB Studio, LLC Number of occupants: 2 Landscape: Urban Cactus Structura l: BDA Engineering, Inc. The main contributing factor in reduction of energy consumption in the hom e is the The designer tested various building envelope solutions by Passive House energy modeling software in order to choose the o ptimal materials and design while putting into consideration the cost. The insulation used in the roof is the blow in cellulose insulation. This type of insulation was used because it has 100% recycled content, a near zero carbon footprint, high R value co mpared to other insulation types, and it can be blown and fitted into any place, sheathing and wall cladding system (Living Future). The passive design str ategies that aided the house in achieving Net Zero Energy were: The House was oriented on a north south axis and to decrease the sun heat gain, there was not any east west fenestration. 100% shading on all glass, by using the vented bent metal pan cladding system that casts its shadow on the windows, and also reducing the heat that is reflected from the ground, as can be seen in figure 6 The house open floor plan which minimized HVAC components.
36 Trees planted on both east and west sides to shade the buildi ng envelope. This study is an exemplary case of a simple net zero energy house in a hot dry region. Many lessons can be gleaned from this case study such as the insulation system, building orientation, shading strategies by the vented bent metal pan cladd ing and the trees on east and west sides, and the fenestration system design. This house proves that the high performance building envelope is greatly effective in reducing the energy demands of the house, which in turn makes it easier to generate energy v ia photovoltaics. Figure 6 : Vali homes prototype I perspective (ArchDaily, 2014 )
37 Figure 7 : Vali homes prototype I Plan and sections (ArchDaily, 2014 )
38 e project is comprised of two houses placed next to each other with an almost identical plan. The first house was constructed to meet the Passivhaus standard and net zero energy, while the other one was built according to conventional construction practice s in Qatar. Both Passivhaus villa (PHV) and the Standard villa (STV) are about 200 m2 in floor area. The villas are designed for a family of four, consisting of three bedrooms, an open living/kitchen space and a central atrium as is illustrated in Figure 8 In March 2013 the project was completed, and the examination of both houses and their efficiency began (Khalfan and Sharples, 2016 ) Figure 8 : PHV and STV perspective and layout ( Khalfan and Sharples, 2016) Although the layout of both villas is practica lly the same, their building envelope materials and components are different. The PHV is entirely insulated, with minimal air leakages and thermal bridges. Table 5 and figure 9 show both the PHV and STV building envelope materials and table 6 shows the U v alue for each component of the building envelope. The building
39 envelope design was not the only factor that was taken into account in the PHV, but there are other aspects that have been upgrade photovoltaic array installed on its roof, and a grey water system (Khalfan and Sharples, 2016). Table 5 : PH V and STV building envelope materials (adapted from Khalfan and Sharples, 2016). Construction PHV STV Wall 200 mm block work + 380 mm Polystyrene layer 300 mm block work + 50 mm cavity in between Roof 200 mm Cast concrete + 380 mm Polystyrene layer 200 m m Cast concrete + 100 mm Polystyrene layer Floor 250 mm Cast concrete + 200 mm Polyfoam layer 250 mm Cast concrete Glazed Surfaces Triple glazing 6 mm clear and coated glass double 12 mm cavity Double glazing 6 mm clear oat glass single 12 mm cavity Table 6 : PHV and STV U values (W/m2K) (adapted from Khalfan and Sharples, 2016). Construction PHV STV Passivhaus Requirement Walls 0.084 1.31 0.10 0.15 Roof 0.084 0.30 0.10 0.15 Floor 0.11 0.50 0.10 0.15
40 Glazed surfaces 1.11 2.61 0.85 Figure 9 : PHV and STV wall section (EU GCC Clean Energy Technology Network, 2017 ) The study shows that the insulated PHV consumes much less energy than STV. The simulated results show that the PHV would con sume approximately half of the amount of energy that STV used; notwithstanding, the existing measurement illustrated that the PHV is using just about a third of the energy used in the STV as is illustrated in Figure 10 The energy consumption of the PHV is around half of the energy generated by the 400 kWh/m2 PV system as is shown in Figure 11 (Khalfan and Sharples, 2016 ). Figure 10 : PHV and STV energy consumption Figure 1 1 : Energy generated by PV ( Khalfan and Sharples, 2016)
41 The results of this study s howed remarkable evidence of how the well designed building envelope can make a significant reduction in the cooling energy load, which is the most dominant factor in energy consumption of a house in hot parts of Saudi Arabia, thus all the design strategies that were used in this PHV can be applied for a house in Saudi Arabia. Other lessons that can be learned from this case study include the efficiency of wall, roof and floor insulation materials and the fenestration system design that is used in the PHV. Figure 1 2 1 3 : Indoor and outdoor perspectives of PHV ( Sweet, 2014 )
42 CHAPTER 4 METHODOLOGY An Overview how it can contribute to achieving net zero energy for single family homes in hot dry climate regions. The investigation includes the selection of the most appropriate building envelope cy, determining the sufficient insulation for the whole envelope, solving challenges associated with hot dry climate, and the installation of the proper photovoltaic type and number. The sampling design is those families who live in the hot dry regions a nd are willing to build a net zero energy house. The research uses data from different sources. These sources include: Publications One of the most prominent methods of collecting data is by analyzing and gathering information from past studies and liter ature that are relevant to my current research. A wide variety of research has been done revolving around this particular research area. Every one of these sources focuses on an aspect of my study, so that will be very beneficial as a base for the research The books and articles that the research relies on are shown in the literature review chapter. insulation, and solar energy types require the newest materials to get the best results. This data can be obtained from conferences and exhibitions that showcase the cutting edge technologies and innovations to date. The AIA Conference on Architecture 2017 is one of the biggest architectural events in the United States, with around 800 leading building product
43 manufacturers showing their architectural products and materials, and a plethora of seminars and workshops. This event gave me a greater understanding of building envelope materials, building envelope design, and fenestr ation insulation. Another beneficial event that I attended was the California Solar Power Expo. This expo is critical for the research because it showcases the latest technologies of solar power, their efficiencies and types. Existing Case Studies Studying from existing case studies and analyzing them is a very useful method that supports the research. The case studies that are used are some net zero energy houses in hot dry climate regions. Since most of the hot dry climate regions have almost the same ch allenges, I targeted just two regions; the first one is a local case study in Phoenix, Arizona, and the other is in Barwa City, Qatar which is in the same climate zone of the proposal design. Design proposal The conclusion of this paper is the culmination of all the knowledge gathered and analyzed from literature reviews, case studies, and conferences to put them within arms reach by a proposal design of a single family home that is net zero energy in a hot dry region. The method that was used to test the b uilding envelope performance is by doing energy simulation analysis for two identical house designs; nevertheless, their envelope designs were different. The first one which is the net zero energy house that has a high efficiency building envelope, and the second one which has a conventional building envelope. These simulation softwares aid the study in providing more accurate and reliable results.
44 CHAPTER 5 DESIGN PROPOSAL The design proposal is for a single family home in Riyadh, Saudi Arabia that is co nsidered as a very hot dry region (BWh) based on the Koppen Climate Classification. The strategies implemented in the design of this home have been selected and adapted from all the research, books and case studies that are mentioned in both chapters 2 and 3. The design shows the powerful effect of the building envelope in decreasing the energy consumption of the house compared to a conventional building envelope design. The process followed to create thi s design proposal was to first mate and condition. Second, by taking into consideration the standard of Saudi single family home design as a baseline. Third, by applying the building envelope design strategies that were learned from the former studies. Fourth, by making energy simulatio ns and energy analyses to estimate the potential energy consumption. Finally, by installing sufficient photovoltaics that generate as much energy as the house consumes, to achieve a net zero energy home; successfully de signing a net zero energy home is the study goal. Site Analysis The site is located in Al Malqa, Riyadh, Saudi Arabia which is in the northeastern part of Riyadh the capital of Saudi Arabia as shown in F igure 14 16. The site is served by all services such as electricity, water and sewage sys tem as in most residential neighborhoods in Riyadh. The primary reason for choosing this site among other sites in Riyadh is due to its long axis oriented to north south axis. Thus, this design proposal can accommodate many sites within Riyadh, and even an y site throughout the globe that is in a hot dry region.
45 Figure 1 4 1 6 : The maps of Saudi Arabia, Riyadh and the site (Google Earth )
46 The climate of Riyadh is very hot dry in the summer and cold in win ter. The summer season is in April, May, June, July, August, September and October while the warmest month is August. However, from November until March Riyadh has nice, cool weather and becomes the coldest in January. Most precipitation is seen in April a nd usually does not exceed 25 mm as is shown in Figure 1 7 (Meteoblue). The humidity in Riyadh is generally low and does not exceed 55% as is seen in January,illustrated in F igure 1 8 (Weather and Climate). Figure 1 7 : Average temperatures and precipitatio n (Meteoblue ) Figure 1 8 : Average temperatures and precipitation ( Weather and Climate )
47 Riyadh also has clear skies for most of the year. Annually, Riyadh has around 277 sunny days. Additionally, there are about 63 partly cloudy days which leave only a bout 25 overcast and rainy days as is displayed in Figure 1 9 (Meteoblue). With only around 25 cloudy days a year, the chance of generating a lot of energy by photovoltaics can be significantly more th an most places around the world Figure 1 9 : Average clo udy, sunny, and precipitation days for each month (Meteoblue ) The Design General Information The house is for a Saudi family of six members. There are two stories and the gross floor area is 4142 ft2 (384 m2). The form of the house is almost rectangular w ith its long axis oriented to the East West axis, with an 18 x 13 ft. courtyard that is centrally located. The first floor includes two entrances, one for guests and the other for the residents, two large guest rooms each with a bathroom, a kitchen and din ing room. The second floor has the master bedroom and bath, two
48 bedrooms that have private bathrooms and one additional bedroom that shares a bathroom with the living room as displayed in F igure 20 2 2 Figure 20 2 1 : f irst and second fl oors
49 Figure 2 2 : t F igure 2 3 : The house section
50 F igure 2 4 : Perspective s of the house
51 F igure 2 5 : The eastern facade of the house F igure 2 6 : The western facade of the house
52 F igure 2 7 : The southern facade of the house F igure 2 8 : The northern facade of the house
53 CHAPTER 6 DISCUSSION AND RESULTS Design Strategies Many strategies that used to make this house a net zero energy building. The form of the house, orientation, the courtyard, the wall and roof systems, the insulation and fenestration system all contribute to achieving the optimal design of the building envelope. The House Layout The shape of the floor plan is almost rectangular and the long axis is on the east west axis to maximize the sout hern and northern facade areas. This orientation is prime due to both the southern and northern facades receiving the least solar radiation, as expounded on in former studies (Morrissey, Moore and Horne, 2011) (Givoni, 1998) (Aksamija, 2013). The southern wall area is greater than the northern because in winter it receives the highest solar intensity that helps to warm the house and as a result, decrease the heating loads. The most efficacious characteristic of the layout is the courtyard. The 18 x 13 ft. r ectangular courtyard is located centrally. The length lies on the north south axis. This orientation envelope in summer, and the sunlit area in winter (Muhaisen, 2006) The courtyard is not completely closed from all sides, as it has an 8.3 ft. wide corridor on the first floor. This corridor, displayed in F igure 2 9 allows the prevailing winds that blow from the southeast (as is illustrated in F igure 30 to flow through cooling down the courtyard and providing ventilation.
54 Figure 2 9 : Air movement through the courtyard. Figure 30 : Wind rose for Riyadh, Saudi Arabia (Revit analysis).
55 Wa ll System The exterior walls are highly insulated and are one of two different sizes and South facades as is displayed in the plans in F igures 20 2 2 The reason behind this placement is due to the fact that those facades get direct solar radiation; however, the thinner walls are in the northern faade and are also surrounding the courtyard because they are shaded for most of the nch thick cement plaster in each side enclosing the wall assembly, two arrays of heavy weight hollow concrete block (HWHCB) each one 6 inches thick, and two layers of expanded polystyrene insulation, each 6 inches thick, and placed on the outside and in th e middle of the wall. The thinner walls have the same elements, but differ in one insulation layer versus two, as shown in F igure 31 The reason for choosing the heavy weight hollow concrete block (HWHCB) and the reinforcement concrete for the structural s ystem is due to them being the most common construction systems that are used for residential buildings, and most buildings throughout Saudi Arabia. Regarding the expanded polystyrene insulation, there are several reasons for its selection. Reasons include its availability, and affordability compared to its efficiency, the variety of sizes to choose from, and its high rating of performance value of the thick walls is 51.5 h ft2 oF/Btu, while th e smaller one is 27.5 h ft2 oF/Btu as is expounded on in tables 1 and 3.
56 Figure 31 : Walls section Roof System strategies to decrease heat gain in homes. To optim ize roof performance, its element first Passivhaus which was tested and showed a high performance rating. The second strategy is a white roof is used to help reflect the solar radiation and to keep it arrays; they were raised about 8 feet to create a shaded area for outdoor sitting. Th e photovoltaics array covers around one third of the roof, therefore a big portion of the roof will have an extensive shading area, as is illustrated in F igure 32 Finally, the roof pond strategy can be seen in the back area that is uncovered to make the s itting area aesthetically pleasing, as well as to reduce the roof temperature as is shown in F igure 32 The depth of the pond is just 0.5 inches in order to avoid adding unnecessary weight to the structure.
57 Figure 32 : Fenes tration System The fenestration system in this house can be seen in windows, doors and shading devices. Windows are the most critical and effective element of the fenestration system, so they were placed in very appropriate positions. As is illustrated in the plans, there are no windows in both the East and West facades.The decision to forsake windows in the design of the eastern and western facades is due to their exposure to extremely high amounts of solar radiation in summer, and their lack of exposure to solar radiation in winter. Although there are no windows in these facades, the sunlight still permeates and reaches inside the home. The reason is because most of natural light without direct sunbeams. Almost all bedrooms except the smallest one have
58 windows in the southern faade because in winter they receive the highest solar intensity that reduces the heating loads. All these windows that are located on the sou thern faade have a horizontal shading device to protect them from the direct sunbeams. The glazed surface that is used is the double pane clear high performance, LowE with a U value of around 0.37 BTU/(hF ft) and its R value at 2.7 hrft2F/Btu as is illustrated in Table 7 Further, seeing that the walls are thick, a valuable technique is to, place the glazed surface inside the wall casts a shadow on the window pane, as is illustrated in F igure 33 Figure 33 : The window frame Table 7: U value and R value of windows ( Autodesk Sustainability Workshop )
59 Energy Simulation Analysis of The Design Proposal The energy simulation tool is very powerful in estim ating the energy consumption of the house and to give a clear vision of the envelope performance. Despite the fact that the results are not very accurate and do not examine every design strategies it can at least help to compare among different design st rategies and show which are the most advantageous and effective. The simulation programs used to obtain these results are Autodesk Green Building Studio and Insight 360 for Revit. The results indicate that the total energy consumption of the building is 19 127 kWh if the entire house works 12 hours every day for the whole year. It should be noted that all spaces working for 12 hours is more than what the actual consumption will be, especially since there are some spaces like most of the first floor that a re used maybe one time per month or even less. But to expect more energy consumption while in the design phase is better than the alternative to install the sufficient solar panels. Around 6 4 % of the annual energy use will be for the HVAC which is 1 2 219 k Wh, 1 8 % for the lighting, and 1 8 % for miscellaneous equipment as is displayed in F igure 34 The dominant energy use is for the space cooling with about 36.6 % of the total energy use. The energy consumption is varied each month, but the peak happens in Augu st. In general, the summer months May, June, July and August as is displayed in Figures 35 36 have approximately double the energy consumption rate than the winter months December, January and February; the house consumes the least energy in December.
60 Figure 34 : The total energy consumption (by Autodesk Revit) Figure 35 : The monthly energy consumption (by Autodesk Revit)
61 Figure 36 : The monthly peak demand (by Autodesk Revit) Energy Simulation Analysis of a C onventional Design The conve less efficient building envelope design. The wall and roof systems that are used are common in Saudi houses, which are HWHCB for walls and the reinforcement concrete for the structural system, but without insulation. The glazing type for all windows is the single pane, with no shading devices for the southern windows. Additionally, the walls and roof color is dark and not reflective. The simulation results showed a significant increase in energy consumption. The total energy consumption is 36,942 kWh All the extra energy is attributable to the raise of the cooling loads as is illustrated in F igure 37 The gap between the summer and winter consumption increased, which made the December energy consumption almost one third of the August energy use due to the drastic increase of the cooling demand as is shown in F igure 38
62 Figure 37 : The total energy consumption (by Autodesk Revit) Figure 3 8 : The monthly energy consumption ( by Autodesk Revit) Energy Simulation Analysis of Each Element of the Building Envelope the energy simulation has been done for the design proposal with downgrading the efficiency of each main system, one by one. First was the wall system, and the results showed that when only
63 this system was changed to the conventional, the total energy consumption dramatically increased by around 10000 kWh per year, as is displayed in Figure 39. Second was the roof system, when stripped of all the strategies, the energy consumption increased about 5000 kWh per year as is shown in Figure 40. Lastly, was the fenestration system efficacy the results showed that by making all windows a clear single pane, the total energy consumption increased by approximately 3000 kWh per year as is illustrated in Figure 41. Thus, the fenestration system is the least effective system among the others. Figure 39 : T otal energy consumption wit h only l ow efficient wall system (by Autodesk Revit). Figure 40 : T otal energy consumption with only
64 Figure 41 : T otal energy consumption with a clear single pane glazing (by Autodesk Revit). The Design Proposal and the C onventional Design Comparison The comparison between the design proposa l and the conventional design shows a significant difference in energy consumption. The high efficient building envelope of the design proposal makes the house consume 48% less electricity than the conventional house, which is about 18,000 kWh less per yea r than the conventional house energy consumption. The difference between the design proposal and the conventional design becomes greater in the summer illustrated in Figure 42.
65 Figure 42 : T he design proposal and the conventional design comparison Photovoltaics System energy that the house needs. Therefore, the sufficient solar ene rgy to generate the house demands of energy can be designed. The methods to calculate and select the proper PV are by PVWatts Calculator of the National Renewable Energy Laboratory and PVSKETCH website. There are several factors that can affect tput, but the most effective factors are the PV type, degree s tilt which means it lies horizontally, and the type that is selected has an efficiency rate of 19%. These 34 phot ovoltaics generate 13.6 kW which give around 23,241 kWh per year, and the house uses about 19 127 kWh of electricity per year. This photovoltaic system can generate up to 24,975 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Comparison Design proposal Conventional kWh
66 kWh per year as expounded on in Table 8 if the angle was 20 o ; however, in this case, it will increase the energy that is generated in winter and decrease the summer production because high demand of energy in the summer for the house as is illustrated in F igure 43 the appropriate tilt should be 0 degrees to maximize the summer production as is shown in Table 9. Table 8 : Photovoltaics energy generation with 20 o tilt ( PVWatts ) T able 9 : Photovoltaics energy generation with 0 degree t ilt ( PVWatts )
67 Figure 4 3 : Photovoltaics energy generation comparison In order to make the convention al house net zero energy with the same PV condition as the one used for the proposal design, more than double the number of PVs should be added. Meeting the demand of energy that the conventional house needs required 81 photovoltaics that generate 27 kW, which produce around 45,255 kWh per year. The reason why it needs substantially more than it consumes is because all the extra energy is attribut able to the raise of the cooling loads in summer, which require tho se extra PVs to make the house net zero energy as is shown in Figure 44 should be covered by these PVs which is an u nreasonable solution. 0 500 1000 1500 2000 2500 3000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Design proposal PV Generated Electricity (with zero degree tilt) PV Generated Electricity (with 20 degree tilt) kWh
68 Table 10 : Photovoltaics energy generation for the conventional house (PVWatts) Figure 4 4 : P V energy generation comparison 0 1000 2000 3000 4000 5000 6000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Comparison PV's generated electricity Conventional house kWh
69 CHAPTER 7 CONCLUSION N et zero energy buildings are inspiring multitudes of communities, companies, and individuals presently due to their appreciating value for owners and their environmental benefits. This study aimed to show the efficacy of the building envelope to reduce the energy consump tion of single family homes in hot dry regions; in turn then producing the sufficient amount of energy needed from the photovoltaics system. The study included several design strategies to accomplish the optimum building envelope design in hot dry regions. Firstly, the study showed the high performance wall system design. Secondly, the roof system and how the light, reflective color and the cool roof pond contribute to the decrease of cooling loads, which is dominant in hot dry regions. Thirdly, th e insulation system which is the most effectual element of the envelope in increasing the thermal resistance (R value). Fourthly, the fenestration system technique for the hot dry regions that includes, strategic window positioning and the appropriate wind ow to wall ratio WWR. Fifthly, the optimal orientation of a building in a hot dry climate. Sixthly, the courtyard design and its role to cool down the envelope. Finally, the solar panels that shaded the roof and generate the needed energy as well. The qual ity of all these strategies has been approved, either by the former research and great examples of several strategies that contribute to making net zero energy h ouses. Then, these strategies were applied to the design proposal and tested. The method used to test the
70 identical house designs; nevertheless, their envelope designs w ere different. The first was the net zero energy house that has a high efficiency building envelope, and the second had a conventional building envelope. The simulation results showed that the house with a high efficient building envelope had around 4 8 % le ss energy consumption than the conventional one. Therefore, making the house a net zero energy structure became possible with just 34 photovoltaics. Additionally the simulation results showed that the wall system is the most efficacy system of the buildin Some aspects that can be useful for future research that were not covered in this paper include the cost of making a net zero energy house in some hot dry regions compared to a conventional house, and more variety of the envelope configuratio n and materials. This study showed that by enhancing the building envelope in hot dry regions, achieving the net zero energy goal can be rather easy as is expounded on in the design proposal of the house in Riyadh, Saudi Arabia. This design proposal can ac t as a prototype that can be adapted within most of the hot dry regions, especially in Saudi Arabia. The aesthetics of the architectural design of the house showed that it is not necessary to have a distasteful or bland design in order to have a net zero e nergy house, but the home can in fact have both a high efficient building envelope and visual appeal.
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