Characterization of Thermal Comfort in a Passively Cooled Building Located in a Hot-Arid Climate

Transcription

1 Proceedings of 8 th Windsor Conference: Counting the Cost of Comfort in a changing world Cumberland Lodge, Windsor, UK, April London: Network for Comfort and Energy Use in Buildings, Characterization of Thermal Comfort in a Passively Cooled Building Located in a Hot-Arid Climate Alfredo Fernandez-Gonzalez 1 1 Natural Energies Advanced Technologies (NEAT) Laboratory, School of Architecture University of Nevada, Las Vegas, USA. alfredo.fernandez@unlv.edu Abstract This article compares the thermal performance and comfort levels produced by dry and wet roofponds monitored during the summer of 2011 in Las Vegas, NV. The measured data shows that under typical summer conditions, a dry roofpond with a depth of cm. installed over typical U.S. residential construction is able to keep the maximum indoor operative temperature approximately 5.1 C below the maximum outdoor air temperature, with the minimum indoor operative temperature remaining approximately 1.8 C above the minimum outdoor air temperature. A wet roofpond with the same depth and construction characteristics is able to improve the performance of the dry roofpond by lowering the maximum indoor operative temperature an additional 3.4 C (for a total reduction of approximately 8.5 C ), while also maintaining the minimum indoor operative temperature approximately 2.2 C below the minimum outdoor air temperature. While neither one of the roofponds achieved comfortable conditions 100% of the time during the harsh summer conditions found in Las Vegas, NV, a wet roofpond applied to a better insulated one-storey house featuring ceiling fans might be able to reduce the uncomfortable period to a few hours per day during the hottest days of the summer season. Keywords: Hot-Arid Climate; Passive Cooling; Roofponds; Thermal Comfort 1 Introduction Passive solar heating and cooling strategies have been extensively researched in the United States for the past four decades. However, in spite of the documented successes and the innovative ideas generated through this research, most buildings in North America feature mechanical systems to satisfy the comfort expectations of their occupants. The energy used by the residential sector for space heating and cooling during 2009 in the United States was 5.12 million TJ (4.86 quadrillion Btu), and constituted 47.7% of all the site energy used by the residential sector (RECS, 2013). The level of energy consumption of the residential sector in the United States will be difficult to sustain in an evolving world affected by climate change and by uncertain future energy supplies. To that end, it seems necessary to revisit the utilization of passive solar heating and cooling systems to satisfy the comfort requirements of residential buildings. 2 Perceived issues affecting the adoption of passive heating and cooling systems If passive solar heating and cooling systems have been widely researched in the United States, why then are these systems not used in residential buildings? The answer to this question is certainly complex, as there are real and perceived issues

2 raised by various constituencies. For example, in the United States the home financing sector generally requires residential developers to install mechanical cooling systems. Consequently, given the extended use of mechanical cooling, the general public is unaware of other passive and hybrid options for space conditioning. But more importantly, there is real scepticism among architects and designers in the United States regarding the use of passive heating and cooling systems as these are not explicitly addressed (with the exception of natural ventilation) in ASHRAE s Standard 55 (ASHRAE, 2010). This issue is of particular importance for those passive strategies that rely on radiation as the primary means to produce comfortable conditions (Fernández-González, 2007). The lack of information about comfort in passive buildings is exemplified in the Load Collector Ratio (LCR) method proposed by Balcomb et al. (1984). The LCR method is the most widely used guideline for the design and prediction of the thermal performance of passive solar heated buildings in the United States. The LCR method does not provide conclusive information about the thermal conditions (air and mean radiant temperatures as well as air velocity) produced by the various strategies included in the guideline. Moreover, the conditions suggested by the LCR method are assumed to be the same across the whole floor area, giving therefore an estimate of the lumped conditions throughout the space. This characteristic of the LCR method, as pointed out by Messadi (1998), makes it miss the dynamic aspects that characterize thermally-massive passive solar buildings, and this is precisely the most important concern if one were to look at passive solar buildings from the thermal comfort standpoint. It could be argued that at the time in which the LCR method was developed, the main concern was to save energy, and therefore, that is why this method doesn t pay much attention to thermal comfort and how it could be evaluated or characterized. Nonetheless, by having put thermal comfort as a secondary concern, the LCR method made passive solar buildings an alternative practice. The same issue also hinders the adoption of those cooling strategies that rely on radiation as the primary means to provide comfortable conditions. To address this lack of information with respect to the thermal conditions produced by roofponds, a heating and cooling strategy that relies on ceiling temperatures to produce a comfortable environment, this paper presents a summary of the experimental results obtained during the summer of 2011 using two different cooling configurations of the roofpond strategy in a hot-arid climate. 3 Basic roofpond principles The roofpond system, conceived and developed by Harold Hay (Hay and Yellot, 1968), is an indirect gain strategy for heating and cooling consisting of a thermal storage roof holding water within transparent polyethylene bags (hence the name of roofpond ). Under the thermal storage roof, a black EPDM liner is required for water proofing and to properly absorb and convert solar radiation into useable heat during the wintertime. The system generally requires movable insulation panels above the thermal storage roof to cover it during winter nights or summer days. The movable insulation is in fact what allows this strategy to perform in both heating and cooling modes, by allowing the system to avoid unnecessary winter heat losses or undesired summer heat gains through the thermal storage roof. Given that the thermal collection, storage, transfer and control takes place on the roof surface of the building, the ceiling under the roofpond must have high thermal

3 conductivity to facilitate the heat exchange between the occupied living space and the roofpond above. Since metal deck is a common, widely available construction material, it is often used as the structural ceiling in roofpond buildings given its high thermal conductivity and structural strength to support the added weight of the roofpond system. As a heating and cooling strategy, roofponds work well because they mimic the ways in which nature tempers and controls the global climate (Givoni, 1994; Hay and Yellot, 1970). 3.1 Heating mode In its heating mode, the movable insulation is removed from the roofpond to expose it to incoming solar radiation between the hours of 9:00 AM and 3:00 PM (solar time). The solar radiation is then absorbed and converted into useful heat at the surface of the black liner. While most of the heat is then transferred to the roofpond, a fraction of this heat is immediately transferred to the occupied living spaces under the thermal storage roof. If there isn t enough solar radiation during the day, the movable insulation may cover the roofpond, acting much in the same way as a cloud cover that minimizes the radiation losses to the sky. Similarly, at night the movable insulation covers the roofpond to minimize heat losses so that the energy collected during the day remains in the roofpond so that it can be radiated throughout the night to the occupied spaces below. 3.2 Cooling mode In cooling mode, the movable insulation covers the roofpond during daylit hours, thus minimizing undesirable solar heat gains through the roof. Throughout the entire day the roofpond absorbs and stores the heat that is generated within the building and also the heat that penetrates through the building envelope. As the day progresses, the roofpond temperature slowly increases until it reaches its maximum temperature, which in a well-designed roofpond would be approximately 26 C (79 F). It is at this point that the movable insulation is removed to expose the roofpond to the night sky. Just as our planet re-radiates heat back to space, the roofpond emits long-wave radiation using the night-sky as heat sink. A properly designed roofpond can reject all the heat that was gained by the building during the daytime, lowering the roofpond temperature enough for it to be able to repeat the process the following day. 3.3 Operation during swing seasons During transitional periods (generally in the spring and fall), the movable insulation typically covers the roofpond throughout the entire day. During these times, the ambient temperature approaches the comfortable range and the thermal mass of the roofpond is used to stabilize the indoor temperature by absorbing the heat that is generated within the building, transferring it back to the occupied living spaces at night. 4 Types of roofponds Different types of roofponds have been developed to achieve the best possible performance in different climatic regions. Based on the way in which they contain and use water, roofponds can be classified in three different categories: dry, wet, and open. Dry roofpond: A roofpond in which the water is contained in plastic bags and no water is exposed to the environment. This type of roofpond may be exposed to the

4 outdoor environment or contained within an attic. While dry roofponds are adaptable to both heating and cooling applications, their cooling potential is limited in very hot or humid environments. Wet roofpond: A roofpond in which water is contained in plastic bags, which are then flooded or sprayed when additional cooling is desired. By wetting the surfaces of the bags that are exposed to the environment cooling occurs by both radiation to the night sky and by evaporation. This type of roofpond is used only for cooling purposes, but may be adaptable for heating if the water covering the surface of the plastic bags is drained. Open roofpond: A roofpond system in which the water is not contained in bags but rather it exists as an open pool within the boundaries of the roof parapet. This type of roof pond is used only for cooling applications. Because of its evaporative losses, this type of roofpond requires constant replenishment of the water body. This type of roofpond may be exposed to the outdoor environment or contained within an attic. The former approach requires constant maintenance to keep the water from developing algae or accumulating debris. When contained within an attic, an open roofpond is only cooled by evaporation and therefore it requires sufficiently large inlet and outlet vents. With respect to their containment within the roof, roofponds are divided in two different systems: exposed and enclosed roofponds. These two configurations respond to the construction methods necessary to accommodate winter climatic conditions. Exposed roofpond: A roofpond system in which the movable insulation panels are the only barrier between the pond and the environment. This configuration may be used in both heating and cooling applications, however it is only recommended for locations with less than 10 cm. (4 inches) of snow precipitation per year, and with a mean monthly minimum ambient temperature for January above 0 C (32 F). Enclosed roofpond: A roofpond system that is totally enclosed in an attic space. Generally, this type of roofpond features sufficiently large equator-facing skylights to collect solar radiation during the winter months. This application is mainly used where heating loads are predominant and winter conditions require that the roofpond remain confined within the building envelope. This type of roofpond also requires the use of movable insulation to prevent losses through the glazing in the wintertime (or solar heat gains during the summertime). In spite of all these differences, all roofponds use the same operating principles described earlier in this article. To determine the ideal depth of a pond one needs to examine local climatic conditions. Marlatt et al. (1984) suggests pond depths between 10 and 25 cm. (4 and 10 inches), but in colder climates depths over 30 cm. (12 inches) are not uncommon (Fernández-González, 2007). 5 Roofpond system components Water Bags: The thermal storage on a roofpond building typically consists of water enclosed in plastic (e.g., clear 6 mm. UV treated polyethylene) bags. The water does not circulate in and out of the bags at any time, as the bags are permanently sealed. Given that the bags are only exposed to solar radiation during the heating season, the lifespan of the water bags is somewhere between two and four times the stated duration of the UV protection (which assumes daily exposure to solar radiation).

5 Most UV protected polyethylene plastics are guaranteed for four years, and therefore their expected lifespan in a roofpond building would be anywhere between eight to sixteen years. In the United States, a conventional flat-roof is generally resurfaced once every ten years, so the roofpond system is well within that range. Liner: The liner that waterproofs the metal deck should be made of black Ethylene Propylene Diene Monomer (EPDM). The liner s guaranteed life is twenty years under full exposure to weather elements. In a roofpond application the life of the liner is extended somewhere between 1 ½ and 2 times the guaranteed life of the liner. Ideally, the EPDM liner should be installed in a way that an entire piece covers the whole roof area. While this may be difficult to do, minimizing the number of seams helps prevent leaks or condensation problems. Movable insulation: The design of movable insulation panels has been historically the biggest problem in roofpond buildings (Givoni, 1994; Marlatt et al., 1984). This is particularly true in exposed roofponds, where the movable insulation is deployed horizontally, and it is constantly exposed to outdoor weather elements. Recent research at the University of Nevada, Las Vegas shows that the use of standard garage door components automatically operated by a programmable timer can be satisfactorily used to meet the demands of a roofpond (Fernandez-Gonzalez, 2007). 6 Experimental results This article compares the conditions produced by dry and wet roofponds monitored during the astronomic summer (June 21st through September 21st) of The results presented in this section were experimentally measured at the Natural Energies Advanced Technologies (NEAT) Laboratory of the University of Nevada, Las Vegas. 6.1 Experimental setup The experimental setup consisted of two identical test cells, each featuring a cm. (6 inches) deep exposed roofpond (see Figure 1). The only difference between the two roofpond test cells was that one featured a dry roofpond (see Figure 1e) while the other had a wet roofpond (see Figure 1d), with water sprayed at night in order to take advantage of indirect evaporative cooling. Both test cells have interior dimensions of 1.3 m. (4-3 ) by 2.1 m. (6-10 ) and a floor-to-ceiling height of 2.4 m. (8-0 ). A corrugated metal deck is used as structural ceiling. Thermacore automated garage doors provide the movable insulation for the roofponds (see Figure 1b). The R-value of the movable insulation used in this experiment is 1.94 K m²/w (11 h ft² F/Btu). 6.2 Operation of the test cells Between June 12 th and August 20 th, the movable insulation covered the roofponds between 6:00 AM and 8:00 PM (Local Standard Time). The movable insulation panels were retracted at 8:00 PM, when the environment was cooler and could begin to absorb the heat gained by the roofponds throughout the day. On August 21 st the movable insulation cycle was changed and the roofponds were covered from 6:30 AM until 7:30 PM. This change gave the roofponds one additional hour to dissipate the heat absorbed during the day. Starting on September 11 th the operation cycle was modified once again and the movable insulation covered both roofponds between 7:00 AM and 7:00 PM. Both test cells also featured an exhaust fan operated to maintain a ventilation rate of 1 ACH.

6 a b c d e Figure 1. Wet (red dot) and Dry (green dot) Roofpond test cells at the University of Nevada, Las Vegas. To spray the wet roofpond, water was pumped from an adjacent storage tank (see Figure 1c) and delivered to its upper surface using a drip irrigation system (see Figure 1d). This procedure started on June 18 th and was continued until the end of the experiment. During the first week in which the wet roofpond was sprayed with water 37.9 litres (10 gallons) were delivered per night to assist with its cooling. However, after careful observation it was noted that a maximum of 11.4 litres (3 gallons) could be successfully evaporated per night. Therefore, 11.4 litres (3 gallons) were used for the remainder of the experiment. This amount corresponds, approximately, to 3.2 litres / m 2 (1 gallon / 10 ft 2 ) of roofpond surface area. 6.3 Overall summer performance The experimental results obtained during the summer of 2011 confirm that both roofpond types are able to provide remarkable indoor thermal stability, which is in many ways a prerequisite for a building to be considered comfortable. While the average outdoor air diurnal temperature swing during the studied period was 11.3 C (20.4 F ), the daily average indoor operative temperature swing within both roofponds was below 5 C (9 F ). Figure 2 illustrates the hourly outdoor air and humidity conditions measured throughout this study. The highest hourly outdoor air temperature measured during the summer of 2011 was 44.2 C (111.6 F), while the lowest hourly outdoor air temperature was 18.6 C (65.4 F). The lowest temperature occurred during a rainy night in the middle of the monsoon season. A comparison of the hourly outdoor conditions measured throughout the experiment and the graphic comfort zones provided by the ASHRAE Standard 55 in its 2004 and 2010 versions suggest the use of evaporative cooling as the ideal strategy for this climate. However, because water is generally scarce in hot-dry regions, dry and/or wet roofponds could become an attractive passive, low-water use alternative to produce comfortable indoor conditions.

7 Figure 2. Summer of 2011 hourly outdoor air temperature and humidity compared to the graphic comfort zones provided by the ASHRAE Standard 55 in its 2004 and 2010 versions. Figures 3 and 4 compare the hourly indoor operative temperatures measured throughout the summer in the dry and wet roofponds, respectively, and the ASHRAE Standard 55 graphic comfort zones in the 2004 and 2010 versions of this standard. While the comparisons presented in Figures 3 and 4 demonstrate that neither roofpond achieved comfortable conditions 100% of the time, the results obtained in this study (particularly those for the wet roofpond) are quite promising given the unusual ceiling to wall ratio of the test cells and the less than ideal construction of the experimental prototypes (e.g., a steel door with an R-value of K m²/w (5 h ft² F/Btu) constitutes approximately 15% of the entire wall area of each prototype). 6.4 Average hourly summer performance Figure 5 presents a comparison between the summer average hourly outdoor air temperature and humidity and the summer average hourly operative temperatures measured inside the dry and wet roofpond test cells. The information in Figure 5 shows that the average maximum outdoor air temperature for the summer was 38.6 C (101.6 F), while the average maximum indoor operative temperature for the dry roofpond was 33.5 C (92.3 F), displaying a temperature reduction between the exterior and the interior of approximately 5.1 C (9.2 F ). The nightly evaporation of approximately 11.4 litres (3 gallons) of water helped further reduce the average maximum indoor operative temperature within the wet roofpond to 30.1 C (86.2 F), for a total reduction of 8.5 C (15.4 F ) below the average maximum outdoor air temperature. A comparison between the summer average minimum outdoor air temperature of 27.3 C (81.2 F) and the average minimum indoor operative temperature measured within the dry roofpond of 29.1 C (84.5 F) demonstrates that without the assistance

8 of night-time evaporation, minimum indoor operative temperatures remain approximately 1.8 C (3.3 F ) above the outdoor minimum air temperature. Figure 3. Comparison of the hourly indoor operative temperatures produced by a dry roofpond and the graphic comfort zones provided by the ASHRAE Standard 55 in its 2004 and 2010 versions. Figure 4. Comparison of the hourly indoor operative temperatures produced by a wet roofpond and the graphic comfort zones provided by the ASHRAE Standard 55 in its 2004 and 2010 versions.

9 However, once night-time evaporation is introduced, the indoor operative temperature of a wet roofpond remains practically at all times below the outdoor air temperature, achieving a reduction of its average minimum operative temperature of almost 2.2 C (4 F ) below the average minimum outdoor air temperature (see Figure 5). 6.5 Performance during the hottest summer day (August 24, 2011). In a typical Las Vegas summer, the daily maximum outdoor air temperature continues to rise until it reaches its highest values during the month of August. It is during this part of the summer that both roofponds deliver their best performance. Figure 6 illustrates the behaviour of dry and wet roofponds during August 24 th, 2011, which was the day with the highest outdoor air temperature during the period examined in this paper. A comparison between the daily maximum outdoor air temperature of 44.3 C (111.8 F) and the daily maximum indoor operative temperature of 37.9 C (100.3 F) within the dry roofpond shows a temperature reduction of 6.4 C (11.5 F ). While this reduction is significant, the operative temperature measured inside the dry roofpond test cell remains outside the comfort zone during the entire day (see Figure 6). The nightly evaporation of approximately 11.4 litres (3 gallons) of water produced a daily maximum indoor operative temperature within the wet roofpond of 32.9 C (91.3 F), for a temperature reduction of 11.4 C (20.5 F ) below the daily maximum outdoor air temperature. This temperature reduction allows the wet roofpond to remain comfortable during 16 hours of the day. A comparison between the daily minimum outdoor air temperature of 29.2 C (84.5 F) and the daily minimum indoor operative temperature measured within the dry roofpond, in this case 32.3 C (90.2 F), shows that during the hottest day of the summer the dry roofpond s minimum indoor operative temperature remains 3.2 C (5.7 F ) above the daily minimum outdoor air temperature. The minimum indoor operative temperature measured within the wet roofpond during the hottest day of the summer was 27 C (80.6 F), remaining almost 2.2 C (4 F ) below the daily minimum outdoor air temperature (see Figure 6). 7 Conclusions The results presented in this paper suggest that under typical summer conditions, a dry roofpond installed over typical U.S. residential construction is able to keep the maximum indoor operative temperature approximately 5.1 C (9.2 F ) below the maximum outdoor air temperature, with the minimum indoor operative temperature remaining approximately 1.8 C (3.3 F ) above the minimum outdoor air temperature. A wet roofpond is able to improve the performance of the dry roofpond by lowering the maximum indoor operative temperature an additional 3.4 C, for a total reduction of approximately 8.5 C (15.4 F ), while also maintaining the minimum indoor operative temperature approximately 2.2 C (4 F ) below the minimum outdoor air temperature. The measured and calculated temperatures presented in this article demonstrate that a wet roofpond could be a powerful strategy to provide the majority (if not all) of the space cooling needed by a building with low to moderate internal heat gains in Las Vegas, Nevada. During the hottest (and therefore driest) part of the summer, the dry and wet roofponds exhibited their best performance. During the hottest day of the summer, the wet roofpond achieved a reduction of approximately 11.4 C (20.5 F ) between the maximum outdoor air and indoor operative temperatures.

10 Figure 5. Average hourly outdoor air temperature and humidity and average hourly operative temperatures from the dry and wet roofponds for the summer of Figure 6. Hourly outdoor air temperature and humidity and coincident operative temperatures of the dry and wet roofponds measured during the hottest day of the summer (August 24, 2011). During periods of rain and/or high humidity the reduction between the maximum outdoor air and indoor operative temperatures decreases. However, during these times the outdoor air temperature typically registers lower values.

11 It is important to note that the minimum operative temperature of the wet roofpond remained during the hottest part of the summer approximately 2.2 C (4 F ) below the minimum outdoor air temperature. It is also worth noting that the ceiling temperature inside the wet roofpond was, in average, 3.4 C (6.1 F ) lower than the indoor operative temperature, thus providing a cool ceiling that is able to absorb heat from within the space at all times while remaining an effective source for radiant cooling. The ceiling s positive contribution to thermal comfort would be amplified in a building featuring a typical ceiling to wall ratio. Simple design and/or construction improvements to the test cells, such as reducing infiltration from 1 ACH to 0.6 ACH, coupling the building to the ground, or increasing the R-value of building envelope components, should improve the results obtained in the summer of Finally, the experimental results presented in this paper are compared to energy and water consumption figures modelled for several cooling strategies suitable for singlestorey buildings in the United States Southwest. Table 1 summarizes and compares: a) the energy used for cooling (in KWh/m 2 ) for wet and dry roofponds (based on actual, experimental data); three evaporative cooling strategies (passive downdraft, direct, and two-stage); and three compressive refrigeration systems (unitary rooftop, packaged central plant with air cooled condenser, and packaged central plant with water cooled condenser). The modelled results for the evaporative and compressive refrigeration systems are taken from Bryan (2004) and correspond to a single-storey building in the city of Phoenix, Arizona. b) the indirect, consumptive water use (in Litres/m 2 ) attributable to the production of the electricity needed by each of the cooling options. Table 1 uses a water consumption value of litres/kwh (7.25 gal/kwh), which corresponds to the average evaporative losses for electricity production in the State of Nevada (Torcellini et al., 2004). c) the direct, site water consumption (in Litres/m 2 ) based on actual, experimental data for the roofponds and on values reported by Bryan (2004) for the other cooling strategies. Table 1. Energy and water consumption of active, hybrid, and passive cooling strategies appropriate for single-storey buildings located in a hot-dry climate (with data from Bryan, 2004). Cooling Strategy Water Use Water Use Total Thermal Energy Use at Plant at Building Water Use Comfort (KWh / m 2 ) (Litres / m 2 ) (Litres / m 2 ) (Litres / m 2 ) (Quality) Unitary roof-top air conditioners , ,441.8 High Packaged central plant with air-cooled condenser , ,263.3 High Packaged central plant with fluid cooler , ,328.6 High Two-stage evaporative cooler Moderate Direct evaporative cooler Low Evaporative Cool Tower Low Wet roofpond Low Dry roofpond Low

12 The results from this comparison show that roofponds use the least amount of energy from all the systems studied. Furthermore, the wet roofpond uses almost as little water as the passive downdraft (Cool Tower) strategy, with the former having better indoor humidity control during the monsoon season. For these reasons, and based on the results presented in this paper, roofponds deserve further investigation and eventual deployment in hot-arid regions where electricity and water may be scarce. In terms of thermal comfort, the three cooling strategies that rely on compressive refrigeration can easily provide the thermal conditions required by ASHRAE Standard 55. Therefore, these systems are assumed to provide a high degree of thermal comfort (Bryan, 2004). Of the evaporative cooling strategies, the two-stage evaporative cooler provides the best thermal conditions, as it can control indoor temperatures as well as humidity. The direct evaporative and passive downdraft (Cool Tower) strategies have poor humidity control, which renders them ineffective during periods of high humidity and rain. While the wet and dry roofponds failed to produce comfortable conditions 100% of the time, the improvements discussed earlier in this section should help the strategy move from low to moderate comfort without great difficulty or expense in the extremely challenging environment of Las Vegas, Nevada. References ASHRAE ANSI/ASHRAE : Thermal Environmental Conditions for Human Occupancy. Atlanta, GA: American Society of Heating, Refrigeration, and Air-Conditioning Engineers. ASHRAE ANSI/ASHRAE : Thermal Environmental Conditions for Human Occupancy. Atlanta, GA: American Society of Heating, Refrigeration, and Air-Conditioning Engineers. Balcomb, J.D., Jones, R.W., McFarland, R.D., and Wray, W.O Passive Solar Heating Analysis: A Design Manual. Atlanta, GA: American Society of Heating, Refrigeration, and Air-Conditioning Engineers. Bryan, H Water Consumption of Passive and Hybrid Cooling Strategies in Hot Dry Climates. Proceedings of the 33rd American Solar Energy Society National Conference. Boulder, CO: American Solar Energy Society. Fernández-González, A Analysis of the Thermal Performance and Comfort Conditions Produced by Five Different Passive Solar Heating Strategies in the United States Midwest. Solar Energy, 81(5), pp Givoni, B Passive and Low Energy Cooling of Buildings. Hoboken, NJ: John Wiley & Sons Inc. Marlatt, W.P., Murray, K.A., and Squier, S.E Roof Pond Systems. Canoga Park, CA: Energy Technology Engineering Center. Messadi, T Mathematical Simulation for Correct Coupling of Direct Solar Gain to Thermal Mass Inside a Prototypical Space. Proceedings of ASHRAE Annual Conference on Thermal Performance of the Exterior Envelopes of Buildings VII. Atlanta, GA: American Society of Heating Refrigeration and Air-Conditioning Engineers. Hay, H.R. and Yellott, J.I Naturally Air Conditioned Building. Mechanical Engineering, 92(1), pp

13 Hay, H.R. and Yellott, J.I International Aspects of Air Conditioning with Movable Insulation. Solar Energy, 12(1) pp Residential Energy Consumption Survey 2013, Heating and Cooling No Longer Majority of U.S. Home Energy Use, U.S. Energy Information Administration, Available from: < Consumption-b1#> [28 January 2014]. Torcellini, P. A., Long, N., and Judkoff, R.D Consumptive Water Use for U.S. Power Production. ASHRAE Transactions: Research, 110 (1), pp,