NADER V. CHALFOUN, Ph.D.

Transcription

1 ENERGY-SAVING CONSTRUCTION TECHNIQUES PERFORMED BY THE "HOUSE ENERGY DOCTOR "; AN EDUCATIONAL, RESEARCH AND COMMUNITY SERVICE PROGRAM AT THE COLLEGE OF ARCHITECTURE, THE UNIVERSITY OF ARIZONA. NADER V. CHALFOUN, Ph.D. 1. ABSTRACT The "House Energy Doctor " is a program at the College of Architecture, of the University of Arizona, which provides students education, research and training as well as no-cost energy consultation and design prescription services for homeowners. The advanced methods taught to the students provide them with the necessary skills to conduct computer residential energy analysis and performance predictions using up-todate site survey methods and computer energy simulation programs. This paper demonstrates some major projects in Tucson, Arizona all of which were visited and tested by the House Energy Doctor team. The energy savings strategies which were proposed by the students to reduce mechanical heating and cooling consumption and enhance human thermal comfort are given. Innovative devices for passive heating and cooling, such as thermal storage walls and Cool Towers, are also presented to demonstrate how modern technology could be integrated into the residential buildings fabric and the construction industry. 2. INTRODUCTION Current modern technology in construction can dramatically reduce energy consumed in buildings for mechanical heating and cooling. For example, energy consumption in the United States now costs $450 billion dollars a year. The growing awareness of the importance of energy efficiency beginning in 1973 has improved the economy and now Associate Professor of Architecture, Director of the House Energy Doctor program, College of Architecture; University of Arizona, Tucson, AZ 85712, U.S.A. And, Research Associate, Environmental Research Laboratory; 2601 E. Airport Dr., Tucson AZ U.S.A.

2 saves the country $160 billion per year (Harvey et al, 1991)[1]. This was achieved through existing technologies which provided opportunities to improve efficiency without reducing standards of living. But even greater advances are possible. Arizona's climate and growth present particularly challenging design opportunities. Arizona has both the greatest amount of insolation and the second largest population growth in the U.S.A. The total primary energy consumption in Arizona is estimated at 1,079,800 X 10 9 BTU's in 1990; this is an average 19.19% increase in consumption over the 839 X 10 9 BTU's in 1986 (AEO, 1990)[2]. The residential sector consumes 19.6% of the total primary energy. Energy consumed for space conditioning (both heating and cooling) represents approximately two-thirds of the total energy consumed in the typical home and roughly 11% of total U.S. energy consumption (DOE/EIA 0262, 1981)[3]. The House Energy Doctor program illustrates a potential for energy savings in the residential sector introducing new and innovative energy-saving techniques as well as innovative passive heating and cooling devices to be integrated into contemporary construction methods. 3. THE HOUSE ENERGY DOCTOR PROGRAM Developed at the University of Arizona's College of Architecture, by its director Dr. Chalfoun, the House Energy Doctor (HED) is an educational, research and community service program to provide a no-cost energy consultation service for homeowners (Chalfoun, 1991)[4,5]. Research Education HED Community Service Each semester, a group of graduate and undergraduate students are taught the fundamentals to become qualified HED participants. Using up-to-date site survey methods and equipment and state-of-the-art computer energy simulation techniques, the thermal performance of a selected target house is predicted, validated and analyzed by the trainee team. Sets of strategies are then identified as potential solutions. These strategies are individually tested, monitored and optimized by the HED team in terms of energy savings, add-on cost, and a simple pay-back period based on current interest rates. A final optimized case is then identified and reported to the homeowners. The no-cost energy consultation service the HED program offers encourages homeowners of single family detached houses to participate in the program. The energy analysis helps homeowners identify the critical design elements of their houses which contribute most to energy waste and consumption. A study by Chalfoun et al., (1991)[6], showed that this type of energy analysis as applied to a specific house type in Tucson would yield up to 50% saving in the energy consumed for heating and cooling depending on the selected strategies. If needed, innovative energy-saving devices such as Trombe Walls and Cool Towers could be introduced to further minimize or in some instances eliminate energy consumption. For the approximately 125,000 single family houses and condominiums in Tucson the energy saving potential is substantial. The HED team performs the residential energy analysis following a typical ten step procedure. These steps are listed in Table 1 below:

3 Table 1. House Energy Doctor Procedure For Residential and Small Commercial Buildings: 1- SITE SURVEY 6- COMPLIANCE WITH ENERGY CODES 2- DOCUMENTATION 7- PROBLEM IDENTIFICATION 3- BASECASE PERFORMANCE 8- PARAMETRIC ANALYSIS 4- UTILITY RECORDS COMPARISON 9- COMBINED CASE 5- BASECASE VALIDATION 10- FINAL MODIFIED DESIGN: Detailed information about the above ten step procedure is published in Chalfoun (1991)[4]. 4. RECENT RESIDENTIAL PROJECTS During the last few years, the HED director and his team have helped in the design development and energy analysis of several residential projects in Tucson, Arizona. Advanced energy-saving construction techniques have been introduced as well as innovative devices for passive heating and cooling have been studied and constructed. The following is a selection of some of these projects: 4.1. The Mittal Residence: The Mittal residence is an energy conservative and passive solar heated and cooled building located at the foothills of the Catalina mountains in Tucson, Arizona (Fig.1). The house is owned by Dr. Yash Mittal, designed by arch. Robert G. Hershberger, and the energy analysis is conducted by arch. Nader V. Chalfoun and his team at the College of Architecture in Tucson Arizona. Drawing by N.V. Chalfoun Figure 1: The Mittal Residence; Perspective showing the southwest and northwest elevations Design Development: During the design development phase two major challenges had to be faced; first, since the site is located in the foothills, city view to the southwest became an urgent desire and thus a large panoramic window area was required. There was also a spectacular view up the mountain to the northeast which was important to the client. Here a band of high windows was desired. Second, the combined effect of a) the site at a high mountain elevation and b) the severe cold winter nights, caused by the large temperature swing[7], necessitated the use of additional thermal storage mass to provide heating at night. The original design (basecase) performance, as predicted by the CalPas3[8] computer simulation program, required MBTU/Yr for cooling and 47.4 MBTU/Yr for heating with an annual operating cost of $1497/Yr ($976 cooling,

4 $521 heating). This is about four times higher than the energy codes requirement for that region[9]. While the large cooling load is common to most residences in the Tucson area, the heating load, as estimated, is higher than the norms[10]. This is mainly because of the site location and the large window area (over 50% glass to floor area ratio) as shown in the architectural drawings illustrated in Figure 3 below. Parametric Analysis: To achieve the goal of minimizing the cooling load and eliminating the need for auxiliary heat, various passive improvement strategies were first implemented[11]. These strategies were: increased roof and wall insulation, double glazing, vented roof, shade trees, reduced glass area, overhangs, and high efficiency mechanical systems[12]. The CalPas3 computer program was used to investigate and optimize the performance of each strategy. In the finalcase--the case where all strategies were combined together-- a 54.8% load saving was achieved. But most importantly the heating load is reduced by 77% and is now at a level attainable by use of solar collection and storage. While Table 2 below demonstrates the load reduction and cost savings from each strategy, Figure 2 represents graphically the total load reduction achieved throughout the optimization process. Table 2. Energy Conservation Strategies for the Mittal Residence Description of Loads (KBTU/Yr) Costs Savings (%) Strategies Cooling Heating Total $ / Yr Load % Cost % Basecase 128,809 47, ,176 $1, Basic Individual Strategies R-22 to R-30 on Roof 136,481 46, ,924 $1,469 R-11 to R-19 on Walls 127,914 46, ,235 $1,479 Double Glazing 111,157 34, ,766 $1,223 Overhang on South 119,109 51, ,898 $1,472 Combined (all the above) 98,887 36, ,127 $1, % 23.30% Extended Combined Strategies Vented Roof 93,628 36, ,161 $1, % 25.80% Landscape and Trees 85,871 37, ,664 $10, % 28.80% Reduce S. Window Area 84,744 37, ,178 $1, % 96.60% Optimized Overhang Depth 71,900 32, ,893 $ % 39.40% Reduce N. Window Area 62,426 20,956 83,382 $ % 52.80% Winter Thermostat 62,367 10,931 73,298 $ % 62.30% KBTU/Yr 180, , , , ,000 80,000 60,000 40,000 20, ,176 Basecase 135,127 Combined Case 130,161 Vented Roof 123, ,178 Landscape Reduce S. Win. Area 104,893 Overhang Depth 83,382 Reduce N. Win. Area 73,298 Winter Thermostat Strategies Figure 2. Energy Load Reduction at the Mittal Residence

5 Figure 3. Architecture Drawings of the Mittal Residence

6 Thermal Storage Subsystem: Because the house heating load was reduced through energy conservation strategies a carefully sized thermal storage wall subsystem was employed on the southwest facade. Since southwest is also the orientation for city view the thermal mass had to be placed under the collector. This innovative system will not block the main view and will provide most heating requirements through natural convection at night. The thermal storage subsystem is illustrated in Figure 4. The thermal mass is located behind and under the solar collector (double glass) and extends 3' 2" above floor level. Its volumetric heat capacity is estimated at 18,432 BTU/ F and consists of a 576 ft 3 of grouted double CMU walls (12" thick each) running 24 feet long under the southwest collector. A charging fan running at a speed of 2 cfm/ft 3 of mass and controlled by a conventional (non-differential) thermostat is used to charge the thermal mass walls located under the collector during the day. The southwest facing collector is protected by a 4' 3" horizontal overhang to reduce summer heat gain. Figure 4. Thermal Storage Wall Subsystem Diurnal Performance: In a typical diurnal performance the low-angle sun in winter reaches the collector glass during the day. The collected heat --as trapped between the double glass and the mass wall-- is then forced down by the fan to charge the lower mass. At night, two openings (2 ft² each) are opened to allow free convection from the thermal storage into the house while the cold air from the northeast side is pulled by convection through floor vents into ducts in the crawl space and back to the storage. In summer, the collector is opened to the outside to allow ventilation of the mass preventing any built-up heat. The storage diurnal performance is illustrated in Figure 5.

7 Figure 5: Diurnal Heat Collection, Storage, and Distribution Thermal Storage Capacity: The increased thermal mass and the addition of 2" R-9 rigid insulation on its outside surfaces have optimized the system performance. As illustrated in Figure 6 below. In a typical December night the mass delivers thermal heat at an average hourly rate of 4.79 KBTU/hr (as estimated by computer simulation) from 5 P.M. until 7 A.M. in the morning. Figure 6: Optimum Performance, as Represented by the Heavy Curve Line, is the Result of the Mass Having Higher Thermal Storage Capacity and 2" R-9 rigid Insulation on its Outside Surfaces. KBTU Heat Released (+) or Absorbed (-) from the Mass Wall to House Hours Dec. 21 Single Mass, Unsealed Single Mass, Sealed Double Mass, Sealed Final Case 4.1. The Hodges Residence: Designed by Mr. Carl Hodges and located at the east side of Tucson, the Hodges residence is a 2 bedroom, 1527 ft², one story single family detached house (Fig.7). The house is comprised of two main living zones which are separated by a semi-enclosed interzone. The west zone is the guest house with a kitchen, dining, bedroom and bathroom. This zone is entirely heated and cooled passively through a Trombe Wall and a Cool Tower. The east zone is the private master bedroom, a room converted into a walk-in closet and dressing area, and a bathroom. This zone is mechanically heated and cooled by a heatpump. The house is constructed with a 4" slab-on-grade and

8 high mass 8" thick common double brick walls insulated from the outside with 1½" Styrofoam rigid insulation and stucco. The roof has 6" R-19 batt insulation covered in some parts with wood shingles and in other parts with asphalt rolls. Most of the windows are single glazed except the bathroom. The house is oriented about 2.4 east of south. Parametric Analysis: After the basecase thermal performance was predicted and validated, a set of conservation strategies, suggested by graduate student Maged Ibrahim, was applied to the design as shown in Table 3. The use of slab-edge insulation, double glazing, movable shading devices, inside shutters, increased wall insulation, and optimized winter and summer thermostat settings were all strategies selected for the Hodges house. Figure 7. Architecture Drawings of the Hodges Residence Innovative and Technology Features: The west zone of the Hodges residence uses no mechanical heating or cooling devices as mentioned above. Instead, it uses a Trombe Wall system which captures solar radiation from the south through its double-pane

9 collector and distribute the heat to the north via a ceiling duct. The heat then charges the double brick walls during winter days and release that heat at night when its mostly needed. Another important cooling device is a Cool Tower. The tower was recently added by the owners, Carl and Elizabeth Hodges, who manage an Arizona-based technology transfer company. The tower, designed by scientists at the University of Arizona s Environmental Research Laboratory[13], is a combination of two methods of making life comfortable in hot, dry climates. Traditional Middle Eastern architecture uses tall towers to funnel passing breezes down to a courtyard. Often ponds or fountains are built in the enclosed area to further cool the air through evaporation. In the southwestern United States evaporative coolers are a common means of relief from the heat. These cooling devices use a fan to disperse a cool water vapor. The cool tower is essentially an evaporative cooler atop a tower; but it differs in that no forced air is needed to promote evaporation or circulation as in an evaporative cooler, and no passing breezes are necessary to generate a cooling draft. The hydro unit that caps the tower structure is a cube with cellulose pads exposed on four vertical sides. Water is conveyed through hoses up the tower to the hydro unit where it saturates the pads. As air comes into contact with the wet pads the water evaporates. The exchange of energy between the air and the water results not only in vaporized water, but in cooler air. The cool air is now denser than the surrounding air, and it falls down the tower creating a breeze that escapes out of a vent at the bottom. The falling air pulls more warm air through the pads perpetuating the evaporation process. Troughs around the base of the hydro unit catch excess water, and a pump recirculates the runoff water through the pads. Figure 8. Cool Tower Schematic A recent study, by Dr. N. Chalfoun who developed a computer program to predict cool towers performance, shows that, on a typical June day in Tucson, Arizona, the current configuration of the Hodges Cool Tower yields an average of 23.2 F temperature drop of the air delivered and at a volume of 3105 cfm from the bottom of the tower.

10 5. FUNDING The House Energy Doctor program is funded by Tucson Electric Power Company. 6. REFERENCES 1. Harvey, H. and Keepin, B. (1991). Energy From Crisis to Solution. The Energy Foundation, January, San Francisco, CA, U.S.A. 2. AEO (1990). Arizona Energy Data Quarterly Report. pp 5-7, Phoenix, AZ, U.S.A. 3. U.S. Department of Energy/Energy Information Administration. (1981) Residential energy consumption survey: consumption and expenditures, Part 1: National data (DOE/EIA-0262/1). Washington, D.C.: U.S. Government Printing Office, U.S.A. 4. Chalfoun, N.V. (1991). The House Energy Doctor "; An Educational, Research and Community Service Program at the College of Architecture, The University of Arizona Design for Desert Living Symposium, Jul , Tucson, AZ, U.S.A. 5. Chalfoun, N.V. and Matter. F.S. (1991). "Advanced Low-Cost Residential Energy Analysis Techniques Performed by the House Energy Doctor Team at the College of Architecture, University of Arizona, Tucson. IDEEA ONE; the First International Design for Extreme Environments Assembly. November 12-15, 1991, University of Houston Hilton Hotel, Houston TX, U.S.A. 6. Chalfoun, N.V. et al (1991). "Passive Solar and Energy Optimization for a residential House Type in Tucson, Arizona: A Case Study for the Solar Village Project." The International Solar Energy Society (ISES), Solar World Congress, Conf. Aug , Denver, Colorado, U.S.A. 7. ASHRAE (1982). "Climatic Data for Arizona, California, Hawaii, and Nevada". Southern California and Golden Gate Chapters of ASHRAE, Alhambra, U.S.A. 8. CalPas3 (1982). Program and Users Manual. Berkeley Solar Group. Berkeley, CA. U.S.A. 9. California Energy Commission (1983). Energy Building Regulations for New Residential Buildings, Title 24 of the California Administrative Code, CA., U.S.A. 10. CalRes/AZ (1990). Program and Users Manual. BSG Software for The Arizona Energy Office, Home Energy Rating Program, AZ., U.S.A. 11. Chalfoun, N.V. et al (1990). Planning and Architectural Criteria with Respect to Climate: Thermal Behavior of Building Envelope. Egyptian Academy of Scientific Research and Technology, Cairo, Egypt. 12. ASHRAE (1989). Handbook of Fundamentals. The American Society of Heating, Refrigerating, and Air Conditioning Engineers, Atlanta, GA., U.S.A. 13. Cunningham, W.A. and, T.L. Thompson (1986). Passive Cooling with Natural Draft Cooling Towers in Combination with Solar Chimneys, Proc. of PLEA 86, Passive and Low Energy Architecture. Pecs, Hungary. Sept