APPENDIX A ENERGY PERFORMANCE * Temperatures, relative humidity levels, and energy wall of the building and, with the windows, use in a passive solar, earth sheltered home in cen­ comprise the solar collection system. This com­ tral Kansas were monitored over a seventeen-month bination of passive solar techniques and earth period. Window insulation at night had a significant effect on heat retention, and considerable heat gain sheltering is indeed an attractive strategy, as the and ventilation benefits were realized from two following discussion will show. Trombe walls built into the structure. Daily inside temperatures varied from a low of 62° F in the winter to a high of 87° F in the summer, with an average HOUSE DESIGN room temperature of 73° F. The earth sheltered home used 30 percent less electricity than an The floor plan of the house contains 1,500 aboveground home of similar size. The woodburn­ square feet of living space and 600 square feet ing stove consumed 67 percent less wood than a of garage. The structure is long and narrow, conventional home, and there was no need for pro­ which permits the winter sun to reach the back pane. Overall, at least 80 percent of the heating walls, and the room arrangement is open, which needs were supplied by passive and earth-contact strategies. facilitates air movement and promotes a feeling of spaciousness (fig. A-1). The interior is light in color, and approximately 75 percent of the Many authors claim potential energy savings floor is carpeted. from earth-sheltering techniques, but few pub­ The kitchen has a 30-inch skylight, while a lished studies document these savings. This vent pipe 10 inches in diameter runs beneath paper provides data on the performance of a the floor slab to provide combustion air for the passive solar, earth sheltered home in central wood-burning stove (the only backup heat Kansas. Most earth sheltered homes rely mainly source). Each bathroom has a vent pipe opening on direct solar gain, but two Trombe walls were through the roof, and each is fitted with a small incorporated into the passive solar design of exhaust fan. A ceiling fan and duct system dis­ this home, making it unique in the literature. tribute heat in the winter, and a whole-house The Trombe walls-black, glass-covered con­ ventilation fan can be used to pull in cool night crete structures-make up part of the south air in the summer. The Trombe walls, built as part of the south * Max R. Terman. "Energy Performance of an Earth Sheltered Home with Trombe Walls." Underground Space. 6 (1981): 180- wall, are oriented 28 degrees east of due south; 85. Reprinted by permission of Pergammon Press Ltd. each is 8 feet high, 10 feet long, and 14 inches 158 ENERGY PERFORMANCE 159 111 L. : Patio door I Tr~ Wall • Air intake (balow alab) A·i. Diagram showing the floor plan and energy systems of the Underground Space. Vol. 6. Max R. Terman. "Energy Performance of an Earth Shel­ passive solar, earth sheltered home. (Reprinted. with permission. from tered Home with Trombe Walls." (t; 1981. Pergamon Press. Ltd.) thick, with a mass of approximately 13,920 The hot water heater, insulated with 2 pounds (see fig. A-2). Inside Trombe vents are inches of Fiberglas, receives preheated water at floor and ceiling levels; outside vents for from coils in the wood-burning stove and is on summer use open beneath a 28-inch-wide over­ a timer that turns the power on for three hours hang. Four 4-by-6-foot windows and one 6-by- a day at periods of maximum use. The house­ 10-foot patio door are also located on the south hold appliances are electric. wall and provide about 160 square feet of direct-gain collector surface. The windows are equipped with reflective blinds and heavy cloth draperies. [Note: exterior shutters have since been installed.] A·2. The Trombe walls figure prominently in the facade of this The shell of the house is a poured, post­ passive solar, earth sheltered building. (Reprinted. with permission. from Underground Space. Vol. 6. Max R. Terman. "Energy Performance of an Earth tensioned concrete structure with 9-inch-thick Sheltered Home with Trombe Walls." '" 1981. Pergamon Press. Ltd.) roofs and 8-inch thick walls, the structure being waterproofed with a combination of bentonite and premolded membranes. Six inches of poly­ styrene insulation cover the top of the roof over the living area (1 inch over the garage roof), and 2 inches decreasing to 1 inch cover the walls; the floor, 5-inches thick, is not insulated. The building is covered with 3 feet of soil on the front of the roof, which grades back to 2 feet at the rear. The roof and the side and back walls are in contact with an extensive mass of earth that makes up a hill approximately three acres in size. Maximum excavation depth into the hill is 8 feet. 160 APPENDIX A PERFORMANCE DATA record Kansas heat wave (over forty consecutive days with temperatures over 100° F), a high temperature of 87° F was recorded; however, no Room temperatures and humidity were mea­ shade was yet provided by deciduous trees. The sured from the back living room wall with a average monthly temperatures ranged from meter for temperature and relative humidity. 66° F (February 1980) to 81°F (August 1980). Trombe wall and remote temperatures were The average internal temperature for the study measured with an eight-probe thermistor ther­ period was 73° F. Only air distribution and mometer; a mercury thermometer in a sheltered venting fans were used during the summer, and entrance took outdoor temperatures. a total of 0.8 cords of wood was burned each Temperature winter (table A-1). The wood-burning stove and the window Records of the thermal performance of the insulation (blinds and draperies) influenced the house date from January 1980, three months internal temperatures, as can be seen during after the structure was backfilled. Due to loose two winter cold spells: January 1980 (no blinds) soil structure and lack of vegetation, the ther­ and December 1980 (blinds and draperies for mal characteristics of the backfilled soil were night insulation). The use of draperies and different from conditions that can be expected blinds allowed the wood-burning stove to be after the soil settles and vegetation is estab­ burned at lower temperatures and still maintain lished. a higher room temperature (fig. A-3). Monthly temperature variation, measured The extent of the influence of the sun on on the back wall, decreased from January 1980 house temperatures during each month can be to January 1981, with the coolest temperature ascertained from table A-2. During January and (62° F) occurring in February 1980, when the February 1980, the internal temperatures were house was unoccupied for eight days. During a 40° F higher than outside temperatures (no aux- TABLE A·l Fuel and electrical usage comparison between a well-insulated aboveground farmhouse * and a passive solar, earth sheltered home * *. Winter and summer daily average outside temperatures are given in degrees F. Average Jan. July Monthly Cords of wood Heating fuel Date High/low High/low kwh/person used/winter (gal. propane) Farmhouse 6177-12177 89.2 70.2 300 0.5 402 1/78-12/78 24.9 8.7 89.7 68.9 409 1.8 645 1/79-6/79 20.8 4.1 84.1 67.6 -313 1.2 300 (Monthly average for 2-year period) 341 1.2 449 Earth sheltered house 1/80-12/80 36.6 20.7 97.4 72.9 244 0.5 0 1/81-3/81 40.8 19.8 86.1 70.4 234 0.3 0 - - (Monthly average for 2-year period) 239 0.4 0 • 1,800 square-foot living area, 2 floor levels, root cellar, 1 bath, electric hot water, forced air furnace, airtight wood-burning stove, window air conditioner, water pump. Occupied by 2 adults, both absent from home, 8:A.M.-4:00 P.M., September through May . .. Three feet of soil cover, 1,500-square-feet living space, 2 baths, 1 floor level, electric hot water heater, attached garage, 2 Trombe walls, wood-burning stove with hot water preheat coils, timer on hot water heater, duct fan, whole-house fan, water pump. Occupied by 2 adults and 2 infants continually. ENERGY PERFORMANCE 161 reflected inside the house. (The performance of Blinds/draperies used at night the house is expected to improve as deciduous 75 trees and grass cover are added to the land­ scape.) Table A-3 shows the mean temperatures at 70 various locations in the house during the winter (January-March) and summer (June-July). The .'" <II temperatures of the entryway, an air lock isolat­ .3" 65 ing the living room from the outside, show the '" "<II effects of outside contact and isolation from the a0. ...<II Trombe walls. The walls, floor slab, and ceiling temperatures reflect the earth temperatures ad­ 60L-______~------~------~------~ 6AM 12 N 6 PM 12M 6 jacent to them; the skylight, as indicated by the wide temperature swings in this structure, is a source of heat loss during the winter. A·3. The dotted line shows the effects of using draperies. Note that the temperature stays more constant than when no night insulation (solid line) is used. Wood-burning stove use is also indicated. Note that when no window insulation is used a hot stove is required at night whereas a low stove temperature suf­ fices with the use of night insulation.