capacity) can absorb solar energy. This thermal energy is re-emitted in all directions as

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1 Comfort on the cheap More on Trombe walls Trombe walls make good sense. When the sun shines, the masonry (which has a large heat capacity) can absorb solar energy. This thermal energy is re-emitted in all directions as infrared radiation and can help make a house more livable. The idea of the Trombe wall is old. Middle Eastern architecture used (as did Latin American) thick-walled, mud-brick houses in hot regions to provide natural cooling by day and warming by night (since the desert sky is usually clear, warm objects radiate their heat away very quickly ). (207) Trombe walls do not have to look massive. NREL engineer Otto van Geet s house has many conservation-minded features, including a Trombe wall directly inside the huge windowed space shown (Fig. E09.5.1). Fig. E Otto Van Geet s home located in Idaho Springs, Colorado. (U.S. Department of Energy, NREL)

2 Energy, Ch. 9, extension 5 Comfort on the cheap 2 Water walls (same idea as the Trombe wall, but using barrels of water instead of masonry to store the solar energy) and solaria (sunspaces) also help to mitigate day-night temperature swings. A 0.35 m thick wall will be warmest after the heat has been conducted all the way through 12 hours later. (182) It has been found that the Trombe wall with natural circulation provides the greatest heat flux to the living space. (208) Walls that store energy are 50% more expensive than normal walls, but will pay for themselves in time. (198) Two different views of the same home (Fig ) show how a Trombe (masonry) wall opposite an open glassed-in area can store energy and increase comfort. a. b. Fig. E a. One side must be open to allow sunlight to enter. b. The masonry wall between the windows and the living space stores the solar energy and radiates relatively uniformly. (U.S. Department of Energy, Ref. 81)

3 Energy, Ch. 9, extension 5 Comfort on the cheap 3 Fig. E Mature deciduous trees provide shade in the summer and sunlight filtration in the winter. (U.S. Department of Energy, NREL) The windowed area should ideally face south to maximize winter sunlight penetration (Fig. E09.5.4). It is also helpful if the area is shaded by deciduous trees, because then the windows are shaded by the leaves in the summer. There is little distinction between

4 Energy, Ch. 9, extension 5 Comfort on the cheap 4 homes with Trombe walls and sunspaces. Sunspaces usually contain such energy-storage devices. The vertical windows are arranged to maximize winter sun. Fig. E In northern latitudes, the sun is much lower in the sky in the winter than in the summer. For this reason, vertical glazing receives much more solar gain in the coldest part of the year. Sloped glazing takes in the most solar radiation in the summer. (U.S. Department of Energy, Ref. 209) As was mentioned in the chapter, clever architecture can lead to useful methods of keeping energy in when it is wanted and allowing it to dissipate when that is desired. Old architectural ideas emphasize courtyards (to help midday air circulation), narrow streets (to prevent large areas from being baked in the sun and to protect passersby), and houses built chock-a-block, sharing walls to prevent too much exposure to the incident solar energy. Old architects understood intuitively much of what we have learned through measurement in more modern times. Arab architecture features many overhangs; they must have understood geometry pretty well. The idea is illustrated in Fig. E09.5.5, which shows the recommended arrangement of window and overhang to construct a useful sunspace. Modern architects can make pleasant urban buildings that are energy-efficient by using some old precepts along with modern sensibility. (210)

5 Energy, Ch. 9, extension 5 Comfort on the cheap 5 Fig. E Overhang details are shown for making a good sunspace. (U.S. Department of Energy, Ref. 211) More on shade trees and cool roofs The Heat Island Group at Lawrence Berkeley National Laboratory (see Ch. 13) has studied shading and related issues. It is not only the shade, but also the cooling from evapotranspiration that cools the air around a home. Studies by the group found summer daytime air temperatures to be 3 to 6 cooler in tree-shaded neighborhoods than in treeless areas. (212) In areas where the demand for summer cooling is not major (such as California or Texas, say), strategically-placed trees can potentially eliminate all need for cooling.

6 Energy, Ch. 9, extension 5 Comfort on the cheap 6 Heat Island Group leader Hashem Akbari was quoted in Ref. 206: [I]n inland areas where an extensive amount of cooling is required, strategically planted trees can save 10% to 15% of summer cooling load, which would produce an annual savings of $30 to $50. Akbari and other LBNL scientists have long championed cool roofs. Painting a roof white substantially reduces cooling costs (a stratagem adopted by many tropical cities in earlier days). This was discussed in Ch. 13. So-called green roofs may also have a place. These are roofs that are covered with dirt and planted over. (213) The dirt and vegetation lengthen the water pulse that follows rain in urban areas. Energy savings do follow, as they do with white roofs. The disadvantage is that a green roof is considerably more expensive than a white roof. Commercial green buildings With the cost of energy rising in the early 2000s, it may not be surprising that commercial builders are more likely to be willing to build green. It is still usually the client who wants to make the statement, but the rising demand has decreased some prices, and buildings can be built green for about the same cost as conventional buildings. (214,215) A study for the State of California found that the benefit for green construction was over ten times the average initial investment required to design and construct a green building. (214) The study said that green buildings are saving (in terms of life cycle costing) from $550 to $765 per square meter. To help this trend along, the U.S. Green Building Council awards Leadership in Energy and Environmantal Design (LEED) Green Building ratings to buildings meeting standards dealing with recycled materials, a sustainable siting, solar energy use, low water heating demand, indoor environmental quality, and other criteria. (214,216) To achieve overall low energy use, the building must be

7 Energy, Ch. 9, extension 5 Comfort on the cheap 7 smart, usually involving computer-controlled systems for monitoring occupancy, running fans, and so on. (217) LEED is becoming a de facto building standard. About 3% of new construction applies for LEED certification, but LEED design is being used even when certification is not applied for. (214) There are four levels of LEED certification based on the number of criteria met, each awarded a certain number of points, in order of increasingly greenness : LEED Certified (26-32 points), Silver (33-38 points), Gold (39-51 points), and Platinum (over 52 points). (214,216) The EPA Energy Star program offers help to businesses on all sorts of energy saving measures, including for buildings, (218) and is another source of support for green construction. The National Association of Counties is cooperating with EPA to encourage construction of green courthouses. (219) Several buildings have reached the gold or platinum level for green achievements. Most prominent is the LEED gold Toyota American headquarters building in Los Angeles, which received wide attention in the press. ( ) It was built at a cost of $688 per square meter [$63/ft 2 ] (buildings in southern California typically run between $590 and $830 per square meter [$54/ft 2 and $76/ft 2 ]), (220) so it was much more efficient without being much more expensive. Genzyme Corp. s building in Cambridge, Massachusetts is another such building; though more costly than comparable construction, water and energy use are dramatically lower than for comparable buildings. (221) The LEED platinum southern California office of the Natural Resources Defense Council has many more people-friendly energy-conserving features, and did cost more than prevailing construction but uses 60% less water and far less energy than a similar building would. (222)

8 Energy, Ch. 9, extension 5 Comfort on the cheap 8 California, based on the Sustainable Building Task Force study, plans to construct state green buildings, including dormitories at state universities. Carnegie Mellon University was first, however, to open a green dorm. (223) Green design has even come to homebuilding, partly due to local government subsidies. (224) Evaluating solar and conservation measures The 1970s brought an explosion of developments in passive solar heating. To see which techniques (conservation and passive solar) performed best, the Buildings Energy Use Compilation and Analysis project was initiated in the United States. The results of the class-b monitoring program were reported in several places. (159, ) The most important findings are listed next. Heating costs in multifamily dwellings are smaller per family than costs in single-family dwellings. Heating costs in passive solar homes, which ranged from $320 to $915/m 2, are comparable in cost to conventional homes in the same area, which ranged from $430 to $760/m 2. Median annual savings are about 500 to 300 kwh with passive solar heating. Passive solar met about 37% of the total heating load. Thermal loads ranged from 0.83 to 1.53 W/m 2 /degree-day ( C). Little difference was noted among the types of passive solar device (Trombe wall, direct gain, sunspace) used. Good overall performance of passive solar devices and climate are not connected. Proper site selection, collecting area, and orientation of collectors are very important system characteristics.

9 Energy, Ch. 9, extension 5 Comfort on the cheap 9 Movable insulation was not used properly, but it has the capability of providing great energy savings in cloudy, colder climates. Proper insulation is essential to performance. It would seem that conservation measures and use of solar energy does save energy and the environment. However, research in China has shown that, at least there, helping individual home buyers see the economic benefits of natural lighting and ventilation, the better quality, and the savings in heating and air-conditioning energy costs is more effective than an appeal to environmental consciousness. (228) It seems that human nature is constant; that sounds like home.