85. Thermal comfort zones in buildings have been defined for occupants (at various levels of activity) based on
the indoor air temperature and relative humidity. For example, sedentary occupants in the summer will be equally com 
fortable at a temperature of 80 F with a relative humidity of 30 percent as they are at 73 F with a relative humidity of
70 percent (American Society of Heating, Refrigerating, and Air Conditioning Engineers. 2001.  Thermal comfort.  In
2001 ASHRAE Handbook Fundamentals. Atlanta, GA).
86. Duct energy losses can be reduced by a combination of testing for leaks and then sealing the leaks. The
tests are performed using a fan to pressurize the duct system and measure the leak rate. Sealing the leaks can be chal 
lenging. Some duct leaks are accessible, such as those around room registers, but others are hidden inside walls or are
otherwise difficult to reach. A system has been developed to spray an aerosol sealant into the duct system that seals
these hard to reach places (Berkeley Lab  Research News,  May 16, 2003, http://www.lbl.gov/Science 
Articles/Archive/EETD aerosol injection.html, February 4, 2005).
87. American Council for an Energy Efficient Economy,  Top Rated Energy Efficient Appliances: Central Air
Conditioners,  http://www.aceee.org/consumerguide/topcac.htm, February 4, 2005.
88. Hadley et al., 2004, op cit.
89. Central forced air furnaces have a lifetime of 10 to 25 years; the lifetime of hydronic heating systems is 20 to
30 years. The replacement market for oil fired systems would therefore be approximately 5 percent of the existing inventory
(EIA. 2003. The Assumptions to the Annual Energy Outlook 2003, Residential Demand Module. DOE/EIA 0554(2003), U.S.
Department of Energy, http://www.eia.doe.gov/oiaf/archive/aeo03/assumption/residential.html, February 4, 2005). Approximately
eight million homes heat with fuel oil, or about 7.5 percent of U.S. households. (EIA. 2001. Residential Energy Consumption
Survey. U.S. Department of Energy, http://www.eia.doe.gov/emeu/recs/recs2001/detail_tables.html#space, Februray 4, 2005).
At a replacement rate of 5 percent per year, about 400,000 oil fired units will be purchased as replacement units for existing
houses each year. Considering that most of these units are located in colder climates (more than half of these units are located
in climates with more than 5,000 heating degree days), the energy saving potential of newer and more efficient technology is
90. The AFUE rating is determined by specific test procedures to give a comparable indication of furnace effi 
ciency. This figure reflects both the steady state thermal efficiency and the thermal losses that occur when the unit is
cycled on and off throughout the season.
91. HUD PATH, 2003, op cit.
92. A heat transfer coefficient is an experimentally measured value that enables calculation of the amount of
energy that will travel from one location to another, based on the temperatures of the two locations. Within a heat
exchanger, a higher heat transfer coefficient means that more energy will be removed from the hotter fluid, even if the
inlet temperatures of the two fluids are not changed. For example, in a gas furnace the hotter fluids would be the hot
gases, and the cooler fluid would be the return air from the duct system. If more energy is taken from the hot gas and
transferred to the cooler air, the furnace is more efficient and won't need to run as long to heat the house.
93. HUD PATH, 2001, op cit.
94. U.S. Department of Energy. 2004. Letter to ENERGY STAR partners from R.H. Karney, Manager, ENERGY STAR
Program, January 6], http://www.energystar.gov/ia/partners/prod_development/new_specs/downloads/water_heaters/DOE_water 
heaterletter_final_1.6.04.pdf, February 4, 2005. 
95. Tomlinson, J.J. 2002.  All pumped up.  Home Energy 19(6):30 35, November/December.
96. The estimated retail cost of the water heating dehumidifier is approximately $500. In comparison, a 30 
pint dehumidifier, typically adequate for a 1600 ft
area over 24 hours, costs about $160; a 65 pint dehumidifier costs
about $250; and a standard 40  to 50 gallon electric water heater costs around $200 or $300.
97. Waste heat is used to pre heat the water in the HPWH. The waste heat source varies depending on whether the
space heat pump is set for heating or cooling mode. When it is in cooling mode, a series of motorized dampers direct the warm
air from behind the refrigerator into the HPWH closet to be used by the HPWH evaporator. The outlet air stream from the
HPWH is then cooled, dehumidified, and directed back into the kitchen to help air condition the house. When the space heat
pump is in heating mode, air is pulled from the crawl space by the HPWH fans, directed to the HPWH evaporator, and then
exhausted outside the house. The result is an annual water heating bill of less than $100 (Oak Ridge National Laboratory.
2004. ORNL's EERE Program  In hot water.  Science and Technology Highlights 2:10 11, http://www.ornl.gov/eere).
Towards a Climate Friendly  
Built Environment

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