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To do this, we selected CONTAM, a program developed by the National Alside and replacement Institute for Standards and Technology and available flee through its Web site (see information at the end of this article). CONTAM calculates instantaneous values of air flow through windows openings in buildings, using the flow characteristics Alside of each opening, orientation, height, and other factors, based on a weather file replacement and windows that provides temperature and wind information. We set up our CONTAM runs to calculate air flow for each hour of the typical year, and then summarized the results by month.To complete the energy simulation inputs, we gathered information on building envelope construction and estimated appliance loads, hot water usage, and occupancy for each unit type. Water-to-air heat pumps installed in each unit provide heating and cooling at McLean Gardens. Alside Six central plants equipped with boilers and cooling towers provide replacement conditioned water at roughly 70[degrees]F to the heat pumps as a source or sink for energy. We took advantage of Visual DOE''s ability windows to model this system Alside by grouping an upper, middle, and lower unit together with a central plant replacement for each analysis. The cooling results brought another windows surprise in projecting only tiny energy savings Alside for the storm windows or non-low-e replacement replacement windows. This occurs because reduced conduction and reduced air leakage, according to the simulation and weather file used, don''t save energy during the cooling season. That is, energy windows gained by conduction and leakage during hot days is balanced Alside by energy removed during cool evenings in the Washington, D.C., replacement climate. Note the implicit assumption that residents windows keep their windows closed and air conditioners operating Alside even on cool evenings. We didn''t replacement have any quantitative basis for altering this assumption. The window replacement options with low-e glass, on the other hand, show significant projected cooling savings, largely as a result of reduced solar Calculated as energy windows savings/[ft.sup.2] of window sash area, typical savings for the highest-performance window option are about 0.50 MMBtu/[ft.sup.2] per year in heating and 0.45 MMBtu/[ft.sup.2] per year in cooling. Projected Cost SavingsWe Alside calculated cost replacement savings for the residential units in a spreadsheet, using monthly energy consumption windows results from Visual DOE and the applicable utility rate, which includes seasonal differences and a block rate that makes energy more expensive after the first 400 kwh. (Visual DOE can do cost analysis, but not using the combination Alside of rates that we needed.) Similarly, we estimated central plant operating costs by applying commercial electric and gas rates to the estimated monthly energy consumption and demand (see Table 2).The value of replacement energy savings attributable to window replacement windows fell between $.072 and $.092 per kWh of electric energy saved. Estimated Alside total savings across all 720 residential units and the central plants range from about $35,000 per year for storm window replacement to $91,000 per year for the most efficient windows. These savings represent about 5%-12% of the total gas and electric bills for McLean Gardens residents replacement and plants. The simple payback based on energy savings is estimated at around 65 years for windows storm window replacement, and over 80 years for full window replacement.
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