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