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We performed a total of about 100 simulations, estimating energy use for the six test case residences Windows modeled with the current windows and with each of five replacement options. Thirty McLean Gardens residents responded to our request for a waiver to access utility records, and we checked our simulation results for Shell and Replacement the existing-windows case against these bills, tweaking some of our assumptions as a result. We also did some basic sensitivity runs to evaluate the effect of Windows and Shell orientation and shading.The results brought some surprises (see Figure 3 for typical results for one apartment type). The first is Replacement the large projected heating savings for the storms-only replacement, an option with Windows a far lower cost than full window replacement. This results from the Shell combined effects of reduced infiltration and the estimated reduction in U-value attributable to a tighter system. It''s clear that energy savings alone won''t justify window replacement (see "Other Considerations Replacement in Window Replacement"). If windows are to be replaced in any case, however, the Windows analysis provides justification for an upgrade to high-performance glass. At a cost of Shell $60 per window, the payback on low-e argon filled glass is a reasonable 9 years.And there are other issues to be considered. The companion study on window condition estimated the current Replacement value of deferred maintenance at over $1 million, which reduces the comparative cost of window replacement. Comfort and other effects may be difficult to quantify in dollar terms, but they have important Windows costs and benefits. Energy saving is just one factor to be weighed in this complex and expensive decision.Energy savings resulting directly Shell from window replacement Replacement is just one of many things to consider in deciding whether and when Windows to undertake a major window replacement project. Shell Several Replacement and Windows other important factors are discussed below. To do this, we selected CONTAM, a program developed by the National Institute for Standards and Technology and available flee through Shell its Replacement 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 of each opening, orientation, height, and other factors, based Shell 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 Replacement year, and then summarized the results by month.To complete the energy simulation Windows inputs, we gathered Shell information on building envelope construction and estimated appliance loads, hot water usage, and occupancy for Replacement each unit type. Water-to-air heat pumps installed in each unit provide heating and cooling at McLean Gardens. Six central plants equipped with boilers and cooling towers provide 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 to model this system by grouping an upper, middle, and lower unit together with a central plant for each analysis.
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