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There are three basic configurations of residential American units at McLean Gardens: bi-level units on the first two floors, middle-level replacement units, and upper-level units that include loft space under the slope of the roof (see Figure 2). For our energy simulations, windows we selected six American and replacement actual floor plans, two each of lower, middle, and upper units, with one of each type having a relatively small window area and one a large area. The idea was to bracket the energy use of most units with high and low estimated energy use and energy savings.[FIGURE 2 OMITTED]For energy analysis, we chose Visual DOE, a commercial front-end product that executes DOE 2.1E in performing hourly simulations of energy use in the building. windows Visual DOE doesn''t perform air leakage calculations, however, which we needed to get a good comparison between existing and replacement options. Cleaning. The existing window system is almost impossible to clean thoroughly from inside the building. As a result, many residents pay for professional cleaning, at a cost of $100 or more, once or twice a year. Tilt-in replacement windows, and elimination of the separate storms, would allow relatively easy cleaning of all surfaces from the interior. Thus, residents who drop professional cleaning in favor of doing it themselves, and consider it a free-time activity, might save more in cleaning American costs than in energy costs.Ventilation. Although the McLean Gardens buildings don''t have mechanical ventilation systems, reports of excess moisture accumulation and mold growth are uncommon. The leaky windows are undoubtedly a major factor in providing natural ventilation rates sufficient to limit moisture accumulation during cold weather. replacement (Air conditioning limits moisture accumulation during the summer.) Window replacement would significantly reduce overall building infiltration. Our project windows did not include measurement of overall building leakage, but we believe that overall natural infiltration rates would be cut by more than 50%, and that the resultant increase in interior humidity and condensation would probably cause paint failure and mold growth in some units. This issue could be addressed directly through the installation of mechanical ventilation systems. American The risk of excess moisture accumulation and the cost and complexity of installing a ventilation system are significant factors to be weighed in planning window replacement. We performed a total of about replacement 100 simulations, estimating energy use for the six test windows case residences 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 American our simulation results for 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 orientation and shading.The results brought some surprises (see Figure 3 for typical results for one apartment type). The first is the large projected heating savings for the storms-only replacement, an option with a far lower windows cost than full window replacement. This results from the combined effects of reduced infiltration and the estimated reduction in U-value attributable to a tighter system.
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