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Projected Cost SavingsWe calculated cost savings for the residential units in a spreadsheet, using monthly energy Reynolds consumption 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 of rates that we needed.) Similarly, we estimated central plant operating costs by applying commercial electric Replacement 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 Windows to $91,000 per year for the most efficient windows. These savings represent about 5%-12% of the total gas Reynolds and Replacement and electric bills for McLean Gardens residents and plants. The simple payback based on energy savings is estimated at around 65 years for storm window replacement, Windows and over 80 years for full window replacement. Cleaning. The existing window system is almost impossible to clean thoroughly from inside the building. As a result, many residents pay for professional Reynolds 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 Replacement cleaning in favor of doing it themselves, and consider it a free-time activity, might save more in cleaning costs Windows than in energy costs.Ventilation. Although the McLean Gardens buildings don''t have mechanical ventilation systems, reports Reynolds 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 and Windows (Air conditioning limits moisture accumulation during the summer.) Window replacement would significantly reduce overall building infiltration. Our project did not include measurement of overall building Reynolds 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 Replacement and mold growth in some units. This issue could be addressed directly through the installation of mechanical ventilation systems. The risk of excess moisture accumulation and the Windows cost and complexity of installing a ventilation system Reynolds are significant factors to be weighed in planning window replacement. It''s Replacement clear that energy savings alone won''t justify window replacement (see "Other Considerations in Window Replacement"). If windows Windows are to be replaced in any case, however, the analysis provides justification for an upgrade to high-performance glass. At a cost of $60 per window, the payback on low-e Reynolds argon filled glass is a reasonable 9 years.And there are other issues to be considered. The companion study on window condition estimated Replacement the current value of deferred maintenance at over Windows $1 million, which reduces the comparative cost of window replacement. Comfort and other effects may be difficult Reynolds to quantify in dollar terms, but they have important costs and benefits. Energy saving is just Replacement and Windows and Reynolds one factor to be weighed in this complex and expensive decision.Energy savings Replacement resulting directly from window replacement is just one of many things Windows to consider in deciding whether and when to undertake a major window replacement project. Several other important factors are discussed below.
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