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The cooling results brought another surprise in projecting camper only tiny energy savings for the storm windows or non-low-e 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 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 keep their windows closed and air replacement conditioners operating windows even on cool evenings. We didn''t have any quantitative basis for altering this assumption. The window replacement options with low-e glass, on the other hand, show significant camper projected cooling savings, replacement largely as a result windows of reduced solar Calculated as energy 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. Cleaning. camper and replacement The existing window system is almost impossible windows 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 camper cleaning in favor of doing it themselves, and consider it a free-time activity, might save more in cleaning costs than in energy replacement costs.Ventilation. Although the McLean Gardens buildings don''t have mechanical ventilation systems, reports of excess moisture accumulation and mold growth are uncommon. windows The leaky windows are undoubtedly a major camper factor in providing natural ventilation rates sufficient to limit moisture accumulation during cold weather. (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 leakage, but we believe that overall natural infiltration rates would be cut by more than replacement and windows 50%, and that the resultant increase in interior humidity and condensation would probably cause paint failure and mold growth in some units. camper This issue could replacement be addressed directly through the installation of mechanical ventilation systems. 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. Projected Cost SavingsWe calculated cost savings for the residential units in a spreadsheet, using monthly energy 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 and gas windows rates camper to the estimated monthly energy consumption and demand (see Table 2).The replacement value of energy savings attributable to window replacement windows fell between $.072 and $.092 per kWh of electric energy saved. Estimated total savings across all 720 residential units and the central plants range camper from replacement 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 and plants. The simple payback based on energy savings is estimated at around 65 years for storm window windows replacement, and over 80 years for full window replacement.
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