High-Performance Windows Cut Residential Cooling Costs

Most previous studies used computer/statistics modeling to estimate the energy-savings potential of high efficiency windows, but this study compared two homes which were virtually identical except for the types of windows installed. The Centre worked with Mercedes Homes in selecting two new homes for testing. The homes - which were on the same street only 152.4m apart - were identical in all possible ways, including orientation to the sun, the amount of shading provided by neighboring homes, floor plans, exterior color, and construction materials. In one home clear, single-paned windows in aluminum frames were installed. In the other were installed double-pane, thermally broken windows with PPG Sungate 1000 Solar Control Low-E glass in aluminum frames. These windows were provided by the manufacturer, PPG Industries Inc. Monitoring equipment was installed in each 646.8 m² home during construction, and data was collected for a year, including a 17-day period in which both homes were unoccupied. During this 17-day period, the thermostats in each home were set to identical settings in order to compare the cooling loads of both houses

The Florida Solar Energy Center recently concluded a detailed study on the potential of double-pane, spectrally selective, thermally broken windows to produce energy savings for cooling residential homes.

The study found that the home with high efficiency windows consumed about 17% less energy for cooling.

Technical data

The PPG Sungate 1000 Solar Control Low-E windows have a solar heat gain coefficient (SHGC) of 0.36; the single-pane window SHGC is 0.77. The Sungate window's centre-of-glass U-value is 1.9W/m²K; the single-pane window's is 6.1W/m²K. The Sungate windows are spectrally selective, providing a daylight transmittance of 60% instead of the 76% for standard single-pane windows. Total solar energy transmittance for the Sungate window is 35%; the single-pane window's is 83%.

Energy data

The home with standard windows consumes about 5,408 kWh annually for cooling. The home with the Sungate windows consumes about 4,471 kWh, a 17% reduction. On a peak cooling day, the cooling load of the standard house is 144.9 kWh; the cooling load for the house with Sungate windows is 121 kWh.

Economic data

The 17% reduction in kWh consumed by the home with Sungate windows - 937 kWh -translates to about $75 (USD) at typical Florida electricity rates. In addition, because the home with the improved windows is much better insulated, its cooling load can be handled by a heat pump with a cooling capacity of one ton less. Since the incremental cost per ton of cooling equipment is at least $400/ton, this represents significant savings. The study did not calculate simple payback for the incremental cost of installing the improved windows during home construction.

Contacts:

Mercedes Homes

6767 N Wickham Rd

Melbourne, FL 32940

321-259-6792

321-752-4020 (fax)

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