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High-performance windows not only provide reduced annual heating and cooling bills; they
reduce the peak heating and cooling loads as well. This has benefits for the homeowner, in
that the size of the heating or cooling system may be reduced, and it also benefits the
electrical utilities, in that load factors are reduced during the peak times in
summer.
The peak load for a building is the maximum requirement for heating or cooling at one
time. These loads determine the size of the furnace, heat pump, air conditioner, and fans
that must be installed. The table illustrates typical reductions in cooling peak loads
that occur with different window types used in a typical house. The consumer can benefit
directly from peak load reduction, because heating and cooling systems can be sized
smaller, resulting in initial cost savings in some cases. Test homes have been built in
various U.S. climates (Las Vegas, Phoenix, Lakeland) have demonstrated significant peak
demand savings as a result of using efficient windows. Recently, several houses were built
in Las Vegas with energy efficient improvements including spectrally selective windows.
The total size of the air conditioning system was reduced by 30 percent.
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