1990-02-01

Effects of Glazing and Ventilation Options on Automobile Air Conditioner Size and Performance 900219

A preliminary analysis of the effects of glazing and ventilation on automobile cooling loads and air conditioner capacity was completed as part of the Environmental Protection Agency's efforts to reduce the release of chlorofluorocarbons (CFC) into the earth's atmosphere from automobile air conditioners. We investigated the characteristics of standard and sports model sedans using numerical simulations of the heat transfer processes under static soak conditions. We conclude that: Glazing is a major contributor to the cooling loads that dictate the size of automobile air conditioners. The use of new glazing technology in conjunction with other design features, e.g., ventilative cooling when parked, provides a viable means of reducing cooling system size in many parts of the country. Additional analytical and experimental investigations under highway driving conditions are needed to determine the magnitude of the cooling unit size reduction possibilities. Several promising new glazing technology options provide substantial reductions in solar heat gain. Spectrally selective glazings are available today that substantially reduce cooling loads by rejecting infrared heat while maintaining a high visible transmittance. Optical switching films now under development will provide additional solar load control capability in the future. This has important implications in the effort to reduce CFC emissions from the current generation of automotive air conditioners. Improved glazings may lead to lower CFC emissions in the following ways: Reduced solar heat gain and lower interior air temperature may lead fewer people to select air conditioning in some climatic regions in the U.S. This will reduce the total number of CFC-charged systems and reduce emissions. Smaller air conditioning systems could provide equivalent levels of comfort in cars with improved glazings. Existing CFC-charged systems of smaller capacity could be used, reducing total CFC volume per vehicle in use and ultimately reducing total CFC emissions from leakage or when the cars are scrapped. If the peak cooling power and system size can be reduced, alternative cooling system approaches that reduce or eliminate CFC emissions may become possible. There are few practical alternatives to air conditioning systems of current design as long as the peak cooling capacity must remain high.

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