Quote:
Originally Posted by Hersbird
Side note I just read somewhere that a normal car AC system is a 5 ton 60,000 BTU system. So even if everything was 100% efficient in getting 120,000 BTUs out of a gallon of gas that would be 1/2 gallon per hour at full load. That takes a 30 mpg car at 65 down to 23 mpg. Luckily I don't think it needs 60,000 BTUs continuously. I wonder if better insulation would do more to limit heat gain/cooling loss would help much.
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That's not how an A/C works. The 60,000 BTU is the amount of heat it can remove from the cabin, but the amount of power the compressor needs is some smaller number. The ratio of heat moved to power input is called the coefficient of performance. For a car A/C the COP is between 2 and 6, probably. Depending on operating conditions.
For example, Toyota says their Prius A/C consumes 4500 watts (about 15000 BTU/H) and I guess it is capable of about 60,000 BTU. So the COP is about 4.
15000 BTU/H is about 1/8 gallon of gas.
-mort