A chiller's cooling capacity depends on the rate at which it pumps water and the extent to which it reduces the water's temperature. Calculating the machine's capacity also takes into account water's specific heat capacity and other conversion factors, producing the machine's power in British Thermal Units (BTUs) per hour. A further conversion step can convert this value to tons, a common unit of power when describing heating and cooling devices. You can instead convert your result to a more standard unit of power  the kilowatt.

Subtract the temperature of water entering the chiller from that of water leaving it. If water enters the chiller at 63 degrees Fahrenheit and leaves at 49: 63  49 = 14 degrees.

Multiply the result by the chiller's volumetric flow rate, measured in gallons per minute (gpm). If 230 gallons of water move through the chiller per minute: 14 x 230 = 3,220.

Multiply the answer by 500, finding the chiller's capacity in BTUs per hour: 3,220 x 500 = 1,610,000.

Divide your answer by 3,412 to convert your answer to kilowatts: 1,610,000 / 3,412 = 472 kW.
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