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Heat removal can be measured in many ways. The most common is BTUs.

Another is in Horsepower.

As this list can go on and on, I have only included the most common methods of measuring heat load or removal.

How can I calculate these numbers?      shortcut to formulas chart

Well, there are some fairly simple equations to use. Here is some specific information that you may have to gather to complete the equations.

The flow rate of the fluid to be cooled. Either the gallons per minute or liters per minute are the most common methods of flow rate measurement.

The Delta T or the change in temperature of the fluid as it enters the process and then as it returns back to the source or reservoir. This change in temperature is known as the Delta T and is typically measured in degrees Fahrenheit  or Celsius.

The common formulas are:

BTU = GPM x Delta T x 500 (constant for water)

EX: 20 gpm x 10 deg F Delta T x 500 (constant) = 100,000 BTU to be removed

BTU = GPM x Delta T x 243 (constant for hydraulic oil)

EX: 15 gpm x 8 deg F Delta T x 243 (constant) = 29,160 BTU to be removed

BTU = Weight ( of fluid in pounds ) x specific heat of fluid x Delta T / time per hour

EX: 50 gallons of water (x 8.3 for water) x 1 (specific heat) x 10 deg F Delta T / 1 hours = 4,150 BTU to be removed

The specific heat of water is 1

The specific heat of hydraulic oil is typically .486 (you should always check with the fluid manufacturer for specific heat of fluid)

The weight of water is 8.3 pounds per gallon

The weight of hydraulic oil is 7.2 pounds per gallon

If you know the input horsepower or the amount of horsepower that is causing the heat load, you are almost at the end of the work. If you have a 30 HP motor in a fluid circuit and it is this motor only that is generating the heat load, you simply multiply the 30 HP by a constant of 2545 and this will give you the total input heat load in BTUs. Now, for motor cooling, typically only 35% of the total horsepower is input as heat. We like to design around 40% due to motor inefficiencies. So, 40% of 30 HP is 12 HP. 12 HP x 2545 = 30,540 BTUs to be removed.

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