Determining Chiller Size

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We cannot overstate the importance of selecting a correctly sized chiller. Undersized chillers won’t correctly cool your process equipment or materials. Oversized chillers will work just fine, but why pay more than you need to? When you select a chiller of the proper size, you can rely on several years of efficient cooling. Use the formula below to determine the chiller size that will most optimally meet your needs.

North Slope Chiller System

The Formula

Regardless of what you are cooling, this formula will determine your needed chiller size. Before jumping in, identify the following variables:

  • Incoming water temperature
  • Required chilled water temperature
  • Flow rate

To illustrate how this formula works, let’s say we need to cool 4 GPM (gallons per minute) from 85 °F to 75 °F. This makes our incoming water temperature 85 °F, the required chilled water temperature 75 °F and the flow rate 4 GPM.
Determine the Chiller Size You Need

Step One:  Calculate Temperature Differential (ΔT°F)

ΔT°F = Incoming Water Temperature (°F) – Required Chilled Water Temperature.

Example: ΔT°F = 85°F – 75°F = 10°F

Step Two:  Calculate BTU/hr.

BTU/hr. = Gallons per hr x 8.33 x ΔT°F

Example: (4 gpm x 60) x 8.33 x 10°F = 19,992 BTU/hr

Step Three:  Calculate tons of cooling capacity

Tons = BTU/hr. ÷ 12,000

Example:  19,992 BTU/hr. ÷ 12,000 = 1.666 tons

Step Four: Oversize the chiller by 20%

Ideal Size in Tons = Tons x 1.2

Example: 1.666 x 1.2 = 1.9992

Most likely, your “Ideal Size in Tons” is not going to come out to an even 1 ton, 5 tons, 20 tons, etc. Round up to determine which chiller size you will need. In this example, our final answer is 1.9992, which means we will need a  2-ton chiller.

We hope this was helpful! Of course, if you have any questions or would like us to size your chiller for you, please give us a call at (866) 826-2993.