# Thread: GSHP Heat of Extraction/Heat of Rejection

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I am looking for a formula to calculate both the Heat of Extraction (HE) and Heat of Rejection (HR) for Ground Source Heat Pumps.

I have the following variables to plug into the formula:

Return Air temp
Supply Air temp
CFMs
EWT
LWT
GPMs

The unit is in the HEATING mode.

If you can help me out I would greatly appreciate it!

2. Heat of Extraction/Rejection formaula is:
HE or HR = Delta T (water) x GPM x brine factor.
pure water brine factor is 500
anti-freeze is 485

From what you have listed, you will still need to know if it is pure water, or a mix to get your brine factor.

swany

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Isn't there another formula to figure the gallons per minute involving Delta P (pressure)

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Thanks swanny!

5. Originally posted by lynn rodenmayer
Isn't there another formula to figure the gallons per minute involving Delta P (pressure)
There would be Lynn, but every water to refrigerant heat exchanger would have a different flow vs pressure drop relationship.

For a particular unit there could be a published table or a chart to get the flow from once you measured the pressure drop.

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So you can't figure HE/HR without figuring GPM first. And you have to have the manufacture's published data.

7. Yes you need to know the flow. You can install a flow meter and read direct or take pressure readings and use the manufactuers data. You could make a formula for each type of heat exchanger to use the pressure readings without looking at a table or a chart.

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