# Thread: Heat of Rejection Calculation

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## Heat of Rejection Calculation

I am looking for a formula to calculate heat of rejection of a refrigerator. Is it as simple as the inverse of the the amount of work done in Btu/Hr?

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## Does this work?

total heat of rejection for a system with
the following performance characteristics would be
calculated like this:

Compressor Performance

110°F condensing temperature
10°F evaporating temperature
75°F incoming water temperature
Refrigerant R–22
Evaporating Watts = 6500
40,200 Btu
watts x 3.4 = Heat of Compression
Heat of Compression + Evaporating Load =
Total Heat of Rejection
6500 watts x 3.4 = 22,100 Btu
Heat of Compression = 22,100 Btu
Total Heat of Rejection = 62,300 Btu

Total Heat of Rejection (THR) is the heat absorbed
at the evaporator plus the heat picked up in the
suction line plus the heat added to the refrigerant in
the compressor.

3. A good calc for a suction cooled compressor. An heat from the compressor radiated to the air should be subtracted. Regards TB

4. crane,

THR = compressor capacity @ a given SST X the HOR factor.

Open this attachment and scroll down to page two for more information.

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I agreee with the above if the refrigeration system operated 24 hours a day. Since a properly designed system operates 16 hours a day or less the operation factor needs to be considered.

6. Originally Posted by HeatMover
I agreee with the above if the refrigeration system operated 24 hours a day. Since a properly designed system operates 16 hours a day or less the operation factor needs to be considered.
I think you may be confusing "selecting a condensing unit" and "selecting a condenser".

While it's true box loads are based upon a Btu/24 hour load calculation where the system's daily operating times are then factored in to arrive at the Btu/hr requirement, the Btu/hr requirement for the condenser is only related to the heat rejected by the system at design conditions.

So...at design...the total heat of rejection (THR) is the sum of the compressor capacity plus the motor power input expressed in Btu/hr.

The energy in equals the energy out.

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