Calculating condensing unit heat of rejection

[kengineering]

Hi everyone, We are putting a Lab together to do our DOE testing. Other t han the typical loads, lights, appliances, ect. when sizing the cooling unit how do i calculate the heat of rejection of the largest condensing unit that will run for testing. It is a copeland FJAM-A300-CFV-020 air cooled rated at 21,600btu. I know years ago we would have shot from t he hip and added 20% the the 21,600 for the mechanical heat of compression but not sure thats good enough today?

Thanks , Ken

I love projects that challenge me, keeps me humble enough to reach out for help.

[nevinjohn]

The compressors used today are rotary type which uses discharge gas for its cooling, unlike the traditional hermetic compressors where suction gas is used for cooling! So its a warning to consider the old value. Moreover since ambient temp are high, the condensors would have been designed for a higher heat rejection?

[moideen]

Hi,kengineering,
I think you are looking the formula to calculate the capacity of air cooled condenser if you know the capacity of evaporator or compressor. The heat rejected from the condenser called total heat of rejection (THR), is equal to the evaporator heat input, plus compressor work input.
For open type compressor:
THR=compressor capacity (Mbh) + (motor bhp*2.545)
For hermetic or semi hermetic
THR=compressor capacity (Mbh) + (input kw*3.413)
· First calculate the design THR as per the compressor type.
· Determine the design TD. (For higher temp.application assuming ambient condition 50C(122F),TD is 17C(30F).
· Check the total capacity to be sure it is still equal to or greater than design THR.:cool:

[kengineering]

Moideen, Thanks for the reply.
We have completed the environmental room and we're quite pleased. With winter aproaching its been dry so we've had to beef up our humidification system but I'd say it's been worth the effort.. Kengineering

[nike123]

Copeland has software witch calculates heat of rejection for their compressors and condensing units for any given condition.
http://www.emersonclimate.com/europe/en-eu/Resources/Software_Tools/Pages/Download_Full_Instructions.aspx

Unfortunatley, it looks like the small hermetics are not covered with software.