What is the lowest temperature with a ammonia refrigeration system?

[powersoff]

What is the lowest temperature you could measure if using a ammonia refrigeration system?
If you have any references they would be much appreciated.
Thanks

 

[mtngreen]

-60F is about as low as you can get.

 

[Compositepro]

The lower limit for any refrigerant is usually set by the fact the you don't want the refrigerant in the evaporator to go below atmospheric pressure (vacuum). Air can leak into the system, and the mass flow rate will be limited, which limits refrigeration capacity.

 

[NXTCOLD]

Compositepro's observation about not going into a vacuum is a good one. This would limit the design temperature to -28F. However, ammonia will operate with reasonably good efficiency down to -40F. A good purger takes care of the air. Ammonia vapor volume increases drastically as the temperature is lowered further. mtngreen's comment that -60F is about as cold as one can reasonably achieve is also accurate, but even there higher pressure refrigerants than ammonia should be considered.
NXTCOLD

 

[DRWeig]

Taking the evaporator into a vacuum is a given in large Trane water chillers. R-123a normal operating evap is in the 17" to 19" Hg vacuum when making 45°F water. Ammonia at that amount of vacuum is in the -60°F to -70° range.

However, the points above about sucking in air are important. Excellent sealing and a good purge system for non-condensables are needed.

Best to you,

Goober Dave

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[NXTCOLD]

Frick rates their screw compressors down to -80F. Not the best eff there, but interesting to know.