Demand Cooling in Low Temp R22 w/ Jeremy Smith
In this podcast, Jeremy Smith joins us to discuss demand cooling in low-temperature applications that use R-22 refrigerant.
R-22 is NOT an ideal low-temperature refrigerant because it leads to high compression ratios. The discharge gas also gets really hot and can burn up the oil in the system. (The head of the compressor is even hotter than the discharge line, so if the temperature is high enough to cause oil breakdown in the discharge line, it's almost surely worse inside the compressor). However, R-22 is starting to go away in rack refrigeration.
Demand cooling injects saturated refrigerant into the compressor to help mitigate the high discharge temperature and oil damage. It may seem like demand cooling intentionally slugs the compressor. However, the saturated refrigerant should boil off almost immediately, and it should not make it to the head of the compressor under typical conditions.
On the diagnostic and repair side, demand cooling is usually pretty straightforward; if a sensor fails, then it's likely a thermistor issue. In the case of thermistor problems, you can diagnose those issues with the information given in the application engineering bulletin. Loose connections and valve restrictions can happen, but those are also pretty easy to diagnose and repair. Perhaps the most complicated issue occurs when rack systems have low liquid levels. The injector valves can't get a solid column of liquid, but many other components will work fine.
Demand cooling solutions are usually brand-specific; each manufacturer has a slightly different setup. To learn more about the Copeland Discus compressors with demand cooling, check out the AE4-1287 bulletin.
Jeremy and Bryan also discuss:
- Outdoor air and head pressure
- DTC valves
- Desuperheaters and hot gas bypass
- Tube-in-tube heat exchangers as “subcoolers”
- Seasonal changes in discharge temperature
- Why should we pay more attention to discharge line temperature?
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