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Old 01-01-14, 04:34 PM   #27
Lurking Renovator
Join Date: Dec 2013
Location: Powell River BC Canada
Posts: 15
Thanks: 3
Thanked 2 Times in 1 Post

Hi all,
Been lurking here for a while learning lots. Thanks to all of you.

RB, thanks for that explanation. Perhaps you could help me fill in some blanks in my understanding.

"Above the critical temperature, a liquid cannot be formed by an increase in pressure, even though a solid may be formed under sufficient pressure." That said, you dont ever want to go near this region. To name a few, R-12 233*F, R-22 204*F, R-134 213*F, R-290 206*F, R-410 161*F. So as youll notice, 410 is by far the lowest, but 161*F equates to 688psi! Not a good gas for heating beyond say.. 110*F. (and the reason why desuperheater reclaimers dont work as well these days)"

Having your refrigerant becoming supercritical would be a problem if your condenser became overwhelmed and couldn't reject enough heat to condense it before cap tube / txv. Or if it were to exceed the pressure rating of the machine and potentially rupture something. But what else would happen?

If the fluid failed to condense it would whistle through a cap tube as vapour and equalize pressure between the high side and low side (basically turning your evaporator into another condensor). I'm thinking a txv would do the same because the vapour would be superheated entering the evaporator already. So basically pressure in the evaporator would render it incapable of absorbing more heat. No pressure diff = no phase change= no heat pump.

If the pressure of the fluid in the supercritical condition didn't exceed design spec, would it not just sit there blowing heat until the condensor started to condense again? Or would a critical failure result?

I haven't even started trying to think how efficiency would be affected.

I'm a marine engineer not an hvac guy. My experience is mainly with steam, so I could be making some incorrect assumptions or poor analogies.
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