this post was submitted on 03 Jul 2024
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Define efficient.
You can easily almost double that if you're willing to break the pump in a few years.
But usually that's more expensive per BTU/other heat unit because the pumps are expensive. That's why I asked.
Double would be a COP of over 10. That's a stretch for an overbuilt GSHP and not even slightly feasible for air-air.
High COPs are usually easy on a compressor as they represent low compression ratios and low differential temps. For example I can hit around COP 7 in cooling on my scrap heap GSHP, with an evap temp around 10C and condenser temp around 20C. That's a high side pressure around 100 psi and only 30 psi of differential, "barely working" as far as the compressor is concerned.
The only way I know to get high COPs is to have an oversized condenser and a way to get your refrigerant below ambient, like evaporative, ground source or overnight radiant so you can get the compression ratio down, unless you know a secret in which case I'm not afraid to burn out a compressor or two trying it out!
I don't rember the details of how it works. I think it just reduces the torque or something? Maybe it doesn't work on newer pumps or they already do it.
Oh I think I know what you're talking about, abusing a minisplit by idling the inverter back too far. Effectively you have a hugely oversized condenser for the tiny flow, under the right conditions like a cool night you can get ridiculous subcooling.
But COP is irrelevant in this case because you've derated the actual BTU to near zero, you aren't moving any refrigerant.
Also yes this will kill your compressor because the minimum speed is set where it will get enough oil flow. Run it too slow, and it won't pick up oil and eventually seize up. You also could end up running the suction in vacuum which is also hard on compressors.
Thats it thank you.