JohnMo Posted September 17, 2022 Share Posted September 17, 2022 3 hours ago, dpmiller said: "single phase" there means it doesn't apply to any inverter units as they use a 3-ph compressor and slowly ramp up speed, automatically clearing down gently with no "protector" to trip out anyway... No following the logic, unless a big ASHP the supply would be single phase. 1 Link to comment Share on other sites More sharing options...
dpmiller Posted September 17, 2022 Share Posted September 17, 2022 @JohnMo yes the supply to the ASHP is singlephase, but the inverter converts it to a nice controllable voltage-, current-, and frequency- controlled 3phase. Link to comment Share on other sites More sharing options...
JohnMo Posted September 17, 2022 Share Posted September 17, 2022 I know that 'means it doesn't apply to any inverter units as they use a 3-ph compressor' This is bit where the logic makes no sense. The heater is just a single phase and would there whether the compressor motor is single or three phase or even DC driven. The heater has nothing to do with motor driving the compressor. Link to comment Share on other sites More sharing options...
dpmiller Posted September 17, 2022 Share Posted September 17, 2022 no the logic is that the startup of the compressor is controlled, and so oil and gas can be gently redistributed rather than with a switch-start 1ph machine the pump is "blocked" from starting by the liquid refrigerant same thing applies to air compressors- a switch-start machine has a valve built into the pressure switch to "unload" the pump head until the rpms and output pressure build. Switching the compressor on at the wall instead of the airswitch results in a humming noise and a blown fuse... Link to comment Share on other sites More sharing options...
JohnMo Posted September 17, 2022 Share Posted September 17, 2022 The mitsubishi ASHP with higher than ideal standby electric usage are inverter driven, so I am still missing what you are trying to say. They have a crankcase heater and a requirement to heat up prior to starting. It's easy to dump air and water not so easy to dump refrigerant. Hense the need to heat the crankcase and turn the liquid refrigerant back to a gas state. An inverter doesn't get around the science that a liquid isn't compressible. Nor that lube oil diluted with refrigerant is a rubbish lubricant. Link to comment Share on other sites More sharing options...
SteamyTea Posted September 17, 2022 Share Posted September 17, 2022 2 hours ago, JohnMo said: Nor that lube oil diluted with refrigerant is a rubbish lubricant. Would a silicone oil get around that problem, silicone is very inert. Link to comment Share on other sites More sharing options...
JohnMo Posted September 18, 2022 Share Posted September 18, 2022 I think you have to use an oil that is hydroscopic to the refrigerant gas. I know in industrial screw compressor that is the case. It's matter of clearing enough condensate to restore lubricity, you don't have to clear all of it. And also enough condensate so the fluid can makes its way through the compressor without undue load being placed on thrust bearings. As the the compressor increases pressure the refrigerant naturally phase changes back to gas. You often get operators that think they know better, and over ride the heat up timers, this does two things, accelerates bearing wear and places huge loads on thrust bearings, which gives premature failure. Link to comment Share on other sites More sharing options...
dpmiller Posted September 18, 2022 Share Posted September 18, 2022 9 hours ago, SteamyTea said: Would a silicone oil get around that problem, silicone is very inert. some info here ST https://refrigerationclub.com/oil-compatible-coolant/ Link to comment Share on other sites More sharing options...
SteamyTea Posted September 18, 2022 Share Posted September 18, 2022 (edited) 8 minutes ago, dpmiller said: some info here ST No mention of polydimethylsiloxane, but I guess if it has not been tested, they cannot report on it. It is a shame that the chemist I knew at university has retired, she was brilliant, even explained, in less than a minute, why CO2 causes energy to be trapped when in mixed with other gases. Edited September 18, 2022 by SteamyTea Link to comment Share on other sites More sharing options...
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