While pondering my summer electricity bills I came upon an article by John Cantor about crankcase heaters… This explains that heat pumps use electrical power to warm the compressor crankcase while not in use. The purpose of this is to prevent refrigerant mixing with the compressor oil when idle, which could otherwise cause bearing failure on start-up.
Now, we have a monster set up here with two big Daikin high temp heat pumps (so two compressors on each one). I quickly decided to invest in an EmonPi to investigate.
A bit of online research revealed that the crankcase heaters use 33W each, and maintain the temp at 70-75C, so I was expecting maybe 150W tops. Well, that would be bad enough but actually, our system guzzles over 400W doing absolutely nothing…! OMG…! And this is meant to be good for the planet???
Now, the manual also says that the system should be left on for 8 hours to warm the compressor through before use, so it’s really not possible to hook the heating/hot water demand signals into some big power relays and clunk everything on and off when needed.
I am an experienced electronics engineer and hacker, so I’m ready to get in there and do something drastic. My current thought is to add an Arduino with a temp sensor plus a relay and bypass the built-in controls for the crankcase heater. Then I can shut the system down fully, keeping it warm myself until it’s actually needed. If I also leave one fully off until I really need both heat pumps, my calculations show that I can reduce my standby power use by nearly 80%. That will be my next project then…
My question is - is anyone else similarly outraged about crankcase heaters and the standby power use of their heat pumps…? Has anyone else tried any other drastic solutions…? Does anyone know of any other reason not to hack my system this way (apart from a wide range of electrical safety concerns that is…)