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Old 07-16-13, 10:47 PM   #1
NiHaoMike
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Default Thermal storage crankcase heater?

After an experiment to induction heat a compressor for crankcase heating with 5 turns of AWG18 wire connected to a modified PC power supply (very successfully, I should add), I realized how silly it is to be making heat in a device that is supposed to cool, even more so when the discharge line is very hot in operation.

So what about route the discharge line through an insulated container full of wax? The hot gas melts the wax, storing the heat. Later, as needed, a pump can circulate water (or some other coolant) through a copper coil in the container as well as one thermally glued to the sump of the compressor, acting as the crankcase heater.

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Old 07-17-13, 06:25 AM   #2
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Why do you need crankcase heat on it? Are you operating the compressor at low ambient temperatures? Sounds like you are talking about crankcase heat for a central AC unit. If that's true, normally residential AC units are specced to only need it if it will be started at 55 degrees or lower. You could always put a thermostat on it to turn on the crankcase heat when it gets that cold. Although I'd personally be inclined to put a thermostat on it so it won't fire up below 60 degrees rather than heating the compressor.
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Old 07-17-13, 08:13 AM   #3
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I'm using ES22a refrigerant (mostly R290) and crankcase heat is an especially good idea since hydrocarbons dissolve in the oil very well. Great for oil return, not so good for lubrication on startup.
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Old 07-17-13, 09:09 AM   #4
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Default Non-Existent Problem...

Quote:
Originally Posted by NiHaoMike View Post
I'm using ES22a refrigerant (mostly R290) and crankcase heat is an especially good idea since hydrocarbons dissolve in the oil very well. Great for oil return, not so good for lubrication on startup.
I believe that the relevant bearings in the compressor are already immersed in lubricant at startup.

As I recall, your unit will be installed in Texas, and also indoors, right?

I think you might be trying to fix a non-existent problem with regards to the crank case heater machinations. The real reason for them is to reduce the viscosity of the oil in the crank case sump so that starting current doesn't blow the breaker that you have dedicated to your heat pump. (The breaker should be sized to be considerably less than your compressor's LRA, and comfortably larger than your 'running amps'.)

But there might be other people who are working in climates where crank case heaters actually matter. Posting some photos of your efforts (even photos of diagrams) could be very helpful for them.

BTW, if you don't happen to already own a digital camera, you can easily find serviceable ones in thrift stores like Goodwill. Five mega-pixel models seem to be going for $10 or even less... such a deal, and such a help in communicating.

I can't speak for anyone else, but I'd really like to see what you're doing.

-AC

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