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Old 02-13-16, 08:44 PM   #1
stevehull
Steve Hull
 
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Default rebuilding GTHP with low COP

I have a 12 KBTU water source heat pump (R22) that keeps the office in my shop warm in winter and cool in summer. The problem is that the COP is rather low - about 2. Draws about 6 amps and I bet I can decrease that to 3 amps with a more efficient scroll.

The reason is likely the old reciprocating compressor and I am betting that a newer scroll would work in its place - and far more efficiently.

Is it too much to think I can literally cut out the old inefficient compressor, rebraze in a new one, evacuate/refill - and have it done? And it is a 120 V compressor . . .

The unit is a late 80's demo model made for WaterFurnace. I picked it up about 20 years ago for $50, hooked up some garden hoses for inlet/outlet water lines and away it went. Confirmed the COP by measuring the difference of in/out water temps and the water volume through the system. The plate also says 12,000 . . . . but it was fun to verify.

In all that time, I have never had to recharge it and the only fix was a deteriorating start capacitor that was simple/cheap to replace.

The newer scroll compressors look quite nice - but will they work as a braze in replacement?


Steve

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Old 02-14-16, 09:16 AM   #2
jeff5may
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Default

6 amps @ 120 volts sounds about right for a 1 ton compressor. 720 watts input power. 12000 btu heat transfer divided by 3.4 btu per watt equals nearly 3500 watts heat transfer. 3500 watts divided by 720 watts equals nearly 5. Did I make a wrong assumption somewhere? Sounds about right for a w2w heat pump: cop around 5, eer around 50/3 or 16.67.

You're not going to save much electric power by swapping for another compressor rated for the same capacity. You may pick up some mass flow through the compressor if your hx's and metering device react favorably to the new compressor. Assuming it is not modded already, another compressor may or may not bring you to a higher level of efficiency.

If the unit is cap-tube metered, and has relatively small heat exchangers, you may be better off installing a smaller compressor and some tx valves to reach your target cop at the same heat transfer rate.
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Old 02-14-16, 12:05 PM   #3
stevehull
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Default

Made a mistake on the amps in heating mode - it is 9.5 amps (@116V). I knew something was wrong when I read your post. So the kW input is about 1.1 and the COP about 3.2 or so. All in all not too shabby . . .

I have a 7.5 kBTU R22 scroll out of an dehumidifier that would physically fit and the old HP unit has cap tubes for orifices. Maybe a project, but I hear your caution that it might not be worth it.

Thanks!


Steve
ps still struggling to find the leak on the bigger 3 ton GSHP unit; nothing with bubble mix

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