Author Topic: Water-to-water heat pump rebuild advice?  (Read 2319 times)

Offline Bill Sanford

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Water-to-water heat pump rebuild advice?
« on: January 05, 2013, 01:24:02 PM »
Hey guys,

I have a 20 year old Florida Heat Pump WH50 - 50k BTU water to water, heating only heat pump that needs help.

I had the compressor fail several years ago.  I found a Copland scroll compressor online that was listed as a direct replacement sub for the old piston compressor that was in it.

I brought the entire unit with the new compressor to a local HVAC shop and had them change it for me and recharge the unit (R22).  That they also changed the TXV because they felt that it may be contaminated by the burnt up compressor.  They didn't consult the heat pump manufacturer regarding the type of TXV.  The TXV is not an adjustable type.

Since that time, the unit works, but doesn't seem to put out much heat compared to before the original compressor failed.

The heat source is well water in a pump-and-dump setup with the well water at 50 degrees F.

I think my problem is that the temperature of the R22 coming out of the TXV valve is 43.7 degrees and the well water is only 50 degrees.

The suction pressure is 54psi, which on the R22 chart is 30 degrees F, so my superheat is 13.7 degrees.  The source water temp never changes from 50 degrees.

My question is:  How can I lower the R22 temp coming out of my TXV?  If it was 34 degrees, I'd be able to extract a LOT more heat from the well water through the heat exchanger (evaporator).

If my TXV had adjustable superheat, I assume I could lower it quite a bit and this would lower the R22 temp leaving the TXV, right?

What would more charge do?

My temps and pressures are as follows:

High R22 pressure 240 PSI
Suction R22 pressure 54 PSI
R22 line temp entering the evaporator  43.7 degrees
R22 line temp leaving the evaporator  44 degrees
Source water temp entering the evaporator 49.9 degrees
Source water temp leaving the evaporator 45.5 degrees

Again, how do I get my R22 temp lower leaving the TXV and entering the evaporator?  Doing this should solve my efficiency problem.

Thanks for any advice!

Bill

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Re: Water-to-water heat pump rebuild advice?
« Reply #1 on: January 07, 2013, 04:43:19 PM »
Well there's a lot that can go wrong with that type of repair.  It wouldn't be the first time I saw "a direct replacement compressor" that was not in fact a direct replacement or sized the same as the original.  Let me know the model numbers of both compressors.  Your old reciprocating compressor probably needed a bleed type TXV and a hard start kit.  They probably changed the TXV when they installed the scroll compressor to a non bleed type TXV. 

Hopefully they installed a new capacitor with the new compressor. 

I wouldn't be concerned with the 13.7F Superheat.  I would try to measure the subcooling though.  You're suction pressure seems low.  I'm assuming they weighed in a charge but maybe you need some more added due to a long lineset etc...  That would be my first step is to calculate subcooling and verify the system is not low on refrigerant, but the high side pressure would be much lower if you were undercharged and it's unlikely there's a restriction in the sytem as the high side pressure would be higher.

Normally I suggest checking the airflow but in your case it did the job before the heat pump was repaired, so it's probably not the problem.  What kind of temperature rise are you getting?

I would hire the shop that did the repair to come out and service the unit in the field and to verify the new compressor and TXV are in fact sized and operating correctly.