Water-to-water heat pump rebuild?
 

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 HVAC shop doesn't have a clue. They don't seem to understand anything other than how to change parts.

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.

Bill

Bill,

My thinking is that the thermal expansion valve (TXV) is sized incorrectly. An adjutable one would allow you to alter this.

Thanks Steve. That was my thinking as well.

I was thinking of getting a 4 Ton Sporlan RCVE-4-GA

ADJUSTABLE TXV, INLET: 1/2" ODF, OUTLET: 1/2" ODF, EQUALIZER: EXTERNAL 1/4" ODF, 30" CAPILLARY TUBE WITH BULB, REFRIGERANT: R-22

I found one on EBay relatively cheap.

Now I just need to find someone who has a clue to put it in. Kind of a big job and requires skills I don't have.

A 24,000 BTU unit should be really pumping out the heat. The use of a constant temp supply rules out a lot of things. What is your flow rate out in gallons per minute?

Yes, replacing the TXV with an adjustable one appears to be it, but I would defer to the many people on this site that are FAR more expert than I (where are you AC-hacker?).

I don't think putting more R-22 is going to help.

I'm right here...

stevehull, I think your advice is about right, and Bill, the TXV you selected sounds like the correct one, too.

Adjustable TXV, yes by all means.

> R22 coming out of the TXV valve is 43.7? This sounds just awful. Do you see frost around the output of the valve?

Bill, are you gonna do this yourself or haul it back to the shop?

Best,

-AC

I think your comp is slightly smaller than the original one so you will need turn down the TXV somewhat but not much because you only need a 2-3deg increase in superheat (which the comp will like). Ideally you will want to get some more subcooling out of the condenser and to do that you may want to increase the liquid flow rate through the condenser a bit. Are there any balancing valves on it?

You may want to try doing that before changing the TXV but you may need to do both.

My gut feeling is the compressor does not have enough capacity. The TXV will determine the superheat, but if the SST is too high and the TXV is maintaining any form of proper superheat, the the problem is your compressor can't suck the vapor fast enough to drop the evaporation temperature.

<edit> after re-reading your original post I'm certain the problem is the compressor. Do you have links to the model numbers for both compressors (or better, data-sheets).

<edit 2> You can reduce your evaporation temperature by throttling the water through the evaporator to effectively reduce the capacity of the evaporator. The lower your evap temperature, the higher your compression ratio and power consumption, which will dump more heat into your condenser.

We seem to be attacking the same idea from different directions.

Yep. I had a long explanation here, but I had the wrong end of the stick, so I've deleted it.

What folks say about the compressor being too small is right on.

13.7F for a txv is a little on the high side for water evap but close enough. The txv closes down to maintain the 13.7F SH - aka allows less liquid into the evap to boil, hence also less total heat gain of the refrigerant cycle. If the txv has to close down to maintain SH, it means either the compressor is too small as mentioned as a possibility - or, there is a piece of junk in the line before the compressor, the screen in the compressor is clogged from debris left in the lines during the txv and compressor changeout (true if the 54psi is right at the compressor inlet) , etc.

The shop DID put in a new filter dryer and purge the lines when they did the work, right???? If not, time to buy a vacuum pump and learn some more diy <G>