Water-to-water heat pump rebuild?

Bill Sanford · 01-05-13, 09:21 AM

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

stevehull · 01-05-13, 04:38 PM

Bill,

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

Bill Sanford · 01-05-13, 05:39 PM

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.

stevehull · 01-05-13, 06:01 PM

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.

AC_Hacker · 01-05-13, 06:56 PM

Quote:

Originally Posted by stevehull

(where are you AC-hacker?)...

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

Bill Sanford · 01-06-13, 07:00 PM

Quote:

Originally Posted by AC_Hacker

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

First, thanks to everyone for your help. Sorry for the delay in posting here. I have been helping a friend move all day! :-( Not fun, but done!

There are no balancing valves in my heat pump. Concerning the size of the compressor and specs on it, I think it's plenty big for the job. I don't have the specs for the original compressor, but it was a Tecumseh (sp?) 3-1/2 ton piston type compressor. I replaced it with a Copeland ZR40K3-PFV-830 scroll which is also a 3-1/2 ton unit. Attached is the data sheet for the compressor.

I think there are mainly two issues. First is I think that the charge is low in the system. Second is the existing VTX valve. It is not adjustable and allows for way too much superheat for the system to work properly with 50 degree well water. The R22 entering the condenser at 43.7 degrees is indeed awful and just isn't cold enough to extract much heat from 50 degree well water. There is no frost around the VTX valve. The temp is too warm to freeze anything! A new valve is indeed needed and I ordered the Sporlan model I mentioned above.

Hauling this thing back to a shop is a big pain in the rear! I'm very comfortable soldering and cutting and fitting copper, but I've never done any brazing and the current VTX looks to be brazed in. I think the rental place in town has a refrigerant recovery unit that can be rented, but I've never used one before. The charge in this thing is around 6 pounds, so there is a lot of R22 to pull out of the system even if it is low on charge right now.

The other issue is that it is now working, but not great. It's winter here in northern Minnesota and I need heat. :-) I do have two 5kW spa cartridge heaters as a backup and they will heat the house as well, so I could take it in if I really had to.

I'm inclined to hire someone to come out and recover the R22 and replace the VTX valve and recharge the system. I'm sure they could do it here on site.

The main problem I see is that I'm not quite sure how to determine the right amount of R22 the system needs to function properly. Most of the HVAC people around here are parts changers. After talking with a few, it's clear that they really don't seem to thoroughly understand these systems. This is my main fear, and this is why the unit is not working correctly now. The guy that replaced the compressor and VTX valve a few years ago should have known to install an adjustable VTX valve based on the low well water temp.

I've read a lot and learned a lot about subcooling, superheat, and the entire process. This by no means makes me an expert, but I've read enough that I know enough to be dangerous! :-)

So, what would be the right way to charge this unit? How can I tell if there is too little or too much R22 in the system?

Again, thanks for the help and advice!

Also, one quick piece advice for others considering well water for a heat source. I read a few threads where some folks seemed concerned about wearing out their well pump because it will run a lot. My system is about 20 years old and I'm on my original submersible well pump. I can't imaging how many millions of gallons that thing has pumped over the years. When the heat pump is on, it's running at 10 GPM and it runs a lot in the winter, so no worries about your submersible well pumps. Originally I did put in a bit bigger pump and well. It's a 6" well with a 3/4 HP submersible pump. Pressure tanks are another story. I end up replacing mine about every 3-4 years. The bladders rupture and they are done. Get a BIG tank. I forget the gallon capacity of mine, but it's about 4' high. This helps the pump cycle less. They do make variable frequency drive submersible well pumps, but the are well over $1,000!

As I mentioned, my system is a pump-and-dump. Getting rid of the water is no big deal as I have a bit of a swampy area on the edge of my property and dump the water there. It's amazing how little the wet spot is. The water just soaks into the ground and goes away!

I read in another post that you like pictures, so I'm posting a few of my installation. I installed it myself along with the entire heating system. While the heat pump isn't quite home brew, with its age and all the fixes, it's getting there! :-)

The main floor in my house is about 1600 sq ft and the second floor is about half that. We're on a lake, so no basement. The main floor is a slab on grade with 2 EPS foam below the slab with Wirsbo tubing in the slab. Second floor is hot water baseboards... lots of them due to the low water temp! :-)

Considering I put this in 20 years ago, I was heating with geothermal before it was in style to do so! Geothermal is indeed the way to go. This thing has saved me a TON of money over the years! :-)

Again, thanks! This forum is just wonderful!

Bill

Bill Sanford · 01-06-13, 07:06 PM

Quote:

Originally Posted by stevehull

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.

Flow rates are as follows:

Well - 10 GPM Constant 50 degrees F
Load - 8 GPM Inlet is typically less than 100 degrees F

Mikesolar · 01-05-13, 08:01 PM

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.

BradC · 01-06-13, 06:25 AM

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.

Mikesolar · 01-06-13, 07:24 AM

Quote:

Originally Posted by BradC

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.

01-05-13, 09:21 AM	#1
Bill Sanford Helper EcoRenovator Join Date: Jan 2013 Location: Northern Minnesota Posts: 32 Thanks: 1 Thanked 0 Times in 0 Posts	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

01-05-13, 04:38 PM	#2
stevehull Steve Hull Join Date: Dec 2012 Location: hilly, tree covered Arcadia, OK USA Posts: 826 Thanks: 241 Thanked 165 Times in 123 Posts	Bill, My thinking is that the thermal expansion valve (TXV) is sized incorrectly. An adjutable one would allow you to alter this. __________________ consulting on geothermal heating/cooling & rational energy use since 1990

01-05-13, 06:01 PM	#4
stevehull Steve Hull Join Date: Dec 2012 Location: hilly, tree covered Arcadia, OK USA Posts: 826 Thanks: 241 Thanked 165 Times in 123 Posts	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. __________________ consulting on geothermal heating/cooling & rational energy use since 1990

01-06-13, 06:25 AM	#9
BradC Apprentice EcoRenovator Join Date: Dec 2010 Location: Western Australia Posts: 148 Thanks: 1 Thanked 48 Times in 34 Posts	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. Last edited by BradC; 01-06-13 at 06:37 AM..

01-05-13, 05:39 PM	#3
Bill Sanford Helper EcoRenovator Join Date: Jan 2013 Location: Northern Minnesota Posts: 32 Thanks: 1 Thanked 0 Times in 0 Posts	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.

01-05-13, 08:01 PM	#8
Mikesolar Master EcoRenovator Join Date: Aug 2012 Location: Toronto Posts: 958 Thanks: 40 Thanked 158 Times in 150 Posts	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.