Water-to-water heat pump rebuild?

[Bill Sanford]

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]

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

[Bill Sanford]

How low of superheat can I actually run?

The well water temp and flow rate is constant, so I assume I can get by with a relatively low SH without issues because everything is so stable. Right?

[mejunkhound]

Based on water flow and delta T, your system is extracting about 22KBTU/ hr from the water.

Very rough calc of enthalphy from R22 charts and your temps:
Somebody can double check the calcs, but looks like the R22 flow rate, based on liquid to comp outlet changes, shows only a 240#/hr flow rate. If I read the ZR40K correctly off your pic, that unit should be able to compress near 600#/hr - so you should be getting close to 45kBTU vs. 22k., and the water temp shoud be dropping more than 2x as much as the 4.5F indicated.

So, blockage in line or low refrigerant level is indicated. This is one of those cases where an 'antiquated' sight glass can be useful - e.g bubbles means there is not a full liquid line prior to the txv, etc.

Another way to look at this is for a blockage, the comp cannot pull enough R22 b past the blockage to lower the evap outlet temp, or that there is not enough R22 to compress due to low charge.

Of course, this could all be BS subject to peer review <G>

[Bill Sanford]

Originally Posted by mejunkhound

Based on water flow and delta T, your system is extracting about 22KBTU/ hr from the water.

Very rough calc of enthalphy from R22 charts and your temps:
Somebody can double check the calcs, but looks like the R22 flow rate, based on liquid to comp outlet changes, shows only a 240#/hr flow rate. If I read the ZR40K correctly off your pic, that unit should be able to compress near 600#/hr - so you should be getting close to 45kBTU vs. 22k., and the water temp shoud be dropping more than 2x as much as the 4.5F indicated.

So, blockage in line or low refrigerant level is indicated. This is one of those cases where an 'antiquated' sight glass can be useful - e.g bubbles means there is not a full liquid line prior to the txv, etc.

Another way to look at this is for a blockage, the comp cannot pull enough R22 b past the blockage to lower the evap outlet temp, or that there is not enough R22 to compress due to low charge.

Of course, this could all be BS subject to peer review <G>

Yup, your numbers all look correct to me. Initially the well water would drop close to 10 degrees! This is no longer the case.

I think a new TXV and a recharge should make it work like new!

I'm fairly certain the charge is low. Just installing and pulling gauges twice and I can notice reduced efficiency. The charge is on the lower ragged edge of barely working!

Bill

[mejunkhound]

and a recharge

with R22 running close to $10/# these days, you may want to review the thread(s) on R290 (propane). Propane would be ideal for a water/water HP, esp if any leakage could flow downhill.

BTW, if you watch ebay or Clist, you can come by a good used vacuum pump for under $100. Then get an O2 tank for brazing with propane as the fuel. Since you already have the pressure and temp gauges, you will then have as good of tools as many 'pros'.

[Geo NR Gee]

Originally Posted by mejunkhound

So, blockage in line or low refrigerant level is indicated. This is one of those cases where an 'antiquated' sight glass can be useful - e.g bubbles means there is not a full liquid line prior to the txv, etc.

Where is the best place to locate the sight glass? Would you install more than one?

[Bill Sanford]

Originally Posted by mejunkhound

and a recharge

with R22 running close to $10/# these days, you may want to review the thread(s) on R290 (propane). Propane would be ideal for a water/water HP, esp if any leakage could flow downhill.

BTW, if you watch ebay or Clist, you can come by a good used vacuum pump for under $100. Then get an O2 tank for brazing with propane as the fuel. Since you already have the pressure and temp gauges, you will then have as good of tools as many 'pros'.

Since this thing is running inside on the main floor of our house, I don't think I want 6-7 pounds of propane in the system due to concerns if a leak were to occur.

Concerning brazing, is the following a reasonable solution for limited use:
Benzomatic OX2550 Torch Kit Cutting Welding Brazing Torch | eBay

Also concerning a vacuum pump, don't I need a recovery unit that will save the R22? I assume that this means a tank as well. If I recover what R22 I have, can I put it right back in, or does it need to be "cleaned" somehow?

I don't think I'd have too much trouble changing the TXV. I've plumbed two houses with copper. I just haven't brazed since I had hot metals in college back around 1980. That said, I'm sure I could do it.

The main issue is getting more R22. Don't you have to be licensed to buy it? I did see sellers on EBay, but they all state that you need some type of certification to buy it. Any insight regarding this?

I'm sure that if I hire someone to come out and do this, I'll spend between $500 and $1,000, so I'm not afraid to spend some money on tools to do the job myself if I feel like I have a good chance of success. I'm a very handy guy with above average skills for this kind of work with an engineering background, so I'm not afraid to get my hands dirty. :-)

Thanks for any insight.

Bill

[BradC]

Originally Posted by Bill Sanford

Concerning brazing, is the following a reasonable solution for limited use:
Benzomatic OX2550 Torch Kit Cutting Welding Brazing Torch | eBay

I've never heard anyone say anything good about those units. The majority of comments are along the lines of "it's unregulated and a pig to keep adjusted" and "the oxy bottles last 5mins max".

I've done well with a bernzomatic ts4000 handheld though if I had to do it again I'd get a ts8000 as they are reportedly hotter. I've got more fun toys to use now, but I still use the ts4000 for smaller stuff.

[Bill Sanford]

Originally Posted by BradC

I've never heard anyone say anything good about those units. The majority of comments are along the lines of "it's unregulated and a pig to keep adjusted" and "the oxy bottles last 5mins max".

I've done well with a bernzomatic ts4000 handheld though if I had to do it again I'd get a ts8000 as they are reportedly hotter. I've got more fun toys to use now, but I still use the ts4000 for smaller stuff.

Thanks Brad.

Will the ts8000 be hot enough to braze properly just using propane as a fuel? I thought to braze properly you needed oxygen to get enough heat.