Water-to-water heat pump rebuild? - Page 6

Bill Sanford · 01-09-13, 10:59 AM

Also, I did arrange with the HVAC company that put in the replacement compressor a few years back to come out and evacuate the system, install the new TXV, and vacuum out and recharge the unit.

I couldn't find a recovery unit I could rent or borrow and I didn't want to jump through the hoops to get licensed to get the R22 for just this project.

As much as I wanted to DIY this and like to tinker, it just didn't make sense financially or time wise to buy a bunch of equipment like a recovery unit, tank, new MAPP torch, rods, flux, etc. to do it myself for this one-time project.

Don't write me off guys! I really am a DIY kind of guy!

Bill

AC_Hacker · 01-09-13, 12:45 PM

Quote:

Originally Posted by Bill Sanford

FYI: Surplus City Liquidators has several of the Copland scrolls on their site right now in various sizes up to 5 ton for very good prices.

Thanks for the tip. But they're all too big. My house is not large and it's getting the deluxo insulation & infiltration treatment. PLUS I live in a pretty mild area (see picture):

...so my heating needs are quite modest. It's very rare that I come across a quality scroll compressor that is small enough (3/4 Ton or so). While at the same time, I am able to find an overwhelming abundance of smaller compressors (non-scroll) that are all in the range I want, for under $20 dollars (actually, I aim for $10).

That is why I did this whole Homemade Heat Pump Manifesto saga... to share this amazing discovery... that at the intersection of modest heating needs and the massive waste stream of discarded air conditioners, there exists an astoundingly cheap and efficient solution to heating needs.

It just takes a bit of self education and gumption.

But Bill, I do appreciate your information.

Best,

-AC

Bill Sanford · 01-09-13, 09:51 PM

AC,

It's amazing what you and others have built for so little money. I looked into a replacement 4 ton water to water heat pump and the local dealers want $5-$6k. When I look at what the parts cost, this seems crazy to me. They immediately justify the price by saying things like "you get a big tax credit", or "look how much you'll save", etc... This doesn't justify robbery in my opinion.

In another year or two I want to build a large detached garage and I'll likely put tubing in the floor. This is when I'll take a crack at building my own water to water heat pump from parts. Tube in tube heat exchangers look fairly easy to make and I think I can figure the rest out.

My 4 ton TXV showed up today and I have someone lined up to do the work Friday. I'll post back after the repair job and let you all know how it's working. Again, thanks for all the help and suggestions diagnosing the problem!

Bill

AC_Hacker · 01-09-13, 10:40 PM

Quote:

Originally Posted by Bill Sanford

...I have someone lined up to do the work Friday. I'll post back after the repair job and let you all know how it's working...

If it's not too much of a hassle, maybe you could do a series of photos of the job... could be useful info.

Best,

-AC

Bill Sanford · 01-09-13, 10:45 PM

Quote:

Originally Posted by AC_Hacker

If it's not too much of a hassle, maybe you could do a series of photos of the job... could be useful info.

Best,

-AC

I'll see what I can do.

I don't want to make the HVAC tech paranoid with me both watching and taking pictures of his work! :-)

I think he's already a bit on the defense since I actually seem to understand his black magic and am supplying him with the diagnosis and TXV!

AC_Hacker · 01-09-13, 10:55 PM

Quote:

Originally Posted by Bill Sanford

...I think he's already a bit on the defense since I actually seem to understand his black magic and am supplying him with the diagnosis and TXV!...

Well, don't do anything that would make anyone, including yourself uncomfortable.

However... when I was a young tot, we had a furnace repairman come to fix our malfunctioning furnace. My mother (a single parent) made a batch of cookies and sat and chatted with the repairman while he did his repair work. Then, the next time the furnace went out, she knew all the tools and procedures that were required and did the repairs herself.

She did the same thing with auto repairs, too. She was a very resourceful mom.

Best,

-AC

Bill Sanford · 01-11-13, 08:00 AM

Hey guys,

No one gave me a good answer to the following question: If you don't know the refrigerant capacity of a water to water system like this, what is the best method to fill it to the proper level? I can't see how pressures alone would do it. You could have substantially different amounts of liquid R22 in the system and the pressures wouldn't vary too much due to the fact that the TXV will maintain the suction pressure and temp. Is the charge level measured on the high pressure side?

Thoughts?

Bill

BradC · 01-11-13, 08:28 AM

That is a curly one. My gut reaction would be to put the pump in cooling mode (reject heat into the water) and to charge by monitoring the subcooling at the entry to the TXV.

If it's not a reverse cycle heat pump then you will need to get the house nice and hot (or restrict the air flow to the internal coil to create about the highest head pressure you are likely to experience in operation) and then charge until you get at least 4K of subcooling at the TXV entry. Ideally you want the least you can get away with, but the conventional wisdom I've heard is about 4K. If your internal coil is higher than your evap & txv and you have little restriction in the liquid line (sight glass, filter, solenoid, whatever else) then you might get away with less.

This is all theory absent any literature from the manufacturer telling you how to do it properly.
I'd get the TXV changed, weigh the charge back in and use that as a starting point.

If the fridgy is unsure of how best to charge it, explain to him it's just a normal split heat pump with one coil replaced by a HX, and ask him how he'd charge a normal unit.

AC_Hacker · 01-11-13, 11:03 AM

Quote:

Originally Posted by Bill Sanford

...If you don't know the refrigerant capacity of a water to water system like this, what is the best method to fill it to the proper level?...

Not to contradict BradC, who is much more experienced than I...

(this procedure assumes a single refrigerant, and not a mixed, or aziotropic, refrigerant)

Assuming you have proper high-side & low-side service ports installed, and that the unit has been vacuumed with a micron gauge and you have satisfied yourself that the unit is hermetically sealed and that no moisture remains...

With the unit NOT powered... begin by introducing some liquid refrigerant into the high-side port, a bit at a time, and watch both the high-side gauge and the low-side gauge. you should see them rise & fall as you begin introducing liquid refrigerant in, and it flashes from liquid into into gas. Keep introducing the refrigerant in small amounts until you see that the gauges no longer settle back to zero. You want some gas in the system before you power it up... kind of like priming the pump.

Then, adjust your gauge set so that you are no longer sending refrigerant into the high-side port. From here on, you will be introducing refrigerant into the low side, and it should be vapor, not liquid.

At this point, you need to know what the low-side and high-side target charge level is.

Power up the unit, and keeping an eye on the gauges introduce refrigerant in small measures. It is better to be timid at first and bolder by degrees, rather than the opposite.

You will see the system 'acclimate' to the charge level as the gauges rise and fall. Part of this is the refrigerant finding it's vapor/liquid equilibrium (this happens fairly quickly). Part of this is the refrigerant/lubricant finding it's equilibrium (this happens more gradually). The TXV, if you have one installed will play it's part, but eventually an equilibrium will be reached. As this process continues and you approach the correct charge level, you will see that the excursions of the gauges become less, and that the settling time of the gauges becomes longer. Toward the end of this phase, the intervals of time between charge introductions may be 30 minutes or more. At the end of this, you should let the system run for a few hours and the pressure level should be very close to the target level.

At this point, it is time to attend to superheat adjustment as BradC outlined.

-AC
-

Bill Sanford · 01-11-13, 06:15 PM

Thanks both AC and Brad.

Well the job is done. Kyle the HVAC guy was FAST. He was here for about 1:45 total!

I removed the control cabinet before he got here so he could get at the old TXV that was behind it. He got right to work. It took maybe 15 minutes to recover the R22. Next he removed the old TXV and put a piece of copper tubing in place of the old TXV because I asked him to put the new TXV on the side of the control cabinet so it could be easily accessed from the front of the unit. He agreed that this was the best place for it and installed it there quickly and efficiently.

When he was done brazing, he used nitrogen and pressure tested the system. He said everything looked good, but he sure didn't leave it pressurized too long to determine this... Just seemed like a few minutes. I hope it really is tight!

He then hooked up the vacuum pump and evacuated the system. This seemed to go much faster than I thought as well... seemed like much less than 10 minutes. When he felt it was good, he then hooked up the recovery tank and put some R22 back in to get the system out of a vacuum, but didn't charge the system yet.

Then I then jumped in and replaced the control cabinet and reconnected the wires from the compressor and the LP and HP lockout switches.

Next he put a bit more R22 back in and fired up the system. He used what he recovered and then used some of his R22 he brought with him. He had the R22 tank turned upside down, so he must have been recharging with liquid. He was working quickly and the utility room is so small that I couldn't see what port he was using to recharge, but I assume it has to be the suction side.

He said the best way to measure the charge and insure the system was working properly was to measure the subcooling. He filled it until he had about 7-8 degrees of subcooling. At this point I was seeing frost on the output of the VTX valve! Success! On the old TXV, I measured the output temp in the low 40s before.

He spent very little time actually measuring temps and verifying the performance. He said: "This is as good as its going to work. You should get plenty of heat now."

The pressures and temps were as follows:

Low side 49.5 PSI
High Side 192 PSI

Load in water temp 79.8 F
Load out water temp 88.7 F
(It's in the 30s outside today, so the slab water loops are relatively cool...)

R22 line into TXV 86 F
R22 line out of TXV 31 F

Well water in 45.5 F
Well water out 34.7 F

I honestly don't trust these temps because depending on how he clamped his probe on to the pipe, they varied some. That said, I could immediately tell that the new VTX was working MUCH better and the system was now really putting out some heat!

Based on his measured temps, I also don't trust the temp measurements I made over the past few weeks and posted in this thread. My measured well water temp was 49.9 F, not 45.5 F like he measured. I used a cheap Radio Shack digital thermometer with a remote probe. While my measurements may have been off some, the delta (difference between in and out of well and load) should have been fairly accurate, so my estimated BTU heat output should have been good.

My digital thermometer issue will soon be rectified. Last week when I ordered the new VTX, I also ordered a dual channel digital thermometer that will display delta temps between Channels 1 and 2. When I get this, I will make some better measurements and see how the system is really performing. With an accurate delta T between in and out, it will be easy to calculate efficiency.

I was very impressed with Kyle the HVAC guy. He was really great about explaining what he was doing and why. He knew I was interested and understood what he was doing and I think he actually appreciated that.

I've attached a few pictures for you to check out. When I get my new thermometer I'll post my measured results.

Again, thanks everyone for your advice. It looks like our diagnosis of a bad TXV and a low charge was right on.

That's all for now.

Bill

01-11-13, 06:15 PM	#60
Bill Sanford Helper EcoRenovator Join Date: Jan 2013 Location: Northern Minnesota Posts: 32 Thanks: 1 Thanked 0 Times in 0 Posts	Thanks both AC and Brad. Well the job is done. Kyle the HVAC guy was FAST. He was here for about 1:45 total! I removed the control cabinet before he got here so he could get at the old TXV that was behind it. He got right to work. It took maybe 15 minutes to recover the R22. Next he removed the old TXV and put a piece of copper tubing in place of the old TXV because I asked him to put the new TXV on the side of the control cabinet so it could be easily accessed from the front of the unit. He agreed that this was the best place for it and installed it there quickly and efficiently. When he was done brazing, he used nitrogen and pressure tested the system. He said everything looked good, but he sure didn't leave it pressurized too long to determine this... Just seemed like a few minutes. I hope it really is tight! He then hooked up the vacuum pump and evacuated the system. This seemed to go much faster than I thought as well... seemed like much less than 10 minutes. When he felt it was good, he then hooked up the recovery tank and put some R22 back in to get the system out of a vacuum, but didn't charge the system yet. Then I then jumped in and replaced the control cabinet and reconnected the wires from the compressor and the LP and HP lockout switches. Next he put a bit more R22 back in and fired up the system. He used what he recovered and then used some of his R22 he brought with him. He had the R22 tank turned upside down, so he must have been recharging with liquid. He was working quickly and the utility room is so small that I couldn't see what port he was using to recharge, but I assume it has to be the suction side. He said the best way to measure the charge and insure the system was working properly was to measure the subcooling. He filled it until he had about 7-8 degrees of subcooling. At this point I was seeing frost on the output of the VTX valve! Success! On the old TXV, I measured the output temp in the low 40s before. He spent very little time actually measuring temps and verifying the performance. He said: "This is as good as its going to work. You should get plenty of heat now." The pressures and temps were as follows: Low side 49.5 PSI High Side 192 PSI Load in water temp 79.8 F Load out water temp 88.7 F (It's in the 30s outside today, so the slab water loops are relatively cool...) R22 line into TXV 86 F R22 line out of TXV 31 F Well water in 45.5 F Well water out 34.7 F I honestly don't trust these temps because depending on how he clamped his probe on to the pipe, they varied some. That said, I could immediately tell that the new VTX was working MUCH better and the system was now really putting out some heat! Based on his measured temps, I also don't trust the temp measurements I made over the past few weeks and posted in this thread. My measured well water temp was 49.9 F, not 45.5 F like he measured. I used a cheap Radio Shack digital thermometer with a remote probe. While my measurements may have been off some, the delta (difference between in and out of well and load) should have been fairly accurate, so my estimated BTU heat output should have been good. My digital thermometer issue will soon be rectified. Last week when I ordered the new VTX, I also ordered a dual channel digital thermometer that will display delta temps between Channels 1 and 2. When I get this, I will make some better measurements and see how the system is really performing. With an accurate delta T between in and out, it will be easy to calculate efficiency. I was very impressed with Kyle the HVAC guy. He was really great about explaining what he was doing and why. He knew I was interested and understood what he was doing and I think he actually appreciated that. I've attached a few pictures for you to check out. When I get my new thermometer I'll post my measured results. Again, thanks everyone for your advice. It looks like our diagnosis of a bad TXV and a low charge was right on. That's all for now. Bill Attached Thumbnails

01-09-13, 10:59 AM	#51
Bill Sanford Helper EcoRenovator Join Date: Jan 2013 Location: Northern Minnesota Posts: 32 Thanks: 1 Thanked 0 Times in 0 Posts	Also, I did arrange with the HVAC company that put in the replacement compressor a few years back to come out and evacuate the system, install the new TXV, and vacuum out and recharge the unit. I couldn't find a recovery unit I could rent or borrow and I didn't want to jump through the hoops to get licensed to get the R22 for just this project. As much as I wanted to DIY this and like to tinker, it just didn't make sense financially or time wise to buy a bunch of equipment like a recovery unit, tank, new MAPP torch, rods, flux, etc. to do it myself for this one-time project. Don't write me off guys! I really am a DIY kind of guy! Bill

01-09-13, 09:51 PM	#53
Bill Sanford Helper EcoRenovator Join Date: Jan 2013 Location: Northern Minnesota Posts: 32 Thanks: 1 Thanked 0 Times in 0 Posts	AC, It's amazing what you and others have built for so little money. I looked into a replacement 4 ton water to water heat pump and the local dealers want $5-$6k. When I look at what the parts cost, this seems crazy to me. They immediately justify the price by saying things like "you get a big tax credit", or "look how much you'll save", etc... This doesn't justify robbery in my opinion. In another year or two I want to build a large detached garage and I'll likely put tubing in the floor. This is when I'll take a crack at building my own water to water heat pump from parts. Tube in tube heat exchangers look fairly easy to make and I think I can figure the rest out. My 4 ton TXV showed up today and I have someone lined up to do the work Friday. I'll post back after the repair job and let you all know how it's working. Again, thanks for all the help and suggestions diagnosing the problem! Bill

01-11-13, 08:00 AM	#57
Bill Sanford Helper EcoRenovator Join Date: Jan 2013 Location: Northern Minnesota Posts: 32 Thanks: 1 Thanked 0 Times in 0 Posts	Hey guys, No one gave me a good answer to the following question: If you don't know the refrigerant capacity of a water to water system like this, what is the best method to fill it to the proper level? I can't see how pressures alone would do it. You could have substantially different amounts of liquid R22 in the system and the pressures wouldn't vary too much due to the fact that the TXV will maintain the suction pressure and temp. Is the charge level measured on the high pressure side? Thoughts? Bill

01-11-13, 08:28 AM	#58
BradC Apprentice EcoRenovator Join Date: Dec 2010 Location: Western Australia Posts: 148 Thanks: 1 Thanked 48 Times in 34 Posts	That is a curly one. My gut reaction would be to put the pump in cooling mode (reject heat into the water) and to charge by monitoring the subcooling at the entry to the TXV. If it's not a reverse cycle heat pump then you will need to get the house nice and hot (or restrict the air flow to the internal coil to create about the highest head pressure you are likely to experience in operation) and then charge until you get at least 4K of subcooling at the TXV entry. Ideally you want the least you can get away with, but the conventional wisdom I've heard is about 4K. If your internal coil is higher than your evap & txv and you have little restriction in the liquid line (sight glass, filter, solenoid, whatever else) then you might get away with less. This is all theory absent any literature from the manufacturer telling you how to do it properly. I'd get the TXV changed, weigh the charge back in and use that as a starting point. If the fridgy is unsure of how best to charge it, explain to him it's just a normal split heat pump with one coil replaced by a HX, and ask him how he'd charge a normal unit.