Hpwh 2 (heat pump water heater #2) - Page 4

randen · 02-14-17, 07:31 PM

Idlemind

Did you experiment with the low end of suction pressures. The one I had built for my parents pressures were very low, start was 18 psi and climbed to almost 30 psi. I didn't monitor the high side. I was monitoring power used and heat gained.

Randen

Ron342 · 02-15-17, 07:46 AM

Man, you are persistant! And I bet this is not something you do for a living so you have to fight to learn it!
I keep looking at your suction pressure and , while it has come down, it still seems way high to me, as Jeff and Randen noted. That may be the key to better cop if you can figure it out. A sight glass is about $12 - and gives you a cheap look at whats happening.
Looks like a refrig compressor? Was it an r134 unit?
I am doing much the same thing as you but with a small ground loop for the evap water and a slinky coil inside the 80 gal water heater. I think you would get some immediate results from gettin a more stable evap heat source temp. That unit has got to be working to pull heat out of such rapidly declining water temp!

IdleMind · 02-15-17, 05:21 PM

You are right, I don't do this for a living and it is very new to me. I am a retired mechanical engineer and worked a lot of years on water meters and valves so I have an understanding of liquid flow. I've spent a lot of time running tests to find the effects of making small changes to improve performance, including recording and charting data. So the spread sheet work and record keeping comes naturally to me.

I've been shooting for 55/60 psi low and 250/300 psi high. That gives 33/37F evap temp and 127/142F cond temp. This keeps the evap from freezing and still gives enough delta T between evaporator and heat source water which in a typical 15 minute cycles runs around 45/52F. And gives a good delta T between condenser and water tank.

If you look at the photo of the installation, the evaporator is located straight down in the left side vertical tube, below the top horizontal tube. As the water temp drops convection flow gets going to circulate the heat source water.

Whenever I tried to lower P1 below 50psi it either caused the evaporator to freeze or it slowed refrigerant flow so the whole evaporator was not being utilized. But, I do believe a slightly lower charge to lower both P's just a little would help. It is a small refrigerator compressor and if I increase the cap tube restriction much it seems to slow the refrigerant flow down and drops the efficiency. There are certainly other improvements that I could hunt for.

When i had it on the bench I could make changes and run tests and collect good enough data for valid comparisons. Now with it installed those experiments are much harder to do. For now, I have other things I need to do so this will have to wait.

The compressor was running r134. I drained it, flushed with alcohol, and refilled with mineral oil.

jeff5may · 02-16-17, 09:48 AM

Well now... consider that most (R134a) refrigerators pull down initially to just above atmosphere, then run evaporator pressures between 0 and maybe 25 PSIG. The high side pressure floats with ambient temperature, and in your target range (hot water temp), R134a would be around 200 PSI. The compressor can obviously climb this hill, but it was designed for a lower pressure range. Its lower than optimal compression ratio is hurting your COP.

However, it is what it is and it does its job. If you're satisfied with the design, call it done and let it save you money. I doubt you have a leak, because if you did, the rig would go flat in no time.

Ron342 · 03-07-17, 08:05 AM

I wonder if anyone has built one of these using R134? Did you possibly try it before you converted to propane?
I have my small vertical ground loop pumping and am about to braze mine together but the idea of propane in my basement makes me edgy particularly since r134 can be had easily and i am not sold on using reclaimed r22 either.
To my inexperienced eye, the r134 pressures look better as well but with all this someone must have tried it or there's a bugga i can't see?
Does anyone know the btu rating of a fair sized residential refrig compressor (friges stand in rows like lost children at the dump) or of a hack that used r134?.

jeff5may · 03-07-17, 12:02 PM

Refrigeration/heating capacity would be smaller using R-134a than R-22 or R-290 using the same compressor. Most of the residential HP water heaters use R-134a.

IdleMind · 03-07-17, 02:52 PM

I did not try 134a. With the whole system containing only 3.0 oz of propane I do not have any safety concerns. And since I can't stop myself from tinkering with it, the propane is more convenient for me.

03-07-17, 08:05 AM	#35
Ron342 Apprentice EcoRenovator Join Date: Feb 2010 Location: Maryland Posts: 120 Thanks: 26 Thanked 12 Times in 8 Posts	Speaking of R134?? I wonder if anyone has built one of these using R134? Did you possibly try it before you converted to propane? I have my small vertical ground loop pumping and am about to braze mine together but the idea of propane in my basement makes me edgy particularly since r134 can be had easily and i am not sold on using reclaimed r22 either. To my inexperienced eye, the r134 pressures look better as well but with all this someone must have tried it or there's a bugga i can't see? Does anyone know the btu rating of a fair sized residential refrig compressor (friges stand in rows like lost children at the dump) or of a hack that used r134?.

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02-14-17, 07:31 PM	#31
randen Uber EcoRenovator Join Date: Apr 2011 Location: Strathroy Ontario Canada Posts: 657 Thanks: 9 Thanked 191 Times in 129 Posts	Idlemind Did you experiment with the low end of suction pressures. The one I had built for my parents pressures were very low, start was 18 psi and climbed to almost 30 psi. I didn't monitor the high side. I was monitoring power used and heat gained. Randen

02-15-17, 07:46 AM	#32
Ron342 Apprentice EcoRenovator Join Date: Feb 2010 Location: Maryland Posts: 120 Thanks: 26 Thanked 12 Times in 8 Posts	Man, you are persistant! And I bet this is not something you do for a living so you have to fight to learn it! I keep looking at your suction pressure and , while it has come down, it still seems way high to me, as Jeff and Randen noted. That may be the key to better cop if you can figure it out. A sight glass is about $12 - and gives you a cheap look at whats happening. Looks like a refrig compressor? Was it an r134 unit? I am doing much the same thing as you but with a small ground loop for the evap water and a slinky coil inside the 80 gal water heater. I think you would get some immediate results from gettin a more stable evap heat source temp. That unit has got to be working to pull heat out of such rapidly declining water temp!

02-15-17, 05:21 PM	#33
IdleMind Helper EcoRenovator Join Date: May 2016 Location: SE Wisconsin Posts: 55 Thanks: 3 Thanked 14 Times in 10 Posts	You are right, I don't do this for a living and it is very new to me. I am a retired mechanical engineer and worked a lot of years on water meters and valves so I have an understanding of liquid flow. I've spent a lot of time running tests to find the effects of making small changes to improve performance, including recording and charting data. So the spread sheet work and record keeping comes naturally to me. I've been shooting for 55/60 psi low and 250/300 psi high. That gives 33/37F evap temp and 127/142F cond temp. This keeps the evap from freezing and still gives enough delta T between evaporator and heat source water which in a typical 15 minute cycles runs around 45/52F. And gives a good delta T between condenser and water tank. If you look at the photo of the installation, the evaporator is located straight down in the left side vertical tube, below the top horizontal tube. As the water temp drops convection flow gets going to circulate the heat source water. Whenever I tried to lower P1 below 50psi it either caused the evaporator to freeze or it slowed refrigerant flow so the whole evaporator was not being utilized. But, I do believe a slightly lower charge to lower both P's just a little would help. It is a small refrigerator compressor and if I increase the cap tube restriction much it seems to slow the refrigerant flow down and drops the efficiency. There are certainly other improvements that I could hunt for. When i had it on the bench I could make changes and run tests and collect good enough data for valid comparisons. Now with it installed those experiments are much harder to do. For now, I have other things I need to do so this will have to wait. The compressor was running r134. I drained it, flushed with alcohol, and refilled with mineral oil.

02-16-17, 09:48 AM	#34
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Well now... consider that most (R134a) refrigerators pull down initially to just above atmosphere, then run evaporator pressures between 0 and maybe 25 PSIG. The high side pressure floats with ambient temperature, and in your target range (hot water temp), R134a would be around 200 PSI. The compressor can obviously climb this hill, but it was designed for a lower pressure range. Its lower than optimal compression ratio is hurting your COP. However, it is what it is and it does its job. If you're satisfied with the design, call it done and let it save you money. I doubt you have a leak, because if you did, the rig would go flat in no time.

03-07-17, 12:02 PM	#36
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Refrigeration/heating capacity would be smaller using R-134a than R-22 or R-290 using the same compressor. Most of the residential HP water heaters use R-134a.

03-07-17, 02:52 PM	#37
IdleMind Helper EcoRenovator Join Date: May 2016 Location: SE Wisconsin Posts: 55 Thanks: 3 Thanked 14 Times in 10 Posts	I did not try 134a. With the whole system containing only 3.0 oz of propane I do not have any safety concerns. And since I can't stop myself from tinkering with it, the propane is more convenient for me.