Mini HPWH - Page 6

IdleMind · 10-11-16, 10:49 AM

This little device has been pumping along for over three months now. I have some data and observations about performance. Remember this is a 2.5 gal heater and only serves the kitchen and dishwasher, so not much volume of water. Here's a chart of data taken over the last month. It shows KWH and ounces of water removed per day. It also shows the basement temp which has been at 70F for most of the summer. but is now starting to drop, in January it will be down near 50F. The chart also shows a horizontal line representing the KWH that would be used when running with the resistance heater.

It uses about 60% of the electricity that it would use with resistance heat, not really great.
During the summer it also removes 30 ounzes of water per KWH. I have a good dehumidifier that removes 58 oz per KWH, so its about half as efficient as a good dehumidifier.
Where I live natural gas is less than half the cost of electricity for equal energy. I have a gas water heater which is probably about 85% efficient so in the summer I might save a little energy, but not much.

As the basement temp drops and the air gets drier this might not work well at all. But the resistance heater is in tact and I can easily switch back to that.

There are other benifits. First the temp is set at 100F, much lower than the main water heater. This temp is good for hand washing and rinsing dishes.
The biggest benifit is not pouring water down the drain while waiting for hot water to make it through 30 feet of 3/4 copper pipe.

randen · 10-11-16, 12:25 PM

Idlemind

Good work, it is saving you a few bucks. I made one for my parents. They rented a propane water heater so now they paid about $19-$24 per month depending on usage on energy costs and there rental costs were $22 per month. We have no idea how much the propane costs were. So that was a win. It will depend on a few factors on how many bucks will stay in your pocket.

Again good job!

Randen

jeff5may · 10-11-16, 03:57 PM

What? It lives? Awesome!

I guess there wasn't a leak, or the leak was plugged. So besides a learning experiment, the unit is slaving away, not dying. Good job.

IdleMind · 10-11-16, 05:51 PM

Yah, it's been working for about 3 months without adding refrigerant or getting any maintenance. It's such a small scale that it's not really saving anything I would call money. I like not waiting for hot water so much that I have been scraping up parts to make one for the bathroom sink.

I have seen the PT charts for propane/butane blends and am wondering if adding butane would allow the evaporator temp to be lowered for better heat transfer when the basement air temp drops into the 50's.

jeff5may · 10-12-16, 12:18 AM

Butane has a lower boiling point and saturation pressure than r-12 or r-134a, so you need a higher displacement compressor to move the same mass of refrigerant. To use a commonly available r-134a compressor, a propane / butane blend is perfect. Look around this forum, and you will find more info on performance of these "natural refrigerants".

IdleMind · 10-12-16, 08:13 AM

I have started building another HPWH, this has a 6 gal tank and a newer type dehumidifier. However the dehumidifier was using r22 so maybe not the best compressor for butane/propane blend, but that's what I got. I will be able to try various blends while it is still sitting on my work table. Sometime in the next few days I will start a thread for this project and post some photos.

IdleMind · 11-07-16, 08:48 AM

Two days ago I took some data on this little 2.5 gallon HWHP. It has been running without attention since 8/13/16 when the basement temp was 70F. Now the basement is 65F and the cold water is 62F. So I unplugged it and ran enough water through to lower the temp to 71.2F, then plugged it in and recorded data until it shut itself off.

Then I repeated the test but using the resistance heater to get a comparison and to check that my COP calculation was correct.

Here's a photo of current setup, on 8/13/16 I added gauges so I could check pressures without attaching manifold set which would leak out some gas. I don't really know if there is a small leak, but it has changed a little probably due to ambient temp and humidity being lower.

And here's the data, I am just now starting to do a COP calc so I don't yet have older data for comparison.

The "Step 4 COP" column is the COP between the row it's on and 3 rows up. This indicates how it changes as it's running. The SH has dropped over the last 3 months, with the colder ambient it needs more fan on the evaporator.

Anyway, I wanted to show how this is doing, I don't think COP of 1.77 is very good. But I am happy with this system for instant hot water and the savings from using lower temp water. It also shows the other one that I am working on needs a lot more development, but I can use this for comparison.

jeff5may · 11-08-16, 03:06 PM

Looks to me like the phase change heater is just about twice as efficient as the resistance heater. From this one-shot run, 243 is nearly twice 122. That's what the power meter counts anyway. I would be tickled with saving half (or even 40 percent long-term ).

Overanalyze the specifics and the following can be assumed: your refrigerant loop is probably more than twice as efficient, but some heat gets lost. Since the resistance heater is immersed in the tank, effectively all its heat goes in the water. Not so with the condenser loop. There is plumbing leading to and from the tank that radiates heat not into water.

IdleMind · 11-09-16, 08:32 AM

The thermostat is right over the resistance heater so it's in a hot spot and after shutdown the overall temp drops a bit. The condenser loop is opposite the thermostat so when it is shut down the temp rises a bit. I used the initial and final temps to calculate COP so the heat pump is 1.8 times better than resistance. And I am happy with that, it will be interesting to see how it does in late January when the basement temp is 55F.

Ron342 · 11-13-16, 08:08 AM

Here in southern Md, we don't have natural gas to compare our hpwh costs to and your numbers would make us happy campers, so congrats on a great project!
And thanks for all your careful logging and reporting of your progress and to those who helped you along.
Was looking at your data and it looks like the T drop across your condenser is pretty low which has got to be wacking your cop number as well as the roughly 30* diff between tank temp and T at the condenser, if i'm reading your chart right? I'm trying to get my head around it as it looks like the heat transfer from the tubing thru the solder to the tank wall would be very good and that there would be a lot of tank surface to then transfer it to the water so i can't figure why it doesn't drop the condenser T more?
Also there is a 4 channel temp logger on ebay for $15 delivered which runs on windows thru a serial port but no display on the logger, no probes and i don' t think it records unless connected to the laptop. Also another with display, bluetooth and probes for $55 so you could save some pencil time!
How did you measure water flow?

11-08-16, 03:06 PM	#58
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Looks to me like the phase change heater is just about twice as efficient as the resistance heater. From this one-shot run, 243 is nearly twice 122. That's what the power meter counts anyway. I would be tickled with saving half (or even 40 percent long-term ). Overanalyze the specifics and the following can be assumed: your refrigerant loop is probably more than twice as efficient, but some heat gets lost. Since the resistance heater is immersed in the tank, effectively all its heat goes in the water. Not so with the condenser loop. There is plumbing leading to and from the tank that radiates heat not into water. Last edited by jeff5may; 11-08-16 at 03:48 PM..

11-13-16, 08:08 AM	#60
Ron342 Apprentice EcoRenovator Join Date: Feb 2010 Location: Maryland Posts: 120 Thanks: 26 Thanked 12 Times in 8 Posts	From us non natural gas folks! Here in southern Md, we don't have natural gas to compare our hpwh costs to and your numbers would make us happy campers, so congrats on a great project! And thanks for all your careful logging and reporting of your progress and to those who helped you along. Was looking at your data and it looks like the T drop across your condenser is pretty low which has got to be wacking your cop number as well as the roughly 30* diff between tank temp and T at the condenser, if i'm reading your chart right? I'm trying to get my head around it as it looks like the heat transfer from the tubing thru the solder to the tank wall would be very good and that there would be a lot of tank surface to then transfer it to the water so i can't figure why it doesn't drop the condenser T more? Also there is a 4 channel temp logger on ebay for $15 delivered which runs on windows thru a serial port but no display on the logger, no probes and i don' t think it records unless connected to the laptop. Also another with display, bluetooth and probes for $55 so you could save some pencil time! How did you measure water flow?

10-11-16, 10:49 AM	#51
IdleMind Helper EcoRenovator Join Date: May 2016 Location: SE Wisconsin Posts: 55 Thanks: 3 Thanked 14 Times in 10 Posts	This little device has been pumping along for over three months now. I have some data and observations about performance. Remember this is a 2.5 gal heater and only serves the kitchen and dishwasher, so not much volume of water. Here's a chart of data taken over the last month. It shows KWH and ounces of water removed per day. It also shows the basement temp which has been at 70F for most of the summer. but is now starting to drop, in January it will be down near 50F. The chart also shows a horizontal line representing the KWH that would be used when running with the resistance heater. It uses about 60% of the electricity that it would use with resistance heat, not really great. During the summer it also removes 30 ounzes of water per KWH. I have a good dehumidifier that removes 58 oz per KWH, so its about half as efficient as a good dehumidifier. Where I live natural gas is less than half the cost of electricity for equal energy. I have a gas water heater which is probably about 85% efficient so in the summer I might save a little energy, but not much. As the basement temp drops and the air gets drier this might not work well at all. But the resistance heater is in tact and I can easily switch back to that. There are other benifits. First the temp is set at 100F, much lower than the main water heater. This temp is good for hand washing and rinsing dishes. The biggest benifit is not pouring water down the drain while waiting for hot water to make it through 30 feet of 3/4 copper pipe.

10-11-16, 12:25 PM	#52
randen Uber EcoRenovator Join Date: Apr 2011 Location: Strathroy Ontario Canada Posts: 657 Thanks: 9 Thanked 191 Times in 129 Posts	Idlemind Good work, it is saving you a few bucks. I made one for my parents. They rented a propane water heater so now they paid about $19-$24 per month depending on usage on energy costs and there rental costs were $22 per month. We have no idea how much the propane costs were. So that was a win. It will depend on a few factors on how many bucks will stay in your pocket. Again good job! Randen

10-11-16, 03:57 PM	#53
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	What? It lives? Awesome! I guess there wasn't a leak, or the leak was plugged. So besides a learning experiment, the unit is slaving away, not dying. Good job.

10-11-16, 05:51 PM	#54
IdleMind Helper EcoRenovator Join Date: May 2016 Location: SE Wisconsin Posts: 55 Thanks: 3 Thanked 14 Times in 10 Posts	Yah, it's been working for about 3 months without adding refrigerant or getting any maintenance. It's such a small scale that it's not really saving anything I would call money. I like not waiting for hot water so much that I have been scraping up parts to make one for the bathroom sink. I have seen the PT charts for propane/butane blends and am wondering if adding butane would allow the evaporator temp to be lowered for better heat transfer when the basement air temp drops into the 50's.

10-12-16, 12:18 AM	#55
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Butane has a lower boiling point and saturation pressure than r-12 or r-134a, so you need a higher displacement compressor to move the same mass of refrigerant. To use a commonly available r-134a compressor, a propane / butane blend is perfect. Look around this forum, and you will find more info on performance of these "natural refrigerants".

10-12-16, 08:13 AM	#56
IdleMind Helper EcoRenovator Join Date: May 2016 Location: SE Wisconsin Posts: 55 Thanks: 3 Thanked 14 Times in 10 Posts	I have started building another HPWH, this has a 6 gal tank and a newer type dehumidifier. However the dehumidifier was using r22 so maybe not the best compressor for butane/propane blend, but that's what I got. I will be able to try various blends while it is still sitting on my work table. Sometime in the next few days I will start a thread for this project and post some photos.

11-07-16, 08:48 AM	#57
IdleMind Helper EcoRenovator Join Date: May 2016 Location: SE Wisconsin Posts: 55 Thanks: 3 Thanked 14 Times in 10 Posts	Two days ago I took some data on this little 2.5 gallon HWHP. It has been running without attention since 8/13/16 when the basement temp was 70F. Now the basement is 65F and the cold water is 62F. So I unplugged it and ran enough water through to lower the temp to 71.2F, then plugged it in and recorded data until it shut itself off. Then I repeated the test but using the resistance heater to get a comparison and to check that my COP calculation was correct. Here's a photo of current setup, on 8/13/16 I added gauges so I could check pressures without attaching manifold set which would leak out some gas. I don't really know if there is a small leak, but it has changed a little probably due to ambient temp and humidity being lower. And here's the data, I am just now starting to do a COP calc so I don't yet have older data for comparison. The "Step 4 COP" column is the COP between the row it's on and 3 rows up. This indicates how it changes as it's running. The SH has dropped over the last 3 months, with the colder ambient it needs more fan on the evaporator. Anyway, I wanted to show how this is doing, I don't think COP of 1.77 is very good. But I am happy with this system for instant hot water and the savings from using lower temp water. It also shows the other one that I am working on needs a lot more development, but I can use this for comparison.

11-09-16, 08:32 AM	#59
IdleMind Helper EcoRenovator Join Date: May 2016 Location: SE Wisconsin Posts: 55 Thanks: 3 Thanked 14 Times in 10 Posts	The thermostat is right over the resistance heater so it's in a hot spot and after shutdown the overall temp drops a bit. The condenser loop is opposite the thermostat so when it is shut down the temp rises a bit. I used the initial and final temps to calculate COP so the heat pump is 1.8 times better than resistance. And I am happy with that, it will be interesting to see how it does in late January when the basement temp is 55F.