Dxgshpwh (ground source heat pump water heater) - Page 14

stevehull · 06-10-15, 01:51 PM

Why is the COP so low? I would have though with an virtually infinite "sink" (expansion in cold highly conductive water) that a COP in the 4-5 range would be expected. There are no lossy heat plate of coaxial heat exchangers and the efficiency of the coil in the hot water tank has a very high dT indicating superb exchange.

With water that approaches the condenser temp (170F), I was expecting a decrease in COP, but only 2.5 to start?

Nothing wrong with something 2.5 times the efficiency of a resistance element! But as the hot water tank heats up, will this COP approach 1.0?

Concentrating water temp is a huge thermodynamic task.

How might this system of direct exchange be made better. I was hoping for 15-20K of BTU to come out of the hole.

Would a different gas work better than propane?

Thoughts?

Steve

AC_Hacker · 06-10-15, 08:04 PM

Quote:

Originally Posted by stevehull

...I was hoping for 15-20K of BTU to come out of the hole...

What exactly are you basing your hope on, Steve?

Is there any math that would support your hope?

-AC

jeff5may · 06-10-15, 08:05 PM

Oooh, those latest numbers look so, so good. you are now at the points where most engineers would stop optimizing the capillary tube size and move on to the charge. Your superheat and subcooling temperatures are beginning to converge at 30 to 35 degrees each. The COP has broken 3. This unit is now into the 1500 to 2000 retail price range, not counting installation. Awesome!

stevehull · 06-10-15, 08:13 PM

AC, I think you had the same thoughts on the efficiency being better than 2.5 or so. Rather than my math, here are your calculations on COP . . . (copied from your post)

CALCULATE COP

COP = (power-out) / (power-in)

COP = (4279.1 watts) / (1350 watts)

cop = 3.2

I think that your efficiency will be better.

Best,

-AC

stevehull · 06-10-15, 08:17 PM

AC, here is a post where you estimate 15,000 BTU/hr coming from the hole if only the bottom half is in water. Memphis said he has water up to within 6 feet of the surface, so perhaps 15,000 - 20,000 BTU/hr.

I think we agree, don't you?

Also consider if there is water in the bottom of the hole. Migrating or not, a massive body of water in direct contact with your copper pipe is going to transfer orders of magnitude more heat than dry or moist earth per square inch. 10 Meters of 1/4 inch pipe may be good for up to 15000 BTU/H if the bottom half of it is sitting in an aquifer.

MEMPHIS91 · 06-10-15, 08:38 PM

I have more data to post but want to touch on the things said so far.

Ac, Thanks for graphing the data, that is really cool. I'm going to print them so I can look all official when someone ask me about it.
That is some very interesting info from that article. You are amazing with math. And thank you again for the COP calculations. I do not think the numbers are that far off, I do think people underestimate just much heat can be transferred with copper tubing in water.
I held off really assuming too much til I got the system in its sweet spot. Your guess is not as far off as you might think (more on that soon(and I am using tabs this time))

Steven, I'm pretty sure Jeff answered all your questions WAY better than I could have. And I think you will be happy with the latest data. I can for sure say that my COP will not be anywhere near 1. (more on that soon)

Jeff, thanks for putting things in a way my brain can understand them. Your post the past few days have led to where this system is now. My fingers are crossed as well. I went a head and trimmed some more. System is running really well, kinda playing with the charge and fine tuning because this temp (112) is where it will probably be the most.

Ac, you said it well a few post back. Its amazing to see everyone pull together on this project. I owe a lot of people a beer.

jeff5may · 06-10-15, 09:45 PM

Like usual, AC has nailed the math and performance analysis of this setup. His two custom charts tell the story pretty well. Memphis did his homework on this one pretty well. The borehole is sized just about exactly for the intended load. What I see is a stable rig moving around 900 watts of heat or better going into the tank using around 400 watts of electric power. That's simply amazing for a first project!

Steve, to get 3 tons of capacity out of the ground, there must be enough surface area to gather heat with. Assuming the same conditions witnessed in this project, multiply by 9. 9 runs like Memphis has, spaced out enough not to interfere with each other. If you are shooting for a COP of 5, double that figure. Then you might not run out of evaporator surface area. If Mr. Memphis in MS had a larger compressor to bust or confirm the myth on this site, the ground might shake and rumble from what we might unleash! The main point here is that how much you want to get out of something depends on what you put into it. Too many owners regret not putting more ground loop into the earth at build time.

MEMPHIS91 · 06-10-15, 10:03 PM

ime in Minutes - Water Temp F - Watts - Borehole F - COP
00 99.5 00 63.5
30 103.5 .15 54.7 3.25
60 107.5 .34 51.8 2.56
90 111.5 .53 50.0 2.56
120 114.5 .72 50.0 1.93
150 118.5 .92 49.5 2.44
170 121 1.05 49.5 2.34

Just a note, all water temps were taken at about the half way point in the tank. The top of the tank was normally 3+ hotter.

Water temp in tank:107.7
Discharge line temp at entrance of tank:167
Line temp at exit of tank:117.2
Discharge temp at compressor: 169 @ 245 psi
Suction line temp at compressor: 64 @ 55 psi
Amps: 3.45 Borehole temp: 51.8

Water temp in tank:116.5
Discharge line temp at entrance of tank:175
Line temp at exit of tank:123.1
Discharge temp at compressor: 177 @ 262 psi
Suction line temp at compressor: 67 @ 54 psi
Amps: 3.55 Borehole temp:50

Water temp in tank:119.5
Discharge line temp at entrance of tank:176.5
Line temp at exit of tank:127
Discharge temp at compressor: 181 @ 272 psi
Suction line temp at compressor: 66 @ 55 psi
Amps: 3.62 Borehole temp:49.3

Charge of 5.7oz (weight)

I think my cap tube is just right. I'm gonna hook this tank into the main water heater tomorrow and just watch the savings happen. I also bought I kilowatt meter that will save the data when the power goes off so I can record usage over a long period of time.

I am humbled by this reading. And tank of hot water heated by sucking the heat out of a 30 foot borehole. The top reading is water temp the bottom is the bottom of the borehole.

AC_Hacker · 06-11-15, 02:02 AM

Quote:

Originally Posted by stevehull

AC, I think you had the same thoughts on the efficiency being better than 2.5 or so. Rather than my math, here are your calculations on COP . . . (copied from your post)

CALCULATE COP

COP = (power-out) / (power-in)

COP = (4279.1 watts) / (1350 watts)

cop = 3.2

I think that your efficiency will be better.

Best,

-AC

SH, this post was intended to illustrate how to determine COP, as I have done for many other hackers. These numbers were generated to aproximate what was realized from an ASHP hack in California. Nothing at all to do with your estimate of 15-20K of BTU from a 30 foot hole in Mississippi.

While it is true that I had an unexamined hope that the COP from this project would be higher... and it may prove to be higher yet. But if you bothered to read my post on this thread (#130) that compares historical studies to the results that MEMPHIS91 has gotten, I have cautiously de-rated my previous expectations.

My question is what is YOUR math that would lead you to your 15-20K of BTU out put? You are an engineer, right?

Quote:

Originally Posted by stevehull

AC, here is a post where you estimate 15,000 BTU/hr coming from the hole if only the bottom half is in water. Memphis said he has water up to within 6 feet of the surface, so perhaps 15,000 - 20,000 BTU/hr.

Where is the post you are referring to?

Quote:

Originally Posted by stevehull

I think we agree, don't you?

I do not think we agree. What would make you think that?

Quote:

Originally Posted by stevehull

Also consider if there is water in the bottom of the hole. Migrating or not, a massive body of water in direct contact with your copper pipe is going to transfer orders of magnitude more heat than dry or moist earth per square inch. 10 Meters of 1/4 inch pipe may be good for up to 15000 BTU/H if the bottom half of it is sitting in an aquifer.

First of all, it is true that wet sand conducts better than dry sand, and the difference is in the charts I posted above.

Second, wet sand is not a massive body of water. It concerns me that someone who claims to be an engineer would not know the difference.

Thirdly, do you realize that order of magnitude refers to 10X, and when you say "orders of magnitude" you are implying 10X, 100X 1000X and upward. We are not theorizing about celestial mechanics here, we are talking about a hole in the ground in Mississippi.

I am not seeing any convincing understanding of physics in your statements here, let alone math.

Do you actually have any information or math of your own that supports you expectation of 15,000 - 20,000 BTU/hr from a 30 ft hole?

Pretty simple question SH, from one engineer to another.

-AC

jeff5may · 06-11-15, 08:00 AM

Guys, it was me who made the exaggerated claims. This is what the people who are not scientists do to rile up the starving masses who do the labor. When the project is done, the scientists reconile the projections, claims, and the reality. If the project turns out as least as well as was projected, everyone is happy. This one has already done better than it should have on paper.

06-10-15, 01:51 PM	#131
stevehull Steve Hull Join Date: Dec 2012 Location: hilly, tree covered Arcadia, OK USA Posts: 826 Thanks: 241 Thanked 165 Times in 123 Posts	Why is the COP so low? I would have though with an virtually infinite "sink" (expansion in cold highly conductive water) that a COP in the 4-5 range would be expected. There are no lossy heat plate of coaxial heat exchangers and the efficiency of the coil in the hot water tank has a very high dT indicating superb exchange. With water that approaches the condenser temp (170F), I was expecting a decrease in COP, but only 2.5 to start? Nothing wrong with something 2.5 times the efficiency of a resistance element! But as the hot water tank heats up, will this COP approach 1.0? Concentrating water temp is a huge thermodynamic task. How might this system of direct exchange be made better. I was hoping for 15-20K of BTU to come out of the hole. Would a different gas work better than propane? Thoughts? Steve __________________ consulting on geothermal heating/cooling & rational energy use since 1990

06-10-15, 08:13 PM	#134
stevehull Steve Hull Join Date: Dec 2012 Location: hilly, tree covered Arcadia, OK USA Posts: 826 Thanks: 241 Thanked 165 Times in 123 Posts	AC, I think you had the same thoughts on the efficiency being better than 2.5 or so. Rather than my math, here are your calculations on COP . . . (copied from your post) CALCULATE COP COP = (power-out) / (power-in) COP = (4279.1 watts) / (1350 watts) cop = 3.2 I think that your efficiency will be better. Best, -AC __________________ consulting on geothermal heating/cooling & rational energy use since 1990

06-10-15, 08:17 PM	#135
stevehull Steve Hull Join Date: Dec 2012 Location: hilly, tree covered Arcadia, OK USA Posts: 826 Thanks: 241 Thanked 165 Times in 123 Posts	AC, here is a post where you estimate 15,000 BTU/hr coming from the hole if only the bottom half is in water. Memphis said he has water up to within 6 feet of the surface, so perhaps 15,000 - 20,000 BTU/hr. I think we agree, don't you? Also consider if there is water in the bottom of the hole. Migrating or not, a massive body of water in direct contact with your copper pipe is going to transfer orders of magnitude more heat than dry or moist earth per square inch. 10 Meters of 1/4 inch pipe may be good for up to 15000 BTU/H if the bottom half of it is sitting in an aquifer. __________________ consulting on geothermal heating/cooling & rational energy use since 1990

06-10-15, 10:03 PM	#138
MEMPHIS91 Journeyman EcoRenovator Join Date: Apr 2015 Location: Oxford, MS USA Posts: 496 Thanks: 69 Thanked 87 Times in 61 Posts	ime in Minutes - Water Temp F - Watts - Borehole F - COP 00 99.5 00 63.5 30 103.5 .15 54.7 3.25 60 107.5 .34 51.8 2.56 90 111.5 .53 50.0 2.56 120 114.5 .72 50.0 1.93 150 118.5 .92 49.5 2.44 170 121 1.05 49.5 2.34 Just a note, all water temps were taken at about the half way point in the tank. The top of the tank was normally 3+ hotter. Water temp in tank:107.7 Discharge line temp at entrance of tank:167 Line temp at exit of tank:117.2 Discharge temp at compressor: 169 @ 245 psi Suction line temp at compressor: 64 @ 55 psi Amps: 3.45 Borehole temp: 51.8 Water temp in tank:116.5 Discharge line temp at entrance of tank:175 Line temp at exit of tank:123.1 Discharge temp at compressor: 177 @ 262 psi Suction line temp at compressor: 67 @ 54 psi Amps: 3.55 Borehole temp:50 Water temp in tank:119.5 Discharge line temp at entrance of tank:176.5 Line temp at exit of tank:127 Discharge temp at compressor: 181 @ 272 psi Suction line temp at compressor: 66 @ 55 psi Amps: 3.62 Borehole temp:49.3 Charge of 5.7oz (weight) I think my cap tube is just right. I'm gonna hook this tank into the main water heater tomorrow and just watch the savings happen. I also bought I kilowatt meter that will save the data when the power goes off so I can record usage over a long period of time. I am humbled by this reading. And tank of hot water heated by sucking the heat out of a 30 foot borehole. The top reading is water temp the bottom is the bottom of the borehole. Attached Thumbnails

06-10-15, 08:05 PM	#133
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Oooh, those latest numbers look so, so good. you are now at the points where most engineers would stop optimizing the capillary tube size and move on to the charge. Your superheat and subcooling temperatures are beginning to converge at 30 to 35 degrees each. The COP has broken 3. This unit is now into the 1500 to 2000 retail price range, not counting installation. Awesome!

06-10-15, 08:38 PM	#136
MEMPHIS91 Journeyman EcoRenovator Join Date: Apr 2015 Location: Oxford, MS USA Posts: 496 Thanks: 69 Thanked 87 Times in 61 Posts	I have more data to post but want to touch on the things said so far. Ac, Thanks for graphing the data, that is really cool. I'm going to print them so I can look all official when someone ask me about it. That is some very interesting info from that article. You are amazing with math. And thank you again for the COP calculations. I do not think the numbers are that far off, I do think people underestimate just much heat can be transferred with copper tubing in water. I held off really assuming too much til I got the system in its sweet spot. Your guess is not as far off as you might think (more on that soon(and I am using tabs this time)) Steven, I'm pretty sure Jeff answered all your questions WAY better than I could have. And I think you will be happy with the latest data. I can for sure say that my COP will not be anywhere near 1. (more on that soon) Jeff, thanks for putting things in a way my brain can understand them. Your post the past few days have led to where this system is now. My fingers are crossed as well. I went a head and trimmed some more. System is running really well, kinda playing with the charge and fine tuning because this temp (112) is where it will probably be the most. Ac, you said it well a few post back. Its amazing to see everyone pull together on this project. I owe a lot of people a beer.

06-10-15, 09:45 PM	#137
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Like usual, AC has nailed the math and performance analysis of this setup. His two custom charts tell the story pretty well. Memphis did his homework on this one pretty well. The borehole is sized just about exactly for the intended load. What I see is a stable rig moving around 900 watts of heat or better going into the tank using around 400 watts of electric power. That's simply amazing for a first project! Steve, to get 3 tons of capacity out of the ground, there must be enough surface area to gather heat with. Assuming the same conditions witnessed in this project, multiply by 9. 9 runs like Memphis has, spaced out enough not to interfere with each other. If you are shooting for a COP of 5, double that figure. Then you might not run out of evaporator surface area. If Mr. Memphis in MS had a larger compressor to bust or confirm the myth on this site, the ground might shake and rumble from what we might unleash! The main point here is that how much you want to get out of something depends on what you put into it. Too many owners regret not putting more ground loop into the earth at build time.

06-11-15, 08:00 AM	#140
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	Guys, it was me who made the exaggerated claims. This is what the people who are not scientists do to rile up the starving masses who do the labor. When the project is done, the scientists reconile the projections, claims, and the reality. If the project turns out as least as well as was projected, everyone is happy. This one has already done better than it should have on paper.