Dxgshpwh (ground source heat pump water heater)

[MEMPHIS91]

I remembered your advice and I was slowly backing the pressure down when the water temp was at 105F. Anything below 27psi the end of the cap tube would completely melt the frost off. Is that OK? It was still cold just not enough to freeze it. BTW someone asked awhile back about how much my power cost. Its at 11 cents a kwh. Yes I know that is really cheap compared to most people.

[BradC]

Originally Posted by randen

Memphis91

Your experiencing what I had seen with my build. More charge did not mean more heat just more current draw (more energy)

Except he did get more heat. The discharge gas did not get any hotter, but the condensing temperature was 113F and increased to 117F (210 vs 220 PSI). Not a massive, but a tangible increase.

[MEMPHIS91]

Yes I did get some more heat. Brad can you explain more why the txv is a bad idea. I understand it was not designed for this exact application, but I am thinking that being more adjustable due to changing water temp in the tank would be a good thing. Not disagreeing just curious.

[MEMPHIS91]

With the system back at 27 psi here is the latest run info.
Time in minutes - Water Temp in F - Watts used
0 - 68.5 - 0
30 - 70.5 - .13
60 - 72.9 - .26
90 - 75.7 - .40
120 - 78.3 - .55
160 - 80.9 - .73
180 - 82.5 - .84
210 - 84.9 - .97
245 - 86.7 - 1.15
270 - 88.4 - 1.27
295 - 90.4- 1.39

At this rate I will have to only shower every 4 days..... And the COP is not that great either.

[jeff5may]

The main difference between randen's rig and yours lies in the evaporator side. He used his existing evaporator, an air-source window unit with matching cap tube. Two thirds or better of his factory setup did not change drastically. He swapped out his condenser coil with the water heating tubing. I don't remember if he plumbed the condenser hx inline with the evaporator or not. Just like yours, it worked meh until he set the charge to the new conditions. Lots of testing and trials revealed the most efficient mass of charge for his unique rig.

With your rig, both sides of the circuit have changed. It looks like your condenser is doing great at lower temperatures, and will probably do just fine at operating temperature. The evaporator is anyone's guess, you are breaking ground here. I'm sure you can find research and white papers on this specific configuration of direct exchange boreholes somewhere on the internet. I have a feeling that your limiting factor, if pushed, is how much refrigerant you can push through the line until it burps. The borehole is a superconductor for your purposes and capacity. You are running an underground propane still.

Just for research purposes, you may want to take the three inch piece of cap tube you chopped off the factory tube and rig it in as a metering device. You will quickly find out if you can get enough mass flow to raise your suction pressure before the condenser runs out of liquid. From your limited data, it still looks like you have your charge way too low or a restriction somewhere. These cap tube systems are very predictable once you match the evaporator to the compressor.

To get more heat transfer, you need to move more mass. This happens with either more charge or less restriction. Given your recent data, your compressor rated for 400-500 watts is running at only 60% of its normal amps. That would be great if you were moving enough gas. You also moved a proportional amount of heat, around 2000 btu per hour plus losses. With 90 degree F water, your system should be in ramp-up mode. With a window ac or dehumidifier, this is where the unit frosts up the cap tube. Once the gas and/or liquid in the evaporator is sucked out, the condenser begins to back up with liquid and gain pressure, forcing more liquid thru the cap tube. You have not hit that point yet.

Again, for testing purposes, you can run this thing in electric element (or heat pump) mode for awhile until you get up to operating temperature. With these rigs, a few degrees in the right direction makes them act like they should. A few grams too much or too little refrigerant will throw them out of the sweet spot. This is why cap tubes are known as "critically charged" systems.

Just keep twiddling with it and soon you will gain knowledge and confidence. The numbers will tell the tale: pressures, temperatures, watts, etc. I have a feeling that you will figure out what to do sooner rather than later. Before you know it, your numbers will be good enough to leave it alone.

[MEMPHIS91]

My plan was to run the test til the thermostat turned it off. But the power went off and stayed off for an hour. So the last data I posted was all I have for that test.
Thanks for that last post Jeff, it was very helpful. I know how to put stuff together and come up with ways to make things work. But I should have said from the very beginning that I only understand the basics of a refrigeration cycle. The window unit hack looked awesome but I was not thinking messing with the evaporator would make so many more variables. This is a challenge that I am willing to try to tackle though, and have been doing a lot of research.
What you said about more mass flow makes sense to me. I might have good temperatures of 177F into the water tank, and 108F out, but the 177F might only go in a foot or 2 before cooling down to 108F therefore when my water was at 106, 2 degrees difference is not that much. That is why BradC was saying to increase charge because 110 is still 2 degrees more throughout the tank, therefore speeding up the heating rate.
But I can only push so much charge through the cap tube til the evaporator (borehole) starts to flood.
Therefore my goal should be to increase charge til the desired rate of heat exchange is happening or I start to flood the evaporator. If the heat exchange rate is not reached before that happens I need a more restrictive cap tube and try again.
I would be very interested in the other heat pump water heater builds and store bought ones to know the in and out temperatures of the condenser.
Am I interpreting all this info right or am I totally off track?

[AC_Hacker]

Originally Posted by MEMPHIS91

...Am I interpreting all this info right or am I totally off track?

I haven't run all the numbers yet but as you know, your rig should be doing better.

I'm wondering if the bore hole is able to yield heat as fast as the compressor can take it?

You have relatively warm soil, and 30 feet is a pretty good depth. Can you give some details on how you treated the hole-filling / grouting part of the project?

-AC

[MEMPHIS91]

Sure thing AC, I filled to about 10 feet from the top with pea gravel/limestone/powered lime, then I started mixing in sand with the pea gravel heavier and heavier sand til I got to about 2 feet from the top. Then I went with a layer of good ole Mississippi clay to the top. I hole is under a small paving stone patio I made a while back.

[randen]

AC

Memphis had measured the bore hole at 65.5 Deg. F and a suction temp. at the compressor at 65.5 Deg. F That is all excellent!!!!His suction pressure of 27psi is very close. I believe he needs to have some good data for 24 hrs with the temperature sensor in the bottom of the tank set at about 110-120 and see what the kill-o-watt will tell as the system holds the temp there.

Graph the information for a week adjusting very little to find a sweet spot holding a temp for the least amount energy, because this is how it will be operating in the real world.

Randen

[AC_Hacker]

Originally Posted by MEMPHIS91

Sure thing AC, I filled to about 10 feet from the top with pea gravel/limestone/powered lime, then I started mixing in sand with the pea gravel heavier and heavier sand til I got to about 2 feet from the top. Then I went with a layer of good ole Mississippi clay to the top. I hole is under a small paving stone patio I made a while back.

OK... Didn't you say something about hitting the water table at 8' down?

-AC