Dxgshpwh (ground source heat pump water heater)

[MEMPHIS91]

Got some numbers for you. I charged up to 35 and let it run for 2 hours. With in 20 running at full charge my high side was right back at 185-190F. Coming back from the ground loop the line did start to condense which I think is a good sign but any cooling effect it has for the compressor is lost because its back warm again after making the wraps around the compressor.

Time (in minutes)- Power(in KWH)- Average water temp - bore hole temp
00 - 00 - 85.5F - 66F
30 - .25 - 89.8 - 65.7
60 - .33 - 91.6 - 65.5
90 - .51 - 94.4 - 64.4
120 -.69 - 99 - 64
150 - .88 - 102.2 - 62.7

I still think something isn't quite right. But much better than last night.

[BradC]

To be honest, unless the coil surrounding the compressor is pretty much bonded to the shell it's doing almost nothing for you. Radiant heat from the shell will superheat the gas in the pipe which will admittedly slightly cool the air between the shell and the pipe, You'd be so much better off just removing the pipe coil as the cool gas will do far more effective cooling of the compressor being piped straight into the shell (which is how the compressor is designed to work).

Now, your photo appears to be a rotary unit, so the suction gas does not get dumped into the shell but passes the compressor first. Cooler intake will still result in a cooler discharge.

[MEMPHIS91]

Yeah your very right. I had not thought about cooling needs until after the build. 190F for a discharge temp is pretty high. So tomorrow The coil will come off.

[BradC]

So that is about 87C. Most compressor data sheets I've checked seem to think that over 100 is worth worrying about (212F). It's hot, but it's not out of the ballpark for a refrigeration system.

This links suggests 225F is the limit A Look At Compressor Discharge Temperatures

This discussion has some good info and similar temps.
High Discharge Temperature

[MEMPHIS91]

I kicked it up to 40 psi last night before calling it a night. I was pulling 3.3 amps with the discharge at 275 psi. I'm thinking once I remove the coil going around the pump, the try even higher suction pressure. This build might need a larger compressor, or the cap tube more fine tuned.

[BradC]

Look, the reality is that a refrigeration system is a balance. A properly designed system will have a defined heat load on the evaporator, a condenser to suit and a compressor and cap tube to suit the required mass flow. Start with the heat load and work back.

Yours is kinda arse about, where you have an undefined evaporator load, an undefined condenser size and you are working with a fixed compressor size. The only variables at your disposal are cap tube and charge, but the reality is you don't want to be optimising the evaporator characteristics. You just want to optimise the COP.

We can get all scientific with looking at heat transfer coefficients, tube sizes and lengths and spend hours running numbers to allow you to buy the right compressor and size the cap tube right. Or you can just tweak the cap tube and charge to get it pretty good. Personally I'd do the latter, and I'd only start thinking about the cap tube if you just can't get it where it should be by charge.

It sounds like you are already well on the way. The two critical variables are :
A) Discharge temperature
B) Compressor power draw

As long as you keep both of those below the maximums on the compressor data sheet, then you can tweak to your hearts content. Do understand though that there is the old law of diminishing returns. Once you get it going "pretty right" with numbers you are happy with, further tuning will begin to consume more and more time for less and less gain.

Can you find a copy of the compressor data sheet and link it here for us to look at?

<edit> I've edited this because I forgot to give you a massive whack on the back and say "well done". You've already gone far past where your average beginner gets to and made a hell of an introduction. We just want to help you get it as good as you can so that your second attempt is even better.

[jeff5may]

Yes, the engineers will tell you this can't work, without all new everything. I tend to disagree. It all depends on how far you want to push your envelope.

A 5000 BTU compressor will move more than its rated capacity under some conditions. It will move less and less as the compression ratio increases. With your rig, you will probably not be able to fully work your borehole because it moves lots of heat. You can try to, though.

The condensing section in your rig will also be a superconducting heat well. Water absorbs lots of heat fast. The condensing pressure should closely follow the water temperature if the circuit isn't overcharged. The discharge temperature will be higher than normal because of the high superheat of the suction gas. Like brad said, set the charge at your max tank temperature to avoid cooking your oil or change metering devices.

To eliminate the metering device conundrum, install a txv. You can find them at surplus city liquidators or on eBay for under 20 bucks. Then set your discharge temp at max tank temp.

[MEMPHIS91]

Awesome info. Thanks Jeff and Brad.
So looks like I have some options all of which include taking out the coil wrapped around the compressor.
Option 1: Leave the current compressor and play with the cap tubes of different length and size.
Option 2: Put in a larger compressor (that I already have, the whole unit is rated at 880 watts.) and play with cap tube sizing.
Option 3: Leave current compressor and install TXV (that I picked up today)
Option 4: Put in larger compressor and TXV.

I'm really thinking option 3 or 4, but what are ya'lls thoughts?

Data I found on current compressor.


The TXV I got from one of my AC friends in town.

[randen]

Memphis 91

I've used the same size compressor 5000 BTU with a cap tube. Its working extremely well. I would go with option 3 A larger compressor will just cost more for operation. I think take a few days and with the Kill-o-watt meter and pencil slowly drop the charge and see what you get for energy in and energy out. Don't get too hasty. You may be adding some variables that could cause further complications. I would do some additional tests before adding the TXV valve.



Randen

[AC_Hacker]

Originally Posted by MEMPHIS91

...This build might need a larger compressor, or the cap tube more fine tuned.

I think you should stick with this compressor, and work with it until you get it to work as well as possible for you.

A smaller compressor, correctly set up will just take longer to heat the water. It's COP can be just as good, maybe better than a bigger compressor.

Don't be so quick to start throwing hardware at the problem.

-AC