11,000 BTU DX GEO Heating

[MEMPHIS91]

In my case I have a large "outdoor" coil. Just not the fancy expansion valve and compressor.
I am shooting for around a 1 ton compressor and txv. I believe this will be a middle-of-the-road size that will put out heat and have good efficiency. Again its all a guess. While I wait for a compressor I am going to tune the suction to around 95psi and the discharge to about 210. I believe that should be about right. Temps are still not low enough to need heat.
Thanks again for all the word pictures, it helps my brain process new concepts.

[jeff5may]

Good deal in your area:
Samsung Window AC 8000 BTU Air Conditioner with Remote

[MEMPHIS91]

Thanks, I sadly am an hour and a half from Memphis, THOUGH for $35 bucks its tempting!
Heat pump is pretty well tuned and ready for a cold night, the TXV came in today.

[MEMPHIS91]

I just ran a measured test on the heat pump heating the water tank.
Detail on the water tank. I have 275 gallon IBC tote with 70% of it buried in the ground with NO insulation around it. It got down to 45F last night.
I turned off the water pumps and ran the air pump for a minute before test to get a good temp reading for all the water. Water was 60.3F. I turned on the heat pump and it ran for 55 minutes til it hit 62.8F. It used .45 kwh of power. This was done with the sun still down so I was getting no help at all, in fact it was harder because the tank wasn't insulated.
CALCULATIONS.
275 gallons for water X 8.343 = 2,294.325 lbs
2,294.325 lbs X 2.5F change in temp = 5,735.8125 BTU
5,735.8125 BTU / watt power conversion of 3.421 = 1,676.64791 watts
1,676.64791 watts (power out) / 450 watts (power in) = 3.7258 COP

[Fordguy64]

Those are pretty awesome numbers.. Congrats!

[AC_Hacker]

Originally Posted by MEMPHIS91

275 gallons for water X 8.343 = 2,294.325 lbs
2,294.325 lbs X 2.5F change in temp = 5,735.8125 BTU
5,735.8125 BTU / watt power conversion of 3.421 = 1,676.64791 watts
1,676.64791 watts (power out) / 450 watts (power in) = 3.7258 COP

Music to my ears!

-AC

[jeff5may]

I believe you did better than your measurements depict. An hour is a long time to leak heat. For every 0.1 degF of water temperature lost to the ground or evaporation, that's 230 BTU of heat transfer not measured. This translates to a 0.15 reduction in apparent COP. I could see your IBC donating at least 125 watts to the ground in an hour. This small amount of heat would raise your COP above 4.

Another thing that bugs me is that according to your calculations, the compressor didn't put out its rated BTU's over the course of the trial. Considering a water heat source, buffered by ground, coupled to a huge water heatsink, the pot should have quickly found a balance point where it was moving lots of gas without using its rated power. Your kWh reading confirms this condition.

If you didn't lose 250 watt-hours of heat or better out of your IBC, there is something really wrong with the metering device or the charge. If the charge is right, you could use a longer cap tube. If the cap tube is right, there is either something non-condensible in the system, or too much refrigerant. If there were too much cap tube or not enough charge, your cap tube would be frosting up where it entered the evaporator,along with low suction pressure, and/or the compressor discharge line would not feel hot to the touch.

Please don't take this the wrong way. A COP close to 4 is pretty darn respectable. The numbers you posted suggest there is something missing somewhere,and I believe you can squeeze more out of this rig. Besides, I feel bad about having you chop up a perfectly good compressor.

[MEMPHIS91]

Jeff you are SO very right. That is why a 1 ton TXV is on my table right now. Just waiting on a better compressor. I am seeing better suction temps. Pond is still around 64F and the suction is right around 50F.

[jeff5may]

Originally Posted by MEMPHIS91

Jeff you are SO very right. That is why a 1 ton TXV is on my table right now. Just waiting on a better compressor. I am seeing better suction temps. Pond is still around 64F and the suction is right around 50F.

Without pressure numbers, there is no way of knowing what your superheat or subcooling conditions are. In the quoted post, there is no way to tell if your leaving gas is barely picking up any heat from the water, or is full of superheat. The heat transfer mechanism is more complicated than a liquid/liquid hx because of the latent heat component of the refrigerant. To find the saturation temperature which drives the latent heat flow in the evaporator, the suction pressure must be used to plug into a pt chart. Yes, you have a temperature gradient between the pond and the end of the tube, but how hard is the DX loop actually working? We can't tell.

Same thing on the other side, in the condenser loop. Without knowing the discharge pressure, along with the liquid line temperature, there is no way to tell how much desuperheating vs. latent heat transfer vs. subcooling is occuring.

A TXV will take care of the evaporator side of this balancing act for you if you rig it up correctly. The sensing bulb vs. the equalizer port pressure will maintain as much heat flow as possible, while still maintaining a set level of superheat in the loop. The 1 Ton one you bought will work with your 2/3 Ton compressor just fine. On the condenser side, the subcooling can be tweaked by adjusting the charge quantity.

[MEMPHIS91]

Jeff, You are exactly right as normal, I took no readings from the system during test(I was in a hurry). AND I know I can get more out of this system. I really would like a larger compressor before I do too much tuning though. I was heating the greenhouse for .25kwh with the 10.5BTU compressor and now I using over 7kwh with the 7.5BTU.
I do know the intank coil is working nicely because just feeling of it by hand. The line coming out is the same temp as the water.
I still think my discharge pressure is too high (210psi), but my cap tubes are still restricting too much.

So I wait for compressor, but if it is more than a week I may just go ahead and put the TXV on. This txv has no external equalizer port. I know only what I have read about the though, so I may have no idea what I'm talking about. I bought the one you linked me too. In has inlet and outlet and the sensing bulb.

Thanks again for all your good advise, I can't wait to hit 5 cop when this system is running right.