DX Geothermal Pond 4 ton Heat Pump

[daliti]

You don't need an oil separator as long as you have sufficient speed in your lines.
A coil of 70 m (+/- 200ft is max length as well) will extract +/- 2,5 to 3 kW.
We mainly use 1/2" coated Geocopper from Wieland for this.
Don't make two headers, only one on the suction with an oil syphon. At the inlet, a distributor on the outlet of the TXV with as many injections as you have crcuits of course.
We installed many DX/DX systems.

[jeff5may]

Originally Posted by daliti

You don't need an oil separator as long as you have sufficient speed in your lines.
A coil of 70 m (+/- 200ft is max length as well) will extract +/- 2,5 to 3 kW.
We mainly use 1/2" coated Geocopper from Wieland for this.
Don't make two headers, only one on the suction with an oil syphon. At the inlet, a distributor on the outlet of the TXV with as many injections as you have crcuits of course.
We installed many DX/DX systems.

How to post pics:

http://ecorenovator.org/forum/forum-...-pictures.html

So you're saying you need 70 meters of 1/2 inch dx pipe per ton? Seems like a lot.

For this setup, 4 tons of capacity equals roughly 14KW heat flow per hour. This would require 5 loops, 200 feet long each.

[daliti]

That's what we measure in the field after 15 years installing DX systems. Better a little to much than too less copper. Evaporating 1 K lower due to insufficient length results in 2 tot 2.5 % more energy consumption.

[ToddT]

Memphis91, please keep us posted on your earth tube research. I'm not too far south of you latitude wise, south Arkansas. My ancient sub-10 SEER central unit died this year and I'm researching options for replacement. My goal is energy independent... someday. For me, that's biofuels more than solar. But, energy efficiency is the first priority.

[MEMPHIS91]

Welcome Todd. I will be starting a thread on it soon, so far I know it will work, and that I will be doing a test with 2 tubes this fall when I install my DX lines for the 6,500 BTU heat pump greenhouse heater I am building.

[dhaslam]

I think that WyrTwister has a fair point about transferring water. The normal GSHP setup using a ground array and heat exchanger has two inefficiencies compared to DX. There is something like 10% of power needed for the circulation pump and perhaps 10% temperature loss at the heat exchanger due to it's size. There wouldn't be anything like these losses in a system that transfers water to a tank. If the tank is sunk to the same level as the pond the normal pond circulation pump will transfer at a rate more than ten gallons per hour per watt pump size and the DX system will work as in the pond but with less pipe.
Also you could add a small solar panel or any spare source of heat to boost the water temperature by a few degrees.

[WyrTwister]

You are suggesting , dig something like a well , for the water tank ? With the surface of the water , down there = to the surface level of the pond ? And let that be the tank ?

Had not thought of that . This would eliminate the pumping loss due to lifting the water the distance from the pond to the tank .

God bless
Wyr

[MEMPHIS91]

Daliti, so your saying it would be better to make a manifold near the compressor with a max of 200 feet of 1/2 copper loops. I would need 5 of them for 4 tons as Jeff said. Total elevation would be close to 20 feet is that ok in your experience? I still will want to use a henry oil separator, but knowing that any oil that gets by WILL make it back is a good thing. Only problem with 5 loops from the compressor is more digging, but that is doable.

I may be on grid longer than I thought. So I am picking this project back up but will be hacking my existing unit so that I can simply turn 2 ball valves and have the unit working like it was just in case this doesn't work. Then if money is available in a year or so I will do the the new indoor coils, 3 phase compressor, and vfd.

[mejunkhound]

I've only read the first few posts (up to pump and dump) and the last few.

Folks are greatly exagerating the amount of coaxial tube in tube evaporator needed for HP operation. The tube in tube when you are BOILING the refrigerant with water has a very high thermal transfer ratio.

I have 85 feet (only eighty five!)of 3/4 Cu water pipe inside 1-1/4 PVC water pipe, with a 9 GPM flow and 56F water intake. The high Reynolds number of the water in the annular space give a high thermal transfer. The 85 ft is comprised of 2 ea straight runs.

Have a 4T scroll compressor with R22 (R290 just as good) driving a 7.5T surplus condenser thru txv but charged for subcool so a few ounces of refrigerant pooled in the bottom of the condenser as a receiver.

I get 59,000 BTU/ hour out of this setup for 69F DB air inlet temp, and COP is 5.2 (not counting water pumping).

Think I may have put more info in another thread a couple of years ago, cannot find though.

BTW, I used old surplus water pipe for the evaporator, cleaned it with ferric chloride inside for a day then 1 hour rinse, and suction line filter - no problems last 5 or so years since built.

[jeff5may]

Originally Posted by mejunkhound

I've only read the first few posts (up to pump and dump) and the last few.

Folks are greatly exagerating the amount of coaxial tube in tube evaporator needed for HP operation. The tube in tube when you are BOILING the refrigerant with water has a very high thermal transfer ratio.

I have 85 feet (only eighty five!)of 3/4 Cu water pipe inside 1-1/4 PVC water pipe, with a 9 GPM flow and 56F water intake. The high Reynolds number of the water in the annular space give a high thermal transfer. The 85 ft is comprised of 2 ea straight runs.

Have a 4T scroll compressor with R22 (R290 just as good) driving a 7.5T surplus condenser thru txv but charged for subcool so a few ounces of refrigerant pooled in the bottom of the condenser as a receiver.

I get 59,000 BTU/ hour out of this setup for 69F DB air inlet temp, and COP is 5.2 (not counting water pumping).

Think I may have put more info in another thread a couple of years ago, cannot find though.

BTW, I used old surplus water pipe for the evaporator, cleaned it with ferric chloride inside for a day then 1 hour rinse, and suction line filter - no problems last 5 or so years since built.

That is one of the advantages of a pump and dump or recirculating loop system: Your primary heat water-to-refrigerant heat exchangers are much smaller. The best coax exchangers use corrugated tubes for the refrigerant side, and are almost as small as brazed plate exchangers. You either dump the waste water or have a secondary loop to gain or lose heat through.

These primary hx's need a water pressure source and shutoff control method to operate. Usually, this means a pump is needed, which adds initial equipment cost and perpetual power draw to the system. Some members have rigged thermosiphons to their rigs in order to eliminate the pumping requirements (heat pump water heaters/pool heaters) with resounding success. These rigs take a larger mass of water in direct contact with the tubing to transfer the heat through for the same efficiency and capacity as a forced-flow heat exchanger. The larger vessel and the added copper is comparable in price to the cost of a pump, but then there is no pump power draw to drag down efficiency and add running cost to the unit.

With the straight dx setup, there is no massive fluid flow to move the heat in or out through the pipe wall. The copper can conduct heat like crazy, but a heat gradient builds up between the ground and the copper that flows quite slowly. If there was a cheap material to use for a heat exchanger loop that could handle the pressure and was as noble as copper in the ground conditions, we could use it. Heat transfer ability is not as important; some companies have experimented with nylon and such for the outdoor loop with heat transfer figures close to that of copper pipe or tube. But copper pipe has proven itself to be durable, reliable, and not that expensive, so we use it.