DX Geothermal Pond 4 ton Heat Pump

[mejunkhound]

Have thought about using pex with bbq propane an big filter/dryer for DX system for the barn heat, never have gotten around to trying it. Pex only on evaporator, no reversing valve so pressure always at or below propane vapor pressure under 120 psi at 60F max ground temperature.

[MEMPHIS91]

So I've been doing some thinking, Jeff mentioned a long time ago about doing a dump and pump system. I didn't like this idea because I really didn't want to have to power a water pump 24/7 during the winter to keep things from freezing. BUT I was thinking today that if I had a way to make the pipe drain back into the pond via gravity after every time the system turned off then I wouldn't have to run it all the time.
My next concern was piping. I would need the pipe insulated even under the water, and insulation floats. I can always just add tons of weight but is there pipe insulation that doesn't float?
I'm thinking 2 coaxial heat exchanges with at least 15 gpm.
Water quality and quantity is not a problem, this is great water and pulling it from that deep it will not have leaves and stuff in it.
This is really starting to seem like the best option. DX is awesome, but the extra power the compressor takes to move that much refrigerant is about the same if not more than the water pump.
Also I was thinking of still using the air source coils on days that are warmer/cooler than the pond water. And just have some 4 way valves (like on my greenhouse dx build) the automatically swap the flow to the air coils or the pond depending on which one is warmer/cooler.

Ideas? Concerns?

[stevehull]

Memphis,

Let's continue your thought. Pump at water source and pump water uphill through the heat pump, overcoming both pipe resistance and gravity. Then provide an air break and allow the water to flow passively (gravity gradient) downhill back to the pond just overcoming pipe resistance. Sounds good, but it isn't.

By using a pipe system without an air break, the gravity gradient down will exactly balance out the uphill gradient. Then the pump only has to overcome the frictional pipe resistance.

Low flow rates through wide pipe over short distances results in very low frictional resistance.

I can do all the numbers for you (as you can), but you need only a tiny fractional HP pump to overcome pipe resistance. A far larger pump is required to pump water up a gravity gradient.

Stick with a closed (no air break) "pump and dump" . . . .

Steve

[MEMPHIS91]

Ok so your saying the pump would do better at the compressor?
I thought that it was harder for a pump to "pull" up hill than to "shove" water up hill. Totally not disagreeing you will forget more about geothermal systems than I will ever know.
From water level to the compressor is only 6 feet in elevation.
So if I bury my pipe at 4 feet deep with it super insulated, I only have about 1 foot of pipe and the coaxial heat exchangers that will be unprotected. Or could I insulated the crap out of them too? And if so would that be enough to keep it from freezing?
Thanks steven

[superlen]

Memphis,

Keep the pump near your pond and push the water uphill as you had planned. However, make sure that the pipe your pumping into returns all the way back down the hill to the pond. Do not let the water spill out at the top of the hill and run down in a trench.

In your case, the hill is only 6 ft (vertical, not horizontal) & by keeping the pipe closed and returning to the pond vs letting it flow down in a trench, the water in the pipe flowing down the hill will "pull" the water in the pipe up the hill. The pump will actually not be "pumping" the water up the hill, it will only be overcoming the friction in the pipe. If you used a trench, not only would the pump have to overcome the friction it would also have to pump water vertically 6' continuous and use a lot more power.

Note: with only 6' of head you could most likely place the pump anywhere in the circuit (not necessarily at the pond) & once it was primed (uphill pipe filled) it would have no problem moving the water.

Len

[MEMPHIS91]

That makes sense, and that was the idea to pipe it back to the pond, but to have to solenoid open after each run to let the pipe drain so it won't freeze. Then the valve would close and the pump would only have to run max power for maybe 20-30 seconds to fill the pipe back up when the system called for heat again.

Most open loop and even closed loop systems have to compressor and coils inside so freezing is not a problem, in my case everything is outside and will either need to auto drain or be super crazy insulated.

[MEMPHIS91]

I should totally be able to make this. 4 Ton Evaporator Coaxial Spiral Heat Exchanger Condenser | eBay

[superlen]

Originally Posted by MEMPHIS91

That makes sense, and that was the idea to pipe it back to the pond, but to have to solenoid open after each run to let the pipe drain so it won't freeze. Then the valve would close and the pump would only have to run max power for maybe 20-30 seconds to fill the pipe back up when the system called for heat again.

That makes sense. Good idea. I'm going to borrow it.

Since you will continually lose prime during normal operation, I would try to locate your pump at the pond so it will prime easily & fast. Hopefully, you have power down there close.

BTW, You also won't use hardly any power priming the line since it's only 6' of head. Calculate how many gallons are in that line from the pond to your evaporator, multiply that by 8.3 to get lbs of water , then by 6 to get ft-lbs. Take that and divide by 2655220 & you will have how many kwhr it take to prime the line. 1kwhr - 2655220 ftlbs.

Len

Len

[MEMPHIS91]

cool, I'll run the numbers, yes I was looking for a submersible pump with inlet and out ports. I would love to have into about 6 feet into the pond so it won't freeze.

[mejunkhound]

Originally Posted by MEMPHIS91

I should totally be able to make this. 4 Ton Evaporator Coaxial Spiral Heat Exchanger Condenser | eBay

Don't bother trying to coil it, simply use straight pipes, 180 deg bend at one end.


Own house has 5T HE, 80 ft of 3/4 Cu pipe inside 1-1/4" PVC pipe. 40 ft across basement ceiling and back. Sloped to control return oil flow of course.