geothermal pond loop?

[Rob-D]

Here's a shot of the pump that was installed with my system. This is for 8 tons of cooling. I have a similar pump center for a 3 ton, and the only difference is it has only one pump on it.

The brass circles on the right are valves that come out on sides (well, top and bottom in this pix) that allow the water to be pumped in, air pumped out, and allow the methanol to be added to the system (as an antifreeze).

These are 240V pumps. They are labeled as drawing 1.8 amps each, listed as 377 Watts (yeah, the math doesn't quite work out....). You can also see the valves so you can work either the heat pump or the field independently.

IIRC, the system is pressurized at about 50 PSI. The two lines go outside, and the manifold pit is buried. It's clear from various posts that how and where the manifold is done varies greatly, and it's not too hard to figure out the pros and cons of each approach.

The wires above are not related, they go to the outbuilding. You can see the bottom of the gas tubes (just like telephone company uses) at the top of the picture. It was a big win running 5 3" pipes for 80 feet so they were way outside the perimeter of the house. It let this field be installed after construction, and let me get things to the outbuilding. I also ran a 3" electrical conduit. I mention this because nature abhors a vacuum, so while the ground is open thing about if there is anything else you want to put in there.

Pete

Hi Pete,
What I'm weighing is the difference in cost on a daily basis for a field or my well. That is, does the well that has higher temps(~55F) and the need to pump water up 175 feet every time the system calls for it cost more or less to run than pipes run out in my field or pond that are 6 to 7 feet down but only run ~42F? Also the fact that if there's a failure your pulling your well pump up.
Rob

 

[boggen]

Hi Pete,
What I'm weighing is the difference in cost on a daily basis for a field or my well. That is, does the well that has higher temps(~55F) and the need to pump water up 175 feet every time the system calls for it cost more or less to run than pipes run out in my field or pond that are 6 to 7 feet down but only run ~42F? Also the fact that if there's a failure your pulling your well pump up.
Rob

it is kinda comparing apple to oranges to a certain point.

#1 in diagram (pump is either in well or in house) there will be no difference between #1 in diagram and #3 in diagram and #4 in diagram exception friction loss of pipe, and possible thermal mass for heating and cooling.

#2 in diagram, has a pump located in bottom of well. and pumping water up to house. and then the return water is just falling back down into the well. this to me would be the worst when speaking $$$ both long and short term.

#3 in diagram is horizontal loops same as 1 and 4

#4 in diagram is vertical loops same as 1 and 3

in above i am looking at friction loss, or static head in feet loss, which can add up rather quickly. the more friction loss you have. more pump power you will need.

when both ends of pipe (sending and returning lines) both end below the water line in a well. there is no static head. but as soon as one or the other end of pipe ends up above the water line. then you end up with #2 in diagram.

 

[buckeyefarmer]

There are also vertical closed systems. My brother sells the equipment in Europe. They are popular because most houses sit on small parcels. They are tricky to design correctly due to the fact that wells are expensive. There is a fine line between overkill (costly) and proper function. He told me that they design them such a way that the well will be about halfway frozen at the end of the heating season.

Closed loop vertical and closed loop horizontal are designed the same. The length of the loops depend upon the thermal conductivity of the soil or rock you put the loop in. Rock has an average thermal conductivity of 1.4 and clay is .64 (Btu/hr ft F). With a vertical system you have to grout the hole after the pipe is installed, with a thermal conductive grout so it seals up the hole. Bentonite is normally used. With a horizontal loop you need good soil washed in around the loop pipes. You don't want rocks and even sand around the pipe, as it leaves air pockets. If you have a lot of large rocks, your installer will probably suggest vertical loops. A pump and dump, or open loop system, will require a much larger pump than the small circulation pump used in the closed loop system, so they are not as efficient, but as someone pointed out, the water temp will be constant, and a little better for heat transfer. The problem is the minerals in the water will wear out a heat exchanger much faster than a closed loop system, so the life of the equipment can be a lot shorter.

 

[Chilly807]

Closed loop vertical and closed loop horizontal are designed the same. The length of the loops depend upon the thermal conductivity of the soil or rock you put the loop in. Rock has an average thermal conductivity of 1.4 and clay is .64 (Btu/hr ft F). With a vertical system you have to grout the hole after the pipe is installed, with a thermal conductive grout so it seals up the hole. Bentonite is normally used. With a horizontal loop you need good soil washed in around the loop pipes. You don't want rocks and even sand around the pipe, as it leaves air pockets. If you have a lot of large rocks, your installer will probably suggest vertical loops. A pump and dump, or open loop system, will require a much larger pump than the small circulation pump used in the closed loop system, so they are not as efficient, but as someone pointed out, the water temp will be constant, and a little better for heat transfer. The problem is the minerals in the water will wear out a heat exchanger much faster than a closed loop system, so the life of the equipment can be a lot shorter.

My thoughts exactly.

Sean

 

[20 20]

A pump and dump, or open loop system, will require a much larger pump than the small circulation pump used in the closed loop system, so they are not as efficient, but as someone pointed out, the water temp will be constant, and a little better for heat transfer. The problem is the minerals in the water will wear out a heat exchanger much faster than a closed loop system, so the life of the equipment can be a lot shorter.

That is why I figured I'd go with a closed loop system, the water in this area is very hard. I don't know of one person within a couple miles that has nice clear water.

 

[eepete]

I had an open loop at the other house, got 12 years out of it. Shut it down because the well capacity was dropping. Put it in because it was easy (ran of of the existing well) and the switch to trying out a geothermal was a last minute decision. Vertical or horizontal, not much pipe cost difference on a closed loop and the pump is only combating friction, not always doing heavy lifting like a open loop from a well.

As for temperatures, there is a ton of YMMV due to latitude and soil differences. Here, ponds might be 40 degrees, horz. loops 51, and wells can run 55 or so.

On my horz. loop I put a light covering of fine clay over the bottom pipe in the trench. This was both to help the thermal conductivity as it was to protect the pipe from any rocks during the fill in. Most geo installers don't do this.
After fill in, I had a pump set up at the pond and flooded each trench many times with a few thousand gallons of water to help get all the air out as the silt from the clay filled any gaps. And of course there's no good way to verify how effective any of that was. It did take about 18 months for the trenches to finally settle out.

As for power cost differences, a 3 ton geo loop would need 1.8 amps on the loop pumps. A well pump (3/4 HP, 8 GPM for 150' well) would need about 6.8 amps. So it's an extra 1.2 KW for the well pump but you might be 5 degrees warmer than a horz loop. Close call since other factors like your cost of electricity, lower run time on the geo unit (due to more heat from the vertical well), possible additional cost of heat exchanger repair if it goes at 10 years on a system with a 20 year life, etc.

I think you could make the number go either way for you, but at the end of the day there are so many factors that are either estimates or SWAGs that it's hard to say. I think an advantage of the closed loop system is less uncertainty. You know how big the circulation pumps are. You don't have to worry about water quality and heat exchanger life. And the few things left that are uncertain are things you can't change like the temperature of the water you get from your loop. I've already weight in on my "I don't like ponds 'cause they're cold" viewpoint.

I suspect that if you knew the difference in water temperature that someone well versed in HVAC design could tell you the difference in run times for some scenario (like taking a 68 degree room of some volume to 72 degrees). You could then compute the electricity costs. But maintaining that temp would then require some knowledge of the cycle time/duty cycle and then you get too many variables such as house insulation, outside temperatures, house air leakage, wind speed and direction, etc.

At some point in every HVAC design, you're punting. It's just some folks are better kickers.

Answers are never easy, are they :laughing:?

Pete

 

[20 20]

Answers are never easy, are they :laughing: ?

That's for sure

 

[Rob-D]

Pete,

I think you hit the nail on the head with the uncertainty factor. How well the system holds up, basically avoiding premature trouble, is important to me. No one wants to be sitting in the middle of the winter with a compressor down!

Rob

 

[Redneck in training]

Pete,

I think you hit the nail on the head with the uncertainty factor. How well the system holds up, basically avoiding premature trouble, is important to me. No one wants to be sitting in the middle of the winter with a compressor down!

Rob

My geo has direct electric heat backup built in the hot/chilled liquid accumulator.

 

[Chilly807]

My geo has direct electric heat backup built in the hot/chilled liquid accumulator.

Mine does too, we used a 40 gallon electric hot water tank for an accumulator or "buffer tank". The elements are still in it and hooked up, just switched off unless they're needed.

Sean