Heat extraction from deep well

kurtFisch

Hi all, I am designing a co2 heat pump system using a deep water well as a source for heating domestic and radiant floors. The 50f well water is rather hard so I would like to run a closed loop of 200 ft 3/4” copper loop submerged in the well water with 3 Gpm flow, what btu gain could be achieved? I could add a counter flow circulation of well water through an outer PE pipe if needed.
Any thoughts , Kurtfisch

ethicalpaul

There's a lot to unpack here. I don't know much about a co2 heat pump so I'll defer on that.

IMO you always want to run a closed loop. Even in areas where an open (pump and dump) system is allowed, you don't want it, and it sounds like you are already on board with that.

I don't think it's standard to use copper in the loop. Besides the expense, I'd be concerned about the longevity of it.

In my very limited experience, you can get 3 ton per 500 feet of vertical well.

leonz

You are going to waste good money doing what you propose.

You should be using the "Semi Open Loop Method" for heat exchange with black or blue polyethylene pipe and a submersible pump with a two tapping jet pump sanitary seal in the well casing to allow the well water to be returned to the well in the lower tapping of the sanitary seal.

Any water pumped out of the well will be returned to the well as hot water and sink back to the bottom
of the well to be chilled by the surrounding rock/gravel

The polyethylene pipe should have a check valve for every 100 feet of depth.

The deep well submersible pump has a check valve in the top of the 220 volt single phase submersible pump turbine stack.

The pipe string will need a torque arrestor, pump pulling rope, 2 wire pump wire and poly pipe centering discs that center the poly pipe in the well casing and also hold the pump wire in place to prevent it from being damaged while lifting the pump string out of the well and lowering the pump string in the well.

What is the static water level?
What is the pumping water level?
What is the actual well depth?
What is the pumping water level?
What is the drawdown? The drawdown is the difference between the pumping water level and the static water level.

How deep is the actual well casing??
Does the well have a well screen below the casing?
Is the well casing sunk in bedrock or glacial till/gravel?
Does the well water have colloidal clay in it?

We need more information from you for this.

ethicalpaul

Hmm, leonz that doesn't seem right:

> Any water pumped out of the well will be returned to the well as hot water and sink back to the bottom of the well to be chilled by the surrounding rock/gravel

He said he's using it for heating, so the water returning will be cooler

Also if you go with a closed loop, you won't need any check valves, nor a submersible pump. You just need a small loop circulator pump. You won't have to worry about a screen, you won't have to worry about clay in the water, or hardness. You won't have to worry about drawdown, or a pump string, or any of that.

Just drop a loop down the hole, fill the loop with clean water and you are done.

hot_rod

One loop in one well?

ethicalpaul

I had a 3 ton heat pump (not co2 heat pump mind you) on a single 500 foot well with one loop, yes. Were you asking me or the OP?

kurtFisch

Thanks for all the comments I appreciate it, more details.
As ethicalpaul pointed out heat only. And I agree with all his other points
I have reclaimed copper so other than scrap valve it is free to me and much better heat transfer.
Well is 350’ deep , static 40’ , cased to 40 ( 10 into shale) no clay but hard enough water that it would void most warranties.
My thought was to run poly to the well and down below the water level 10 ft or so then a 100ft leg down U and 100 back up that way the cool water would thermosiphone down to the bottom.
Another reason for closed loop is with a bit of antifreeze it is less likely to freeze in the evaporator if that’s a concern.
Not that anyone suggested it but Personally I think pump & dump is unethical and inefficient , unless you have an overflowing spring that’s already running free. Clean water is a finite resource.
Anyway, I digress, the main? Was what btu gain from 200’ of 3/4 cu or point me to the appropriate formula please.
Thanks,Kurt

leonz

kurtFisch said:

Thanks for all the comments I appreciate it, more details.
As ethicalpaul pointed out heat only. And I agree with all his other points

I have reclaimed copper so other than scrap valve it is free to me and much better heat transfer.


Well is 350’ deep, static 40’, cased to 40 (10 into shale) no clay but hard enough water that it would void most warranties.

My thought was to run poly to the well and down below the water level 10 ft or so then a 100ft leg down U and 100 back up that way the cool water would thermosiphone down to the bottom.

Another reason for closed loop is with a bit of antifreeze it is less likely to freeze in the evaporator if that’s a concern.

Not that anyone suggested it but Personally I think pump & dump is unethical and inefficient , unless you have an overflowing spring that’s already running free. Clean water is a finite resource.


Anyway, I digress, the main? Was what btu gain from 200’ of 3/4 cu or point me to the appropriate formula please.
Thanks,Kurt

You may be able to strip 3 tons of heationg and cooling from the 325 foot depth.

A closed loop like that will not transfer heat very well if at all.

The open loop method of heating and cooling works best with a free flowing year round water course or a deep water installation.

You need the actual well water to pass through the heat exchanger and return to the well and you will need to dig up the casing and install a 2 pipe jet pump sanitary seal unless you plan on insulating the two pipe trench to get it to work right using a 2 pipe jet pump with a split 2 pipe well casing cap.

You need to spend time with a water well driller not a geothermal well contractor.

kurtFisch

Thanks Leonz,
I agree that pulling well water directly from near the top of the well and returning to the bottom would be best, but it will have to go through a heat exchanger before getting to the heat pump because open loop with hard water voids the warranty.
I have excavation equipment & experience with well work so properly installing pit less adapters isn’t a problem . I will be burying the pipes and pit less adapters 6 ft under with line to well uninsulated to absorb heat and return Insulated .
I will sketch up a in well heat exchanger that should be high enough efficiency based on others I have built.
Back later, K

leonz

When implementing a drilled well for a heat pump it is a semi open loop.

Why build a heat exchanger when you can purchase a heat exchanger from the MESABI radiator people?

The well water used in the heat pump has to be pulled from the bottom to extract the energy from it and allowed to settle to the bottom and become cooled again.

Using a single 2 pipe jet pump pitless adapter is the simplest way to do this. All you need to do is let the return to well water pass through the lower jet pump pitless adapter and drain back into the well.
You do not need 2 pitless adapters for this.

ethicalpaul

I'm sorry leonz, that's not making sense. The water he is returning to the well (and I'll say again, the loop should be closed and not copper IMO, but setting that aside) is going to be colder than the water in the well.

You seem to be saying that the water being returned to the well is warmer and will be cooled by the earth, which would be true if he were running a chiller, but he is heating with this water, so it will be cooler when it goes back into the well.

If I'm misunderstanding something, feel free to let me know!

Maybe you meant to say something like "the well water used in the heat pump has to be pulled from the bottom to extract the energy from it, then returned to the top of the well in its cooler state where it will settle to the bottom to be warmed again" ?

hot_rod

Do you gave enough land to trench in some slinky loops?

kurtFisch

Yes Hot-rod , but I already have a well 50ft from the house that is not being used.

leonz

ethicalpaul said:

I'm sorry leonz, that's not making sense. The water he is returning to the well (and I'll say again, the loop should be closed and not copper IMO, but setting that aside) is going to be colder than the water in the well.

You seem to be saying that the water being returned to the well is warmer and will be cooled by the earth, which would be true if he were running a chiller, but he is heating with this water, so it will be cooler when it goes back into the well.

If I'm misunderstanding something, feel free to let me know!

Maybe you meant to say something like "the well water used in the heat pump has to be pulled from the bottom to extract the energy from it, then returned to the top of the well in its cooler state where it will settle to the bottom to be warmed again" ?

=================================================================

The deep well water has been pumped through the heat pump and returns to the top of the well and eventually drops to the bottom of the well to be cooled again before it is pumped back to the geothermal heat pump like the water furnace brand of heat pumps.

Look up Water Furnace heat pumps please.

leonz

kurtFisch said:

Yes Hot-rod, but I already have a well 50k from the house that is not being used.

This water well is 50,000 feet from the residence???

ethicalpaul

Well I installed one (granted it wasn't a Water Furnace brand) and used and monitored it for several years, and I'm pretty sure that when you heat your house with some water, that water is returned to the well cooler than it was taken out. But we might be talking past each other in some way I can't figure out so that's why I asked. Oh well, that will remain a mystery I guess!

leonz

kurtFisch said:

Thanks Leonz,
I agree that pulling well water directly from near the top of the well and returning to the bottom would be best, but it will have to go through a heat exchanger before getting to the heat pump because open loop with hard water voids the warranty.
I have excavation equipment & experience with well work so properly installing pit less adapters isn’t a problem. I will be burying the pipes and pit less adapters 6 ft under with line to well uninsulated to absorb heat and return Insulated.
I will sketch up a in well heat exchanger that should be high enough efficiency based on others I have built.
Back later, K

================================================================
Whose heat pump are you using??

Have you had the water tested for its hardness?? A heat exchanger of any type will NOT change the hardness of the water, it has to be done by ion exchange.

To obtain the highest energy extraction you need to pump cold water from the bottom of a well to allow the water to water or water to air geothermal heat pump to work well.

You need to read about the Water Furnace and the semi open loop method of geothermal heating and
cooling.

A small water softener would work for you in this case to solve the hard water problem.

kurtFisch

Ethicalpaul said “not copper IMO, but setting that aside) “
So what size polyethylene pipe has a coefficient of heat transfer that equals 3/4” copper?
And why do you think it would not last?
Just curious

ethicalpaul

For my well I think it was 1-1/2" but I think they told me that others use 1-1/4". My well was also grouted and the grout thermal transfer was tested by my engineer on installation day.

I don't know what size PE has a coefficient of heat transfer that equals 3/4" copper, but do you NEED a coefficient that equals 3/4" copper? My system had a 10 degree delta T that I was able to adjust just with a limiting valve after the pump (increasing head basically if that's the right term, to reduce flow rate). Granted my well was deeper.

It might last a long long time, but it won't last as long as PE that's a 100% certainty. And it could fail within couple years...didn't you say it was salvaged pipe?

A ground source heat pump system should last an easy 20 years without any service (and the loop will last much longer if it's PE), why roll the dice? Although if you do go with a semi-open scenario, a leak in the pipe won't matter anyway, I guess, but I would only use a closed loop.

leonz

It's not the pipe so much as it is the total length of the pipe run,
the size of the heating and cooling unit in "total tons" and the
fluid used in the system.

A friend of mine up the road from me has a geothermal-Carrier?
hot air furnace/whole house air conditioner which is connected
to a single buried loop 2 feet in the ground that is three thousand
feet long at a grass airfield they own to allow the ground to act
as the heat/cold transfer medium.

That heating and cooling loop is 3/4 black polyethylene pipe.

Using a water to water semi open loop system rather than a
closed loop water system will be easier to implement with a deep well.

Using a toro dingo with a trencher to lay poly pipe would work well if
there is enough open land and would have to be sized to work correctly
for heating and cooling.

Four feet in the ground around here the temperature is 52 degrees and
it is that temperature the year round.

If your ground has good soil that will shed heat from a long poly piping run
as well as bring chilled water or alcohol back in the cooling season all the better.


You need to visit the folks below to learn more.



www.ashrae.org

kurtFisch

Grouted vertical loops would need more depth for sure , they don’t have the heat transfer of a 6” diameter column of water in shale/ bedrock.
The reclaimed type m copper was only used for a couple years and judging from the tube in tube heat exchangers I built 40 yrs ago for my solar DHW and radiant floor heating is not leaking yet , I believe it will certainly outlive me.
Here in Vermont 5 ft would be considered minimum depth for a ground loop.
My water is over 250grains hard , one of the many reasons a closed loop is better is I can fill it with soft water with the proper PH so it won’t harm the evaporator in the heat pump . And even if I used the hard water it would be a small amount of water and therefore very little scale buildup. In a semi open loop the quantity of minerals would be constantly renewed
I have no need for AC where I live so I will only be taking heat out of the well and only when my solar does not have enough sun to heat the house & DHW.
Anyway thanks to you both for the conversation, I will post what I end up building when I have results to share. I n the meantime I f you would like to see some of my other creations you can check out Kurt Fischer’s solar greenhouse on my YouTube channel it turns to track the sun along with a parabolic trough water heater. also a bandsaw mill that I built .
K

ethicalpaul

Cool Kurt good luck and thanks! My system in CT did get to bedrock (and I assume water) by about 20 feet (they had to fill the loop with water to sink it) so I imagine that waterlogged grout was a pretty good conductor. I definitely had enough delta to drive the heat pump no problem.

Too bad you don't need any cooling, that's where the 50 degree water really shines!

kurtFisch

Thanks Paul , I found the information I was looking for on https://prcrepository.org to summarize in a 9’5” long tube in tube counter flow heat exchanger comparison of pvc to copper inner tubes pvc transferred 617 watts and the copper transferred 4761 watts.
That was with 1” inner tube and 2” outer tube with a 40 degree differential .
So I think I will start with a 100’ 3/4 copper inner tube flowing up to the house through the down flowing well water that will be piped to the bottom of the well. Will load the drawing tomorrow, K