# Can you do geothermal heat pump building heating with just an existing water well?



## velvetfoot (Jan 12, 2012)

I have a well that is 450' deep.  Would it be possible to do geothermal heat with just that one well as well as continue to use it for potable water?


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## DickRussell (Jan 12, 2012)

Given that the water quality is satisfactory for passing through the heat exchanger of a GSHP, you need on the order of 80 ft of standing water column per ton (12,000 BTU/hr) of heat output. Without knowing just where the static water level is in your well and how much it drops during normal water usage, I'd guess that the well could support a four-ton heat pump. You'd need to have a proper heat loss calculation done for your house and have the whole situation evaluated by an installer who knows his stuff. Some would argue that you should spend the first money on improving the thermal shell of the house, to reduce the heat demand (locating and sealing air leaks, insulating the rim joist area and bare concrete basement walls, etc).


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## velvetfoot (Jan 12, 2012)

Good info, thanks a bunch!  I didn't think it'd even be possible.
I've done all the conservation stuff you mentioned.  I'm sure there's a little more to be done with air sealing, but not sure what could happen 
I'll have to check out the well conditions. 
As I understand it, a pipe loop would have to be dropped down the well-might get tight.  I can't imagine using the well pump as a circulator would be a good idea?


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## semipro (Jan 13, 2012)

Our ground source HP works like this.  Its called a standing water column system.  Ours is open loop so the same pump that supplies drinking water also flows through HP heat exchangers before being returned to a nearby sinkhole.  The water used to be returned to the well but we found it works better to return it to a sinkhole.  Our well is about 500 ft. deep.  The pump is set at 400 ft. and the water is about 200 ft. below the surface when no pumping is going on.  Our well flows about 10 GPM and has about a 1.5 HP pump.


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## Highbeam (Jan 13, 2012)

This open loop system seems to be a huge waste of potable water.


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## DickRussell (Jan 13, 2012)

Semipro's operation is called pump and dump. It saves needing enough water column to reheat the return water back to temperature by contact with the rock. That's why I said around 80 feet per ton is needed for the standing column well design where water is returned. With only 200 ft of water above the pump, that well can support perhaps 2.5 tons, or 30,000 BTU/hr sustained load. I'm guessing his heat pump is bigger than that, and that the house loses more than that on a cold winter night. He could get perhaps another ton of capacity out of that well by adding a 100 ft length of pipe to the suction side of the pump, capped at the bottom and perforated from say 20 to 40 feet up. That would force the return water down the extra distance below the pump, picking up extra heat from the rock, before entering the pump suction pipe. Still, 3.5 tons of capacity might be marginal, depending on the house.

There are various ways to address the pump issue when the well is used for both domestic water and circulation through the heat pump. One is to have a variable speed pump, which ramps speed up or down according to flow requirements. Another is to have the pump supply just enough pressure to circulate through heat pump and return to the well, with a booster pump on a side branch to provide higher pressure for the house plumbing. Of course there also is the need for a second pitless adapter for returning the water to the top of the well. Actually the return normally goes comfortably below the surface level in the well, which varies according to draw on the system at different times.


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## semipro (Jan 13, 2012)

DickRussell said:
			
		

> Semipro's operation is called pump and dump. It saves needing enough water column to reheat the return water back to temperature by contact with the rock. That's why I said around 80 feet per ton is needed for the standing column well design where water is returned. With only 200 ft of water above the pump, that well can support perhaps 2.5 tons, or 30,000 BTU/hr sustained load. I'm guessing his heat pump is bigger than that, and that the house loses more than that on a cold winter night. He could get perhaps another ton of capacity out of that well by adding a 100 ft length of pipe to the suction side of the pump, capped at the bottom and perforated from say 20 to 40 feet up. That would force the return water down the extra distance below the pump, picking up extra heat from the rock, before entering the pump suction pipe. Still, 3.5 tons of capacity might be marginal, depending on the house.
> 
> There are various ways to address the pump issue when the well is used for both domestic water and circulation through the heat pump. One is to have a variable speed pump, which ramps speed up or down according to flow requirements. Another is to have the pump supply just enough pressure to circulate through heat pump and return to the well, with a booster pump on a side branch to provide higher pressure for the house plumbing. Of course there also is the need for a second pitless adapter for returning the water to the top of the well. Actually the return normally goes comfortably below the surface level in the well, which varies according to draw on the system at different times.



That all sounds about right.  We use this system to maintain a temp of about 62-65 in the house then use a wood stove and small space heaters when needed.  

Our returning water to a sinkhole about 100 ft. away instead of to the well has the effect of extracting more heat from the aquifer.  

I've never heard it called "pump and dump" but that makes sense.  This site has pretty good descriptions of the systems including ours as a "standing column" system.
http://www.geoexchange.org/index.ph...eat-pumps&catid=375:geothermal-hvac&Itemid=32

The HP system has been operating for about 25 years and for at least the last 12 years the same pump has supplied HP and drinking water at 60 PSI max.  This is wasteful as the HP doesn't need that kind of pressure.  I'm just now converting to a system where I'm adding a booster pump for domestic use at 70 PSI and adjusting the pressure sensor to shut the well pump off at a much lower pressure (about 30 PSI).  I'm doing this to save energy and wear and tear on the well pump.  For various reasons, this makes more sense than going with a variable speed well pump.

I do have concerns about well contamination and so forth with this type of system.  If I ever have the need to trench around my place I might well consider converting to a closed loop system.


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## hemlock (Jan 13, 2012)

velvetfoot said:
			
		

> I have a well that is 450' deep.  Would it be possible to do geothermal heat with just that one well as well as continue to use it for potable water?



What is the physical size of your well casing?  If you use a closed loop system, you have to drop a "U-bend" down the well, along with the potable water line.  Might not be an issue at all, but might be worth a look.


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## maple1 (Jan 13, 2012)

Semipro said:
			
		

> DickRussell said:
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Why not just turn your pressure down? Our domestic water pump cuts in at 20psi & shuts off at 35psi. I can't imagine needing 60 or 70psi.


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## semipro (Jan 14, 2012)

maple1 said:
			
		

> Semipro said:
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Several reasons.  Our house is tall and you lose pressure with all the pipe and elevation. We also have an inline filtration system with a particulate filter in front and activated charcoal behind it.  There's pressure drop across both those.  Plus the pressure drops when the HP water valves open and water starts flowing to the HP heat exchangers.  

I've tried lower settings and the shower pressure is pitiful at the lower end of the pressure switch setting.


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## maple1 (Jan 14, 2012)

I've got filters too. A parallel pair of 5 micron sediment ones, in series to a parallel pair of charcoal ones. The only time the upstairs shower gets bad pressures is when the filters need changing (the charcoal ones seem to plug first). Might come down to what your use to though. We don't have 'water saving' shower heads. I could definitely see a drop when the HP comes on. How much does it flow? My buddy put in a ground loop 5 ton HP this summer, I'm waiting to see how much his electric bill ups when the winter's over. Very interesting but don't really want to tear up the yard & beyond like he did.


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## semipro (Jan 14, 2012)

maple1 said:
			
		

> I've got filters too. A parallel pair of 5 micron sediment ones, in series to a parallel pair of charcoal ones. The only time the upstairs shower gets bad pressures is when the filters need changing (the charcoal ones seem to plug first). Might come down to what your use to though. We don't have 'water saving' shower heads. I could definitely see a drop when the HP comes on. How much does it flow? My buddy put in a ground loop 5 ton HP this summer, I'm waiting to see how much his electric bill ups when the winter's over. Very interesting but don't really want to tear up the yard & beyond like he did.



I'm not sure what the HP flows.  I have a flow meter on it but can't remember the rate.  Its a split system too (upstairs/downstairs) so there are two valves and heat exchangers that that run in parallel.  If both of those run at once, and the pump is on the low end of the pressure cycle shower head flow is really low. 

One option for a geoexchange system is having boreholes drilled and the tubing placed vertically in those.  You still have some trenching though not as much.


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## gtjp (Mar 7, 2012)

I've tried lower settings and the shower pressure is pitiful at the lower end of the pressure switch setting.[/quote]






GEOjon:

GTJP

We found Sq-D has a reverse-acting pressure switch"  off at 30 on at 50   to cycle off GT systems at lower well pressure so you can finish a shower.
Then some bronze pumps (I also rep) can boost 16- any pressure 
 ... I have a customer wanting to sell an unused 2006 Grundfos 70 psi booster all SSteel for 18 GPM from 1/2 HP  (add a small bladder tank and they last a long time, over 10 years to - date , even though they are off the market~ might sell ~ 200 bucks, I might just buy it ! Plugs in 120, auto-sets not to get over 45 psi into it allows gt at ~30-45 settings at well switch with this booster. (VOLUME ? Or depth lifting water? Maybe already addressed, I'll read again)


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## Jerry_NJ (Mar 9, 2012)

Just reading for information and may have overlooked the answer to my point  First thing first, be sure open loop is allowed.  In NJ or at least where I live open loop to wells is not allowed, or wasn't 16 years ago.  My closed loop system has only slightly lower efficiency specs for closed loop, and mine are vertical and run deep into the water table.  My well pumps from about 100 feet.  I wonder too how much power it take to pump from 450', that is part of you efficiency equation. As a closed loop is pumping liquid around a "full" loop, it doesn't take as much power to move the liquid down the loop, or up the loop.  I think my pumps (I have two for a two stage heating/cooling design) are about 1/2 HP each.  

My 3 ton system delivers a COP of over 3.5 in stage two (the lower efficiency high output stage) with a closed loop temperature at 32 degrees.  I do not believe the loop has ever been that cold, but I do not have a temperature reading other than the temperature of the plastic (PVC) pipe under the insulation sleeve.    My design is 32 degrees when the HP is running 100% of the time in Stage II and it is supposed to keep the house at 70 degrees with the outside at 0 degrees (Fahrenheit).


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## gtjp (Mar 25, 2012)

Loop circs efficiencies are up to 23 + System "tons" per  hp of pump.

Fluid at 38-deg looping is more PD and less flow  than charts, and subtract 15% more for changes over time, looking at charts with your supplier-tech. 
For many years since the 1980 runs,  a cistern and a 1/2 hp well pump on an 18 gpm head , watching over-amping---  on1.1/2" lines getting nearly 6 gpm/"ton" -
worked well with a 3.1/2 Compressor-Ton (Todays rated 4-'ton') at a UNIT pressure-drop under 5 psi ( ~ under 12TdhWater)


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## gtjp (Mar 25, 2012)

NOTE:
Cold (well) ANY-loop summertime START WARNING:
cooling flow (cooling the Heat-Pump in condensing mode )  MUST have some method of shutting down -  slowing flow, or circs "OFF" at below 95 deg rfg ( keep 410a above condensing pressures of 290 psig)
either by T-In "300+ 'OFF' -upTO- 420 'ON'" PRESSURE -compressor-saver switch at hot gas valve for gauges, etc, elsewheres,  to SAVE COMPRESSOR

Too: IN HEATING MODE (GT "CHILLER" ACTING ON WELL LOOP)

view add-on plumbing, as a possibility to reduce well pump GPM:
Eficiency does fall by ~ 2.1/2% per NET MEAN- (avg) degree of middle temp of Water-IN less WATER Out temp differential...
IN 40-
out 36:  MID MEAN TEMP is 38
Below can drop that 2-deg,
but gives a working system...
(BUT NOT 2% better than NatGas Heating, in your above description, at OHIO's gas/electric COP and etc...GEOTHERMALLY.
SAVES outside water required:
by 'ripping' more heat off unfrozen water- at higher velocity (be careful, but works 'well' since 1981 installations):::

an "H" attached to inlet-outlet of GT Unit
a pressure-regulator by Parker, and a bronze- recirc pump like NRF-36, PL-36, or GFRos up26-116Bronze 230 v to compressor contactor, fused 10a, and all code, etc,,,
can be arranged with the pump on a nipple at "inlet" to GT; feedwater-circ into leg below the T (say right side of "H")
T- being mid-bar of "H" 'T-ing' in ...
and outlet from other (then upper left) side of "H", past "t-Bar", 
to finally passing out through regulator, set ~ 29.1/2 to 30-deg refrigerant, usually resulting in ~ 34 -deg discharge, from 36.1/2to 37.1/2-deg inlet temp, but whipping through a 3 - to -  ton unit at 22-24 GPM ( check mfg for 'erosion' gpm)
and how we got down from a 52-deg open well feed TO:  only 3.8 gpm needed at 52-deg well water, ( Heat Pump running over 100-degrees (R-22 200 psig) Head Pressure on gauges, suction above 30-deg barely.

With a closed looping well , you WILL have to set refg-press-flow-regulator to say 31-32 discharge, and but test and see after "on" an hour, what might freeze up at the instant all shuts off OR but a delayed-open-relay circuit in like blowers overrun in off of heating modes, for the circ-pump(s) say for 30-45 sec. after compressor is off-line, leaving cold refrigerant against the water-coil-hx section.

at unit little 1/6hp may greatly off-set other inefficiencies. These pumps last over 15 years, usually correctly applied. One 1983 System lost a GFos-bronze, 26 years later.
pH over 6.8
iron PPM under 3/4= .7~ (unless it is the non-dropping-iron, even 5PPM just a translucent film in 6 years, 'ferric' not 'ferrous')
hardness under 33 grains (thirty-three)

cooling flow (cooling the Heat-Pump in condensing mode )  MUST have some method of shutting down -  slowing flow, or circs "OFF" at below 95 deg rfg ( keep 410a above condensing pressures of 290 psig)
either by T-In "300+ 'OFF' -upTO- 420 'ON'" PRESSURE -compressor-saver switch at hot gas valve for gauges, etc, elsewheres,  to SAVE COMPRESSOR, or parallel a HIGH PRESS regulator sett at above 280-psig, discharge flow control of  of GT outlet.

geopros.org

jp


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