We have a well in our garage, apparently about 8m deep and with good water, although I would hesitate to drink it. it is tempting to use this as a source for a closed circuit heat-pump. Has anyone had experience of these devices?
Why complicate things ?
Air to air is so easy and practical.
Better cold season performance potential. Thats said I doubt 1 well would be sufficient.
Yes John, that’s what I was thinking.
Water supply is potentially limited but air is plentiful.
The winter down here has so far been quite cold and damp compared to previous years and my heat pump has been brilliant.
It doesn’t require a constant water supply its ground source heat but you do need the required area of pipes to collect it. Just the one well may not be sufficient, A chap I know in Wales had 6 wells dug. Only slightly more money than the one as equipment to site is the expensive bit, a few hours extra on more holes wasn’t so bad.
Where does the returning water go ? Surely, you would need another reservoir/well for the returning water, once heat had been extracted from it ? Or would you just throw it away ? I probably need to read up a bit more on how such systems work.
You don’t take the water, just the thermal energy from it (closed circuit heat exchange system)
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Yes, I understand that, but if the advantage of the closed circuit is the heat differential, surely extracting heat from the well water in the heat exchanger to return it to the same well is at best going to cause temperature layering in the well, and at worst lower the temperature even further in the well ? Is there something I’m missing ?
Is this what we’re talking about (closed loop single well GSHP/WSHP)?
The “heat” is replenished from the ground the water comes from. The earth below a few metres is generally at a fairly constant temperature, so the warmer ground heats the colder water. The deeper you go, the warmer it is.
But the well needs constantly replenished water. Without that the water in the well will just get colder and colder as the heat is taken from it.
For a water source you need a pond which has water flowing through it. See this example
Thats why I said a single well most likely couldn’t support the heating required.
One of my biggest regrets was not installing ground source heat pump tubing below the swimming pools we dug.
As a former caver, I can appreciate how warm it can get underground 
That still doesn’t answer my question about layering though. Presumably, if the well is fed from an underground current, it maintains, give or take, a constant level of water at a constant-ish temperature at that depth. Does the height at which I reintroduce the lower temperature water returning from the heat exchanger into the well make a difference, in order to avoid temperature layering within the well ? Do I need to agitate the water in the well to avoid layering, or is the layering effect insignificant due to the replenishment rate of the well ? I know I’m kind of obsessing over the details here, but genuinely interested as to the overall efficiency of such a system.
I’ve done a fair bit of caving in my time too.
As for a ground source heat pump using a well, the warmer water will be towards the surface, but it probably won’t make a whole lot of difference whatever depth as the water coming into the well won’t be from a single point
It might be worth reading this article Using Well Water for an Open Loop although I’ve no idea where the calculation of the figures comes from or how they should be applied (or even how relevant it is!)?
It uses American units. However 1 ton (refrigeration) = 12000 Btu (IT)/hour = 3.5kW
4.5 gallons = 20 litres.
The amount of water required for the operation of a geothermal heat pump on an open loop is 1.5 gallons per minute, per ton of capacity. For example, if you need a 3-ton geothermal heat pump, your water requirements would be 4.5 gallons per minute. The temperature of the water may increase the flow requirements. During heating mode, if the water temperature is lower than 41 degrees F, the flow must be increased until the leaving water temperature stays above the freeze protection settings. In warmer climates, during cooling mode, the water flow rates may need to be increased so the geothermal heat pump efficiency will be acceptable.
The annual amount of water used by a 3-ton geothermal heat pump is about one million gallons a year.
Heavens! What are we doing to our planet? Is that an ok thing to do?
To be fair there’s no actual shortage of water and it is naturally recycled with near 100% efficiency.
What there is, is a shortage of clean drinking water in many parts of the world and droughts in some areas as climate change alters the balance between wet and arid areas.
As to the heat pump:
Yes, but you need fresh warm(er) water coming into the well, so you need to remove some water - hence, I suspect, the calculations for open loop. If you just stick a heat pump heat exchanger down a well I think the most likely outcome will be a block of ice as there is no way to get enough new heat into the system - ground source is all about surface area, either spread out horizontally or vertically in multiple bore holes.
Per ton of capacity seems a very odd way of expressing it. SI units are easier by far.
Water has a heat capacity of 4.2J/°C/g - 1W of heat output (1 joule per second) needs 1g of water dropped by 0.23°C per second.
That is 3.6kg of water per hour (for 1W), if we make the drop in temp 40x the above (9.5°) then we need 90g per hour, make the output a more useful 15kW and that multiplies back up to 1350kg of water or 1350l if you prefer. So, yes, about 5 (imperial) gallons per minute.
That’s quite a lot of water!
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To start with, it isn’t being used up, just getting a bit cooler as the heat is extracted (and then the sun/earth core will reheat it.
Those are American gallons. According to Wiki an Olympic swimming pool (50m x 25m x2m) is 2,500,000 L (550,000 imp gal; 660,000 US gal) so you can imagine it isn’t much compared to the water in many rivers.
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Yes, however over-extraction of water from aquifers is a problem in many areas.
Sure, one guy and his heat pump might only use a couple of swimming pools worth a year
Now multiply that by a few million.
Not following here, are you just refering to the heat?
No, the demand for water if your population scale solution is open loop extraction from wells (i.e aquifers). Chances are the water would then be pumped into rivers and lost to the aquifer, but even if used for, say, irrigation (and also noting that the peak use - i.e winter won’t correspond to peak need for irrigation) it tends not to get back into the aquifer but evaporates.
Anyway that starts to drift away from ground source heat pumps.