boreholes for ground source heat pumps......

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"837 400 000 joules = 232.611111 kilowatt hours"

Close enough for jazz ... I used 0.00000027 as the conversion factor

8 decimal places obvioulsy isn't quite enough. B-)

Did you miss the change from 20,000 to 2,000 l/day giving 22(ish) kWHrs?

Reply to
Dave Liquorice
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Yes. Over 24 hours so extractable heat of 9.7kW. This still seems huge compared to calculations done by others in the original threads.

Reply to
Tim Lamb

Yes you can freeze the ground, which is not good as ice is a pretty good insulator and in the case of a ground water system stops the water flow...

The amount of heat gained is very low by the time you've moved it somewhere useful you've probably expended more enrgy moving it than you gained...

Reply to
Dave Liquorice

Not enough decimal places in the conversion factor I used. B-)

Well that is shifting 20 cu metres (20 tonnes) of water or nearly 14 l/min but haven't you just said you can only shove back 10,000 l/day so that limits things to half the above. It's also assuming that the temperature difference is 10 degrees, seems a reasonable but how practical?

Reply to
Dave Liquorice

I must look at this more carefully. The closed borehole system is subject to localised cooling and (I think) needs multiple holes to extract much heat.

However, the open system is only limited by the unlicensed volume which can be returned. ( The EA may veto or charge for volumes above 10cu.m)

I have a rather different situation in that my subsoils are linked to the water in the nearby river. A *well* 2m deep would easily supply

20cu.m/day. The return via an existing, mostly dry, drainage ditch should avoid the low temperature limitation imposed by the EA on discharges to streams. Just have to avoid upsetting any Water Voles or Great Crested Newts! 10 years ago I would have been looking to heat office/b&b space but, having just passed my biblical allocation, I think payback time is much too short. >
Reply to
Tim Lamb

I agree with Tim Lamb that the closed loop system does cause localised cool ing. As soon as the system starts it extracts heat from the liquid in the l oop and then recirculates the cooled liquid through the array of boreholes. Although the closed loop pipes are surrounded by thermally enhanced grout, the system must become more inefficient with use as the ground will be coo led by the colder liquid circulating though the pipes. The best case scenario would be to go for an open loop system and then have a discharge borehole above the aquifer so that it picks up heat from fissu res in the rock as it makes it's way back down to the aquifer. A system requires approximately 3 litres per minute to produce 1Kw, therefo re a 10Kw system will require a flow rate of 30 litres per minute. A "COP" (coefficient of proficiency) should be provided by an installer. A COP of about 4 should be aimed for, this means that for every Kw of power u sed to operate the system, the system will produce 4 kilowatts of heat. Met ers can be installed which measure the COP, although many installers don't bother. I suspect that this may be as they don't really care. If the COP wo rked out at 1, the whole system is an expensive waste of time. The EA may change the rules and up the abstraction quantities allowed where the water is recharged back into the aquifer. Although this is being consi dered I have no dates on when this will be announced. Due to the massive variations in geology across the UK some areas are ideal ly suited to this technology and in other areas it will never work efficien tly. I would therefore advise anyone contemplating such an installation to make sure that their supplier is prepared to guarantee a coefficient of pro ficiency which makes the project worthwhile.

Reply to
boreholedriller1

I did one of those lunch time CPD "courses" on commercial GSHPs few years ago. At that time I was told the EA were insisting....

Oh, hang on. The OP is Jim K. Forget that.

Reply to
Onetap

I would want to see a sensitivity analysis of the viability of the system.

- The design thermal output vs capital/ongoing expenditure (p/kWhr)

- The worst case thermal output vs capital/ongoing expenditure (p/kWhr)

What is wrong with a CO2 based air heat pump? The CoP is considerably better than conventional R410A, and likewise so is the price as in £4-9k. However in terms of viability I think parity is -2

5oC or so.

Equally, cost out new wallpaper and 80mm Celotex on the walls :-)

Reply to
js.b1

I would want to see a sensitivity analysis of the viability of the system.

- The design thermal output vs capital/ongoing expenditure (p/kWhr)

- The worst case thermal output vs capital/ongoing expenditure (p/kWhr)

What is wrong with a CO2 based air heat pump? The CoP is considerably better than conventional R410A, and likewise so is the price as in 4-9k. However in terms of viability I think parity is -25oC or so.

Equally, cost out new wallpaper and 80mm Celotex on the walls :-)

Yep they are available now. Aslo using propane as a refrigerant

Reply to
harryagain

As I understand it any air sourced heat pump has the same problem. If the weather is cool and damp (not common in the UK obviously) the cold end goes below freezing, water condenses out, and it freezes up. It then has to waste power to defrost itself.

Andy

Reply to
Vir Campestris

I have been running an air source heat pump for the last 12 hours and have zero ice on it so far. Lots of condensation but thats a good thing as its more energy extracted from the air.

Ice would be a good thing if they fitted a mechanical defrost as it would allow even more energy to be extracted.

Reply to
dennis

What's the air temperature?

I suspect this would be hard to do.

Andy

Reply to
Vir Campestris

About 4C in.

They do it on aircraft.

Reply to
dennis

So above freezing - which would stop it dead - but how cold is your cold end? If it's above freezing you can't be getting much heat out of it.

De-icing on aircraft wings used to be by rubber boots which they could pump up and deflate, the movement breaking the ice. Sometimes the ice would refreeze just out of reach of the boot :( I think these days they use engine bleed air, and mostly fly where it's too high and dry for it to be much problem.

Andy

Reply to
Vir Campestris

No idea, it feels very cold

Reply to
dennis

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