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Any experts out there on Ground Source Heat pumps ? Hopefully we will be moving into a property shortly which is heated by a ground source heat pump, my challenge is that possibly the area I have earmarked for the new garage is also the area where some of the heat pump pipe array is so my questions are;

Can I 'float' a garage foundation slab over the array, the coils should sit at a depth of 1.2 Meters and I don't anticipate going that deep for the garage slab.

I believe that even if I could build over the array the 'shading' that this would create plus the general shading the garage would create with its shadow will reduce the efficiency of the array, so how practical is it to expand these arrays to take this into account.

From what I have read on the subject I could change the shallow array for a heat exchanger fitted in a bore hole but this could cost as much as £18K ! 

I know the easy answer is move the garage but unfortunately the site doesn't readily allow for this. 

I have also put calls out to a couple of local suppliers but 'non partisan' advise always welcome. 

 

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As the ground has been excavated to a depth of 1.2m the soil above is not stable enough  . You would need to go below the pipes to a stable foundation.

Interesting project though and will be interested in any replies you get.

Roy

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Graham

some things to consider

Firstly, have you good reliable evidence that the GSHP actually works as it should? Those at shallow depths are susceptible to surface ground water ........surface water is cold, rendering the system very inefficient.( An example, I have a well water supply and a bore hole to a depth of 165ft. Well water now is at 3-4 C , bore hole ,always, all year is 12C. If I ran a GSHP it’s a no brainer I would have to use a dedicated bore hole to maximise my heat gains. Using a slinky at 1.5m would be very inefficient as the water table is above this all winter.)

Secondly.Having established it works efficiently and effectively. (You need to see the electricity bills since installation by month. Also does the property have additional supplementary heating? If so why and how much does that cost?)  What ever you do you will need to ensure that you do not damage the slinky pipe work. This will result in you loosing all the glycol and a very expensive repair.

Third. Do you really want to bury under concrete a system that could need repair at some future date?

I use ASHP routinely in my business. GSHP are great if the ground conditions are perfect. They rarely are and I have seen some very expensive failures, due to inadequate assessment of the site and resultant installation of an inappropriate system.

Iain

 

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Not sure the flat array pipes at that depth are the most efficient. 
 

perhaps trade in for air source hear pump version as the garage is the critical aspect of this design and available space!! Just add solar to the garage roof. 

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33 minutes ago, iain said:

Graham

some things to consider

Firstly, have you good reliable evidence that the GSHP actually works as it should? Those at shallow depths are susceptible to surface ground water ........surface water is cold, rendering the system very inefficient.( An example, I have a well water supply and a bore hole to a depth of 165ft. Well water now is at 3-4 C , bore hole ,always, all year is 12C. If I ran a GSHP it’s a no brainer I would have to use a dedicated bore hole to maximise my heat gains. Using a slinky at 1.5m would be very inefficient as the water table is above this all winter.)

Secondly.Having established it works efficiently and effectively. (You need to see the electricity bills since installation by month. Also does the property have additional supplementary heating? If so why and how much does that cost?)  What ever you do you will need to ensure that you do not damage the slinky pipe work. This will result in you loosing all the glycol and a very expensive repair.

Third. Do you really want to bury under concrete a system that could need repair at some future date?

I use ASHP routinely in my business. GSHP are great if the ground conditions are perfect. They rarely are and I have seen some very expensive failures, due to inadequate assessment of the site and resultant installation of an inappropriate system.

Iain

 

Hi Iain I'm guessing it must work ok as this is the only source of heating the place has  doesn't even have a log burner (yet!) electricity works out at £2500 PA and thats everything apart from an LPG range cooker and an immersion heater,  currently I'm paying that for my LPG alone plus electric but yes take you point about burying the coil, the sellers are not aware of the specific location of the coils only that 'they are in that field there !" so I may have to get a GPR survey done to fine the exact location hopefully they are not where I want to stick the garage ! 

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Hi Graham, that’s a lot of electricity,have you seen the monthly analysis? 12000Kwh roughly. Is the domestic hot water not fed from the same heat storage tank as the heating system?

Do you know how old the system is? This is a field that shows massive advances in efficiency in the last few years. The C.O.P (coefficient of performance) of the heat pumps have improved very significantly. It would make sense to know how old your proposed system is and what it’s C.OP was when new.

Iain
 

 

Edited by iain
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1 hour ago, iain said:

Hi Graham, that’s a lot of electricity,have you seen the monthly analysis? 12000Kwh roughly. Is the domestic hot water not fed from the same heat storage tank as the heating system?

Do you know how old the system is? This is a field that shows massive advances in efficiency in the last few years. The C.O.P (coefficient of performance) of the heat pumps have improved very significantly. It would make sense to know how old your proposed system is and what it’s C.OP was when new.

Iain
 

 

Iain to be honest a lot of it is Vodoo to me from my understanding is that during the summer they use the immersion to heat the water rather than run the pump but during the winter the pump provides both heating and hot water system is 10 years old 

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Yup that sounds correct for usage months.........a 10 year old pump is OLD technology. I would want a heating engineer to assess that system and check it’s as efficient as it could be. Let’s face it it could be a negotiation point on purchase and you need to know the cost of the pumps replacement it could approach £10k for just the pump.The under ground stuff is probably fit for service, it’s the efficiency of the pump that’s very much in question.

Iain

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costings depend on square footage and cubic footage. So not really relevant as a judge.

I have had projects using both types and some with heat recovery systems as well. These properties all have under floor heating which dose not require excessive heat.

All seem very happy customers with the results.  I think that this is the way forward but would assume a secondary heating for the winter to give a boost would be good . wood burner etc

Just my views as not involved in the technical spec / fitting

Roy

 

Edited by roy53
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Oh correction from SWMBO the electricity bill was £2k not £2.5k

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21 hours ago, Hamish said:

Not sure the flat array pipes at that depth are the most efficient. 
 

perhaps trade in for air source hear pump version as the garage is the critical aspect of this design and available space!! Just add solar to the garage roof. 

My understanding is that ASHPs don't work effectively below 4 deg. C which makes them impractical in winter.  We used to have an apartment in Spain with an ASHP and it was great there, it was the A/C in summer and heating in Winter and only used moderate amounts of electricity.

Rgds Ian

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my only real experience with various heat pumps was swimming pool heating when i spec'd and sold commercial and domestic pools  and equipment in the 1980's

very much summer use unless an indoor pool when we had full air handling systems with heat recovery.

I'm quite out of touch now

H

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Absolutely  Ian, an ASHP in the UK climate is a challenge for domestic heating. COP is low with low ambient temperatures, hence the norm to have them feeding a calorifier, to store heat for when it’s wanted. The units I routinely use give the following results. At  air temperature of 4c the COP is 1 kw of electricity in to generate 3 kw of heat. COP being 1:3. At an air temperature of 15c the COP is around 8. That’s is 1kw  of electric in generating 8 kw of heat. At an air temperature of 25c they can be as much as 1:15. They are very effective if specified correctly.

The benefit of GSHP is that with a good installation  the ground will always be returning a source temperature of about 12c with little or no variation.

Iain

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We have a  140 foot borehole for our water supply. Is it feasible to  retro-fit a GSHP ?

Retro-fitting underfloor heating does not seem feasible, but beefing up insulation on external walls ( solid stone) could be done. Roughly how much bigger would radiators need to be (compared with oilfired c/h)?

Peter

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There is some info on radiator size here Peter:

https://www.castrads.com/uk/resources/how-it-works/hydronic-hot-water-radiators/

Basically it is down to water temperature.  Radiators are rated at 50C difference between room temp and water temp. Reduce that to 30C and the output drops by half so the rad would need to have twice the area to give the same heat output. 

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17 minutes ago, Peter Cobbold said:

We have a  140 foot borehole for our water supply. Is it feasible to  retro-fit a GSHP ?

Retro-fitting underfloor heating does not seem feasible, but beefing up insulation on external walls ( solid stone) could be done. Roughly how much bigger would radiators need to be (compared with oilfired c/h)?

Peter

Tks for that link Iain, an Open Loop system looks interesting https://www.gshp.org.uk/Open-Loop_GSHP_SouthEast_Domestic.html

-the discharge could be run into the stream 15 feet from the pump.

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45 minutes ago, RobH said:

There is some info on radiator size here Peter:

https://www.castrads.com/uk/resources/how-it-works/hydronic-hot-water-radiators/

Basically it is down to water temperature.  Radiators are rated at 50C difference between room temp and water temp. Reduce that to 30C and the output drops by half so the rad would need to have twice the area to give the same heat output. 

Tks Rob, that's doable. But we shall keep the log/coal burner for the black-outs when everyone is charging their ecars. Peter

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My eldest son lives in a large open plan house in rural Norway, his main source of heating is an air source heat pump backed up with a log burner. The heat is not delivered through radiators, instead they have a sort of AC unit that blows hot air around. At the moment his outside temperature is -8°C and the heat pump is working fine. This arrangement is the standard form of heating in his area as its cheap to install (a kit from the local DIY is about £3k). Ground or water source units are more efficient but more expensive.

I have seen retaining walls that are hollow and full of water being used as a water source pumps reservoir so long as its in a sunny place.

George 

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On 1/9/2021 at 11:41 AM, harlequin said:

My eldest son lives in a large open plan house in rural Norway, his main source of heating is an air source heat pump backed up with a log burner. The heat is not delivered through radiators, instead they have a sort of AC unit that blows hot air around. At the moment his outside temperature is -8°C and the heat pump is working fine. This arrangement is the standard form of heating in his area as its cheap to install (a kit from the local DIY is about £3k). Ground or water source units are more efficient but more expensive.

I have seen retaining walls that are hollow and full of water being used as a water source pumps reservoir so long as its in a sunny place.

George 

I don’t see how it could be a standard ASHP. It must have something special fitted because the physics doesn’t work for a regular one at -8 degrees. There’s no heat there to concentrate. 

Rgds Ian 

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