Ground Source or Air Source Heat Pump?

[diablo_pete]

Hi guys.

Assuming my plot is big enough for either option and the property isn't for my own occupation, does anyone out there have enough experience to give advice regarding which way they would go? Concerned that the garden will take too long to recover from works required for ground source and that air source may no be up to it?

Need around a 15KW single phase system.

Thanks

[JCB123]

From experience of fitting both in projects I've managed, both around 14kW, the air source was much cheaper, but has been less reliable and often needs boosting with the gas boiler, especially over last winter.

The ground source seems to be much more efficient, providing a good constant temp.

Both sites were new builds so the sites were completely stripped and turfed, so don't really know about recovery times........

Sorry I've just waffled and not really given you an answer....

[diablo_pete]

JCB123 said:

From experience of fitting both in projects I've managed, both around 14kW, the air source was much cheaper, but has been less reliable and often needs boosting with the gas boiler, especially over last winter.

The ground source seems to be much more efficient, providing a good constant temp.

Both sites were new builds so the sites were completely stripped and turfed, so don't really know about recovery times........

Sorry I've just waffled and not really given you an answer....

Thanks for the response. I guess I thought as much. My trouble it over an acre of land is being used by the ground array. So long as it's worth it and I'm not discounting air source without reason, it's ok I guess.
This is newbuild too.

Thanks again.

[herewego]

Don't like to state the obvious but the first priority is to maximise the insulation.

[caziques]

JCB123 said:

From experience of fitting both in projects I've managed, both around 14kW, the air source was much cheaper, but has been less reliable and often needs boosting with the gas boiler, especially over last winter.

The ground source seems to be much more efficient, providing a good constant temp.

Both sites were new builds so the sites were completely stripped and turfed, so don't really know about recovery times........

Sorry I've just waffled and not really given you an answer....

There are times an air sourced unit in the UK will struggle - but they are a lot cheaper than ground source. There is no correct answer - just a variety of solutions based on the available criteria.

One important factor that you may overlook.....

An air sourced unit is best run during the day (more efficient) - and the energy stored in a thick floor slab (at least 100mm thick). Ground source gives you more options as it can be used as a conventional heating system with the floor pipes in a thin screed (you are going to fit pipes in the floor aren't you?).

[Tuna]

I'll assume you've done all the analysis on alternatives - you'll know that heat pumps are expensive to install, produce relatively low grade heat and only serve to bring the cost of heating with electricity down to roughly that of mains gas.

You really need to speak to someone who has the same make/model of kit you're planning to install. The theory is all well and good, but variations in real-world performance are not trivial, so your installation will be as strongly affected by the quality of the kit and your installer as the difference between air and ground source pumps.

You might want to consider a combined heat source - using a thermal store to mix heat from a variety of sources - which gives you more flexibility and less dependence on a single supply.

Incidentally, you could investigate vertical bores for ground source, which may reduce site disturbance. Also search out GetCarter on here - his self-build build uses a heat pump I believe.

Good luck.

[JCB123]

Agree with the above, a comined heating system with thermal store is a great option, and heat recovery is also fantastic.....there is so much out there, it's really worth spending some time with a reputable heating contractor to find out which system suits you the best....

[RedLeicester]

JCB123 said:

Agree with the above, a comined heating system with thermal store is a great option, and heat recovery is also fantastic.....there is so much out there, it's really worth spending some time with a reputable heating contractor to find out which system suits you the best....

Then when you have finished asking him, ask another one. We spent the last 8 months researching GSHP/ASHP and other such systems, along with thermal stores, vented and unvented DHW and sealed or unsealed heating systems.... coming off heating oil, anything was going to look good financially, but no matter how hard we tried, we simply couldn't get the heatpump figures to stack up - the systems themselves were "relatively" affordable, simple enough, but the colossal changes we'd need to make to the house in renovation terms in order to make them actually have one iota of hope of being efficient were horrific: overall the cost spiralled from around £18k for the GSHP boiler, coils, associated paraphenalia and so on, to nearer £60k for the "finished" house ready to cope with it.... even with a £4k a year oil habit, that was simply too much to stomach, especially as it still left us facing a £1600pa electricity bill to run the pumps...

We ended up going with a biomass system - slightly higher install cost on day one, but zero/minimal running costs, will pay back in just over 5 years, and plugs straight in to the existing heating system with no modifications. Result.

[herewego]

RedLeicester said:

JCB123 said:

Agree with the above, a comined heating system with thermal store is a great option, and heat recovery is also fantastic.....there is so much out there, it's really worth spending some time with a reputable heating contractor to find out which system suits you the best....

Then when you have finished asking him, ask another one. We spent the last 8 months researching GSHP/ASHP and other such systems, along with thermal stores, vented and unvented DHW and sealed or unsealed heating systems.... coming off heating oil, anything was going to look good financially, but no matter how hard we tried, we simply couldn't get the heatpump figures to stack up - the systems themselves were "relatively" affordable, simple enough, but the colossal changes we'd need to make to the house in renovation terms in order to make them actually have one iota of hope of being efficient were horrific: overall the cost spiralled from around £18k for the GSHP boiler, coils, associated paraphenalia and so on, to nearer £60k for the "finished" house ready to cope with it.... even with a £4k a year oil habit, that was simply too much to stomach, especially as it still left us facing a £1600pa electricity bill to run the pumps...

We ended up going with a biomass system - slightly higher install cost on day one, but zero/minimal running costs, will pay back in just over 5 years, and plugs straight in to the existing heating system with no modifications. Result.

I assume you are burning your own wood as logs or do you chip it?

[RedLeicester]

herewego said:

I assume you are burning your own wood as logs or do you chip it?

CHoice - pellets bought in should we so wish, our own logs (so the "cost" is my time, two stroke, diesel, and repeated chain sharpening!), or bought in logs at around £30 a ton.

[diablo_pete]

Thanks for the advice guys. Still in a spin, and with the plumber now on first fiz (underfloor heating already in), I need to toss a coin I recon.

[JCB123]

diablo_pete said:

Thanks for the advice guys. Still in a spin, and with the plumber now on first fiz (underfloor heating already in), I need to toss a coin I recon.

Be careful if the UF is being installed now, as the heating system you decide to install may have different requirements for the centres that the UF heating pipes are installed at (for example UF connected to a gas boiler doesn't need the pipes as close together as those connected to an ASHP for example).......

[JM]

JCB123 said:

diablo_pete said:

Thanks for the advice guys. Still in a spin, and with the plumber now on first fiz (underfloor heating already in), I need to toss a coin I recon.

Be careful if the UF is being installed now, as the heating system you decide to install may have different requirements for the centres that the UF heating pipes are installed at (for example UF connected to a gas boiler doesn't need the pipes as close together as those connected to an ASHP for example).......

As above.

If the pipes are in the floor you are restricted to the spec they were installed for.

Air source units are cheaper to buy and install, but slightly more expensive over a year to run. Though in this weather they will be more efficient than a ground source but will be less efficient in winter.

[herewego]

diablo_pete said:

Hi guys.

Assuming my plot is big enough for either option and the property isn't for my own occupation, does anyone out there have enough experience to give advice regarding which way they would go? Concerned that the garden will take too long to recover from works required for ground source and that air source may no be up to it?

Need around a 15KW single phase system.

Thanks

Does that mean you're looking for about 50 kW of heating power? That seems a heck of a lot. Are you sure you've got the insulation level right?

[JM]

herewego said:

diablo_pete said:

Hi guys.

Assuming my plot is big enough for either option and the property isn't for my own occupation, does anyone out there have enough experience to give advice regarding which way they would go? Concerned that the garden will take too long to recover from works required for ground source and that air source may no be up to it?

Need around a 15KW single phase system.

Thanks

Does that mean you're looking for about 50 kW of heating power? That seems a heck of a lot. Are you sure you've got the insulation level right?

No he needs a 15Kw rated unit, i.e one that produces upto/around 15Kw, depending on the conditions. not one that draws 15Kw of energy to run.

Edited by JM on Wednesday 27th July 17:46

[Throttle Body]

I looked into this at length before my new build. If you have access to mains gas, gas is more efficient than an ASHP. GSHPs are better, but you need a really big ground area free from trees, and the garden will be completely trashed to install it. I decided to go for gas.

The Energy Saving Trust is doing some interesting research in this area: http://www.energysavingtrust.org.uk/Generate-your-...

[JM]

Throttle Body said:

gas is more efficient than an ASHP.

The most efficient gas boiler or heater can only ever be 100% efficient, and air source heat pump can be 4-500% efficient.

A bore-hole for a GSHP does not require large areas of ground or gardens to be trashed.

[Tuna]

This is very misleading:

JM said:

The most efficient gas boiler or heater can only ever be 100% efficient, and air source heat pump can be 4-500% efficient.

True, but electricity generation (needed to power your heat pump) is something like 30% efficient and power line losses equate for the rest - so the net result is that your air source heat pump is no more efficient (either in actual fuel used or real world cost) than gas.

People forget that the electricity that comes out of their sockets doesn't just arrive there magically.

[JM]

Tuna said:

This is very misleading:

JM said:

The most efficient gas boiler or heater can only ever be 100% efficient, and air source heat pump can be 4-500% efficient.

True, but electricity generation (needed to power your heat pump) is something like 30% efficient and power line losses equate for the rest - so the net result is that your air source heat pump is no more efficient (either in actual fuel used or real world cost) than gas.

People forget that the electricity that comes out of their sockets doesn't just arrive there magically.

How efficient is gas production?

It doesn't just arrive at your meter magically either.

The OP doesn't mention where he is getting his electricity or gas from, so how can you debate his or anyone else's 'efficiencies' unless you know the complete picture.

[JCB123]

I think ASHP's and GSHP's will come into their own when fossil fuel prices start increasing (by start, I mean REALLY start)....

....at which point, it'll be easy to hook your pumps up to a PV panel, and away you go....


I'm not a great believer in the whole 'we're killing the planet thing' (mainly becuase I understand that energy cannot be made nor destroyed), but we cannot hide from the fact that we are using up natural resources at a hell of a rate......if you can harness free energy, why not? Even if it costs the same?