Is Air Source taking over from Ground Source?

[GLPinxit]

Hi,

I'm at the planning stage for a replacement for a 20/25KW oil fired boiler with a heat-pump for heating and hot water. I'd originally assumed that I'd be going with ground-source (vertical borehole most likely as we've only got a medium-size garden). But I've noticed that most of the discussion on this forum is about air-source and next to none about ground-source. Why is this?

I'm asking the question rather than making assumptions. But if I was making assumptions then I can envisage that reasons might include that air pumps seem to be closing the efficiency gap with ground. And the capital cost of air is likely to be considerably lower. Am I on the right lines? 

(For background the house is in the south of England and was built in 2003 and the EPC says it has no recommendations to make about the insulation so it sounds, to me at least, like a prime candidate for one or the other.)

[IanR]

6 minutes ago, GLPinxit said:

And the capital cost of air is likely to be considerably lower. Am I on the right lines? 

 

It boils down to the extra cost of a GSHP installation not providing enough of an efficiency improvement over ASHP.

 

[SteamyTea]

GSHP have, over the last decade, declined in popularity because of the higher initial cost for only a tiny performance improvement.

We also tend to have small gardens in the UK, do borehole drilling is best for most people.

The UK has very mixed geology and drilling easily in one place may become really hard just a few miles away.

Even down here in Cornwall, with some of the best understood geology in the world, and a £1m to play with, the Jubilee Pool project went disastrously wrong.

[saveasteading]

1 hour ago, SteamyTea said:

GSHP have, over the last decade, declined in popularity because

......they were often used in inappropriate ground and just don't work properly.

Many installers  didn't know/care and did it anywhere....they are gone.

(I spoke to many of them about real projects, when i was learning...they all said yes.

When I learnt of the importance of ground conditions i asked them all at an exhibition re a project on dense clay.

Only one (of 5?) stated that it was not appropriate.

 

Some good companies remain, tarnished by the others.  It really should work well in the right conditions, esp with water movement underground.

 

BUT our project is on deep sand, and GSHP still doesn't come out favourably compared with ASHP, as turning up with the boring equipment costs the same as the heat pump.

 

In summary I think it is for big projects with ideal ground conditions.

[jack]

Compared with ASHP, GSHP kit is more expensive to buy, much more expensive to install, is potentially more disruptive in terms of earthworks (less of an issue with vertical boreholes), and costs more in ongoing maintenance due to the need to replace a lot of glycol every few years.

 

Some have mentioned that the pump itself is quite noisy, although I can't see why that can't be located outside in an enclose to keep the noise down.

There have also been some horror stories on performance. Things like ground icing up and killing lawns/plants due to the loops not being buried deep enough, and soils with low thermal conductivity with not enough loop area causing the ground to freeze over the heating season to the point where little or no heat can be extracted any more. Most of these are installation issues that shouldn't happen in a properly designed system, but how do you as a lay-person know if a system's been designed and installed properly?

For all this, you get a nominal bump in efficiency that will take decades or more to pay back in reduced energy consumption.

[Dan F]

There are a couple of situations where I'd consider a GSHP:

- If I lived somewhere a lot colder than the U.K.   (the improvement in efficiency between ASHP and GSHP is greater the colder the climate)

- If I has a large property that isn't particularty well insulated.  (higher usage in this case means the improvement in efficiency will give a shorter ROI)

 

But otherise, ASHP.

Edited October 5, 2021 by Dan F

[GLPinxit]

Thanks for all the helpful comments. All very useful- looks like the saving can be allocated to solar then.