2 x 100m or 1 x 200m borehole

[ronaldgibbons]

Hi there, I'm having a borehole installed for a ground source heat pump. I've been told I can save money on transport costs if I can use 2 x 100m boreholes instead of a

1 x 200m borehole. I'll be doing some research later but I just wondered if anyone knows if it makes any difference?

 

Many thanks, Jonathan.

[Conor]

The issue there is that you'll be accessing a smaller "pool" of groundwater and might suffer from repletion issues.

 

Out of interest how come ground source instead of air source? Don't hear of many being installed for domestic projects these days, don't normally compete in terms of cost.

[ronaldgibbons]

Thanks for replying. It's only for heating and hot water so we won't be accessing any water within the ground. We've been told an air source pump won't provide the amount of energy we need and we had to go with a borehole rather than the trench type because the plot is mostly bedrock just below the surface. The contractor says if we can use two boreholes instead of one he will use a smaller machine that won't need as much ground prep and a police escort during transport.

Thanks, Jonathan.

[Originaltwist]

Could we know how much power you are needing to make please.

[saveasteading]

2 hours ago, Conor said:

Don't hear of many being installed for domestic projects these days, don't normally compete in terms of cost.

They don't normally work properly at all.

Is the rock hot?

Otherwise you are taking heat out of the rock, but it can't replace it quickly and you run out of energy.

Near me, a development with 12 borehole systems  90m into clay has had at least 4 replaced by air source, because they weren't working. All agreements to replace were private, so there may be more.

 

There used to be a lot of cowboys in ground source. Most have gone, and so those left are perhaps giving you great advice.

Anybody near you with GSHP so you ca see how well it works?

 

what guarantees will you get? what happens if it doesn't work well

28 minutes ago, ronaldgibbons said:

borehole rather than the trench type

Trench type is actually air source. The ground warms in the summer from the sun and air, and stores it for winter. you only need 1m or so.

A borehole needs the heat to be replenished from hot rock, or from water flowing past, eg in sand or fissured rock.

28 minutes ago, ronaldgibbons said:

It's only for heating and hot water

That's what we'd expect. For a 200m2 house you'd probably pay about £10,000 for the ashp and internal gubbins (excluding the plumbing around  the house which applies to any system).

I'm guessing the gshp will be many times that cost.

28 minutes ago, ronaldgibbons said:

We've been told an air source pump won't provide the amount of energy we need

??? there is no limit to the energy available in the air. Unless you are in the arctic Id expect air source to be a better bet.

[Moonshine]

12 minutes ago, saveasteading said:

That's what we'd expect. For a 200m2 house you'd probably pay about £10,000 for the ashp and internal gubbins (excluding the plumbing around  the house which applies to any system).

 

minus the rebate as well

[Jenki]

50 minutes ago, ronaldgibbons said:

 We've been told an air source pump won't provide the amount of energy we need

So, this leads to the obvious question, what size is the build what are the heat loss calculations.  IMHO if a GSHP can supply the required heat so can an ASHP.

 

Drilling bedrock just sounds like ££££££££££££££££££££ and you can get a LOT OF ASHP FOR ££££££

 

 

[Kelvin]

Yes I’d slow right down here and do more research on this. Few people install borehole based GSHP and many renewables companies that did both now just do ASHP. 

Edited January 30 by Kelvin

[Declan52]

200m is a long way down so will be a massive rig. That cost plus all the pipe you need plus bentonite gravel etc to seal it up and all the associated ground works will be easily more expensive than an ashp.

I would as above work out your heat demand and get a price for an ashp and then compare both systems.

[Kelvin]

My water supply borehole is 145m deep and it alone cost £18,000 (paid by the original land owner) 

[Conor]

4 hours ago, ronaldgibbons said:

Thanks for replying. It's only for heating and hot water so we won't be accessing any water within the ground. We've been told an air source pump won't provide the amount of energy we need and we had to go with a borehole rather than the trench type because the plot is mostly bedrock just below the surface. The contractor says if we can use two boreholes instead of one he will use a smaller machine that won't need as much ground prep and a police escort during transport.

Thanks, Jonathan.

 

Just a couple follow ups. It's actually the groundwater where the heat is extracted from. The borehole needs to hit rock / gravel with decent movement of water. The deeper you go, the greater the water column you can use. The two 100mm boreholes close together, the same water in each strata will be cooled twice by the coolant. You need to make sure they are far enough apart. Then again, if you hit a decent karst at 10m then your sorted. Don't know until the drilling starts.

 

Secondly, is the GSHP company reccomending this option or is it the driller? The driller has likely been subcontracted by the GSHP installer and you'll need to make sure they are happy with this option.

 

Finally, just get an ASHP. Spend the spare £10k on a nicer kitchen and bathroom.

[ronaldgibbons]

16 hours ago, Originaltwist said:

Could we know how much power you are needing to make please.

Hi there, thanks for replying.

I'm in the early stages. I don't have any accurate calculations. The house design is still going through the initial planning process so I don't have engineering drawings. I sent enquiries to a few heat pump installers with design details.

Floor area (220m2), number of baths (1), showers (4), toilets (4), sinks (6). There's 2 floors with underfloor heating throughout. There's large triple glazed South facing windows in 6 of the rooms.

[ronaldgibbons]

16 hours ago, saveasteading said:

They don't normally work properly at all.

Is the rock hot?

Otherwise you are taking heat out of the rock, but it can't replace it quickly and you run out of energy.

Near me, a development with 12 borehole systems  90m into clay has had at least 4 replaced by air source, because they weren't working. All agreements to replace were private, so there may be more.

 

There used to be a lot of cowboys in ground source. Most have gone, and so those left are perhaps giving you great advice.

Anybody near you with GSHP so you ca see how well it works?

 

what guarantees will you get? what happens if it doesn't work well

Trench type is actually air source. The ground warms in the summer from the sun and air, and stores it for winter. you only need 1m or so.

A borehole needs the heat to be replenished from hot rock, or from water flowing past, eg in sand or fissured rock.

That's what we'd expect. For a 200m2 house you'd probably pay about £10,000 for the ashp and internal gubbins (excluding the plumbing around  the house which applies to any system).

I'm guessing the gshp will be many times that cost.

??? there is no limit to the energy available in the air. Unless you are in the arctic Id expect air source to be a better bet.

Hi there, thanks for replying. We basically made our decision based on the advice of an architect friend who had experience with GSHP's. I did some Internet research on different heat pumps and sent enquiries to a few heat pump installers with details of the house design. We can't use the trench type because of ground conditions and there was a lot of conflicting advice on ASHP's so we went with the borehole but we're not signed up to anything and are still researching.

[ronaldgibbons]

12 hours ago, Conor said:

 

Just a couple follow ups. It's actually the groundwater where the heat is extracted from. The borehole needs to hit rock / gravel with decent movement of water. The deeper you go, the greater the water column you can use. The two 100mm boreholes close together, the same water in each strata will be cooled twice by the coolant. You need to make sure they are far enough apart. Then again, if you hit a decent karst at 10m then your sorted. Don't know until the drilling starts.

 

Secondly, is the GSHP company reccomending this option or is it the driller? The driller has likely been subcontracted by the GSHP installer and you'll need to make sure they are happy with this option.

 

Finally, just get an ASHP. Spend the spare £10k on a nicer kitchen and bathroom.

Thanks for that, I'd thought it was the ambient temperature in the rock that provided the warmth. So is it better to go deeper with one bore? It was the heat pump installer who recommended the borehole but we had said it was our preferred option based on advice we'd been given from an architect friend with experience of them. We'd been put off the idea of an ASHP by some conflicting information and reviews. Particularly regarding their performance in the winter.

[ronaldgibbons]

16 hours ago, Jenki said:

So, this leads to the obvious question, what size is the build what are the heat loss calculations.  IMHO if a GSHP can supply the required heat so can an ASHP.

 

Drilling bedrock just sounds like ££££££££££££££££££££ and you can get a LOT OF ASHP FOR ££££££

 

 

Thanks for replying. I don't have details of heat loss calculations yet. The house is

220 m2, 1 bath, 4 showers, 6 sinks, 4 toilets and underfloor heating throughout.

The GSHP option was recommended by an architect friend with experience of them and the ASHP was advised against because of the amount of energy needed and the conflicting information about their performance, particularly in winter. However we're not signed up for anything and are still open minded.

[saveasteading]

7 minutes ago, ronaldgibbons said:

preferred option based on advice we'd been given from an architect

Ask them to guarantee the performance. Ie who pays to replace it if it doesn't work properly?

 

The ambient temperature of the rock drops as the heat is drawn from it. At some stage it may freeze, and then your system reverses to thaw it.

Hence they need 200m, which will cost you many tens of thousands.

 

We aren't telling you what you want to hear, i know.

The great thing about buildhub is that most people stay quiet if they don't  know about a subject. But between us we are more likely to know than are most architects.

I'd love to know what your advisers are saying about air source not being suitable.

 

Get comparitive quotes for air source.

[ronaldgibbons]

13 hours ago, Kelvin said:

My water supply borehole is 145m deep and it alone cost £18,000 (paid by the original land owner) 

Our quotes for borehole and all external works up to the plant room were £11000, £14000 and £18000. The two higher quotes are from companies that required overnight accommodation and one had huge transport costs. The plant room, underfloor heating and all internal works came in at £13000 and £17000. Again the higher quote involved accommodation costs.

[AppleDown]

24 minutes ago, ronaldgibbons said:

Hi there, thanks for replying. We basically made our decision based on the advice of an architect friend who had experience with GSHP's. I did some Internet research on different heat pumps and sent enquiries to a few heat pump installers with details of the house design. We can't use the trench type because of ground conditions and there was a lot of conflicting advice on ASHP's so we went with the borehole but we're not signed up to anything and are still researching.

There'll be lots more qualified people than me answering you, but I wouldn't settle on that yet. You say it's still going through planning? Don't sign anything until you've got the full go-ahead. Also there's no point going one direction until you are able to calculate your heating requirements.

 

Also that's a lot of sinks for a 220m2 build!

[JohnMo]

3 minutes ago, ronaldgibbons said:

Our quotes for borehole and all external works up to the plant room were £11000, £14000 and £18000. The two higher quotes are from companies that required overnight accommodation and one had huge transport costs. The plant room, underfloor heating and all internal works came in at £13000 and £17000. Again the higher quote involved accommodation costs.

Gee you have deep pockets, and at those costs you should be doing a mansion.

 

Your house is slightly bigger than ours. I am running a 6kW heat pump which is oversized. Full retail price is around £2.5k to £3.5k depending on brand, you need a plinth to stand it on and a couple flex pipes, power and coms cable and that's the external work done.

[ronaldgibbons]

7 minutes ago, saveasteading said:

Ask them to guarantee the performance. Ie who pays to replace it if it doesn't work properly?

 

The ambient temperature of the rock drops as the heat is drawn from it. At some stage it may freeze, and then your system reverses to thaw it.

Hence they need 200m, which will cost you many tens of thousands.

 

We aren't telling you what you want to hear, i know.

The great thing about buildhub is that most people stay quiet if they don't  know about a subject. But between us we are more likely to know than are most architects.

I'd love to know what your advisers are saying about air source not being suitable.

 

Get comparitive quotes for air source.

Thanks for that. I'm absolutely open minded about our options and looking for useful info to make the right choice. It was the conflicting information on ASHP's regarding their performance, especially in winter that put us off but I'll be having another look before making any decisions. The quotes for the borehole were £11000, £14000 and £18000. The larger quotes including accommodation and long distance transport. Regarding my original post, you seem to be saying there could be a crucial difference between using two shallower bores or one deeper?

[ronaldgibbons]

4 minutes ago, AppleDown said:

There'll be lots more qualified people than me answering you, but I wouldn't settle on that yet. You say it's still going through planning? Don't sign anything until you've got the full go-ahead. Also there's no point going one direction until you are able to calculate your heating requirements.

 

Also that's a lot of sinks for a 220m2 build!

Thanks, we're still gathering all the info we can. She wanted an outside sink as well.😄

[JohnMo]

New build house, with decent insulation and airtightness.

 

UFH pipes on 200mm centres generally, do 150mm centres in bathrooms.

 

No buffer or plate exchanges

 

3 way valve to divert between UFH and cylinder.

 

3m2 coil cylinder around 250 - 300L

 

Most likely a 6kW heat pump would be fine, based on heat loss calc.

 

Our build was completed with gas boiler, but added an ASHP last summer. Heating this year NE Scotland, has a couple of weeks at or around -7, with zero issues. Heating costs during the really cold period is more expensive than gas, but during less cold cheaper than gas. My self install cost around £2k as a retrofit. UFH materials were around £1k and it took me alone 2 days to install. A cylinder is £1k ISH.

 

 

[ronaldgibbons]

10 minutes ago, JohnMo said:

Gee you have deep pockets, and at those costs you should be doing a mansion.

 

Your house is slightly bigger than ours. I am running a 6kW heat pump which is oversized. Full retail price is around £2.5k to £3.5k depending on brand, you need a plinth to stand it on and a couple flex pipes, power and coms cable and that's the external work done.

Thanks, I've got lots more enquiries to make and research before I make any decisions. 

[ronaldgibbons]

22 minutes ago, JohnMo said:

New build house, with decent insulation and airtightness.

 

UFH pipes on 200mm centres generally, do 150mm centres in bathrooms.

 

No buffer or plate exchanges

 

3 way valve to divert between UFH and cylinder.

 

3m2 coil cylinder around 250 - 300L

 

Most likely a 6kW heat pump would be fine, based on heat loss calc.

 

Our build was completed with gas boiler, but added an ASHP last summer. Heating this year NE Scotland, has a couple of weeks at or around -7, with zero issues. Heating costs during the really cold period is more expensive than gas, but during less cold cheaper than gas. My self install cost around £2k as a retrofit. UFH materials were around £1k and it took me alone 2 days to install. A cylinder is £1k ISH.

 

 

I'll need to speak to those installers again (or different ones). I was told that an ASHP wouldn't be able to provide the amount of hot water required throughout the year for all the heating and hot water.

[Moonshine]

3 minutes ago, ronaldgibbons said:

I'll need to speak to those installers again (or different ones). I was told that an ASHP wouldn't be able to provide the amount of hot water required throughout the year for all the heating and hot water.

 

i would speak to a number of different ones just to get different and contrasting views. An ASHP with suitable hot water cylinder / buffer tank should be fine throughout the year especially if its new build house with good insulation and airtightness.

 

Where in the country are you?