New eco house

[CraigCTH]

Hi im Craig, I am the currently in the process of building a single story eco friendly house with a grass roof into a bank side. I am looking for help and advice on the build as I am an amateur on renewable energy sources. Many thanks, Craig.

[CraigCTH]

Which is better air source heat pump or ground source heat pump?

[Redoctober]

Welcome and your opening question, although a good one, will be difficult to pin down, given there are a number of variables to both -

Such as budget / land available / applications etc. I'm sure others far more knowledgeable will be along soon to add their thoughts but for the time being, enjoy and hold on tight!

PW.

[Guest Alphonsox]

Hi and welcome to the forum.

Where abouts are you building, what sort of size and heat load, insulation etc? A few more details may well help answer your questions.

 

In general GSHPs are a lot more expensive to install than ASHPs. Quite a few of us have self installed ASHP systems, I don't know of anyone with GSHP installation. The view in these parts seems to be that the money is general better spent on improved insulation.

However if you are going to generate domestic hot water with a heat pump there are issues with ASHP efficiency that don't tend to occur with a GSHP.

 

[mvincentd]

Hi

I'm also building a mostly single storey grass roof into a hillside.  You might find your building methodology provides a lot of the excavation for free that you would need for gshp and so be drawn to it.  I found in the end that this wasn't a significant enough factor to sway it.

[Jeremy Harris]

Welcome,

 

As above, it really comes down to economics.  A GSHP might be a few percent more efficient than an ASHP, but the installation cost is likely to be at least double, probably triple, the cost of an ASHP if doing a DIY installation.  A fair bit of the cost is hidden, it's things like the much greater volume of antifreeze, and the ongoing cost of replacing that every few years.  GSHPs are also inherently more complex, with an additional brine pump, plus brine heat exchanger, filters etc.

 

When looking at the whole life cost, the tiny efficiency advantage can't usually recover the additional capital cost through life, so overall a GSHP may cost a fair bit more over the life of the unit.  In terms of ecological cost, then again the ASHP wins, not so much because of the energy used, but because it probably has a smaller impact on the local environment.

 

As an example, our house is fairly low energy (it's not a certified Passivhaus, but would easily meet the Passivhaus requirements).  In winter we need a few hundred watts of  heat to keep the whole house at around 21 deg C (the floor area is 130m²), and in general our ASHP fires up for about an hour or two once every two to three days to charge up the slab and keep the house at an even temperature.  IT might come on for an hour or so every day in really cold (sub-zero) weather.  The ASHP cost £1700, including delivery, and took me around half a day to install. The total installation cost was under £2,000.  The cheapest GSHP I could find cost around £4,000, and even with a DIY installation would have cost another £2,000 to install, more if I'd opted to use vertical borehole collectors. 

 

In winter we use between £0.20 and £0.30 worth of electricity per day for heating and DHW pre-heat, for around 100 days, so the cost is around £250 (ignoring our PV generation contribution to that cost).  If we had a GSHP, it might be around 10% more efficient at best (bearing in mind that things like the brine pump increase the energy use over and above the basic COP difference), so a GSHP might save us around £25 a year.  To recover the additional £4,000 cost of the GSHP, without accounting for the cost of antifreeze replacement, would take 160 years.................

Edited July 24, 2017 by JSHarris

[MikeSharp01]

Welcome to THE forum. @JSHarris makes all the key points and has the experience to back it up. Looking at it in the round the only way to make GSHP cost effective will be to get the installed cost down to ASHP levels. The only way to do that is to get the equipment very cheaply and do all the digging in yourself. Go for ASHP unless you can get a supplier to subsidise the install.

[richi]

But think also about whether you need a heat pump at all. If your key criterion is cost, you could save the vast proportion of the capital cost by doubling or tripling the running cost.

 

If your house needs a very low heat input, why invest in a heat pump? Do the maths.

[SteamyTea]

Have you looked into Air to Air Heat Pumps.  They have a good CoP, are cheap to buy and can often be self installed.

 

On a more general note, the best heat pumps are water source ones, then ground source, then air.  They all need to be seemingly oversized and run with the output temperature lower than the maximum.

The downside of ASHP is 'frosting'.  This is caused by a combination of air humidity, external temperature, desired temperature output and amount of time the unit is running.

 

Space heating and domestic hot water should, if possible, be separated, they do different things, at different times and at different temperatures.

 

When trying to decide on the best heating method, start with electrical resistance heating as this is generally considered the lowest capital cost but highest running cost.  If, say an ASHP, comes out more expensive after 7 years, then it is not worth considering.

You will need to have a good estimate of your thermal energy usage, but you need that anyway.

[DavidFrancis]

11 hours ago, JSHarris said:

so the cost is around £250

At 20-30p a day isn't the cost about £25 a year, bringing the payback period (for GSHP over ASHP) up to 1,600 years?

 

(PS wish our heating bill was even £250/year.  It's more like £600.)

 

But I'm with ST, have a look at straight electric heating also.  It's so cheap and simple, especially if used on E7.

[Jeremy Harris]

17 minutes ago, DavidFrancis said:

At 20-30p a day isn't the cost about £25 a year, bringing the payback period (for GSHP over ASHP) up to 1,600 years?

 

 

 

 

I think I got the arithmetic right.  The GSHP option was going to cost about £4,000 more than the ASHP we fitted in the end.  The running cost saving would have been around 10%,  so about £25/year.  £4,000 / £25 = 160 years.  Happy to be corrected if I've made an error.

 

17 minutes ago, DavidFrancis said:

But I'm with ST, have a look at straight electric heating also.  It's so cheap and simple, especially if used on E7. 

 

 

I semi-agree, but everyone needs to do their own sums to see whether or not that argument holds true.  The capital cost of installing direct electric water heating, using something like a Willis unit with a standard immersion heater element, would have been around £80 to £100 at the most, saving over £1,900 on the cost of our ASHP.  Assuming a COP of 3 for the ASHP then our bill would increase from around £250 to about £750, but then adjusting for the reduced unit cost of running direct heating on E7 (not a good thing for an ASHP, as it means running it at night, when it's colder and when the noise may be more noticeable) the direct electricity running cost comes down to around £375 to £400 per year. 

 

The £1900 capital cost difference between direct electric heating running on E7 and an ASHP running on a standard tariff would be enough to pay for about 10 years worth of running costs, as a very rough estimate.  It would be reasonable to guess that 10 years may well be around the life time of an ASHP, so for us it would be a finely balanced economic argument either way.  There is certainly a lot to be said for the simplicity and reduced maintenance cost of a direct electric system, however we also use the ASHP for summer cooling, so there is an additional benefit there.

Edited July 25, 2017 by JSHarris

[sam]

When doing these economic calculations should we include the renewable heat incentives, which I understand are significantly higher for GSHP than ASHP?

 

[reddal]

Hi,

 

We have a GSHP. It works reasonably well - and doesn't use a lot of electricity to provide our heating and most of the DHW.

 

However it was expensive to buy, install and maintain. There have been a couple of problems with it over the last few years - and each time was quite tricky to resolve - given there are very few people around me who know anything about them - and nobody who understands the particular model.

 

If doing it all again I would look at ASHP more closely. In fact I might just look at an old school oil fired boiler! That would cost more to run - but I'll be dead before the GSHP pays for itself through the difference.

 

We have had the GSHP for 5 years now - I guess they don't last forever and in the next few years I may have to replace it. Given I already have the brine loop etc (the tricky underground part) then I will probably be sucked back into getting another GSHP! Not sure how I feel about that :(.

 

- reddal

 

[Jeremy Harris]

23 minutes ago, sam said:

When doing these economic calculations should we include the renewable heat incentives, which I understand are significantly higher for GSHP than ASHP?

 

 

No, as the RHI won't give you enough return to cover the massive increase in installation cost required to comply with the rules.  An MCS install for our ASHP was going to add around £1500 to the cost, and a DIY install isn't eligible for RHI.  Add in that for a low energy house the RHI payments will be small (in our case less than £80 a year for 7 years) and the RHI makes no sense at all.  We'd have paid around £1500 more for an RHI eligible installation of the same system that we have, but received a total of around £560 back over 7 years - not the strongest economic argument in the world!

[jamiehamy]

I didn't take the most scientific approach to it, however we have opted for a 400 litre UVC with 12kw immerser which will in all likelihood be on E11 tariff. The original plans had a gas tank powering a gas boiler and wet central heating system, however having done heat loss calculations they determined a 6kW heat demand for the house, and so we have opted for electric radiators. We have spurs in each room for these however will live in the house over the winter and make decisions based on the performance as to which rooms we will have them in. We do have a MHRV system however which will help recycle some of the heat back in as well as help air quality. 

 

Cost wise, this is many thousands  less than getting a wet heating system in - and significantly less than a GSHP. IN the very long term, we may have saved money going down the renewable heat route, but I doubt it. The final factor was our lifestyle - we work during the day Monday to Friday and that pattern is likely to continue for years - we needed a system that could react quickly to our needs and also be easily programmable remotely, which the radiators will be. 

 

I suppose really the key thing is there is no one size to fit all. I think it's easy to get bought into new technology and feel you must use it, but if you look at your needs, that may not be the case. It's easy to get caught up in the hype!

 

 

[reddal]

1 hour ago, jamiehamy said:

I think it's easy to get bought into new technology and feel you must use it, but if you look at your needs, that may not be the case. It's easy to get caught up in the hype!

 

Agreed. People tend to focus on heating - we certainly did. Heating a house with any kind of sensible insulation / airtightness is easy and cheap to run - however you do it. You can spend a fortune on a 'highly efficient' heating system (we certainly did) but you might be better off putting your money and energy into worrying about other aspects - like cooling, or lighting, or security etc.

 

Don't get me wrong - if you want some fancy technology for heating your house because you think it will be a cool toy, or something you are passionate about - then go for it. If its a pure economic argument then the justification is often borderline at best.

[lizzie]

My hairdresser operates out of converted farm buildings and they are all eco. UFH run by GSH.

 

She says GSH UFH is a nightmare, cant get heat when you need it and its not controllable enough and reaction times are slow. That is the only form of heating so they resort to the fan heaters. She has been there 3 years and they have tried all ways her husband is an electrician so not unused to controls etc.

 

Is it bad UFH or bad GSH supplying who knows!

 

 

[gravelld]

5 minutes ago, lizzie said:

My hairdresser operates out of converted farm buildings and they are all eco. UFH run by GSH.

 

She says GSH UFH is a nightmare, cant get heat when you need it and its not controllable enough and reaction times are slow. That is the only form of heating so they resort to the fan heaters. She has been there 3 years and they have tried all ways her husband is an electrician so not unused to controls etc.

 

Is it bad UFH or bad GSH supplying who knows!

 

It doesn't sound very "eco" to me. If the building was "eco" it would barely need any heat input, potentially none from non-passive means.

 

The whole idea of UFH is low and slow - it's not a radiator. It sounds like bad design to me (although you can never tell without looking).

 

We need to stop using the word "eco" - it's meaningless.

[lizzie]

46 minutes ago, gravelld said:

 

It doesn't sound very "eco" to me. If the building was "eco" it would barely need any heat input, potentially none from non-passive means.

 

The whole idea of UFH is low and slow - it's not a radiator. It sounds like bad design to me (although you can never tell without looking).

 

We need to stop using the word "eco" - it's meaningless.

agree but not my descriptiin that is the way they are described in the blurb about the buildings.  I think bad design too.

[CraigCTH]

We will be going overboard with insulating the property , and really appreciate the advice from you people who have given positive advice obviously this is totally new to us , so on that note a ashp sounds the way forward and it would be best backed up by solar I'm told, so if we are insulated properly will the ashp and solar be sufficient for ufh and domestic hot water thanks in advance

[reddal]

3 hours ago, lizzie said:

She says GSH UFH is a nightmare, cant get heat when you need it and its not controllable enough and reaction times are slow. That is the only form of heating so they resort to the fan heaters. She has been there 3 years and they have tried all ways her husband is an electrician so not unused to controls etc.

 

Sounds like a problem with the UFH design or control - rather than the GSHP. I guess if they were used to a UFH system that circulated water at 60c then any heat pump is not designed for that - its about slow heating at lower temps.

 

However we also struggled a bit with UFH performance. Because the GSHP setup and control is quite arcane and complex - it was hard for anyone to work out what the issues were. We recently changed some things which hopefully will make it work better going forwards - won't know for sure until this winter.

[Ferdinand]

1 hour ago, CraigCTH said:

We will be going overboard with insulating the property , and really appreciate the advice from you people who have given positive advice obviously this is totally new to us , so on that note a ashp sounds the way forward and it would be best backed up by solar I'm told, so if we are insulated properly will the ashp and solar be sufficient for ufh and domestic hot water thanks in advance

 

One good idea is to always think of the cost of running the building for 10 or 20 or 30 years as part of your budget and include it in your spreadsheet models. Even people in normal (ie subnormal) houses can do it using the crude numbers from the EPC - though here we are very rude about EPCs.

 

You may not be there for that long, but it will help you to get the principles right and avoid eg complex things that will need mending.

 

There can be things for using things that are complicated or really cheap and requiring replacement, but each case needs to be justified.

 

KISS is right 99% of the time.

Ferdinand

 

Edited July 25, 2017 by Ferdinand

[Ferdinand]

1 hour ago, CraigCTH said:

We will be going overboard with insulating the property , and really appreciate the advice from you people who have given positive advice obviously this is totally new to us , so on that note a ashp sounds the way forward and it would be best backed up by solar I'm told, so if we are insulated properly will the ashp and solar be sufficient for ufh and domestic hot water thanks in advance

 

You also need to be able to cool it; when if it is designed to keep heat in, it can be tough to get out. This is a particular problem in autumn and spring with low sun..

 

That is things like solar shading via various techniques, some abilty to expell hot air, perhaps the ability to create a secure stack effect with windows (ie one bring in shaded air downstairs and one to take it out of the rofo), something to move heat around the slab is done by some members.

 

Ferdinand

 

Edited July 25, 2017 by Ferdinand

[Guest Alphonsox]

38 minutes ago, CraigCTH said:

We will be going overboard with insulating the property , and really appreciate the advice from you people who have given positive advice obviously this is totally new to us , so on that note a ashp sounds the way forward and it would be best backed up by solar I'm told, so if we are insulated properly will the ashp and solar be sufficient for ufh and domestic hot water thanks in advance

 

If you are going to seriously insulate the place I would suggest another option based on our experience and that of a few other around here. We started off very much where you are - I bought a 4 acre field to fit a GSHP for our new build. Have discovered how much they were going to cost to install I switched my attention to ASHP and actually bought a couple of units from Ebay. I am now not sure they will ever be fitted. Currently I am heating the house using UFH and E7 electricity only. The E7 is used to heat the DHW as well. This has turned out to be a very cost effective. 

The common problem that most of us around here have struggled with over the years is how little heating a seriously insulated house needs. Most of us have over speced the system at the design stage. They really don't need a big heating system.

[Ferdinand]

Just now, Alphonsox said:

 

If you are going to seriously insulate the place I would suggest another option based on our experience and that of a few other around here. We started off very much where you are - I bought a 4 acre field to fit a GSHP for our new build. Have discovered how much they were going to cost to install I switched my attention to ASHP and actually bought a couple of units from Ebay. I am now not sure they will ever be fitted. Currently I am heating the house using UFH and E7 electricity only. The E7 is used to heat the DHW as well. This has turned out to be a very cost effective. 

The common problem that most of us around here have struggled with over the years is how little heating a seriously insulated house needs. Most of us have over speced the system at the design stage. They really don't need a big heating system.

 

Yes. 

 

One of the issues is finding wood burners (if you are going that route) that are small enough. People have to look at burners designed for caravans or small boats.