ASHP versus PV

[davejura]

Evening all. Trying to decide on the best route to take and am hoping for advice! We have been told we need either a 2.5KW PV system or an air source heat pump to pass the SAPS test. Our CO2 estimate is currently 50% above the maximum on our current build make up. To complicate things slightly, we are building an upside down house in the West of Scotland, approx 160 sq M. We have mains gas right outside the property. Any thoughts or other solutions please? 

[ProDave]

BOTH.  We have ASHP and solar PV.

 

I would say ASHP is the better financially. It is hard to make solar PV "pay" for itself unless you can DIY install it now.

 

An ASHP will deliver heating for roughly the same if not lower cost than mains gas, but without the ongoing gas servicing or gas standing charge.

 

What are your insulation levels? I worry not enough to be so far out on the initial SAP.

 

Most people start off viewing SAP as an annoying hurdle they have to get over.  Instead, treat it as a measure of how good (and how low energy) your house is and look at all ways to improve it.

[SteamyTea]

2 hours ago, davejura said:

We have mains gas right outside the property

Any particular reason why you don't want to use this?

As @ProDavesays, use both.

If you design it in the from the start, the costs do not have to be prohibitive.  A roof with an integrated PV system may be cheaper than a conventional roof, and it can help with limiting summer temperatures.

An ASHP is best used with underfloor heating.  This means that you should put in more floor insulation than building regs suggest.

Building Regulations are only setting a minimum, not hard or that costly to improve on them.

[davejura]

Would love to use gas. In fact I was hoping we would get away with a gas system with radiators, but that isn't going to happen without major extra insulation and other measures which could end up dearer than a PV or ASHP. 

Can't afford both unfortunately. If our house wasn't upside down, we would go with a heat pump and underfloor heating. We actually have plenty of room for a GSHP, but again cost could be prohibitive. 

Regarding PV, I balk at paying out £5000 or so to save £100 per year now there is no FIT. Decisions, decisions!

[ProDave]

Give the ASHP serious consideration. It should not cost more than a gas system.  If you take into account not having to pay for a gas connection and not having to pay a standing charge for gas, I would expect it to be cheaper.

 

Even with an upside down house you can have UFH downstairs and upstairs with each room having it's own thermostat so you can have cool bedrooms if you want.

 

What sort of U values does the design have for walls woof and floor?

[SteamyTea]

17 minutes ago, davejura said:

a gas system with radiators

You can have radiators with and ASHP, they just need to have a larger surface area.

18 minutes ago, davejura said:

Regarding PV, I balk at paying out £5000 or so to save £100 per year now there is no FIT

Those days are gone, so no point even regretting it.

Depending on where you are in the UK, the house orientation and your expected electrical usage, they can save you a lot more than £100/year.

8 minutes ago, ProDave said:

What sort of U values does the design have for walls woof and floor?

As Dave says, it is a key point to the design of a house.

Ar you having MVHR fitted.

[redtop]

i think we have gone away from ASHP simply becuase the extra space required inside the house.  Bizarly a worcester combi boiler gets us a better SAP score than ASHP.  Only thing that might sway me back is ability to cool (we are using UFH).

 

Also considering just having UFH downstairs and then ducted AirCon upstairs.  It would be used very occasionally to cool the bedrooms and also occasionalyl provide heating.

[davejura]

16 minutes ago, ProDave said:

Give the ASHP serious consideration. It should not cost more than a gas system.  If you take into account not having to pay for a gas connection and not having to pay a standing charge for gas, I would expect it to be cheaper.

 

Even with an upside down house you can have UFH downstairs and upstairs with each room having it's own thermostat so you can have cool bedrooms if you want.

 

What sort of U values does the design have for walls woof and floor?

That's what I am looking at now. We have a gas engineer / plumber in the family which would save us a lot if we went for a gas system, but I could probably do a lot of the UFH pipework myself. The Nu-Heat Clippaplate system looks interesting for upstairs, and maybe radiators in the bedrooms downstairs? 

U values wise, we are still working on it! The house will be timber frame and am looking at the Cedral cladding system instead of block. Our original plan using an insulated render board on the outside has hit a snag, so having to rethink.

 

[lizzie]

I went for a mains gas boiler (Vaillant) in preference to an ASP as I had heard of lots of issues with ASP (now commonly installed by builders to bump up their ratings).  Figured if all the fancy technology failed we could always bung a few rads in ?

[joth]

5 hours ago, davejura said:

I was hoping we would get away with a gas system with radiators, but that isn't going to happen without major extra insulation and other measures which could end up dearer than a PV or ASHP. 

 

In this case I'd do the insulation and other measures (airtightness + MVHR?) and leave ASHP and PV for future upgrade possibilities.

 

 

PV + ASHP (and other technology solutions) are only going to improve efficiency with time and get cheaper, whereas insulation, airtightness and ventilation have to be done from the outset or are going to be way more expensive to fit later. 

Plus, the ASHP and ufh (and aircon) will work so much better if the house is built to not need so much heat input

[andyr87]

A couple of things to consider;

 

The Energy Trust Scotland will offer you an interest free loan of £10,000 to cover the cost of ASPH and £5000 for Solar PV. You must have an offer from the ETS prior to starting work on site to be eligible. 

 

ASHP will cost more initially and does require more space internally, however you will benefit from the domestic RHI. GSHP will pay for itself much quicker, however you will essentially need a plant room for all of the internal pipework and a lot more capital upfront. 

 

The government has set out plans for the Smart Export Guarantee from 01/01/20. I don't know too much detail on this having only heard about it yesterday, however it looks like they are essentially pushing the onus of something akin to the FIT onto the energy suppliers. Octopus Energy appear to the only provider with any info so far, offering 5.5p per k/Wh assuming that at least 50% of your energy generated is exported. We have been quoted circa £3500 for 8 no 1.7 x 1m solar PV panels (integrated to roof) which should provide 2.4kW of energy. I doubt very much we will generate enough to export at least 50% back to the grid also being based on the west coast of Scotland!

 

You will require require an MCS installer for the ASHP to take advantage of the RHI and assume that the same rules will apply to the Smart Export Guarantee, so not sure if the DIY route is a great idea if this is an option you wish to explore in the future. I believe that you will need an MCS installer for these technologies to achieve your completion certificate, however may be wrong with that one!

[ProDave]

9 hours ago, redtop said:

i think we have gone away from ASHP simply becuase the extra space required inside the house.  Bizarly a worcester combi boiler gets us a better SAP score than ASHP.  Only thing that might sway me back is ability to cool (we are using UFH).

 

Also considering just having UFH downstairs and then ducted AirCon upstairs.  It would be used very occasionally to cool the bedrooms and also occasionalyl provide heating.

What extra space?  A monoblock ASHP is an outside unit. Very little inside, a pump and some controls.  but you do need a hot water tank, which in any event is FAR better than most combi boilers.

 

If you think you might need cooling then an ASHP makes even  more sense. Install one or more Fan Coil Units and appropriate valves and it can do cooling as well as heating.

[newhome]

1 hour ago, andyr87 said:

 I believe that you will need an MCS installer for these technologies to achieve your completion certificate, however may be wrong with that one!

 

No, you don’t need these to be installed by an MCS installer in order to get the completion certificate. 

[ProDave]

9 hours ago, davejura said:

That's what I am looking at now. We have a gas engineer / plumber in the family which would save us a lot if we went for a gas system, but I could probably do a lot of the UFH pipework myself. The Nu-Heat Clippaplate system looks interesting for upstairs, and maybe radiators in the bedrooms downstairs? 

U values wise, we are still working on it! The house will be timber frame and am looking at the Cedral cladding system instead of block. Our original plan using an insulated render board on the outside has hit a snag, so having to rethink.

 

What is the snag with the insulated render board? What were you considering?

[andyr87]

2 minutes ago, newhome said:

 

No, you don’t need these to be installed by an MVS installer in order to get the completion certificate. 

 

@newhome what does MVS stand for?

[ProDave]

3 minutes ago, andyr87 said:

 

@newhome what does MVS stand for?

She means MCS, the organisation that acredit microgeneration installers.

 

You need an install done by an MCS contractor if you are going to claim the RHI payments for an ASHP and previously needed MCS to claim the FIT for solar PV.

 

There has been much discussion here about this.  You can DIY install or just use any plumber / electrician often for a lot less than an MCS contractor will charge, and you need to look carefully.  With a well insulated house, the energy use, and hence the RHI payments might be so low that it is not worth bothering using an MCS contractor or claiming the RHI

[davejura]

ProDave, it's called ECAP and is imported by a local company. Basically has the first coat and mesh embedded, so it can be rendered straight on to it without a base coat. The problem is that my architect (and she says building control) wont accept an unventilated cavity with the ECAP on ply, so the insulation in the board is worthless. The only way round this is to have a layer of cement board below the ECAP, which pushes the price up. I know someone building using this system, but he doesn't need a mortgage or warranty, so can pretty much do what he wants! I'm currently pricing up Cedral Click as an option. 

[jack]

I say this often enough that people probably think I'm getting a kickback from manufacturers, but shower waster water heat recovery units offer one of the cheapest ways of bumping up SAP points. As others have said though, it's concerning that you're short of the minimum points if you're building with any thought for the future.

 

Having experienced underfloor cooling over the last couple of years, I personally would include cooling of some sort (whether ducted air or underfloor cooling) as a minimum for a new house. 

[ProDave]

We used wood fibre cladding with render.  No need for a cavity, it goes straight on the frame. Building control accepted it with no cavity.

[newhome]

34 minutes ago, andyr87 said:

 

@newhome what does MVS stand for?

 

Sorry phone did an autocorrect. As @ProDave says I meant MCS. MVS is an IBM Mainframe operating system and my phone is more used to me typing that ? 

 

[andyr87]

20 minutes ago, newhome said:

 

Sorry phone did an autocorrect. As @ProDave says I meant MCS. MVS is an IBM Mainframe operating system and my phone is more used to me typing that ? 

 

 

I did google MVS and now know more about mainframe operating systems than I did when I got up this morning ?

[newhome]

19 minutes ago, andyr87 said:

 

I did google MVS and now know more about mainframe operating systems than I did when I got up this morning ?

 

Want a job? ? 

[davejura]

1 hour ago, ProDave said:

We used wood fibre cladding with render.  No need for a cavity, it goes straight on the frame. Building control accepted it with no cavity.

Yes but do the mortgage companies and warranty companies accept it?

 

ECAP could go straight on the kit, but my architect isn't happy as any potential water ingress would cause rot. Was that brought up in your case? 

I'd also be interested to know a ballpark figure per metre for the rendering. I presume it is a K rend type system you used?

[ProDave]

I don't have a mortgage so didn't bother with a warranty.

 

It's the Baumit,com render system, very similar to K rend, first coat is mixed from powder and lime based and a glass fibre mesh embedded in the first coat. the top coat is pre mixed in tubs with a primer applied before the top coat goes on.

[Jeremy Harris]

Personally I think it's wise to invest in better insulation and airtightness, than to try to fiddle SAP by adding stuff like PV that will inevitably need replacement at some future date.  I've never, ever, heard of anyone regretting spending money on better insulation.

 

Worth remembering in this hot weather that insulation works both ways.  It keeps heat out in hot weather every bit as well as it keeps heat in during the heating season.