Hi

A friends built a SIP house , 3G glazing , dont know exact wall, fabric thickness but I think its pretty low close to U=0.1 , individual MHRV in kitchen bathroom, PV on roof
Trouble is he's fittted a peat stove and it seems more problematically electric resistance heating rads. as a back up
though he wasnt expecting to use them much.
this has brought his SAP figure up too high for building regs sign off.
originally it was speced ASHP with UFH.
Anyone know the best bang for bucks to get it down.
Assessor told him he'd be better of with an oil boiler and rad with regards to SAP which seems odd given the carbon intensity of grid electric is falling to make it almost close the natural gas.
He's looking for a quick solution to resolve the issue.
I suggested just taking the electric rads out or switching to a couple of air/air heat pump units
thanks for any advice

The other thing he might want to check with the SAP assessor is how the two heating systems have been entered.
If there are multiple electric heaters around the house and only one stand alone peat stove then the SAP assessor may have entered the electric heaters as the main heating that heats most of the house and the peat stove as secondary heating that only heats the main living room.

IIRC, the stove designation is very important. If it is "multi fuel" ie. wood and coal, which peat most likely will be, then that is hugely more CO2 ratings wise, like 20 times.

The SAP person can tell him what has been entered, and how changing to a wood only stove would impact things. That caught me out once, even though the client only burned logs (never coal). So I found a Wood Only stove that looked identical, and sent that literature through to the SAP assessor and BSO.

In previous projects, SAP assessors have always been advised to enter 50/50 for stove and electric heating, which was not a true reflection how it was be used, but since that can't be confirmed, the assessor was advised to enter 50/50.

Aiui in Scotland, the dwelling must have an emissions rate (DER, in kg/yr/m2 of CO2) which is less than the Target rate TER for a building of that size/shape.

The target rate may set using any one of five heating systems: Gas+PV, LPG+PV, Oil+PV, ASHP or Wood Pellets.

IE not using high carbon heating such as either Peat or Electric Resistance heating.

You are free to use any heating you like in the actual dwelling, but you would have to reduce carbon in some other way to compensate. The target rate is set assuming U=0.17 walls and U=0.11 roof, so you'd need to be well below those levels to be allowed to use high carbon heating.

Best plan might be to see what heat source was specified to set the TER in the original Building Warrant application and install it, as specified?

Being the green building forum, we probably should encourage people to comply with the regs/stds, which are doing little enough to reduce emissions from newbuilds. If this were another forum, we could discuss dodges such as fitting a token ashp to get round building standards then ripping it out once the house is signed off, but that's not really what we're about..... !

Actually, they may find that the house uses so little heat that it's not worth the sweat of digging peat. Peat fires are culturally significant in NW Scotland, but like steam locomotives they are best appreciated in a museum!

Posted By: jamesingramI'm all for good regulation but when the structure is unable to recognise builds that perhaps won't require heating it seems odd.

Well if you accept that SAP/EPC isn't good regulation then life all becomes consistent again

Does it pass if he doesn't install the peat stove? And maybe installs PV instead?

James, since he/she already has PV, & better than TER insulation, it is almost certainly down to the use of peat and direct electric, versus the TER utilising ASHP.

Does it fail on Energy Efficiency or CO2 rating, or both?
SAP CO2/kWh rating for Coal (peat is not an option) = 0.4; elect = 0.5; logs = 0.02. I've rounded the numbers a bit but you can see coal is 20 times the CO2 rating for logs, and even with ASHP elect at say 25%, that would be 0.125.

It's unfortunate that your friend has built what is essentially a better than regs structure, but the fuel source for a very unusual setting causes it to fail, when lots of urban houses just scraping regs with G/ASHP and shoddily built, with much higher energy consumption pass. SAP is quite a blunt instrument, but we've a very big nut to crack, so it kind of needs to be blunt. That said, I don't really like the thought of burning peat, and not sure that any amount is sustainable, considering the millions of years it takes to replace it, but your friend appears to have made an effort to minimise his energy consumption (and generate), compared to his neighbours living in stone, single glazed, burning 50 times the amount of that same peat.

If your friend is willing to PM me his full SAP calc, I can have a quick look, and at least highlight the magnitude of the areas of failure to comply, and the extent to which changes would be required.

Hi Red Door, yes that sounds about right, if it is using direct electric heating instead of heat pump, PV, etc in Scotland then it needs to be improved in other aspects to compensate for that - eg 'fantastic' rather than merely 'good' insulation and airtightness. You can't claim any credit for using a renewable supplier, as the supplier could easily be changed straight after the EPC has been issued. The designer should have advised the owner about this, before the building warrant was submitted :-(

As was mentioned, the current version of SAP dates from a few years ago when direct electric heating was very high carbon. They've been talking for a while about updating SAP with changes in grid electricity. Once that happens, gas will become even less favourable than heat pumps etc. They are also planning to ban installing gas boilers, so maybe worth avoiding those as a dead end, which won't show up so well anytime the EPC is re done in future under the revised system.

"it's all about acclimatisation."
Adaptive thermal comfort - is a fancy way I've heard it described.
I think acclimatisation is a larger under considered solution to reducing energy use.
when i was up there fitting the PV in a hail storm in March i was freezing.
I got back to their rented accomodation and i was actually warmer outside,
where as they were happily sitting there with there thick jumps on in front of a open peat fire that barely warmed your face and made your back fill colder.
I gave them £20 and forced them to turn the electric storage heat on in my room

Ed
No idea of the science. There was a good short article in green building magazine years ago on the subject.
the 'adaptive' bit suggests you slowly get use to it, so slowly reducing heat should make it easier to adapt more comfortably one would think.
I asked my friend in the outer hebrides, whilst i was there, whether he think he'd adapted to the climate. His reply was "No, Im just use to feeling cold",