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    • CommentAuthorjamesingram
    • CommentTimeOct 5th 2020 edited

    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
    • CommentAuthorneilu
    • CommentTimeOct 5th 2020
    I agree with you about simply taking the electric resistance heating rads out until he gets his building control sign off? Will that do it or is the DER still too high?
    Your comment about the carbon intensity of the grid falling is correct however the current SAP method still reflects the grid of 7 years ago. This will only change when the new part L and new SAP come into force which is looking like it's gonna be a year away.
    • CommentAuthorneilu
    • CommentTimeOct 5th 2020
    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.
    • CommentTimeOct 5th 2020
    Posted By: jamesingramA 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

    S/he should also be trying to get it airtight (i.e. have a target better than regs, ideally contractual) and as a result should be planning a full MVHR, IMHO. I think it can improve SAP.

    he's fittted a peat stove

    Where is the building? Peat doesn't sound like a sustainable fuel. I don't think it occurs in the SAP rules, so how is it dealt with? Can the stove burn wood? Maybe it's worth stating that as the fuel instead?

    FWIW, Electricity as a fuel is bad for the existing SAP rating. I don't think the new rules are in force yet, except maybe in London? Specifying E7 electricity should help. But with decent insulation, ventilation etc it is possible to get a pass.

    PS SAP is garbage, BTW, IMHO.
    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. :shamed:

    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.
    • CommentAuthorjamesingram
    • CommentTimeOct 6th 2020 edited
    Thanks for the replies
    He's on the outer hebrides and crofts so has rights to cut peats for personal use. in terms of population still cutting and use its sustainable as few still do.
    Air test past Breg and was around 3 with full seal up.
    He's pretty much finished everything and was just trying to sort out final paperwork when the SAP issue came up.
    Early on he was let down by the initial design build outfit in various ways so has been doing what he can to get it finished with local labour as best he can. I've given him a bit of advice here and there ans did his PV system but my knowledge of SAP is minimal.
    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!
    • CommentAuthorjamesingram
    • CommentTimeOct 6th 2020 edited
    Will, thanks that's some good clear info with regard to local regs.
    I think that's the situation , the expectation was little heat would actually be required due to the high insulation levels so investing in a ASHP seemed an expensive tick box exercise for something barely ever turned on.
    Nothing much environmentally beneficial in installing kit that serves little purpose.
    The occupants are use to living in uninsulated Croft cottages so can bear temperature way below what us southern softies can before needing to flick the heat switch on so as we can walk around in shorts a t-shirt whilst its baltic outside.
    I'm all for good regulation but when the structure is unable to recognise builds that perhaps won't require heating it seems odd.
    • CommentTimeOct 6th 2020
    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 :devil:

    Does it pass if he doesn't install the peat stove? And maybe installs PV instead?
    Having re read the OP, it sounds like they had approval for an ashp-heated house but they installed (effectively) a coal burner instead. The building standards folks would have to be asleep not to kick that one out!

    The Standard is intended to allow only lowish carbon houses, if they don't think they'd need low-carbon heating then the standard does allows them to insulate even more and then have minimal direct electric heating, IF that achieves the same CO2 overall. But it sounds like the house isn't insulated enough to pass with the electric heating.

    Your suggestion of a small air-air heat pump(s) sounds good, because as you said the heating demand should be fairly low and they're not that expensive compared to retrofitting wet central heating. Relocate the stove into the sheep shed and light it while they are lambing.

    When I moved to the North of Scotland I thought it was cold here, but now I think that everywhere else in the UK is uncomfortably hot, it's all about acclimatisation. We would roast if we lit a solid fuel stove in a well-insulated newbuild.
    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.
    • CommentAuthorRedDoor
    • CommentTimeOct 7th 2020
    WillInAberdeen - a contact has reported to me that his new build will fail to get a high enough EPC rating if he doesn't install a gas boiler (that is the most economic solution out of the variety of suggestions including extracting waste heat from the bath water) to complement his well-insulated construction that has solar thermal, whole house mvhr and direct electric (from a renewable energy supplier) top-up for space heating.
    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 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"

    I couldnt agree more David. This is one reason (even with my limited knowledge of SAP) I find it annoying.

    thanks for your comment everyone.

    Update: after going to the SAP assessor to check he got the build and fabric details correct and armed with some of the info posted here, and on other connected posts on GBF, the property has now passed as is.
    It appears the assessor probably didn't enter the correct data first time round. :neutral: a bit rubbish really.
    • CommentAuthorjamesingram
    • CommentTimeOct 7th 2020 edited
    "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
    • CommentAuthorEd Davies
    • CommentTimeOct 7th 2020
    Something I wonder about acclimatisation is whether you can do it without being uncomfortable - i.e., can you ramp the temperature down slowly enough that you won't really notice it or do you have to feel uncomfortable for a while in a lower (or higher) temperature for your body to actually adjust? Be interesting to know if there's any science been done on this.
    • CommentAuthorjamesingram
    • CommentTimeOct 7th 2020 edited
    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",
    • CommentAuthormarktime
    • CommentTimeOct 7th 2020
    We're on the other end of the spectrum here in the Canaries. We start feeling cold when the internal temp falls to 21º C and wear winter clothing when the outside temp drops to 17º or so. On the othe hand, that's the average internal working temp. that my son in London "enjoys".

    Absolutely no doubt that our bodies have acclimatised to the local ambient temperature.
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