Green Building Forum - SAP 10 is it an own goal?

SAP 10 is it an own goal?

WillInAberdeen — Mon, 09 Oct 2023 09:57:56 +0100

I should have been clearer sorry, I'll try again!:
"There's an argument that PV panels *generate more power for the benefit of all society when* deployed in solar farms than on rooftops of houses *because of the better slope and orientation and avoidance of shading*- but that's not in tune with the public mood!"

In terms of individual financial benefits for owners, that depends a lot: eg on how much energy you use, when, and what tariffs you can get now and in future, how you raise the capital, whether you have storage or an EV, and whether you might move home. "Annual reconciliation" is a fantastic boost for the householder, but has never been available in the UK afaik. Probably the best prices here are on half-hourly tariffs.

If individuals would rather invest in solar farms than rooftop panels (or in both!), then there are commercial and community firms that do that - eg Nextenergy have 9% dividend yield and cost Â£550 per kW installed, it's cheaper than rooftop solar because of their economies of scale. (Disclaimer: don't take any investment advice from an online building forum, the value of opinions here can go up but usually down, ask a grown-up, etc etc etc!)

Edit: for interest but off topic sorry:
Solar farms have overtaken wind farms as the UK's cheapest source of electricity, according to the government

levelised cost of electricity excluding storage:
Solar farm Â£41/MWh
Offshore wind Â£44/MWh
Onshore wind Â£44/MWh
Gas CCGT Â£114/MWh including carbon costs

https://www.gov.uk/government/publications/electricity-generation-costs-2023

SAP 10 is it an own goal?

an02ew — Tue, 10 Oct 2023 07:14:43 +0100

Posted By: WillInAberdeenDon't really understand the background here?

New builds have to comply with Building Regs, which don't care about the running costs - they're based on (primary) energy consumption in kWh, not Â£:

i have no experience myself with SAP10 , my comment was based on the conversation with SAP assessor ( i probably got it a bit wrong) BUT the fact remains a new build home will fail its design SAP unless PV or HPs are added into the calculation which will have a massive effect on the construction industry going foward (IMO)

SAP 10 is it an own goal?

GreenPaddy — Tue, 10 Oct 2023 08:09:24 +0100

@ WiA,

the last house I designed and built was using SAP rev9, which utilised the cost of energy to establish the "SAP rating", as opposed to the "Env Impact" rating which is based upon primary energy. I've mostly been doing refurbs recently, so haven't had a need for SAP calcs.

Are you saying that SAP 10 has changed (from rev9), and no longer includes energy cost to establish the SAP rating? For good or bad, I'll need to re-set my mental norms ready for the next new build / conversion.

SAP 10 is it an own goal?

GreenPaddy — Tue, 10 Oct 2023 08:37:55 +0100

I had a quick look at SAP 10.2, and the SAP rating seems to be established in the same way as previous rev's (final calc, rather than all reams of calcs that arrive at the numbers to be manipulated)...

------------------cut from SAP 10.2----------
13 ENERGY COST RATING
The SAP rating is related to the total energy cost by the equations:
ECF = deflator Ã— total cost / (TFA + 45) (7)
if ECF ï‚³ 3.5, SAP 10 = 108.8 â€“ 120.5 ï‚´ log10(ECF) (8)
if ECF < 3.5, SAP 10 = 100 â€“ 16.21 ï‚´ ECF (9)
where the total cost is calculated at worksheet (255) or (355) and TFA is the total floor area of the dwelling at
worksheet (4). The deflator is given in Table 12a
-------------------------------------------------

AIUI, building regs stipulate the Target Emissions Rating (TER), and that the Design Emissions Rating (DER) must be less than the TER. SAP is just the calc tool to pull together the numbers to allow the comparison of DER & TER.

The basic model for the physical make up of the notional TER building is set out in the building regs (ie. assumed Uvalues, quantities of solar PV, heating system type and efficiencies, etc). SAP 10 uses those settings to generate a SAP rating and an EI Rating for the TER. A designer can design the dwelling any way they want, as long as SAP10 spews out the two numbers below the TER numbers.

Even in the last few houses I designed and built up to a couple of years ago, using direct electric and not having some form of generation (thermal or PV) made it near impossible to pass.

SAP 10 is it an own goal?

WillInAberdeen — Tue, 10 Oct 2023 09:01:43 +0100

Hi Green Paddy,

It's confusing, because SAP software is used for two completely different things:

- Building regs/standards for building new homes : based on energy usage in kWh. You have to meet the standard. Uses SAP10.

- EPCs for selling existing and new homes : based on Â£ cost (but about to change to kWh in Scotland) and with EI tagged onto the back. You don't have to meet the standard (unless the home is rented sometime after 2028). Mostly uses rdSAP 2012 .

People talk about 'SAP' and we get confused whether we mean 'Building Regs' or 'EPC'!

For English building regs, the previous versions were based on TER and DER (carbon emissions) and they're still mentioned in the 2022 revisions, but the main criteria now is Target Primary Energy Rate (TPER and DPER) in kWh, if you can meet this then the carbon will sort itself out.

In Scotland you no longer need to look at TER and DER (carbon) if you are heating with electricity as that is deemed to be 'zero emissions' here. Instead you use the Target Delivered Energy Rating in kWh (TDER and DDER).

The notional buildings in England and Scotland assume you will use PV, but there is an alternative using ASHP. It will be difficult to pass if you have neither.

Edit: there are very few building pros who are passionate about green building like GP and an02ew and a few others here are. It's shockingly bad how these new regs have been rolled out to those who care deeply, let alone to those who don't care at all. Nobody should have to work this stuff out by trial and error. The 'zero emissions' electric heating rules are buried deep on page 433 of the 2023 Scottish tech handbook which is still 'awaiting conversion to an accessible web format'.

SAP 10 is it an own goal?

Artiglio — Tue, 10 Oct 2023 09:31:36 +0100

At risk of veering off on another tangent, as just a landlord and having an interest in efficiency ,i find many of the discussions on gbf fascinating / enlightening. WIAâ€™s comment regarding the use of an older system to assess EPCâ€™s and how any legal relevance only applies to rented property, throws up how hard it is going to be to change things on that front , the proposed improvements to the MEES for the prs in england has been ditched at least until after the next general election, there is already a shortage of property avaialble to rent and a move to a mandated epcC for rented property would have made it worse, but equally any updating of the assessment and or moving the scale to disadvantage gas and make electricity preferable will equally cause chaos in the rented sector.
Iâ€™ve bought my properties upto a C and locked that in for 10 years by bringing the epc renewal date forward,iâ€™d likely do them again before the assessment procedure changes ( as and when it eventually does) to gain a bit more breathing space. The cost of heating my rental properties via ashp is never going to be financially viable ( unless either, there are lots of grants available or the failure to update ( and any associated legal issues) them makes them lose so much value that it bankrupts me and they are bought cheap enough for the purchaser to be able to afford to do it).
The recent changes to the oversight required for any works coming under building regs is going to make future works ever more expensive ( my last visit from building control led them to suggest that it could increase the cost of works by 10-20% depending on how it all shakes out) and compliance certs ever more important for future mortgages and sales.
The establishment response to grenfell is going to cause huge issues and tie people in knots going forward, all because our civil servants have no idea as to how things work at grass roots level, their thinking blinkered by the view that everything is paid for from an infinite pot of government money and the desire to ignore the history of grenfell and its management in the decades leading upto the disaster.
There really is a lack of joined up long term pragmatic thinking within the corridors of power.

SAP 10 is it an own goal?

WillInAberdeen — Tue, 10 Oct 2023 11:32:04 +0100

Another doozy from the 2023 Scottish regs, this time featured on page 438:

If you have PV as per their spec for the notional building, then you are only credited with the PV that the building consumes itself. Not with the power that you export, or use in your EV or dishwasher.

But obvs PV generates most in summer and heating is needed in winter, so actually most of your PV output will not be included in the heating calculation and your shiny PV will not be much help to you.

Haven't looked if same rules in England.

SAP 10 is it an own goal?

djh — Tue, 10 Oct 2023 11:46:51 +0100

Posted By: WillInAberdeenIf you have PV as per their spec for the notional building, then you are only credited with the PV that the building consumes itself. Not with the power that you export, or use in your EV or dishwasher.

Why is the dishwasher specifically excluded from general consumption? It sounds like those regs will make the use of PV for DHW heating comparitively more important?

SAP 10 is it an own goal?

tony — Tue, 10 Oct 2023 15:00:55 +0100

SAP 10 is it an own goal?

WillInAberdeen — Wed, 13 Dec 2023 19:09:30 +0000

SAP is to be abandoned and replaced by something called the Home Energy Model

https://www.gov.uk/government/consultations/home-energy-model-replacement-for-the-standard-assessment-procedure-sap

SAP 10 is it an own goal?

WillInAberdeen — Wed, 13 Dec 2023 19:41:05 +0000

Replying to this thread as can't start a new one

New English building standards proposed for 2025 - afaics no change to fabric standards, but gas boilers to be banned for new builds:

https://www.gov.uk/government/consultations/the-future-homes-and-buildings-standards-2023-consultation/the-future-homes-and-buildings-standards-2023-consultation

SAP 10 is it an own goal?

Julio — Wed, 13 Dec 2023 21:29:18 +0000

On a slight tangent but similar subjecr. Does the solar that is being inputted into the SAP assessment need to be mounted onto the structure of the building or can they be ground mounted within the curtilage?

SAP 10 is it an own goal?

WillInAberdeen — Thu, 14 Dec 2023 00:33:27 +0000

"PV array is mounted on the building concerned or wholly within its curtilage, and its output is directly connected to the dwelling’s electricity supply" - SAP app M

The new Home Energy Model software that is going to replace SAP is apparently more detailed and has been tested against PHPP..

But problems are still there:

- software has to cope with design phase where key inputs are not known yet, like airtightness results, shading, occupancy for new insulated homes where solar/incidental gains make big difference to whether heating is needed or not.

- same software has to cope with EPCs for old houses where key inputs are not visible, like AT or insulation buried in walls or under floors

Apparently they tested the new software against real world data measured from a passivehouse, it did ok until the occupant started closing the blinds, so keeping the sun out.

Also looks to me that direct electric heating and DHW is not going to meet the TER/TPER even for well insulated homes, will have to have a heatpump or communal heat network.
But only skimmed it so far.

SAP 10 is it an own goal?

WillInAberdeen — Thu, 14 Dec 2023 22:47:46 +0000

Just to confirm that the 2025 standard for new homes is proposed to be

U= 0.11/0.13/0.18 roof/floor/wall,
Air test 4-5 m/h@50Pa

AND
heating and DHW by ASHP or communal network

AND MAYBE (under consultation)
Solar PV AND MHRV AND WWHR

Looks like adding extra insulation and AT (above those standards) will not be sufficient, even if to PH levels, without also having ASHP and other tech.

No mention of the elephant under the floor: embodied carbon.