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How To Cheat And Get An Excellent EPC (Or The Failings Of SAP)


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#1 jsharris

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Posted 30 November 2014 - 12:15 PM

This came up on the AECB forum (which is barely used), but has highlighted an interesting "feature" of the method used to produce the Energy Performance Certificate (EPC) that all new homes have to have. The issue raised on the AECB forum was a builder who had built an "ultra energy efficient" new home, with a SAP derived EPC of A136. A little more information revealed that it had achieved this by having a 50kWp PV array on some adjacent outbuildings. I decided to see what would happen to our house if I swapped the 6.25kWp PV array for a 50kWp one. Rather surprisingly, the EPC Energy Efficiency Rating (EER) went from A107 to A256!

This got me thinking a bit, so I decided to reduce the insulation and airtightness numbers for our house in SAP, keep the 6.25kWp PV array, and see how poorly the house could be built in order to still reach the minimum EPC rating of C that's typically required for new builds. The result is interesting, if a bit shocking. If I had wall and floor U values of 0.25, a roof U value of 0.2, no heat recovery ventilation, the worst allowable air leakage rate of 10m³/m²/hr and natural ventilation through trickle vents etc, with worst case window and door U values as allowed by the building regs (in other words, a house that only just complied with building regs) then I'd get an EPC rating of A97! I couldn't get the house to be under an A rating with the PV array, as reducing insulation levels etc further flagged up non-compliances with Building Regs, so the software wouldn't produce a report.

If I remove the PV array, then the EPC drops to C70, which is pretty much what I'd expect for a new build that just barely meets the regs.

This is barking mad, as although the PV generates some energy, it does next to sod all to heat the house in winter, so the energy bills for the house with an EPC of A97 and the same house with an EPC of C70 are going to be the same in winter. The buyers of the house with the A97 EPC EER rating might reasonably expect their winter heating bills to be lower than those for an identical looking house with an EPC EER of C70, so may well feel a bit miffed when they find out they aren't any lower at all.

In reality, the EER (Energy Efficiency Rating) on the EPC certificate is no such thing at all. The energy efficiency of the house with no PV at C70 is exactly the same as that of the house with PV and an EPC of A97.

#2 recoveringacademic

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Posted 30 November 2014 - 01:02 PM

And that's the difference between intelligent, thoughtful engagement with underlying issues and compliance with regulation.

I'm completely new to building. And what fascinates me in this discipline is how systems, environment and people interact; by turn focus switches from regulation to philosophy, and back.

No matter what the discipline, bad regulation always engenders disrespect and so disregard. And a focus away from the underlying ideas.

#3 SteamyTea

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Posted 30 November 2014 - 03:38 PM

Is it because it all filters back to CO2 reduction. The energy used is a proxy of CO2, so fitting PV is a bit of a fudge.
We used it to sell PV system on houses that were not elegilble because they were an E or once an F.

#4 ProDave

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Posted 30 November 2014 - 03:45 PM

I found the same when I was modelling the EPC of my static caravan (when I was trying to get someone to issue an EPC for it, before I found nobody will in Scotland)

Being creative (replacing the gas stove for a wood burner) just scraped the static 'van into a D. Adding 4KW of PV pushed it up to an A. Bonkers.

#5 jsharris

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Posted 30 November 2014 - 04:05 PM

View PostSteamyTea, on 30 November 2014 - 03:38 PM, said:

Is it because it all filters back to CO2 reduction. The energy used is a proxy of CO2, so fitting PV is a bit of a fudge.
We used it to sell PV system on houses that were not elegilble because they were an E or once an F.

The EER is supposed to be a separate measure from CO2, but clearly it is very tightly linked in SAP. The CO2 measure is supposed to be the Environmental Impact rating (EI), which is given in terms of tonnes of CO2 emitted for the dwelling (ours if built to building regs minimum standards with the PV gets an EI rating of A98).

On the EPC, the labelling for the EER is "A - Very energy efficient - lower running costs" and the labelling for the EI is "A - Very environmentally friendly - lower CO2 emissions"

In reality, a house that's built to an EER of A, but with that rating derived from adding a bit of PV, isn't going to be very energy efficient or have lower running costs at all, because the true EER would be just scraping through as band C.

The whole thing is misleading as far as house buyers are concerned (that's if they actually care about energy efficiency at all).

Edited by jsharris, 30 November 2014 - 04:32 PM.
typo


#6 tony51

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Posted 30 November 2014 - 04:31 PM

View Postjsharris, on 30 November 2014 - 04:05 PM, said:

(that's if they actually care about energy efficiency at all).



Correct. Much money is spent - or rather - wasted - on generating information about the house which is generally low on the list
of priorities when people are looking to buy.
To most buyers, it's location, no. of beds, local schools etc.

#7 sketch3d

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Posted 03 December 2014 - 01:27 PM

I don't tend to work for larger developers these days, however using PV and solar hot water panels are some of the tricks of the trade to save money on the building fabric and still achieve building regs compliance.
With the one off dwellings & refurbishments along with a willful client I look for the fabric first approach then add in the eco-bling afterwards. I have never had a complaint from a client who has gone to town on the insulation with the exception of cost. However their builders are sometimes the hardest to convince and often overlook the specification on site.

#8 jsharris

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Posted 03 December 2014 - 06:13 PM

Tell me about it!

During the housing recession two big name developers mothballed part-completed major developments near me. Being curious, I wandered around the part completed site (site security seemed non-existent - not even fencing was in place properly) and was pretty shocked at what I saw. Missing insulation, rubbish detailing around doors and windows, like no cavity closers or even the slightest indication that there was any intent to prevent air leakage from the (poorly insulated) cavity around the inside of the window frames. It looked very much to me as if they had followed standard practice of getting one house of any design on site inspected (as it was obvious that there was one "good" one and the rest were rubbish) and were ignoring Part L on all the others of the same type.

I feel sorry for the buyers who are being misled, but this is the same big developer who was on Inside Out a few weeks ago for having sold a bunch of apartment with an EPC of Band C that had no insulation or airtightness detailing at all and were, in reality, EPC band G. The problem is no one is policing these cowboys, even our own building inspector admitted that around the office they suspected around 60% of all new homes built failed to comply with Part L, which is a sad indictment of the way the majority of our new housing stock is being built.