Superhome 59 got its Energy Performance Certificate in April 2014. It was necessary to apply to Ofgem for the Renewable Heat Incentive. At the same time we got a “Green Deal Assessment” which recommends what measures a home could economically perform to improve energy efficiency and reduce bills. The EPC is based upon a software assessment of your home and tells you how much energy it should consume. Now you would think this would be non-controversial. On a home that underwent a £45k energy retrofit you would expect a sparkling “A+++” rating and everybody would be happy. Not so.
EPCs had an earlier and equally controversial history when then were scheduled to become part of the Home Information Pack (HIPs) in the UK. That plan was scrapped at the last minute leaving many assessors out of pocket as they had spent £thousands signing up to generate the HIPs. But that is another story for another day. Most people will probably have seen an EPC of some kind. They are familiar items on white goods and they now appear on everything from cars, to light-bulbs, to some public buildings. For example you see such a certificate in local schools and the central Library. They are now part of life and give a snapshot of how energy efficient something is. Useful consumer information – no argument. Anyone can get one for their home (although they are not free) and they are still required when you move. Most of us will probably end up with one if we are home owners. They are a fact of life.
So – to the controversy. The EPC is generated from a computer program – the RdSAP or “Reduced SAP”. SAP itself is a big computer program used by the pros, so the RdSAP is meant to be a simpler version. An assessor comes to your home, measures it, checks your energy bills, asks lots of questions and has a look in every nook and cranny to assess how well the building performs. The numbers are crunched and out pops your certificate.
So, how did Superhome 59 do? Interesting question. It scored “D55”. The average energy efficiency rating for a dwelling in England and Wales is D60. In English this means that Superhome 59 is performing WORSE than average.
Ha ha ha ha ha.
Of course that is insane – unless you assume that the house was some kind of pig sty that had £45,000 thrown at some incompetent builders who ran away with the money to Brazil. In fact this home is a semi built in the 1980s. So slapping in some extra insulation and double glazing should ensure that it gets about as good as it will get. So what is wrong?
This is where it gets interesting. In 2010 we had an NHERS rating as part the Superhome’s Charity assessment. The NHERS is just another assessment process but one that is reckoned (by its advocates) to be a bit more holistic than the SAP variety. That reckoned that the house in 1980 would have an annual heating load of 24,188kWh plus 10,043kWh for water heating +4,101kWh for other electrical usage. That’s a good starting point.
In 2009 we had the biomass boiler installed. This was after cavity wall insulation, after double glazing and after 300mm of loft insulation. The boiler installer calculated the heat load for space heating and hot water (this was before solar panels & wood burning stove) and he came up with a number that was 21,535kWh pa. The baseline, before any improvements, was (24,188 + 10,043 =) 34,200kWh pa (approx.) and, so 21,500kWh is 12,700kWh pa less than THAT. This is a 37% theoretical saving already at that point in the retrofit programme (2009).
So how much energy does Superhome 59 ACTUALLY use? Well according to our own estimates from the last 12 months we use about 2,600kWh pa electrical and 19,200kWh of space & water heating from the Biomass boiler. Add to that about 4,000kWh from the log burner and 2,700kWh pa for the hot water solar thermal panels. This suggests we use more energy than the boiler installer estimated. Over the 1980 theoretical baseline all space & water heating is (19,200 + 4,000 + 2,700 =) 25,900kWh pa. This is still a 25% saving over baseline. Savings in electrical usage represent approx 37% reduction under baseline.
So what does the EPC reckon we use? Combined space and water heating is quoted as 17,724kWh pa (14,824kWh space heating & 2,900kWh water heating). That is 48% lower than the 1980 baseline, 31% lower than actual usage and 17% lower than the 2009 estimate. In short – a bit rubbish.
So we did some digging. In 2008 there was an article published online [behind a paywall] suggesting that there were “errors” in the RdSAP software. It had been found that it gave an “award winning zero-carbon” home a “C” rating when it should have been “A” rated. This sounded spookily like our problem. But 2008 was a long time ago so we kept digging. There was more, a lot more.
Several articles emerged from Energy Assessor Magazine from the end of 2013 (published online here and here) showing case studies where the RDSAP EPC so grossly underestimated the heat load of a home that it was robbing home owners of thousands of £ off their Renewable Heat Incentive entitlement. The example cited had found the EPC suggest energy use 50% lower. This had started to happen after RdSAP was amended in April 2012 (to v9.91 for Green Deal).
We don’t yet know how this problem will impact Superhome 59 because we have applied for RHI for just the water heating solar panels not the space heating. Since the hot water is generated whether you need it or not (and is stored until you need it in a domestic hot water tank) it is displacing other fuels. As 2,700kWh is less than the EPC theoretical hot water requirement of 2,900kWh we might assume that this is not a problem.
It is though, a significant problem for people like social landlords looking to the RHI to justify the capital expenditure of large-scale projects to retrofit technologies like heat pumps for water and space heating. Since Ofgem uses the EPC theoretical energy consumption to calculate the payment then a 50% discrepancy means the landlord gets half the expected payback. In some cases this is leading to renewable heat projects being abandoned.
In our case ours is a sunk cost. The investment was made four years ago.
However, what we don’t get is this: since RdSAP assumes energy regulations from time of construction AND does not recognise improvements made to some homes to upgrade energy performance, then (logically) surely it would over-estimate the energy consumption? It also takes no account of the habits of the occupants hence a frugal family would be using less. No way should the EPC underestimate energy consumption by 50%.
Not everyone has daggers out for the new EPCs. Some claim it is a “reasonably consistent method of estimating typical energy consumption that enables dwellings to be compared on a like for like basis” however I would contest that anyone who thinks a five bedroom house, built in the 1980s, is going to consume only 15,000kWh of space heating energy a year is living in la la land. The results contradict the Green Deal Assessment report for Superhome 59 that suggest household energy bills of £1500 a year versus the average of £2000. Hence the family that lives in Superhome 59 live an economical lifestyle hence their actual usage would be far HIGHER if they were a “typical family”.
We can only conclude that an EPC assumes a hundred years of climate change have come & gone. The British Winter appears to have vanished out of the computer model.
But do you want to know the irony? Page 5 of the EPC contains a section on “impact of buildings on the environment” where it states:
“The average household causes about 6 tonnes of carbon dioxide every year. Based on this assessment your home currently produce approximately 0.2 tonnes of carbon dioxide every year.”
That is a 96% reduction in carbon footprint. On that measurement Superhome 59 scored “A98”. The highest possible with no room for improvement. Unless you wanted to re-build the house to Passivhaus standards. Now there is a thought….
For a Passivhaus the total primary energy use for all appliances, domestic hot water, and space heating/cooling must be less than 120kWh/m2 pa. We estimate Superhome 59 at 243kWh/m2 pa (see here). The EPC has our floor space as 131m2. Hence 14,824kWh (space heating) + 2,900kWh (water heating) + 2,600kWh (electricity) = 155kWh/m2 pa. Blimey! We are nearly a Passivhaus! I don’t think so.
It gets more weird because the EPC also quotes “primary energy use” as 206kWh/m2 pa but doesn’t show the source of the calculation. To get that number based upon 131m2 the total energy usage of Superhome 59 is 27,000kWh pa. This is about where the 2009 estimate was at 25,500kWh pa. But the only way to get that number, based upon the EPC figures, is to assume electrical consumption of over 9,000kWh pa. That is the electrical consumption of three or four average homes. That can’t be right.
Hence the only way to reconcile the EPC with reality is to assume by “primary energy use” it means heating and hot water. Hence that is 27,000kWh pa compared to the actual number of about 25,900kWh pa. If this is so then this is closer to the mark. If true it leads to two questions:
- why does the EPC contradict itself and then quote 17,724kWh pa for space and water heating?
- why is 206 kWh/m2 per year deemed to be “below average”?
Based upon all our work at Superhome 59 over the years we know we are MORE energy efficient than an equivalent home by about 20 to 30%.
So something is amiss here. Nothing about the EPC makes any sense. And that is a big problem. If the public cannot understand something why should they trust it? How can it yield any security when moving home? If it cannot even come close to yielding the right numbers then you don’t know how relatively well a home performs. Is it better, worse or average? In short, what value is an EPC if it doesn’t deliver an assurance of accuracy?
If I was to show the Superhome 59 EPC to a potential buyer they would laugh at it. They would assume that large improvements could be made. However, as the Green Deal Assessment shows, there are no such improvements to be made economically. Hence Superhome 59 is as good as it will ever get. Now that is a worry. If you spend a lot of money perfecting an energy efficient home you would hope that this can be measured objectively.
Sadly it cannot. And that is not going to help us move our housing stock forward into the bright sunlit uplands of a post-carbon future.