Getting an "A" EPC Rating

zeupater

Screwdriva said:

zeupater said:

 especially the comparison between equally sized property energy requirements of an EPC A(93) rated property with PV (SAP 1665kWh/year) and an EPC C(80) rated passivhaus without PV (SAP 644kWh/year) ...

I think this paragraph summarizes the report's primary gripe with the EPC's rdSAP methodology. 

"You might say that’s acceptable as the electrical energy generated by the PV offsets the energy used by the dwelling. However, the problem is that the emission rate associated with electricity is reducing due to more renewables at national level and is already lower than gas. As this reduces further, the emissions associated with a dwelling which uses gas (e.g. for heating and hot water) will far outweigh the emissions saving from generating electricity. This will be reflected in the environmental impact rating shown on the EPC, but, as mentioned earlier, this is rarely used and is not placed prominently on the EPC."

Clearly, the Passivhaus trust does not like gas being used for heating. But the report fails to account for the rather straightforward substitution of gas boiler with a heat pump (entirely compatible with an A rated home's insulation levels). Were this to be enabled in the EPC methodology going forward, as I expect it will be very soon, I wonder if the contrast with a purely electrically (emitters + immersion) heated Passivehaus would be as stark?

Hi

I don't actually think that's the case .... there's a direct comparison used as an example to illustrate the issue with the RdSAP EPC methodology when applied to two equally sized properties, one built with material assumptions as per the BRE assessments as per current build standards, the other representing the materials typically used in current passivhaus builds.

RdSAP assumptions are based on minimum material standard performance in place at time of build, therefore there's effectively a standardised setback of energy efficiency according to property age, regardless of assessment of materials used in the actual build.

What needs to be recognised is that the EPC rating we're discussing related to the property energy performance, not the environmental impact assessment which addresses the heat source and it's assumed efficiency in providing the heat load as per the energy performance calculated, providing an estimate of the CO2 emissions on an annual basis. Our EPC as issued actually stated & illustrated the environmental impact as B(84) with a potential of B(87) if we made the recommendations which would save ~500kgCO2  (ie Floor insulation & biomass heating), which we, as stated above, we already had, stating that our current base emissions (based on an estimate of energy requirements) were 2.4tonnes/year ...

The issue with our own EPC assessment is that the calculated heat load requirement is based on materials and standards that don't apply to our property, in exactly the same way that materials typically used in passivhaus designs don't conform to the assumptions used by the BRE in their simplified RdSAP model ... for us, that means that whatever the heat source employed to assess the environmental impact, RdSAP vastly overestimates the heat load (in our case by ~>3x!!) ... that's the real issue for us and I'm pretty confident that's what the report also attempts to convey.

HTH - Z     

     

[Deleted User]

My faith in the EPC system nose dived after the £1800 smart heating control system in my old home was treated as a two-zoned heating system with standard TRVs. 

Having bought a property rated B86 and put 6.3kWp of solar panels on the roof, my EPC tells me that with 2.5kWp of solar my EPC would rise to A92. I am not sure how the extra 4kWp would be assessed for EPC purposes?

Screwdriva

Dolor said:

Having bought a property rated B86 and put 6.3kWp of solar panels on the roof, my EPC tells me that with 2.5kWp of solar my EPC would rise to A92. I am not sure how the extra 4kWp would be assessed for EPC purposes?

The EPC appears to be limited in its ability to differentiate between several heating system customizations. Our boiler offers vastly superior modulation capabilities, dual zone heating curves etc. but the EPC surveyor was only able to "check" standard weather compensation.

That said, it does differentiate between 2.5 or 4kW PV generation, as well as South/ Non-South facing roof aspects.

ABrass

The SAP calculation (the point score in EPCs) for solar power is quite complex. Solar, or wind turbines, contribute by reducing the cost of fuel.

Slapping a 4kW system on an F rated house will make a difference by reducing the energy bills. But that same 4kW array on a B rated house should give you more points. I believe it's why you get the sequence of improvements.

Fun fact: EPC scores can go above 100 if you're generating enough excess energy.

zeupater

Screwdriva said:

Dolor said:

Having bought a property rated B86 and put 6.3kWp of solar panels on the roof, my EPC tells me that with 2.5kWp of solar my EPC would rise to A92. I am not sure how the extra 4kWp would be assessed for EPC purposes?

The EPC appears to be limited in its ability to differentiate between several heating system customizations. Our boiler offers vastly superior modulation capabilities, dual zone heating curves etc. but the EPC surveyor was only able to "check" standard weather compensation.

That said, it does differentiate between 2.5 or 4kW PV generation, as well as South/ Non-South facing roof aspects.

Hi

That really is the issue at hand .... the EPC in itself is conflicted and there's a general misunderstanding on what it's attempting to convey.

A building's Energy Performance Certificate should be a summary document describing the standardised heat load & base energy requirement of the building under a standardised occupancy profile, and nothing more ... the reason that this is important is that whatever the EPC conveys at date of issue it only really can be seen as a guide for the current & future potential occupiers/owners, which, of course, when looking at costs would be subject to variation as occupancy number/profiles and heat provision technology requirements/preferences change.

Regarding the efficiency of heat sources to provision the heat load, that should really have been considered as being separate from the EPC, therefore exclusive to the Environmental Impact part of the assessment, a non-headline rating which most people typically tend to overlook & ignore ....

The environmental impact & energy cost differential between heat provision by gas, electric resistance or heat pump sources should have absolutely no effect on a building's heat load requirement and therefore the EPC itself, but for some reason a grey area of interrelationship between the two seems to have, for some reason (probably political), crept into the base EPC mix for assessment ...

Something that would seriously improve the information package resulting from the assessment would be a standardised model tabular representation of the existing energy sources for the house, for which (assuming the current model has any real credibility) the data must already exist. This should assess and break down provision of energy by energy source, therefore including energy captured/generated within the home as well as that from imports & purchases and could even provide the basis to provide (report included or by on-line tool) EPC customers the ability to visualise the potential emission & energy cost differentials for various heat sources in that property .... e.g.: current standardised GCH with PV vs various standardised heat pump technology alternatives, maybe even modelling the balancing effect of supplementing PV with domestic battery storage, which would make far more sense.

Of course, all of this actually relies in the basic materials based assumptions creating an accurate assessment of a property's energy requirements under standardised conditions .... there are plenty of articles I've read over the years which are published by seemingly credible organisations & material property experts that tend to point towards accuracy confidence decreasing as housing stock age bands increase ... from memory, one study provided evidence of RdSAP overestimating heat provision by around 66% in homes built prior to the middle of the last century. that's around 1 in 3 of the current housing stock, whilst providing quite accurate assessments against properties built to the minimum standards required today ... one therefore may legitimately interpret this as being the energy performance improvements of current build homes vs old stock properties have been artificially inflated for some undisclosed reason, the alternative being that the BRE have displayed a significant level of incompetence in building/approving the RdSAP model since it's inception.

HTH - Z