What is the effect of EPC changes?

[Ferdinand]

Ideally this is one for a tame EPC Assessor!

 

Do we have any idea how EPCs will adjust under the new values?

 

Has anyone rerun their numbers?

Cheer

Ferdinand 

Edited August 31, 2019 by Ferdinand

[MikeSharp01]

Is this in relation to domestic properties or landlords requirements?

[Ferdinand]

12 minutes ago, MikeSharp01 said:

Is this in relation to domestic properties or landlords requirements?

 

I’ll clarify. Thanks for the response.

 

It is in relation to the changes in the algorithm which have reduced the effective C02 production of electricity relative to gas, as mentioned on another thread.

 

I am trying to get a feel for what difference that will make to the actual number on an EPC. So will the EPC number of a house with ufh / combi boiler (say) go up or down. Ditto a house with say storage heaters or ASHP.

 

I would expect, given that the dataset is not normalised to a curve over the 1-100 number range, for an electrically heated house to get a better value, and a gas heated house to stay about the same with perhaps a small increase in number due to the small impact of he electricity used for other than heating.

 

So this is in relation to understanding how the numbers will change.

 

That will feed into landlord requirements and tenant experience, given that regulation is on the numbers on the EPC, but Inwas trying to understand the algorithm changes with this thread.

 

What I am hoping is that there are few people who have repeated the calculation in Stroma under both definitions, and we can get some data. 

 

F

Edited August 31, 2019 by Ferdinand

[MikeSharp01]

Ok now I see, thanks, I have not run any numbers but the whole thing looks very marginal as things stand although it does give directional thinking in terms of increasing (could be decreasing depending on how you look at it)  the weight of renewable energy and decreasing the weight of gas - hence the general feeling on here that installing gas heating - even for domestic hot water (DHW) is depreciated.

[joth]

33 minutes ago, Ferdinand said:

 

It is in relation to the changes in the algorithm which have reduced the effective C02 production of electricity relative to gas, as mentioned on another thread

 

So the expectation is an all-gas house would see no change, but all-electric would see a rating improvement?

 

Interesting: another reverse incentive nail in the RHI coffin for new installs? if converting from gas to electric, you can have the claim based on the EPC with gas system you're switching away from, but for an all electric install the EPC will necessarily be based on the better performing electric system installed from outset. 

 

I think if they'd introduced RHI as a "dirty old boiler scrappage scheme" it would be much easier to follow.

 

[Jeremy Harris]

The problem was that the emissions data being used to assess the environmental impact of electricity use was hopelessly out of date, and used data from the time when we had little renewable generation and a fair bit of coal and oil fired generation.  The grid has significantly reduced its emissions, so SAP needed to catch up and use a more representative factor for assessing an all-electric house.

 

This failing in SAP bugged me when I did our assessment, as being all-electric we were unfairly penalised.  The assumption then was that our electricity imports generated 0.519kg CO₂e/kWh, when the reality was that the grid was then running at under 0.3kg CO₂e/kWh.  Since then the grid emissions have reduced still further.

 

 

[A_L]

@Ferdinand, The SAP 1-100+ scale is a cost index (of energy for heating & hot water),  changes to the emission factor for an energy source will change the Dwelling Emission Rate (DER) but  should not affect the SAP score.

 

 

[MikeSharp01]

Just thinking about it the scale cannot be linear as at the bottom must be infinite cost so getting over a 100 gets increasingly difficult. Also it is not full cost so may not include all the cost factors out to the limit AND if you change the basis then all the existing values must change and you might find yourself living in an A+++ house that turns out to be Z minus. However @JSHarris is perfectly correct in saying that it should reflect the reality of its surroundings in terms of how it interacts with energy supply / generation patterns and the like.

[A_L]

1 hour ago, MikeSharp01 said:

Just thinking about it the scale cannot be linear

 

It is not linear from about 51 down but appears to be above this.

 

From page 35 https://www.bre.co.uk/filelibrary/SAP/2012/SAP-2012_9-92.pdf

N.B. The deflator = 0.42, The square should be a minus sign

 

 

[MikeSharp01]

1 hour ago, A_L said:

It is not linear from about 51 down but appears to be above this.

Interesting set of fiddle factors then..

[Jeremy Harris]

I've just run our house through SAP again, using the new emissions factor for electricity, and the CO₂ emission has changed from -0.9 tonnes to -1.94 tonnes per year.  That's a change from our house being roughly equivalent to about 40 mature trees, in terms of effective CO₂ sequestration, to it being roughly equivalent to about 86 trees.  The impact of this on offsetting the CO₂ produced when making the concrete in our slab is that the CO₂ "debt" of the ~10m³ of concrete in our slab has now been offset, (assuming that each m³ of concrete released around 410kg of CO₂ during its manufacture) so from now on the house will be pretty much CO₂ negative for the rest of its life.

[Ed Davies]

1 hour ago, JSHarris said:

and the CO₂ emission has changed from -0.9 tonnes to -1.94 tonnes per year. 

 

You're a net exporter of electricity. Electricity is now considered to produce less emissions so why hasn't your “negative emissions” decreased (moved towards zero)?

[Jeremy Harris]

23 minutes ago, Ed Davies said:

 

You're a net exporter of electricity. Electricity is now considered to produce less emissions so why hasn't your “negative emissions” decreased (moved towards zero)?

 

It seems to be the difference between self-generation being counted as negative CO₂, and consumption having a reduced CO₂ emission under the new factor, so we've gone "more negative", as SAP just subtracts the self-generation CO₂ equivalent from the consumption CO₂ equivalent.  The latter has reduced, so the overall negative CO₂ has changed from -0.9 to -1.94 tonnes/year (I don't have the SAP worksheet on this laptop, but the self-generation was around -2,700kg/year).

[Ferdinand]

47 minutes ago, JSHarris said:

 

It seems to be the difference between self-generation being counted as negative CO₂, and consumption having a reduced CO₂ emission under the new factor, so we've gone "more negative", as SAP just subtracts the self-generation CO₂ equivalent from the consumption CO₂ equivalent.  The latter has reduced, so the overall negative CO₂ has changed from -0.9 to -1.94 tonnes/year (I don't have the SAP worksheet on this laptop, but the self-generation was around -2,700kg/year).

 

How did the two different numbers compare, Jeremy, if you have those.

 

I think that your current SAP is a 107? What is the new impact rating?

 

(Will try and comment on the other excellent points from everyone later.]

 

F

[MikeSharp01]

6 hours ago, A_L said:

From page 35 https://www.bre.co.uk/filelibrary/SAP/2012/SAP-2012_9-92.pdf

Just spent a pleasant afternoon reading this while drinking coffee in John Lewis, the other half was shopping with a friend, previously I thought I understood enough about SAP (not much) to be a consumer of other peoples work on our build now I see that you can probably game this in a host of ways and I need to take a few steps / tweaks to ensure the as built is optimised- sadly we are past the as designed and I can do nothing about the slab as built. 

[Ed Davies]

14 hours ago, JSHarris said:

It seems to be the difference between self-generation being counted as negative CO₂, and consumption having a reduced CO₂ emission under the new factor

 

Ah, so electricity exports count at a different kg CO_2e/kWh from imports? That'd make sense as exports, particularly from PV, would tend to be at a time when emissions are lower anyway.

[SteamyTea]

31 minutes ago, Ed Davies said:

would tend to be at a time when emissions are lower anyway.

Is that total emissions (absolute), or CO2/kWh emissions (relative).

[Ed Davies]

26 minutes ago, SteamyTea said:

Is that total emissions (absolute), or CO2/kWh emissions (relative).

Both. But, good point. Maybe not marginal CO₂/kWh.

 

I.e., when PV's exporting it'll tend to be light and warm so less total electricity consumption and more PV generation from others (though likely less wind generation) so lower total emissions (from gas-fuelled power stations) and lower emissions per kWh. But, still, whatever extra is needed is made up by gas generation so if @JSHarris exports another kW it'll the gas power station operators will turn down their generation by that amount resulting in the same emission savings as at any other time of the year.

 

Which brings us back to the question of whether SAP should work for imports on the average emissions per kWh, say 0.3 kg/kWh, or the marginal rate of something more like 0.5 kg/kWh.

[Jeremy Harris]

Right now about 16% or so of our electricity is coming from gas (the rest is coming from renewable generation, nuclear and interconnects) and total grid emissions are 0.088kg CO₂e/kWh.  Yesterday evening grid emissions peaked at about 0.148kg CO₂e/kWh.  Looking back over the past few days it seems the highest emissions were around 0.25kg CO₂e/kWh, close to the figure now used in SAP.

 

Gas generation emissions are around 0.499kg CO₂e/kWh, so anything that reduces gas generation reduces grid emissions by about this much.

 

 

 

 

 

 

[Ferdinand]

This is the definition of the various terms from the document linked:

 

Quote

The indicators of energy performance are Fabric Energy Efficiency (FEE), energy consumption per unit floor area, energy cost rating (the SAP rating), Environmental Impact rating based on CO2 emissions (the EI rating) and Dwelling CO2 Emission Rate (DER).

 

The SAP rating is based on the energy costs associated with space heating, water heating, ventilation and lighting, less cost savings from energy generation technologies. It is adjusted for floor area so that it is essentially independent of dwelling size for a given built form. The SAP rating is expressed on a scale of 1 to 100, the higher the number the lower the running costs.

 

The Environmental Impact rating is based on the annual CO2 emissions associated with space heating, water heating, ventilation and lighting, less the emissions saved by energy generation technologies. It is adjusted for floor area so that it is essentially independent of dwelling size for a given built form. The Environmental Impact rating is expressed on a scale of 1 to 100, the higher the number the better the standard.

 

The Dwelling CO2 Emission Rate is a similar indicator to the Environmental Impact rating, which is used for the purposes of compliance with building regulations. It is equal to the annual CO2 emissions per unit floor area for space heating, water heating, ventilation and lighting, less the emissions saved by energy generation technologies, expressed in kg/m²/year."

 

So, based on the conversation above, the reduction of C02 Emissions Factor for Electricity, the SAP Rating should not change, and the EIR Rating should reduce proportional to electricity usgae, and C02 Emission Rate should reduce similarly.

 

By contrast, in 2018 the SAP algo was adjusted when they found that solid walled and uninsulated walled properties were relatively better in CO2 emissions terms than had been thought previously.

https://www.bre.co.uk/filelibrary/SAP/2016/CONSP-16---Wall-U-values-for-existing-dwellings---V1_0.pdf

 

The assumption had been U-value of 2,1m which was updated to I think 1.69.

 

(The background is that the previously assumed value was derived from that used for sizing heating, so naturally assumed it was worse to help make sure that systems were comfortably big enough.)

 

F

Edited September 1, 2019 by Ferdinand