2021 (SBEM v6) Building Ratings

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England, Scotland and Wales adopted changes to fuel emission factors for BRUKL and EPC calculations from 2022 / 2023.

  *2021 Electricity Factors are monthly dependent ranging from 0.111 in July up to 0.163 in Dec, the figure here is the mean for the year.

**2021 PV Carbon Factors are monthly dependent ranging from -0.092 in July up to -0.197 in Dec, the figure here is the mean for the year. 

• The BER for many buildings may change with the new ratings due to lower electricity factors.
• Scotland bases the rating purely on the BER, thus the majority of buildings will generate a significantly lower rating with these changed rates.

England and Wales base the rating on the ratio: BER / RER. The Reference Building uses Gas for Heating and Hot Water thus the rating will often be dependent on the proportion of gas: electricity use in Actual and Reference Buildings

Case Studies

Note these studies look at a particular scenario for a single zone / activity. Whilst it is rare that a building will comprise zones of only one activity, some activities are dominant in their energy demands and can be the most significant factor in determining the Building Rating.

1. Data Centre with gas heating DHW and electric heat pump for cooling:

56b: BER = 1756kgCO2/m2/year, Rating 107

This activity has a very high equipment energy providing high heat gain in the space and resulting in no demand for heating and high demand for cooling. This activity also has a zero demand for DHW. Thus, whilst both Actual and Reference Buildings are specified with Gas Heating and DHW, both only use electricity due to these factors.

61e: BER = 468kgCO2/m2/year, Rating 107

The BER for the 61e calculation is almost a quarter of BER for the 56b calculation, however the Rating is unchanged

Both in the 56b and 61e calculation Electricity is the only fuel used for Actual and Reference Building. Thus in both cases the ratio of kgCO2/m2(Actual) / kgCO2/m2(Reference) used in deriving the rating =

(Electricity Consumption (Actual) *EmissionFactor(Electricity)) /  (Electricity Consumption (Reference) *EmissionFactor(Electricity))

As the electricity factors vary monthly there will be a slight difference in overall emission factors but we can likely simplify this to:

(Electricity Consumption (Actual) /  (Electricity Consumption (Reference)

Thus the rating is effectively independent of the emission factors 

The total electricity consumption in both the 56b and 61e for both Actual and Reference Buildings are almost identical so it is no surprise the rating is virtually unchanged (in this example it does not change at all).

2. Office with gas heating and DHW:

56b: BER = 50kgCO2/m2/year, Rating 59

61e: BER = 23kgCO2/m2/year, Rating 58

Note the lighting energies are lower in 61e than 56b due to a change in the lux setting for the activity (56b: 400, 61e: 300). See https://designbuilder.freshdesk.com/a/solutions/articles/103000268103 for more on this.

Co2 contributions for Actual and Reference Buildings in 56b and 61e show there is little overall change even though the 61e BER is less than half that for 56b:

Whilst Electricity use is the predominant carbon fuel for 56b, Gas is the predominant carbon fuel in 61e: the ratios for each fuel in Actual and Reference Building remain very similar, hence there is no significant change in rating:

3. Office with horizontally mounted PV System (based on Case 2)

56b: BER = 41kgCO2/m2/year, Rating 48 (B)

9kWp of PV was added to the horizontal roof, generating 16.52kWh/m2 and offsetting 8.57kgCO2/m2

61e: BER = 21kgCO2/m2/year, Rating 52 (C)

9kWp of PV generated 17.28kWh/m2 and offsetting 2.17kgCO2/m2

Whilst the kWh generated is slightly higher due to updated (2016) CIBSE Weather Data compared with 2006 CIBSE weather data used in 56b, the CO2 displaced is one quarter of that displaced in the 56b calculation which means the offsetting of CO2 is one quarter that achieved previously. The CO2 factors for displaced electricity in 61e depend on the month:

Note that as the peak kWh generated occurs when the Displaced CO2 factor is at a minimum, the effective CO2 factor for the PV System is only 0.129kgCO2/kWh compared with a constant 0.519kgCO2/kWh in 56b. Thus, whilst adding the PV to the 56b model enabled the rating to drop 11 points (59 to 48) the PV is less effective in 61e causing a drop of just 6 points (58 to 52). In an all electric building the effectiveness of a PV System (specified as kW peak) to reduce ratings will be better but unlikely to be as effective as in SBEM v5.