SAP 10 – what’s new and how does it affect you?
SAP calculations are used to assess the energy performance of dwellings in the UK and are a key part of Building Regulations compliance.
The SAP documentation outlining how the assessments work and their set levels are usually updated every 4 years.
In July of this year, the Department for Business Energy & Industrial Strategy (BEIS), in conjunction with the technical authors the Building Research Establishment (BRE), published the latest version of SAP, which is known as SAP 10.
Following the published responses from BEIS on the consultation in November last year, many of the changes are not unexpected:
Electric CO2 emissions
Many of the fuel types recognised in SAP have had their fuel prices, CO2 and primary energy factors changed with the most significant being the electricity related carbon emissions – reducing from 0.519 kgCO2/kWh to 0.233 kgCO2/kWh, now only slightly higher than mains gas (0.210). This reflects the increased influence of renewable energy technologies producing electricity for the national grid.
Assumed heating patterns
Within the BEIS consultation, the standardised heating patterns that SAP is based on were discussed – it currently attributes different standard heating patterns for weekdays than for weekends.
However further studies have shown that this is not necessarily the case in real life therefore SAP 10 has been changed to apply the same daily pattern regardless of the day of the week. This will have the effect of reducing energy use and costs across the board.
This calculation has changed significantly. In SAP 2012 the lighting simulation was extremely basic, only accounting for the number of low energy fittings being installed. SAP 10 changes will mean that a much more accurate lighting design to inform the assessment will be used, similar to the SBEM methodology used for commercial and public buildings. This will recognise the use of new lighting types that have higher efficency.
Until now, heat losses owing to junctions in the construction have been offset by using the ACD scheme (Accredited Construction Details). However, after consultation ACD’s are now considered to be inaccurate and not fit for purpose based on current building practices. Therefore the psi values for the MHCLG Accredited Construction Details (ACDs) scheme have been removed from SAP 10.
This will result in assessors having to rely on other established sets of construction details, or encourage more junction details to be modelled to derive accurate psi values.
To add to this, the default y-value used in assessments where no details of thermal bridging are provided has been raised from 0.15 w/m2k to 0.2 w/m2k in SAP 10. This will mean developers that who do not consider heat loss through building junctions will face stiffer penalties.
Hot water Consumption
The number of showers and baths which are present in a dwelling will now be included into the calculation of hot water demand which should result in a more accurate assessment of hot water demand than currently in SAP 2012.
Also electricity use from instantaneous electric showers will now be accounted for in assessments. This has not been the case in previous versions of SAP and will result in higher energy use in assessments where used.
SAP 2012 used a fixed assumption for the proportion of electrical energy generated by Photovoltaic (PV) systems and consumed within the dwelling. This was included within the calculation regardless of whether there was a direct connection to a dwelling, or whether, as is often the case on blocks of flats, only one exists to a landlords supply.
This has now been replaced by a formula which will only factor in a PV supply to those flats directly connected. This will impact on those developments which are relying on a carbon reduction for a planning condition, and much more consideration will need to be taken when designing and installing systems.
The calculation of electricity generated from PV now has the option to account for battery storage technology. Also where PV is directly feeding an immersion coil in a cylinder, known as a PV diverter, this will be able to be reflected in SAP 10.