SAP Calculations are used to demonstrate the energy performance of dwellings in the UK and are a key part of building regulations compliance. The SAP document defines exactly how the assessment works and is updated generally every 4 years.
SAP 10 has been somewhat delayed, and although the new methodology is not for use until Part L of the building regs has been revised (likely to be 2019 or 2020), it does give us a valuable insight into the changes SAP 10 will bring and allows us and our clients to plan ahead.
As always there are a number of changes within the small print, mostly insignificant to designers, but some will have the potential to affect the way we design new dwellings going forward.
Here is a summary of the major changes and what they might mean to you:
The changes to the electricity related carbon emissions may be the most significant factor – reducing from 0.519 kgCO2/kWh to 0.233 kgCO2/kWh, now only slightly higher than mains gas (0.210).
Currently SAP assumes that any electricity used produces 2.4 times the carbon emissions of mains gas – this is because it uses an outdated carbon factor which is not reflective of the current energy mix of the grid. The ‘greening of the grid’ means there is now much more renewable and clean energy online and much less coal being burned.
Targets within SAP are currently based on mains gas, so this heavily penalises electric use, and certainly any new builds with all electric heating are incredibly difficult to pass without additional renewable technologies being installed.
We are pleased to see a much more representative carbon factor being applied, which will certainly give clients more design options going forward.
The fuel prices per kWh have also been updated within SAP 10.
Currently SAP attributes a standard heating pattern which assumes that homes are heated differently on weekdays and weekends. Studies have shown that this is not necessarily the case in real life, and so SAP 10 has been changed to apply a consistent daily pattern for all days of the week. This will have the effect of reducing energy use and costs across the board.
Default distribution loss factors associated with heat networks have been increased
Losses associated with decentralised heat networks have probably been underplayed previously in SAP, and so this change will marginally reduce the effectiveness of connection to a heat network. This may have implications for London schemes where a carbon reduction is being sought for planning requirements.
The current lighting simulation within SAP is rudimentary to say the least, simply accounting for the number of low energy fittings being installed. The changes will mean that we can use a much more accurate lighting design to inform the assessment, much as the SBEM methodology (the tool we use for commercial and public buildings) does. This will allow recognition of new lighting types with higher efficacy.
This is potentially a big one. Heat losses owing to junctions in the construction have, up until now often been offset by using the ACD scheme (Accredited Construction Details). This gives designers and contractors a set of junction specifications to follow, which in turn allows the SAP assessor to apply improved values over the default values.
Due to concerns over the accuracy and age of these ACD junctions, SAP 10 has taken away the option to follow them. This means that the client would need to either use alternative schemes (perhaps from the insulation manufacturers) or have bespoke heat loss values calculated for each junction.
Hot water consumption has until now been based on a standardised usage. Flow rates will now need be entered into SAP 10 so we will start to see a certain amount of variation between shower fittings being used.
Water efficiency calculation are already required under Part G of the building regs, so there will now be some informed cross over between these two assessments.
SAP 2012 used a fixed assumption for the proportion of electrical energy generated by Photovoltaic (PV) systems and consumed within the dwelling. This was attributed 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 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 made when designing and installing systems.
There is now also recognition of the presence of battery storage in the assessment.
A PV diverter prevents electricity produced from photovoltaic panels from being exported to the grid, and instead directs it to an immersion heater in the water cylinder. It will now be possible to account for these systems in SAP 10 which will provide extra design options.
An option will now exist in SAP 10 to allow the overshading factor used for the PV calculation to be taken from Microgeneration Certification Scheme data. This would overwrite the default options currently available in SAP.
To download SAP 10 and for further reading see www.bregroup.com/sap/sap10