SAP 2016

IMG_2131The future trajectory of energy efficiency standards was uncertain even before the EU referendum: the abandonment of the expected Part L 2016 changes left an unfilled void. We have no idea what the policy landscape is going to look like, and whether regulation 25B (nearly zero energy buildings) is ever going to come into force. But in the middle of all the uncertainty SAP 2016 is still going to happen1.

SAP, the UK’s domestic energy assessment tool2, has been revised every three or four years since the first version back in 1993, so a revision is due. We are expecting the consultation draft sometime in July, and BRE already have a SAP 2016 page on their web site (there’s not much there at the minute, but we may as well book mark it now).

So what can we expect in SAP 2016? For an authoritative account we will have to wait for the consultation, but we can get some hints from a paper presented at the CIBSE Technical Symposium in April this year by Deborah Morgan and John Henderson. (The paper is also a good summary of the assumptions underlying SAP.)

The paper describes the update cycle for SAP, and in doing so describes four parts of the methodology which were considered for revision. Those being:

  • Default values for distribution losses in heat networks. The evaluation of community heating systems must account for distribution losses through the DLF (Distribution Loss Factor). Research on actual performance, and modelling of losses indicates that the current default DLF values are too low. Consequently, higher default values will be introduced, which will give more conservative results, and encourage assessors to use design values or metered data for the system.
  • Secondary heating fraction for storage heaters. In dwellings heated by storage heaters a fixed percentage of the space heating requirement is deemed to be provided by another, secondary, heat source. The current value of 15% was thought to be too high, given that the design of storage heaters is based on 10% secondary heating. Re-analysis of an existing data suggested the current default sits within the range of actual use (0.11-0.16), and as such remains valid, with no need for change.
  • Ventilation rates associated with chimneys. The current allowance for air change produced by chimneys is 40 m³/hr. Testing has indicated a value of 80 m³/hr is more appropriate.
  • Assumptions on heating patterns. Every version of SAP has used the same assumptions for heating: the living area is heated to 21ºC while the rest of the dwelling is at 18ºC, on weekdays there are two heating periods, totally 9 hours, while Saturdays and Sundays have one daily heating period of 16 hours. Analysis of survey data showed that in practice most households either used two heating periods during the week and at weekends, or used one heating period during the week and at weekends. Incorporating those figures into the calculations made a difference of about 4% to the overall results. As the overall assumptions within SAP remain broadly appropriate it not proposed to change them.

So, of the four items considered, two are likely to result in changes in SAP 2016, while two will not. It will be interesting to see what other changes the draft proposal will bring, but overall, it looks like tweaks, rather than wholesale changes such as we saw with SAP 2009.

  1. The fact that we can get one without the other is a result of the curious split in responsibilities between government departments. Although DCLG (the Department of Communities and Local Government) is in charge of the Building Regulations and the associated Approved Documents, SAP – the key measurement tool – is maintained and managed by DECC (the Department of Energy and Climate Change). 
  2. SAP is the Standard Assessment Procedure: not the most useful of names, as it doesn’t tell the uninitiated reader what is to be assessed.