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OPINION A CLOUDED VIEW
The government would be wrong to ditch dynamic simulation modelling as a compliance method in Part L, says Chris Yates. In a world increasingly turning to DSM, UK consultants could be quickly left in the shade
Hywel Davies rang alarm bells in December’s CIBSE Journal (Part
L –Should we be worried?). Many of us are affected by changes in energy performance regulation. For example, the changes in 2006 propelled my niche speciality in building physics into the mainstream. However, Hywel’s message makes it apparent that looming changes might be nowhere near as benefi cial – at least to me. As well as the usual victim (consequential improvements), other cuts could be made. A proposal that has eluded the spotlight is one to remove Level 5 (dynamic thermal simulation or DSM) as a compliance option. Under this arrangement, all UK compliance would be performed in SBEM. DSM tools potentially offer greater accuracy but require more careful input. With DSM, solar gain is treated more accurately, as well as external shading and thermal mass. Other effects can be modelled such as inter- zone airfl ow and dynamic HVAC. The Energy Performance Certifi cate (EPC) conventions list building features where a Level 5 analysis is required and SBEM cannot be used (for example, atriums). The reason for removing DSM from
the framework is that as future designs approach zero carbon, the percentage ‘error’ between results from different software will be greater. It follows that the only fair way of performance rating is with one tool – even if it is inaccurate in certain situations. Cost is also a factor. At present,
DSM software must be accredited through rigorous vendor testing and then reviewed independently. The independent review has, up until recently, been a cost to the Department for Communities and Local Government (DCLG). Under new proposals, DCLG are likely to opt for a ‘cost recovery’ scheme where the software vendor pays. This ‘cost recovery’ might also extend to revenue
22 CIBSE Journal January 2013
generation with fees levied to help fund SBEM development (assuming DSM continues to feature).
It’s become diffi cult to enter the UK market if you are an outsider
Who would stand to lose if Level 5 was dropped? Training, loss of BIM integration and a reduction in perceived value would hit consultants. In a world where simulation is becoming the norm, Britain could even be sending out the wrong signal and reducing its experts’ opportunities of delivering to an international market. There is no way to adequately describe the operation of innovative equipment or controls in SBEM’s monthly-average method. On the other hand, DSM software developers have the most ability to model anything innovative – they are where the greatest pool of development talent lies. Daikin, PCM modelling and Tarmac offer a few examples where software companies have collaborated with equipment manufacturers to model innovative technology. So, it would be bad news for innovation if DSM was off the menu. Software companies have invested
much in the National Calculation Methodology (NCM), which underpins non-domestic Part L and EPCs. If you’re
a developer, there’s no other calculation methodology that’s as onerous – so much so that it’s become diffi cult to enter the UK market if you are an outsider. The Swedish vendor Equa Simulation
has implemented the NCM in its IDA ICE software, but accreditation has been delayed because DCLG’s independent review scheme is on hold. At almost the same time, it implemented its ASHRAE 90.1 tools (the equivalent LEED analysis). According to its CEO, Per Sahlin, ‘coding for compliance with ASHRAE has been a dream in comparison to the NCM!’ A combination of public and private
sector delivery is key to success. Collaboration is required. There is a future for SBEM, but let’s remind ourselves of what the ‘S’ has always stood for, ie. simple. The current system is serving needs adequately, but it needs a few tweaks. It doesn’t need reinvention and certainly not cuts. CIBSE and others will continue to push to get behind those ‘closed doors’, but it will take more that this to get heard.
● CHRIS YATES is an independent building physics consultant working with BDP
www.cibsejournal.com
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