Here’s an idea – open up SBEM and DSM compliance methodology to the domestic market, alongside SAP…
Posted: October 13, 2009 by David McEwan, Category:Building Regulations
Responses to consultations on the proposed changes in Part L 2010 have been talking up quite a bit of my time recently. Obviously, an area of particular interest to us is the calculations tools.
The Building Research Establishment (BRE) developed SAP and SBEM drafts to support the Part L 2010 consultation package, both of which we’ve been looking at in-depth. However, in this blog I’m just going to look at the proposed changes to SAP.
For SAP 2009, the proposals centre around the adoption of a monthly calculation method instead of the current annual calculation, with the addition of factors to address thermal mass and cooling. This has a number of ramifications for various parts of the calculation. The justification for this is the need to consider the energy balance at different times through the year with more rigour, for instance within very-low energy dwellings.
While there is certainly a need to ensure compliance methodologies don’t penalise the design techniques required to achieve very low-energy dwellings, could it be that that changing the current SAP methodology is an unnecessary route – one that is both expensive and potentially a disruptive burden on the industry?
The current SAP approach, based on a worksheet, is well understood by its users and is a simple, but reasonably transparent assessment suitable for the majority of conventional dwellings. When you consider that there are other monthly calculation tools already developed and in-use in the non-domestic arena, why would the government invest taxpayers money in the research, development and implementation of another methodology especially when public spending is under severe constraints?
SBEM and DSM could cheaply and easily be extended to the domestic sector at virtually no cost, as could the existing training and accreditation routes. In fact, many designers of low energy dwellings have already tried and tested dynamic thermal simulation in their day-to-day design. SBEM is a monthly calculation (as is being proposed for SAP 2009), whereas DSM is a 8760 hourly annual calculation. SBEM and DSM also provide a way to include treatment of thermal mass and cooling.
By offering a choice of calculation engine at the domestic level; SAP (simple heating only dwellings), SBEM (most dwellings) or DSM (all dwellings), all low energy technologies could be studied in the right level of detail by those with the right level of skills and without needless upheaval and cost.
The current SAP calculation could be left essentially as it is – negating the need to develop yet another publically funded energy calculation tool, with the associated significant upheaval and burden on the industry of re-training and accreditation.
