A bit of a wash out?

But something still does not seem right. I am recording a 50% drop in carbon emission using the new version (for the same data input) and easily achieving a pass on an inner city office block extension – whereas with the old version I struggled to obtain a pass.

The system we are using to achieve this pass is a VRV system with heat recovery (seasonal efficiencies of 4.2 in winter and 3.5 in summer). Has BRE lowered the pass mark to enable water-based systems to pass? For example, rather than putting in biomass boilers and a CHP plant or other renewable energy systems in heated, naturally ventilated buildings, designers are opting for double A rated VRV/split/multi split systems.

How many water-based manufacturers have seen a drop in sales since April 2006?

Have the governing bodies got this all very badly wrong, as intimated in last month’s BSj, so that they are actually driving designers to expend energy all year round?

As for the gobbledygook document Part 2LB, let’s get rid of it and replace it with Asset and Operational rating systems. From my experience and discussions with fellow professionals, it is being ignored in favour of good common sense anyway.

Leonard Blackshaw MCIBSE, Low carbon consultant

BRE responds…

In general, buildings modelled using the latest release of SBEM are likely to get a different answer from that obtained with the previous version. That is the inevitable result of improving the algorithms and assumptions underlying the calculation. In practice, some buildings will perform better, some worse.

A difference of 50% seems high, though not impossible – but without the detailed information we can’t comment further.

The feedback page on the ncm.bre.co.uk website is available to query results that seem unexpected. We have not changed any of the parameters relating to VRV systems, and there is no “pass mark” for individual HVAC systems.

Paul Davidson, director of BRE’s Sustainable Energy Centre