Carbon capers

Defra’s announcement follows the exchange in last month’s BSj between James Thonger of Arup and the GLA’s climate change tsar Allan Jones, following publication of an article by Thonger (BSj 05/07). The article questioned the effectiveness of both combined heat and power (CHP) and combined cooling, heat and power-based (CCHP) systems in delivering their proposed carbonreduction targets. Indeed, last month the article was cited as evidence in the public examination of proposed further alterations to the London Plan.

The exchange between consultant and regulator highlighted the challenge faced by designers and specifiers in the appropriate selection and application of carbon-saving technologies and the importance of an accurate grid carbon emissions factor. Defra’s recent announcement will no doubt further complicate matters. Just to add further uncertainty to an already difficult issue, the DCLG has said the carbon factor used in the Building Regulations is under review and is likely to be reduced.

So what is an appropriate carbon factor for grid electricity? To help answer this question, BSj has teamed up with the UK Green Building Council to host a debate this month (see p11 for details). The assessment of an accurate carbon emission factor is far from straightforward because the carbon content of grid electricity varies, depending on the different generation sources connected to the grid at a particular time. It is an important issue: without an accurate figure it is difficult for designers to verify the effectiveness of a scheme in cutting carbon emissions. This debate should highlight some of the issues involved and will attempt to cover how, and how often, the value should be reviewed. I hope to see you there.