carbon limited

What’s going on?

There’s been a fierce debate among energy bods this summer over the environmental effectiveness of combined heat and power (CHP) and CHP with cooling (CCHP) – a debate closely tied to assumptions about the carbon emissions associated with grid electricity in the UK.

What happened?

As noted in this blog in May, Arup associate director James Thonger opened up with a broadside aimed at the GLA policy of requiring CHP and CCHP on new developments. In particular he refuted LCCA claims that gas CHP saves 54% of carbon relative to grid electricity. The LCCA is headed up by Allan Jones, former green god of Woking and now darling of the London Mayor, who didn’t take the criticism lightly.

At the centre of Thonger’s argument was the carbon intensity of grid electricity, which can vary widely depending on the fuel used. It is a particularly contentious issue, especially in London where predicted carbon savings can make or break a planning application.

There then ensued a wild flurry of rebuttals and counter-rebuttals between Jones and Thonger. This bloody exchange between two giants had the industry on the edge of its ringside seats. While Jones has the east end gangster vibe (a lá Mr Bridger from the Italian Job: “Last night, Mr Governor, my toilet was broken into”), my money was on Thonger, renowned for his stamina, footwork, and looking suspiciously like half of the Alan Parsons Project.

Then just when it was about to get nasty, the fight came to nothing. Jones told Thonger to stop bothering him and take his argument to the government. Thonger capitulated.

But the exchange attracted the attention of Wild Bill Orchard, industry titan and godfather of CHP. As a hush fell over the arena, Bill came down firmly on the side of the GLA and against Thonger, dropping some serious science in the process.

At which point DEFRA further muddied the waters by publishing its greenhouse gas conversion figures giving a long term marginal conversion faction of 0.43kgCO₂/kWh, a figure slightly different from building regs (0.422) and wildly different from the figure given by SAP for intensity of grid electricity saved through the use of CHP or renewables (0.568). It was a stark reminder that the carbon intensity of grid electricity depends on who you’re asking.

Brian Mark, director at Fulcrum, popped up at this point to back Thonger’s figures and say that CHP is only likely to save around 10-12% of carbon on a typical mixed use development. A sentiment I shared until Bill Orchard sowed the seeds of doubt in my mind.

So then came a debate hosted by the BSJ on 14 August, which moved the argument off the printed page and into the lecture theatre. The results were inconclusive, though many participants agreed that carbon trading would increase certainty on the issue as it would heavily influence fuel mix on the grid.

Unsurprisingly, in the end nothing’s changed. There were no clear winners from the summer’s debate, though I think the credibility of the LCCA figures did take a knock. The central issue of emissions from grid electricity and its implications for CHP remains unresolved, and most of us will carry on using the figures dictated by building regs.

So is gas CHP a good thing? Yes, in the right circumstances where the loads and the engines are well matched. How good? It depends on your assumptions. In addition the energy infrastructure associated with CHP is a very good thing – down the road it offers the freedom to hook into larger heat networks or switch to alternative energy sources such as biomass.

And we can say this for sure: engineers need a definitive carbon intensity figure in order to do their calcs. While I agree that we engineers should be involved in the debate, we can’t start every report with a lengthy justification of how we’ve arrived at our carbon figures. Even worse than the current state of confusion, it would be carbon anarchy.