VOICES | CHRIS TWINN Building a zero carbon nation To achieve carbon reduction targets, Chris Twinn says the UK should be looking at large-scale offsite renewables and achievable building performance targets that are rigorously upheld W e are increasingly hearing the media and policymakers demand that we start designing new buildings for zero carbon. When asked how, however, the answer comes back as the mantra that a net zero carbon building should generate as much renewable energy annually as it uses. As most design engineers will tell you, this is nonsense for vast swathes of buildings particularly at urban densities. This mantra is an out-of-date blunt instrument. We no longer need to assess buildings in isolation versus a coal-fired energy supply system. As a model, it has already demonstrated its impracticality for mainstream rollout. It is far more economic to generate renewable energy in bulk off site, rather than on our constrained building sites. Then there is the myth of offsets to make up any onsite deficiencies. Come 2050, it seems more than likely that there will be little or no offsite offsetting available to UK buildings, as anyone with carbon sequestration will retain it for their own zero carbon obligations. Renewable generation is not a function of building energy demand, but a function of building footprint area In principle, the idea that a building is an isolated zero carbon island is a fallacy. They are part of a wider network of multiple energy generators, a whole spectrum of demands and a management system. We need to consider the whole system and think systemically, with the focus on the stated objective of a zero carbon nation, not buildings as islands. So how do we come up with a practical definition of zero carbon that is applicable to all buildings? In essence, we can distil this down to a need to deliver sufficiently reduced energy demand to match the expected national availability of renewable energy supply. To put some numbers to it, what would be a reasonable fair share of this 2050 available renewable energy? The Parisproof method is a way of assessing this.1 The Paris reference relates to the UK needing to be, effectively, zero carbon to meet the UN Paris Agreement of limiting climate change to 1.5C. We already have a good idea of how much zero carbon energy the UK is expecting to generate by 2050.2 This is against a backdrop of wind- The University of Leicesters Centre for Medicine has Passivhaus certification CHRIS TWINN Specialist built environment adviser Twinn Sustainability Innovation 18 July 2020 www.cibsejournal.com CIBSE July 2020 p18-19 Chris Twinn.indd 18 19/06/2020 15:47