The PassivHaus Standard: minimising overheating risk in a changing climate

Building operational energy is responsible for approximately 40% of UK’s CO2 emissions (GOV.UK, 2014) with almost 25% in housing alone, mostly for space heating. This significantly contributes to climate change, which is now considered unavoidable (IPCC, 2013) and could affect occupants’ thermal comfort and health (Public Health England, 2013). Given that our buildings are built for 50-100 year lifespans (de Wilde et al, 2008), measures to adapt our buildings to a changing climate need to be undertaken alongside climate change mitigation strategies. This paper investigates the risk of overheating and the remedial measures required for future UK climate scenarios if the PassivHaus standard is applied. A case-study dwelling was modeled and its performance assessed under present and future climate scenarios in London: 2050s and 2080s for a Medium and High emissions scenario. Findings indicated that while space-heating demand would be reduced by 45% by the 2080s, the case-study dwelling is likely to need some form of cooling from the 2050s onwards, unless passive adaptation measures are put in place. The most effective adaptation measure was found to be a combination of reduction on the glazing’s g-value, summer night-time natural ventilation and solar shading. The performance of the Building Regulations (2013) notional specification highlights that while it is predicted to lead to marginally lower overheating frequencies than the PassivHaus dwelling, its space heating demand will be up to five times higher in the 2080s. Hence measures for reducing space heating demand alongside measures to reduce future overheating are both necessary and need to be balanced. Findings indicated that the PassivHaus case-study performed well in a future changing climate if this goes hand in hand with overheating mitigation measures, taking into account user behaviour and occupancy patterns, applied now and in the future