The unintended consequences of energy efficient retrofit on indoor air pollution and overheating risk in a typical Edwardian mid-terraced house

According to the 2011 UK Carbon Plan, all buildings will need to approach a zero carbon footprint by the middle of this century. This is necessary to achieve the ambitious legally binding target to reduce carbon emissions to 80% below 1990 levels by 2050. Currently, residential buildings are responsible for around 27% of national energy use. This number is likely to increase as a result of population growth and potentially increased comfort expectations. In addition, the large majority of existing buildings will still be standing in the 2050s due to the low turnover rate of the UK building stock. A step change in retrofit practice is, thus, required in the coming decades in order to meet these challenging targets. However, if carbon reduction-driven interventions are not well thought through, they can lead to undesirable impacts. For example, unintended consequences of increased insulation and air tightness levels could entail a rise in indoor airborne pollutant levels, condensation risk (and associated mould growth) and internal overheating during the summer period; the latter is likely to be exacerbated in the future based on current climatic change trends. This paper aims to assess the magnitude of such risks following the energy retrofit of a typical Edwardian mid-terraced house. The physics-based indoor environment simulation tool EnergyPlus was utilised for the assessment of indoor air quality and thermal conditions. The summertime thermal performance of the dwelling was simulated for different levels of fabric efficiency: a) ‘Base case’, b) ‘2010 Building Regulations insulation levels’ and c) ‘Deep retrofit’. The indoor overheating assessment was undertaken using a wide range of PROMETHEUS probabilistic weather data for the UK Climate Projections (UKCP09) Medium (A1B) and High (A1FI) Emissions scenarios for three time slices (2030s, 2050s and 2080s) and two locations (London and Manchester). An overall increase in indoor temperatures was observed in the modelled dwelling under the projected climate change scenarios. Overheating risk was found to vary as a function of the wall insulation positioning with externally applied wall insulation generally leading to a reduction of overheating risk. Increased air tightness appears to reduce the ingress of outdoor air pollutants but the magnitude of internally generated pollutants will also need to be considered. The work raises interesting questions about the way indoor air quality and overheating may be related in retrofitted properties.

The unintended consequences of energy efficient retrofit on indoor air pollution and overheating risk in a typical Edwardian mid-terraced house.

Mavrogianni, A., Davies, M., Taylor, J., Oikonomou, E., Raslan, R., Biddulph, P., ...Shrubsole, C. (2013)

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