CIBSE ASHRAE Technical Symposium, Loughborough, UK 5-6 April 2017
Evaluating Overheating Risk and Mitigation Strategies in Low Energy Houses in the UK: Two Sheffield Case Studies AZLIZAWATI IBRAHIM MSC, BARCH, BSC, School of Architecture, The University of Sheffield
[email protected],
[email protected] (Corresponding author) XI CHEN MSC, BA, School of Architecture, The University of Sheffield
[email protected] DR SOFIE PELSMAKERS PHD, MSC, MRES, PGDIP, RIBA, ARB School of Architecture, The University of Sheffield
[email protected] DR CHENGZHI PENG BARCH, DIPLA, MSC, PHD School of Architecture, The University of Sheffield
[email protected]
Abstract Reducing carbon emissions in the housing sector through building and retrofitting to low energy standards might cause overheating and associated thermal discomfort. This paper presenting the methods of studying overheating risks of a low energy retrofit and a new-build Sheffield dwelling in the current and predicted future climate, using steady-state and dynamic modelling tools. The findings suggest that both retrofitting and building to low energy standards increases overheating risk, unless prevention measures are included. The most effective overheating mitigation strategies suggested are reduction of glazing g-values, temporary internal shading, permanent external shading and night-time ventilation. With a combination of such adaptation measures, overheating is predicted to be minimal or non-existent in a future changing climate and active cooling might not be necessary for dwellings with appropriate passive measures.
Keywords Low energy housing, overheating risks, overheating mitigation strategies, retrofit
1.0 Introduction The housing sector contributes to a significant proportion (27%) of the UK’s CO2 emissions (1) and retrofitting the existing stock is one of the key strategies towards significant carbon emission reductions in the residential sector (2). As a result, there is a drive towards the implementation of fabric energy efficiency improvements in retrofit and constructing new buildings to more stringent standards in the UK and across Europe. The Passivhaus standard, a voluntary approach in achieving ultrahigh building energy performance is increasingly adopted in Europe, including the UK(3). Its certification requirements exceed the UK’s national building regulations. However, a higher fabric standard might lead to overheating risks in low energy housing (4), based on growing evidence of uncomfortable indoor environments of low energy new built dwellings (4–6). One-fifth of homes in England might already Page 1 of 15
CIBSE ASHRAE Technical Symposium, Loughborough, UK 5-6 April 2017
experience overheating in summer and this is likely to increase in a warming climate(7). Increasingly, overheating prevention measures are identified to enhance summer thermal comfort(4). The objectives of this research are (a) to evaluate two case studies in Sheffield, one retrofit and one new built to high energy performance standards; (b) to evaluate the current predicted overheating risks and (c) in a future predicted climate and (d) to test and evaluate effective and practical adaptation strategies for reducing the potential of overheating in the case study dwellings.
2.0 Predicting Overheating Risks for Low Energy House case studies in Sheffield 2.1 Case Study 1, a retrofit project in Sheffield: Knowle Lane The project is a retrofitted detached house in the South-west of Sheffield, located 223.6m above sea level and facing amazing views of the Peak District at the south. The main design strategy was retrofitting to Zero Carbon standard to meet Fabric Efficiency Standards of < 46kWh/m2 (8) for the space heating demand of a detached house. This was achieved with improved (measured) air tightness of
