Low-energy housing retrofit in North England: Overheating risks and possible mitigation strategies

Abstract

In the drive to reduce space heating demand and associated CO 2 emissions as well as tackle fuel poverty, dwelling overheating and summer time occupant thermal discomfort might be the unintended consequences of low energy building retrofits. This paper presents the findings of a steady state modelled low energy retrofit dwelling in northern England and its potential current and future climate overheating risks using UK Climate Projections 2009 (UKCP09) scenarios (2050 and 2080 High Emission Scenarios). Predictive findings highlight that retrofitting to low energy standards increases overheating risk over time, unless passive prevention measures are included in the retrofit design. In addition, the steady state nature of the model might not fully capture the occupants' exposure to actual future overheating risks. Among the most effective individual passive overheating mitigation strategies are temporary internal shading, permanent external shading, and night time ventilation. Most effective is a combination of these adaptation measures, so that predictive overheating is minimised in a future changing climate, reducing the uptake of active cooling in retrofitted dwellings. Practical applications:Much research focuses on building overheating risks in the warmer South east of England. However, this paper highlights how dwelling retrofit in north England (Sheffield) also can lead to increased dwelling overheating risk, unless passive design measures are included in the retrofit design. Among the most effective individual passive overheating mitigation strategies are solar shading devices and increased night time ventilation, though ideally different measures are combined.Using future climate scenarios highlights that retrofits designed today might not be able to provide occupant thermal comfort in a future warming world. Keywords Low energy housing, overheating risks, overheating mitigation strategies, retrofit IntroductionThe residential sector is responsible for around 27% of the UK's CO 2 emissions.1 In addition, roughly 11 % of people in England live in fuel poverty, with especially older, uninsulated dwellings being harder to heat. 2 Hence retrofitting the existing stock is one of the key strategies towards significant carbon emission reductions in the residential sector 3 and to reduce fuel poverty. 2 As a result, in the UK and in Europe there is a drive towards the implementation of fabric energy efficiency improvements in building retrofit and in the construction of new buildings to more stringent standards.The Passivhaus standard is such a standard for achieving high building energy performance and exceeds most countries' building regulation standards. The standard is increasingly adopted in Europe, including in the UK. 4 However, based on growing evidence of uncomfortable indoor environments of low energy new built dwellings, 5 and retrofits, 6 a more energy efficient fabric might Passivhaus standard. In addition to evaluating predicted overheating risks in the current and a future predicted climate...

On the Role of External Walls in the Reduction of Energy Demand and the Mitigation of Human Thermal Discomfort

“…One of the important sustainable design tasks is to use the simplest, passive possibilities to protect the building against overheating [1,11]. The protection methods should be adapted to the current needs and the individual structure of the heat balance of the considered building [32].…”

“…The other easily available measure (night cooling) is well-known, very intuitive, and a widely used cooling method [1,9,10,22,31]. However, the effectiveness of this method is strongly related to the dynamic properties of the building components.…”

“…They can effectively and without any significant extra costs satisfy the need to protect the environment from further degradation, while at the same time, contribute to the protection of human wellbeing. Ibrahim et al [1] suggested even that in the northern England climate, passive overheating mitigation measures might be sufficient enough to prevent summertime discomfort now and in the future.…”

“…Another common and simple measure for overheating prevention, which is not considered in this paper, is to block excessive solar gains by means of permanent or temporary window shading, sun breakers, etc. [1,2,5]. These obvious solutions, however, are often associated with the consequences of restricted access of daylight.…”

“…The thermal efficiency of this process is strongly related to the thermal capacity of the given space [7][8][9]. Evola et al [10] and Ibrahim et al [1] emphasized the synergic effect of mass and ventilation. Long-lasting effects depend on the volume and thermal diffusivity of the storing materials [11].…”