An investigation into future performance and overheating risks in Passivhaus dwellings

Abstract

In response to UK government policy mandating the construction of 'zero carbon' homes by 2016 there have been significant changes in the way dwellings are being designed and built. Recent years have seen a rapid uptake in the adoption of the German Passivhaus standard as a template for ultra-low energy and zero carbon buildings in the UK. Despite genuine motivations to mitigate climate change and fuel poverty there is a lack of research investigating the long-term performance of Passivhaus buildings in a rapidly changing UK climate. This paper sets out to investigate whether Passivhaus dwellings will be able to provide high standards of thermal comfort in the future or whether they are inherently vulnerable to overheating risks. Scenario modelling using probabilistic data derived from the UKCP09 weather generator (WG) in conjunction with dynamic simulation and global sensitivity analysis techniques are used to assess the future performance of a range of typical Passivhaus dwellings relative to an identical Fabric Energy Efficiency Standard (FEES) compliant dwelling over its notional future lifespan. The emphasis of this study is to understand what impact climate change will pose to overheating risks for Passivhaus dwellings relative to the de facto (i.e. FEES) alternative, and which design factors play a dominant role in contributing to this risk. The results show that optimization of a small number of design inputs, including glazing ratios and external shading devices, can play a significant role in mitigating future overheating risks.

The impact of regulations on overheating risk in dwellings

“…McLeod et al (2013) does however point out that Passive House dwellings may offer marginally more protection from overheating than other highly insulated options (Findings for the 2050s heavy weight passive house greater than 25°C for 6.6% of the year whereas a heavy weight 'well insulated' building greater than 25°C for 8.2% of the year). The core reasons for these differences are unclear, although Gupta and Gregg (2012) when considering a range of 'typical' dwelling types in Oxford found insulation position to be of importance.…”

“…This is supported by the findings of Skinner and Grimwood (2005) who note that 54% of dwellings in the UK during the day-time and 67% during night-time are exposed to noise levels in excess of World Health Organisation (WHO) guidelines. In addition there are strong safety related arguments for the inclusion of restrictors on upper floor windows (McLeod et al 2013) which reduce the potential for increased ventilation. As such, the reliance on window opening may be over optimistic and furthermore as suggested by several authors (for example see Peacock et al 2010 andRoaf et al 2015) there may, in the future, be an upper limit to the effectiveness of window opening in reducing overheating.…”

“…In cool or temperate climates such as mid-latitude and northern Europe, characterised by extended winter heating seasons, these regulations aim to mitigate the worst effects of climate change by reducing CO2 emissions and optimising buildings for heat retention. However, as noted by McLeod, Hopfe and Kwan (2013) it is being increasingly recognised that higher global emissions scenarios are becoming more likely, increasing the risk of greater levels of warming. As a result, it has been suggested that dwellings in cool climates may in the future suffer from overheating and indeed there is evidence that this may already be happening (Dengel & Swainson, 2012).…”

Hospital wards and modular construction: Summertime overheating and energy efficiency

“…Currently called 'modern methods of construction' (sic), prefabrication has gained popularity for the construction of flats, student accommodation etc., but it is an approach that is also applicable to hospital wards. There is emerging evidence that thermally lightweight, well-insulated, airtight, single aspect, cellular residential spaces built using modern methods of construction are particularly susceptible to overheating [14,15] and that this is exacerbated by poorly designed and operated mechanical ventilation systems [16]. But will hospital wards built using similar techniques also overheat?…”

Temperature in housing: stratification and contextual factors

“…The latest findings on potential overheating in UK housing (Tillson et al, 2013) show that 99% of housing will be at medium to high risk if average summer temperatures rise by 1.4 o C. There are numerous studies on climate change adaptation for UK housing (DCLG, 2012;Gupta and Gregg, 2013;McLeod et al, 2013;NHBC Foundation, 2012;Porritt et al, 2012) which suggest various positive interventions to address this risk, including guidance on glazing ratios and solar shading alongside good insulation levels. Equally there is a variety of thermal comfort (Hwang et al, 2009;Lomas andKane, 2013, Spataru andGillott, 2010;Soebarto and Bennetts, 2014) and heating practice studies (Gram-Hanssen, 2010, Heubner et al, 2013 which focus on the user, but there is relatively little literature which refers to the stratification of temperatures in housing as part of these overheating scenarios and comfort practices.…”