title: Self-Shading Façade Geometries to Control Summer Overheating in UK Passivhaus Dwellings for Current and Future Climate Scenarios
Creators: name: Lavaf Pour, Y
Publisher: name: University of Liverpool Repository
Year: 2017

description: The German Passivhaus building standard, with its emphasis on airtightness and very high levels of insulation, has become well known. It is widely applied to produce buildings that have a very low heating energy demand in winter whilst providing thermal comfort. However, there have been, over the last decade, instances of summertime overheating in Passivhaus buildings. Research has shown that the high internal air temperatures during summer in Passivhaus dwellings are mainly due to excessive solar gain through large south-facing glazing and a lack of natural ventilation. A number of well-established passive adaptation measures have received a great deal of research attention, and several have been implemented in to Passivhaus designs to reduce summer discomfort. Some of these approaches, such as window opening and blinds, are user-dependent, while other interventions, such as overhangs, are truly passive and do not require the occupants’ attention. Although thermal mass is not a user-dependent intervention, it typically works in conjunction with night purge ventilation, which is controlled by building users. The research presented here investigated a less examined passive approach to reducing overheating - the potential implementation of the envelope shape as an environmental design strategy to self-shade. This approach is architectural in nature, and so could have both aesthetic and environmental consequences. The research tested if altering the geometric form of a UK Passivhaus (by tilting the south facade to give self-shading) might be capable of passively protecting the house from the excessive solar gain in summer, both for current and future climate scenarios. This study used probabilistic climate change scenarios from the UK Climate Change Projections to determine the overheating risk in an existing Passivhaus dwelling under a high emission 50-percentile scenario in London. Dynamic thermal simulation modelling software (DesignBuilder) was used to examine the impact of various inclinations of the south façade of the Passivhaus dwelling to make use of the self-shading that this form created. A sensitivity analysis of internal temperatures and thermal comfort conditions in the dwelling as a function of building facade inclination and prevailing climatic conditions was undertaken. The research found that implementing an optimum angle tilted façade would moderate indoor temperature variations between day and night in summer and could potentially act as an effective shading device and reduce overheating by a significant amount while still being practical for collecting solar gains in winter. The proposed inclined façade could eliminate the risk of overheating for current climates; however, it was found that using only the geometric considerations would not solely be fully capable of eradicating the risk of future thermal discomfort overheating, particularly for UK climate scenarios of the 2080s. The suggested tilted façade was then analysed alongside other conventional approaches, such as overhangs and reduced window to wall ratios, to compare their relative effectiveness in reducing overheating risk. Manipulating the tilt of the south facing façade will clearly have other impacts on, for instance, winter heating demand, daylighting and natural ventilation air flows, and these parameters have also been examined using the lighting and computational fluid dynamics CFD algorithms in DesignBuilder. The consequences of a slight tilt of the south façade on daylight levels and airflows through the dwelling were apparent but not overly large. The research noted a concurrent increase in the heating demand and artificial lighting, but it was concluded that this increase was an acceptable trade-off compared to the reduced summer overheating risk.