Highly insulated and airtight homes designed to reduce energy consumption are perceived as having a greater summer overheating risk than less insulated homes. If true, dwellings built to the well-known low-energy Passivhaus (PH) standard could be at greatest risk due to the use of superinsulation, especially as the climate warms. Existing studies are inconclusive and even contradictory, mainly due to small sample sizes. Hence, this paper presents the first large-scale overheating risk analysis of UK Passivhaus dwellings using high-resolution internal temperature data from 82 homes across the UK. Both the Passivhaus and the recently published Chartered Institution of Building Services Engineers TM59 criteria are analysed. Results show that the whole-dwelling Passivhaus standard, which uses a fixed temperature threshold, is met more frequently (83%) than when applied on a room-by-room basis (e.g. only 60% of bedrooms in houses meet the standard). TM59-1A, which uses an adaptive temperature threshold, is easier to meet with 100% of flats and 82% of houses in compliance. However, 55% of bedrooms assessed under TM59-1B fail, with little difference between flats and houses. This is a remarkable finding given that the summers under consideration were either typically mild or cooler than average, and that sleep impairment can significantly affect both physical and mental health. These results suggest that highly insulated dwellings such as Passivhaus should consider overheating in individual rooms, rather than at whole-dwelling level. Analysis should be undertaken throughout the year with particular attention to bedrooms, using either the good-practice PH-5% exceedance threshold which maps well to TM59-1B, or TM59-1B itself. Practical application: Overheating risk in new dwellings is an industry concern. Having the correct tools to predict this risk at design stage is important to help design comfortable and healthy dwellings for both today's climate and future, hotter climates. Comparing two different tools and their methodologies using in-use data is critical to gain confidence in their application at the design stage and to further understand overheating risk, including which dwelling types and rooms are more vulnerable to overheating.
There are in excess of 70 low or zero energy/carbon building definitions/standards in circulation around the world. However there are few zero energy or zero carbon buildings. This suggests that despite, or possibly because of, a continuing debate over definitions, aspiration has not been met by reality. In this paper the most important 35 standards are reviewed and a correlation between activity in standard generation and completed buildings is presented. Combining this with the requirement for an 80% cut in carbon emissions, a consideration of the proportion of humanity that live in countries without any standards and the ratio of new-build activity vs. pre-existing stock, leads to a conclusion that there is an urgent need for a binding international zero (rather than low) energy/carbon standard that can be adopted world-wide. It is argued this is only possible if carbon is ignored in favour of energy, and many lifecycle issues put to one side. In part this is because of changing national carbon intensities within the energy supply chain, but it is also due to unresolved issues in carbon and energy accountancy. It is hence suggested that such issues are left to optional additional local standards.
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