Last week, as part of a major planning application, we received a request from the Greater London Authority (GLA) asking for dynamic overheating analysis to be undertaken on a major new residential led development using not only the current CIBSE Design Summer Year weather data, but also the recently released future climate change weather data. The GLA assessment criterion refers to the new CIBSE Guides TM52 and TM49 to ensure that the design properly addresses the issue of overheating.
In recent years the construction of contemporary buildings has focused on thermal efficiency, air tightness and improved daylighting strategies resulting in highly glazed facades leading to potential overheating problems. This can be further exasperated in large apartment blocks by communal pipework heat losses in corridors, as well as window opening restrictions, put in place to address air quality, security and external noise issues. In response to this growing issue, CIBSE have issued some new guidance on how to predict future climates and the use of dynamic modelling for undertaking overheating analysis.
TM49: 2014 (Probabilistic Design Summer Years for London) offers new weather data for London. It analyses variations in climate across London based on the ‘urban heat island’, as well as taking account of future climate change projections, allowing designers to more accurately predict the risk of overheating. The new weather data suggests more extreme summer weather will be experienced as average conditions in the future.
In order to assess the impact of these future climate change projections on the overheating risk to homes, Hodkinson Consultancy has undertaken dynamic simulation testing. Figure 1 illustrates two prototype apartments. Plot A is a single-aspect (SW facing) apartment and Plot B is a dual-aspect (SW and NE facing) apartment. Both units are located on the top floor and therefore do not benefit from balcony shading. South facing façades are protected from a build-up of solar gains in the height of summer from high sun angles; however, west facing façades are less protected due to the lower sun angles experienced later in the afternoon.
Figure 1: Prototype Apartments Tested: South-West Facing Façade 21st June 16:00
Four climate change scenarios were then selected for simulation testing from the new data set. These were:
- Design Summer Year (currently recommended data to use to assess overheating risk);
- 2020s (2011–2040): High Greenhouse Gas emissions scenario;
- 2050s (2041–2060): Medium Greenhouse Gas emissions scenario;
- 2080s (2071–2090): Low Greenhouse Gas emissions scenario.
Results of the simulations undertaken are shown for the tested apartments in Figure 2 below. They strongly suggest that apartments being built to comply with current overheating guidance are not acceptable under future climate change predications. It will be important that we therefore need to be considering overheating mitigation measures much more seriously as part of the design process in order to future proof our buildings for future generations.
Figure 2: Percentage of Occupied Hours Spend Over the Acceptable Threshold Temperature – Modelled for Different Future Climate Change Predicted Scenarios
Posted on November 6th, 2014
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