TM52 Limits of Thermal Comfort: Avoiding Overheating
CIBSE TM52 The Limits of Thermal Comfort: Avoiding Overheating in European Buildings 2013
Overheating has become a key problem for building design. The need to reduce energy consumption whilst dealing with global climate change has reduced the options available for building comfortable, low-energy buildings. Research has been directed towards methods for increasing indoor winter temperatures but this can lead to lightweight, highly insulated buildings that respond poorly in the summer. CIBSE has responded by forming the CIBSE Overheating Task Force.
This Technical Memorandum (TM) is about predicting overheating in buildings. It is intended to inform designers, developers and others responsible for defining the indoor environment in buildings. It includes the recommendations of the Overheating Task Force, which has sponsored and published this document.
The Task Force realised that one problem for designers has been the absence of an adequate definition of overheating in naturally ventilated buildings. In the past overheating has been defined as a number of hours over a particular temperature, irrespective of conditions outside the building. Recent work embodied in European standards suggests that the temperature that occupants will find uncomfortable changes with the outdoor conditions in a predictable way. This research informs the CIBSE guidance presented in this Technical Memorandum (TM). The meaning of the research and the link with overheating are explained and a series of criteria by which the risk of overheating can be assessed or identified are suggested.
More detailed information about using simulation to predict the danger of overheating is available in CIBSE Guide A. CIBSE KS16: How to manage overheating in buildings gives information directed at building managers and owners about the cause of overheating and some practical suggestions for avoiding or mitigating it.
Note: In 2015 the Greater London Authority (GLA) published guidance on preparing energy assessments - 'GLA Energy Planning - Greater London Authority guidance' (April 2015) that makes strong reference to CIBSE TM49. The GLA guidance explains the need to take the urban heat island effect in the locality of the development to be taken into account. This makes it a requirement that, where dynamic modelling is carried out, it should be undertaken in accordance with the guidance and data sets in TM49, which are then summarised (see paragraphs 11.9-11.12).
The weather data set WCSYL is re-badged in 2016 as WDD16LON but the sets are identical.
The GLA also directs readers towards CIBSE TM52 Limits of Thermal Comfort: Avoiding Overheating in European Buildings’ as it contains "additional guidance on the limits of thermal comfort."
The GLA title can be accessed from here
2 Comfort and discomfort
2.1 Our thermal sense
3 Predicting discomfort
2.2 How can we judge if a building is overheating?
2.3 Behaviour and discomfort
3.1 The basics
4 The basis of comfort standards
3.2 Investigating and modelling thermal comfort
3.3 Predicted mean vote (pmv) and predicted percentage dissatisfied (ppd) using the heat balance model of comfort
3.4 Other considerations
4.1 Existing standards
5 Risk of overheating
4.2 Problems for standards
5.1 Problems with a single temperature overheating limit
6 CIBSE recommendations for identifying overheating
5.2 Discomfort as a function of a deviation from comfort temperature
6.1 CIBSE guidance
6.2 Overheating in mechanically cooled buildings
Additional sources of information