In the first of a new series of articles, Gavin Harper goes back to first principles to help us understand some of the basic concepts of building physics – and how these apply to sustainable construction. In this article, we will be examining thermal comfort.
This is a four page article. First published in April 2009
Just like Nirvana, thermal comfort is a state of mind. It’s impossible to define an exact temperature/humidity/airflow combination as ‘thermally comfortable’ as we all have different preferences, opinions and ideas. Furthermore, thermal comfort is influenced by how many layers of clothing we are wearing, our metabolic rate (which changes depending on how old we are and what we are doing at the time). Of course, the surface temperatures of the things that surround us, the temperature and humidity of the air, and how fast that air flows around us, all have a bearing on how we perceive our environment (see Fig.1).
The old idiom ‘It’s impossible to please all of the people all of the time’ is true for thermal comfort – at best we can aim to maximise the number of people in a given environment that feel thermally comfortable – and so the models for thermal comfort rely on measures such as ‘predicted mean vote (PMV)’; which is to say, in an average population of people, we try and predict the norm of how they would rate an environment. We will discuss PMV later.
Thermal comfort is as much a psychological concept as a physical one. It is not a ‘given set of conditions’ that result in thermal comfort, it is how the ...
VAT applies to this product (UK only).