Spring has sprung, but it is still pretty cool in much of North America and Europe, and people are still asking the question: Why do I feel chilly? We have looked at this before with engineer Robert Bean, but now Es Tresidder, who got his PhD and MSc studying “the optimisation of low-energy building designs using genetic algorithms” takes a stab at explaining it, sans genetic algorithms. He tweeted recently:
And it is a very interesting blog indeed. Es is now a certified Passivhaus designer, teaches, and consults as Lean Green Consulting from the chilly Scottish Highlands, and points out that most people do not get it right because it is not just about the setting on the thermostat.
Models of thermal comfort are pretty well developed but are poorly understood by most people outside academia. I’ll focus in this post on feeling too cold, but broadly the same principles apply in reverse for overheating in the summer.
As Robert Bean noted in his discussion of the 166,000 thermal receptors on our bodies, it is all about feelings.
Whether we feel warm or cold depends on how fast our bodies are losing heat to the world around them. This depends on the air temperature in part; if the air next to our bodies, or on the outside of our clothing, is cold then we lose heat to it more quickly than if it is warm, but this is only part of the story. Let’s look at the other other factors affecting how fast we lose heat to our surroundings.
These include air movement; lots of it will make you feel colder because the warm layer of air next to your skin gets blown away. Cold walls and single glazed windows create drafts (he is in Scotland so writes draughts). Humidity is also an issue; cold air holds less moisture, and the drier the air, the more moisture evaporates from our skin. But the big one that most everybody misses when they buy their Nest thermostat:
We also lose heat through radiation, regardless of the air temperature, to the solid surfaces surrounding us. This radiative heat loss