Why is it that when I set my thermostat to 73° F in the winter it is comfortable. However, 73° F in the summer feels uncomfortably hot? Shouldn’t the same temperature feel the same indoors in a controlled environment (via the thermostat)?
In: Other
There are several factors that affect your thermal comfort. The big ones are:
* air temperature
* mean radiant temperature; in short, the temperature of the surfaces around you will cause heat to be radiated to/from you, and that will vary with how close you are to those surfaces and how much colder/warmer they are than you.
* air speed; you will feel cooler if there’s a bit of a breeze across your body
* humidity; this is especially important when it’s warm out, because your body loses heat by sweating. The closer relative humidity gets to 100% saturation (there’s only so much moisture that can be absorbed in air) the less effective your sweating will be. This is less of a factor in the cold.
* local effects like “radiant temperature asymmetry”, e.g. where one side of your body feels warmer than the other; air drafts; vertical temperature differences (between head and foot; if one is much colder/warmer than the other you will find it uncomfortable, even if in isolation the temperature would be comfortable overall)
* metabolic rate and external work; if you’re up and about actually doing something physical it will cause you to expend more energy and your body will need to release more heat to keep itself thermoregulated. You will feel colder if you’re just sitting still in a chair vs. walking, vs. doing light manual work, vs. playing a sport, etc.
* **Your clothing!** This is often the big difference-maker in winter vs. summer; you wear heavier clothing in the winter, which keeps you warmer.
There’s actually an industry technical standard written about this by the American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE), called *Thermal Environmental Conditions for Human Occupancy* (ASHRAE Standard 55). Most North American building codes insist that this standard must be met in the construction of large (i.e. anything bigger than a house) buildings.
People are fickle though, so ASHRAE 55 assumes that 5% of people will never be satisfied no matter what the conditions. The target for achievement is to have no more than 10% of people be dissatisfied with the conditions.
Source: I’m a mechanical engineer who designs HVAC systems in buildings for a living.
Latest Answers