Why does the same indoor temperature feel different depending on the outdoor temperature?
I’m sitting here in my apartment with the thermostat set on 68. It’s 29 outside. I’m wearing long pants, a long-sleeved shirt with an undershirt underneath, and socks, and I’m cold. My feet are so uncomfortably cold that I’m about to go put some shoes on.
Yet in the spring or fall, when it’s just cool enough outside for heat to be necessary (say, in the lower 50s,) I’m perfectly comfortable wearing what I’m wearing now and keeping my thermostat at 68.
Most perplexing, in the dog days of summer, when it’s 98 outside, if I keep my thermostat at 68, I can wear shorts and a t-shirt and be perfectly comfortable, even a little warm.
Is there a scientific explanation for this phenomenon?
Generally, people have one thermostat. The temperature you read on that thermostat is only valid in the immediate vicinity of said thermostat. When you go to the next room, it can easily be a few degrees colder (or warmer), depending on how good your air circulation is, quality and quantity of insulation, etc.
Relative humidity is typically lower during the winter months. This increases the rate of evaporation of moisture from our skin, which draws heat away from our bodies.
However, if the temperature and relative humidity are both the same, your level of comfort should be the same, as the rate of heat loss through conduction, convection, radiation, and evaporation would be roughly equal in both cases.
This used to bug me, too. The answer comes down to radiation. In the winter, the surfaces in the room and outside the window are colder, and radiate less energy at you.
Basically, if the mean temperature of the walls and the stuff outside the window falls by 1 degree, you need to increase the air temperature by 1 degree to compensate.
There are several factors. Drafts have been mentioned but this should be easily prevented. Humidity has also been mentioned. In winter the inside (heated) air has a lower humidity than in the summer and this would make it feel a bit colder. Then the temperature of the walls. Suppose the air temperature is 78F inside and outside. The exterior walls will also be at 78F. If the temperature outside goes down substantially and we heat the insiide air to maintain 78 the wall will be colder. The temperature we feel does not depend only on how much heat we lose by conduction but also by radiation. Now we are losing mure by radiation as the wall keeps more of the heat if receives and radiates less back. conversely, in the summer, when it is 90F outside, the same 78F inside will feel warmer because the walls are raditing heat on us.
For some years I had an office inside a building, with no outside walls and with air temperature and humidity tightly controlled and my experience was that this effect did not happen.
OTOH, temperature sensation also depends a lot on personal circumstances. With the same temperature I can feel chilly when I am relaxed working on the computer and start sweating after I have done some physical work. Also, my boss walking in the door asking if that report was ready could get me sweating pretty quick. I also noticed the women generally felt colder than the men and we had many arguments about this. I had to wear a coat and tie which is proper business attire but the women insisted on wearing short dresses and felt cold. My position was that it is not reasonable to heat the building to the point where you can wear beach clothes and it is more reasonable to cover yourself a bit more.
Almost surely radiation to the walls. I lived for two years in a house so badly insulated that in very cold weather (below 0F) ice would form on the inside of the outside walls. I could raise the thermostat (on an inside wall) to 75 and it would still feel cool. Drafts may have made a small difference, but I think it was radiation.