Naked Science Forum
General Science => General Science => Topic started by: chris on 25/01/2010 14:30:34
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How does the humidity of a room affect the efficiency of the heating of that room, and what effect does it have, if any, on an occupant's perception of how warm a room is?
In other words, if a room is very humid, will it not require more energy to warm it up in the first place; therefore an occupant would think that the room feels colder for longer? Also, the water in the air would soak up radiant heat, so would that also alter the perception of warmth coming from a heater?
Conversely, when a humid room is hot, does it stay hot for longer, therefore requiring less maintainance heat to keep the temperature up?
Chris
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Hi Chris, I can say that in Johannesburg in South Africa we are sitting at a relatively high altitude which makes things very dry in winter. We have underfloor heating in our room which works quite well but if we use a humidifier as well, the room gets way too hot. Considering that the humidifier itself only gives off a very small amount of heat, I would say that the humidity has a big affect on the heating efficiency in a positive way. I would say from personal experience that if one had to compare 2 identical rooms that are being heated to say 24 DegC, and then introduced some humidity into one and kept the other dry, the room with humidity would feel more warm than the other. Not very scientific I know but that is how I have experienced it.
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So I guess that if you have heated a humid room then it will require less energy to maintain the temperature, I guess because the water molecules retain the heat better than the air molecules but I have travelled quite a bit and can say without a doubt that a humid 30 Deg C is totally different to a dry 30 Deg C as far as confort level is concerned.
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High humidity at high temperatures certainly contributes to a reduced rate of heat loss from the body because it reduces or abolishes the effects of sweating.
But at lower temperatures, I am not so sure. I suspect the air would cost more to heat because the energy density of the air would be greater because the water would soak up heat. But then, presumably, the higher specific heat capacity of wetter air would mean that it stayed warmer for longer.
What does everyone else think?
Chris
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Just by gut feeling, I would say that indoor temperatures at low humidity can be lower and still feel comfortable. Or the opposite, to feel comfortable in a humid room you have to crank the heat up more. A dryer home can be heated less. Outside, rainy days at 2C are (in my opinion) significantly less comfortable than cold, crisp days at -10C.
Also, humid indoor air can result in damage to your house if it escapes through cracks and holes and condenses into ice (and later turns into liquid water) in the walls or attic. The result can be loss of efficiency of your insulation, rott, mold, etc. This only relates to the heating efficiency issue if money, health, and long-term effects are of concern.