In cold weathers it is suggested to put a humidifier since the air gets too dry. I wonder how the humidity affects how much time is needed to get the air at a temperature of 20 Celsius degrees? I mean suppose you have a cold room and you want to heat the air, Will the process be slower or faster in relation to variations in humidity?
Since the water tends to keep its temperature I feel the process will be slower with higher humidity, but I am not sure.
Answer
Air has a specific heat capacity of slightly more than 1kJ/kgk at room temperature
So it takes a 1kW heater 1 second to heat 1kg (roughly 1 m^3) of air 1 deg C
Fairly humid air (say 60% RH at 20C) will contain around 10g/m^3 of water vapour with a specific heat capacity of 1.8 kJ/kgk - so it takes almost twice as much energy (per unit mass) to heat the water in the air than the dry air itself.
But, only 10g in every 1kg of air is water vapour ( ie 1%) so you only have to do twice as much work to that 1%.
In other words - no you won't see any measurable difference.
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