I'm considering getting an evaporative humidifier for my super-dry Northeast house, but I'm wondering if the evaporation cools off the room and is going to add to my heating bill.
It seems like evaporative humidifier work exactly the same was as evaporative air conditioners — i.e. blowing dry air across water to cause evaporation, thus transferring the heat of the air into water vapor's latent heat.
Am I wrong about the thermodynamics? Or is the effect small enough that it doesn't make much difference?
Best Answer
You are quite correct about the thermodynamics. The heat involved in a phase change of water is so significant that professional HVAC guys specify the performance requirements for cooling as two different parameters: sensible and latent heat to be removed. The latter is the heat involved in phase change of water and is often more demanding than removing sensible heat.
"For example, in 1 kg of waste air at 20 °C with a relative humidity (RH) of 60%, the total energy is 42.5 kJ, more than half of which (22.5 kJ) is latent heat."
You can analyze your situation with a psychrometric chart like this: http://www.truetex.com/psychrometric_chart.gif
Just pick your desired temperature and relative humidity and you can find out how much water exists as vapor under those conditions.