Closely related to Does a humidifier cool the air? but with a different kind of humidifier, and I'd like to know exact numbers.
First question: for the same production volume of vapor, does an ultrasonic mist maker cause the same amount of cooling as an evaporative humidifier?
Second, more practical question: My apartment already struggles sometimes with keeping the unit warm, but it's also far too dry, so I need to humidify. I bought a mist maker with stated vaporizing capacity of 1600ml/h.
It seems since I've had it running, the heater struggles even more than before. How do I convert from ml/h to BTUs I am losing to humidification? Do I need to provide other parameters (like a starting relative humidity and temperature)? I looked at Philip's chart at: http://www.truetex.com/psychrometric_chart.gif but I'm not really sure how to read it.
Best Answer
What you're asking about is the latent heat of vaporization.
It is 970 real BTUs per pound of water, or 2260 joules per gram. A joule is a watt-second. A BTU raises one pound of water one degree F.
That means if you have an ugly bag of liquid water, 1 pound, and it is 112F temperature, and you inject 100 BTU, it is now 212F. If you inject another 970 BTU, it is still 212F but is now vapor. If you inject 30 more BTU to make it an even thousand, it is now 242F. The 970 BTU was eaten by the phase change. Yes, you can use this to air-condition, but it works better with freon, propane, etc.
There's no free lunch. That energy has to come from somewhere.
A gallon of water is 3785 grams (also 3785 ml, by wild coincidence, not). It will take 8.5 million joules or 2400 watt-hours, or 8200 real BTU, to evaporate it. If the humidifier avoids paying it (e.g. By misting), it is stolen from the air, cooling the air.
By "real BTU" I mean BTU is a timeless unit. Remember when a furnace talks about BTU, that is slang. It actually means BTU/hr.