If you have an electric furnace, do steam humidifers cost more to operate?

[NeoPTLD]

Let's compare steam humidifier vs wick evaporative

Steam humidifier must boil and supply the water with latent heat of vaporization. This energy is provided by humidifier itself.

If you use an evaporative type, the humidifier just moves the air and absorbs the energy from room atmosphere. The discharge is colder than intake. The furnace provides the energy to room heating.

Water has a higher heat of vaporization/condensation at room temperature than boiling, so it takes more input to evaporate a unit at room temperature than boiling.
http://en.wikipedia.org/wiki/Enthalpy_of_vaporization

Ignoring the variation between 373K and 293K and assuming you're using electric furnace or a steam humidifier. Assuming 2257kJ/kg, which comes out to 2.37kWh/gallon, don't you end up paying for that in either power going to furnace or power going to humidifier?

 

[Paperdoc]

Bottom line, there is no difference in energy consumed and paid for.

The heat necessary to evaporate water at room temperature is just the Heat of Vaporization of water. Once that process is done, we have in the air a whole big bunch of water molecules at room temperature, 298K (25 C). Plus, you have a room full of air molecules that are just a tiny bit cooler that they started out, because they all gave some of their energy to the water to convert it to gaseous water molecules. To do it by boiling, though, requires heat for two processes - first we heat the water to its boiling point (100C, or 373 K), then we add the same Heat of Vaporization to convert it from liquid to gaseous water. The total heat input this way is more; the difference is the amount of heat used to get the water molecules up to 100C or 373K. But once they are converted to gaseous water, those molecules are NOT at room temperature - they are very much more energetic. As they diffuse around the room and bump into other air molecules and objects (like people) the give up that excess energy and eventually return to the "room temperature" of 298K. At that point they are exactly the same as the molecules that were evaporated at room temperature in a non-boiling humidifier. The difference is that, for a time, they were given higher energy, and they later released that energy to their surroundings. So ALL the excess energy they were given to convert them from 25C liquid water to 100C liquid water now has been distributed around the room and the whole room has higher energy and feels warmer. That did not happen with the non-boiling humidifier. If you wanted to use the non-boiling humidifier and also to have the second effect of warming the room, you would have to provide that same amount of heat to the room air directly, rather than doing it through the intermediate carrier of the water you boil. That amount of heat required to make the room feel just as warm in both cases would be exactly the same, no matter which route you take.

So, bottom line, between the two processes there is no difference in energy consumed and paid for IF you actually get to exactly the same end point.

 

[CycloWizard]

Paperdoc is right - the amount of energy required to achieve a given level of humidity is a state function (i.e. it will be equal no matter how you go about putting the humidity in the air). The only differences you might notice between various methods as far as cost goes will be the efficiency of the unit - how much input energy actually goes to producing water vapor. Different devices will more likely be better at controlling humidity, since you usually want it between 50-70% relative humidity indoors, and how quickly they can add moisture to the air.

 

[Paperdoc]

By the way, for those not versed in thermodynamics, the term "State Function" means that the total change in energy (and hence how much energy you must put it) is dependent entirely on the initial and final states, and has absolutely nothing to do with the pathway from one state to the other. So if the two energy states are identical, then the change between them is identical no matter how you get there.