How effective are central humidification systems?

I am currently working on a post discussing central versus portable humidification systems.  In the midst of it, I realized that I was discussing a lot of issues that might be too much to take in one post.  In other words, it was getting kinda long.  So, I decided to break out part of it for this post.  Well, that and the fact I am beginning to get brain fog in composing the post.

So, for this post, I am going to discuss just how effective a central humidification system might be.  Warning to those who glaze at the use of calculations, they are in here.  If you cannot dig through it, just go to the conclusions.

So, you have a central humidification system that is dumping moisture into the air.  Just how effective is that humidification system at raising the humidity level of the air flowing through the air handler?  Consider this point—to raise the humidity 1% will require about 0.00004 gallons of water for every cubic foot of air (assuming I did my psychrometrics right).  That doesn’t seem like a lot, right?  But, a typical air handler fan pushes around 1200 cubic feet of air per minute.  That means 0.046 gallons (or about 0.7 pints) of water is needed every minute just to raise the humidity in the air flowing through a typical furnace 1%.  Want to try to raise that humidity from 10 to 50%?  That would be nearly 2 gallons of water per minute.  Do you think your humidifier can do that?

Now, consider this point.  Most central humidification systems work by evaporating water into the air passing through the humidification system.  That evaporation process is not 100%.  If you want proof and have one of these systems, check for water coming out of the overfill tube when the system is operating.  Now, the water flowing through the humidification system is not pure–it contains minerals.  As the water evaporates, it leaves those minerals behind to coat the media, as shown in the photo below.  As the media becomes coating, it is less able to absorb the moisture and the surface area of the media that is available for evaporation decreases.  Water that is not evaporated into the air passes through the humidification system to the overfill tube and is wasted.  Whether the water goes into the air or down the drain, you are paying for it.


Mineral encrustation on a wetable media inside a central humidification system.

Mineral encrustations on the humidification system as shown in the photo can also channel water down through only part of the media.  That further decreases the wetted area of the media from which moisture can evaporate.  Less areas from which water can evaporate means lower efficiency.

One more issue I would like to mention.  As the temperature of the water being supplied to the humidification system drops, less water evaporates into the air.  Basically, some of the water flowing over the media is absorbing heat without evaporating into the air.  That means that less water is entering the air.  I don’t know about your water system, but mine sure seems colder in the winter than the summer.  Per my previous post, the water valve supplying water to the humidification system only allows one flow rate.  During the winter, if you water supply temperature is colder, not only is water potentially being wasted, it could also be carrying some of the heat you are supplying to the air down the drain.

In my next (or maybe the one after that or after that or . . . ) post, I am going to get more into central versus portable humidification systems.  I promise.  Stay tuned.

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