PHOENIX, AZ — As you might imagine, the air is very dry most of the time in this part of the country. Because of the low annual rainfall and low relative humidity, you might think this is the prime location to find humidification equipment installed in every residential and commercial application.

You’d be wrong.

There are very few buildings around that use humidification equipment to keep moisture levels at what most consider to be normal (e.g., 50% rh). That’s very surprising, especially since the humidity averages around 35% to 40% throughout most of the year. During the winter months, the humidity can actually fall into the single digits, although a more normal range is around 15% to 20% rh.

All that dry air takes its toll on humans and on buildings. Phoenix residents often experience dry, itchy skin and eyes, while wood furnishings can become dry and brittle. But even with those concerns, the fact of the matter is that there is simply little demand for humidification equipment here.

Outdoor Society

One of the reasons why residential customers don’t usually ask for humidification may be the fact that many months of the year we’re able to live with our windows open, says Mike Donley, vice president and general manager, Donley Service Center, Phoenix.

“We’re able to be outside a lot, and we’re getting a lot of outside air in the house. And, certainly eight months of the year, we’re not very dependent on our comfort system in this market. It’s not like in the East, where furnaces are drying out houses.”

That may be why Donley only has a few requests each year from residential customers for humidification. And those customers are usually transplants from the Midwest and East, who often wonder why more homeowners don’t have humidifiers installed in their homes.

Another reason why humidification isn’t usually used in residential applications is the fact that there simply isn’t much room. Most of the houses built here are tract homes, where the air handler is in the attic. Who’s going to maintain that humidifier when attic temperatures can soar past 160°F?

The other problem with attic installations is that if a leak develops, it can ruin the ceiling before anyone even knows there’s a problem. Although only a handful of customers have humidifiers, Donley says that most have his company take care of their humidifier as an add-on to the regular maintenance contract.

The other option in tract homes is a closet application, and there’s not a whole lot of room there either. “It’s not like elsewhere in the country, where the whole system is located in a basement and there’s a lot more room. Here, everything is drywalled in. The last customer who requested humidification, we could only fit one humidifier in one of their two systems — that is, unless we changed the whole system out and designed it for that application. That was cost prohibitive,” says Donley.

The customers who are surveyed by the contractor don’t usually list humidity as a comfort concern either. Most people are more interested in buying air filtration, programmable thermostats, higher-SEER units, and higher-quality units, rather than spending the money on humidification, notes Donley.

Not Much On The Commercial Side

It’s not just the residential applications that are lacking humidification equipment — commercial and industrial applications don’t usually make use of it either. The one exception to the rule is the semiconductor industry, which has cleanrooms all over the Valley.

“Almost 100% of the humidification equipment we’re installing, we’re putting into semiconductor cleanrooms, where they have tight humidification specifications,” says Don Petty, vice president of W.D. Manor Mechanical, Phoenix.

Most of the cleanroom specifications call for humidity to be in the 40% to 45% rh range, which is difficult to accomplish in the desert. If you consider that getting to 40% to 45% rh means pumping in a whole lot of moisture — especially if you’re starting at 15% — it’s no small feat. In addition, buildings often aren’t built tightly enough to hold in all the humidity. Even if there’s something as small as a hole in the electrical outlet, humidity will literally leak out of that hole.

“Humidity will go in the opposite direction of the airflow. Even though the air is coming into the room, humidity will go through the drywall. You have to have special paint and special ceiling tiles and special floorings. Everything literally leaks moisture,” says Petty.

Petty is particularly fond of ultrasonic humidifiers for larger applications, because these humidifiers don’t use a lot of electricity. In addition, they act as an evaporative cooler, meaning an application may see a 2° to 3° drop in the temperature of the air.

And things here aren’t always as dry as they seem, says Petty. To prove his point, he pulled out a sling psychrometer. On the day we talked, the outdoor relative humidity was about 18%. However, his sling psychrometer showed that the actual relative humidity in his office was about 29% — which isn’t really that dry, he maintains. “People move here for the dry heat. They don’t want to be moist.”

Maintenance is another issue here, because we have very hard water, which can clog up nozzle heads and also leave deposits inside the ductwork. Hard water can also affect steam quality, which is why it is often necessary to take the steam from the point of origin over to another steam-to-steam generator, where it actually becomes clean steam. That can be a big headache for facilities — and many just don’t see a need for it.

“We are an anomaly here in the desert,” says Petty. “We have very low wetbulb temperatures, which is a good thing, because it allows our air conditioning equipment to be quite efficient. We do things with cooling towers that other places can’t do. We’re able to run without chillers longer.

“Having been in the moisture in Georgia a few times, I think it’s wonderful to be dry.”

Publication date: 04/16/2001