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Applications

Office Buildings
Hospital and Institutions
Large Libraries and Museums
Industrial Processes prone to static and fire hazard
Printing
Textiles
Paper products, cardboard, containers
Electronic Facilities

Overview - Why Humidify?

Air that is too dry is just as much of a problem as air that is too wet, and in many cases, much more dangerous. Certain industrial processes, such as box board manufacturing, are prone to fire or explosions when moving materials in dry air builds up static electricity that discharges in the presence of dust, VOCs and other combustibles.

Office buildings, mostly in northern and dry climates, suffer many problems caused by dry air. Including static electricity that ruins electronic equipment to occupant health and comfort issues. ASHRAE Standard 62 has attempted to regulate indoor relative humidity level (Rh) in the same way that it regulates air exchange rates. However, this has been very controversial and has not been uniformly accepted. Therefore, some geographic areas may have Rh standards, while others do not even mention it in their local building codes. Progressive facility managers include humidification systems, even though they may not be required to by code or obvious safety reasons.

Numerous studies done by ASHRAE and other indoor air quality experts, suggest an optimum Rh range of 40 to 60%. Dryer or wetter causes different kinds of problems, at each extreme. See the chart below, based on ASHRAE sponsored research.

Economics

Humidification is a good gas load, but is impossible to isolate from space heating load. Industrial processes may need to humidify year-round, where space conditioning only ADDS humidity during the winter months, and then only in northern climates.

To vaporize 1 pound of water, it takes 212F - 32F = 180 + the Latent Heat of Vaporization = 970 BTUs = (970 + 180) = 1,150 BTUs / Efficiency of the equipment.

Example: 100 pounds/hour, direct fired gas or electric?

100 lbs x 1,150 BTUs/lbs = 115,000 BTUs/80% Efficient = 1.4 CCF x $0.60/CCF = $0.86/Hour to operate.

Electric 115,000 BTUs/99% Efficient = 116,161 BTUs/3,413 BTUs/kWh = 34 kWh x $0.08/kWh = $2.72/Hour to Operate.

Humidifiers tend to be high maintenance items, depending on the local water quality.

Humidification Methods and Equipment

There are several ways to add moisture to air. The two main categories are those that add thermal energy to vaporize the water and those that simply spray water through misting nozzles and count on natural vaporization to do the rest. The best method will depend on how much water needs to be vaporized how quickly, and what equipment may already be available to help distribute the moisture.

The oldest industrial systems used existing space heating steam boilers. If there were not enough steam system leaks to meet humidification needs, additional steam would be vented into the space. When air handlers came along, steam injection manifolds were developed for large scale, controlled humidification. Generally, the same steam was used that provided space heat and perhaps ran industrial processes. However, this steam contained boiler water treatment chemicals. During the initial days of indoor air quality concerns, boiler chemicals became 'tabu'. In some cases, special more environmentally chemicals were used, but in more cases, dedicated boilers were needed. This became expensive to install, especially for small facilities, and facilities that would otherwise not even have a boiler. This gave rise to the electric humidification technology. The most recently developed technology is the direct-fired gas humidification unit.

Steam Humidification

Steam systems are the most economical, when there is an existing boiler and the application requires a lot of volume. Since boiler chemicals are still a concern in most commercial applications, steam-to-steam heat exchangers have been developed. This way, the low operating cost of the central boiler is obtained, and there is a lower first cost than buying a dedicated boiler system. There are also chemicals that are certified safe for humidification applications.

Direct Fired

Direct fired natural gas humidifiers produced steam directly. They are designed to operate with no steam pressure build-up (other than what's needed to deliver the steam) and deal with hard water fouling without the use of treatment chemicals. Direct fired units are the most economical systems for large applications where there is no existing boiler.

The first direct fired unit was introduced by DriSteem, and is called the GTS Humidifier (Gas To Steam). It resembles a large fat-fryer with water instead of oil in the tank. Units are available from 75 up to 600 lbs per hour steam output, 100,000 to 800,000 BTUs per hour gas input.

Carel USA manufactures and distributes a full line of industrial and commercial humidifiers and OEM controls for the HVAC industry. With over 30 years of experience, the Carel line includes steam, air/water atomizing, high pressure water atomizing, electrode, electric element, gas fired and direct steam humidifiers for printing, static control, museums, libraries, hospitals and many other applications.