When using a heating system to provide ambient air at a comfortable temperature indoors, it is often desirable to increase the humidity of the heated air. If the air to be heated is initially very cold, such as outdoor air in winter, the heated air will contain very little moisture. Indeed, indoor air may have a humidity, or moisture content, as low as 10 to 15 percent, which is significantly drier than even desert air. Such dry air can cause skin and mucous membranes to dry out, making people uncomfortable and perhaps increasing their susceptibility to infection by air-borne viruses and bacteria. Dry air can also lead to drying of wood structures, such as flooring and furniture, and it can lead to increased static electricity that may damage electronic equipment, such as computers. Thus, indoor air is often humidified, using one of several types of humidification systems that are currently available for residential and commercial use.
In a bypass type of humidification system, air passes over or through a pad or sheet of wet material that has a large surface area. As the air passes the wet surface, it picks up water that evaporates from the surface. Other systems use nozzles to spray small water droplets into the air. If the droplet size is small enough, the droplets evaporate quickly in the air, thereby preventing significant fogging. These types of systems generally require significant maintenance to prevent scale buildup on the pads or sheets or in the nozzles.
Steam humidifiers use heat to boil water in a reservoir or tank, most commonly with a heating coil located inside the tank. This type of humidifier generally uses tap water, which may contain significant quantities of dissolved minerals. As the water in the tank evaporates, the mineral content of the remaining water increases, and eventually minerals precipitate from the water to form scale deposits on the walls of the tank and the heating coil. Over time, the tank volume decreases, and the scale layer on the heating coil acts as a thermal insulator. As a result, the humidifier becomes increasingly inefficient. Although frequently flushing clean water through the tank can slow down the rate of scale buildup, there is no simple way to remove the scale deposits once they form in the tanks and in associated plumbing, and the tanks must be replaced periodically.
Thus, there is a need for a steam humidifier that operates more reliably over long periods of time and that can be easily maintained, rather than routinely replacing major system components, such as holding tanks, heating elements, and solenoid valves.