| Humidity and Health
Maintaining the proper moisture level in your home is an important part of indoor air quality and contributes to your family's health and comfort. Providing ideal indoor air quality includes air purity, temperature and moisture level. A low humidity level can be as unhealthy and uncomfortable as excessive humidity. Dry air causes dry, rough and flaky skin because the skin's outer layers lose moisture to the surrounding air. Respiratory passages such as the nose and throat also lose moisture from their membranes causing dryness and irritation. Low levels of humidity can also contribute to respiratory infections, allergic and asthmatic symptoms and an increase in airborne dust and allergens. As the following chart demonstrates, there is a recommended humidity range of 40% to 60% that is optimal for indoor air quality. If the humidity level is too low, Bacteria, Viruses, Respiratory Infections and Allergic Asthma will increase. If the humidity level is too high, Dust Mites and Fungi/Mold will proliferate and Allergic Asthma will also increase.
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Relative Humidity Chart |
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Relative Humidity
Relative Humidity is the amount of water vapor contained in the air compared to the maximum amount that could be contained in the air at a specific temperature. For example, a measurement of 40% relative humidity means the air is 40% saturated with water vapor at that particular temperature. It is important to understand the impact of temperature on Relative Humidity. Opening windows when the outside air is cold will not add moisture to indoor room air. The reason is that cold air can not hold as much moisture as warm air. Bringing cold air into the home can actually lower the interior humidity levels. This is one reason why humidity levels drop inside during the winter months as there is less moisture in the outside cold air.
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Temperature / Humidity Relationship |
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As the above chart illustrates, the same amount of water vapor in the air will produce less relative humidity as the temperature increases. The chart also illustrates that more water vapor can be absorbed by the air as temperature increases. For example, at 32°F the water vapor in the air results in a relative humidity level of 70%. When the temperature is 68°F, the same amount of water vapor in the air only provides 17% relative humidity.
Humidification Technology
Adding moisture to the indoor air through artificial humidification is the common method of increasing the relative humidity of the room air. There are several technologies used for portable room humidifiers.
Humidifier Types
- Fan Forced Humidifiers - these units usually have a wicking device that absorbs water from a reservoir and a motorized fan that blows air through the water soaked wick to distribute moisture into the air through evaporation.
- Air Washers - circulating discs pull water up from a water filled pan and a motorized fan blows air over these discs to distribute moisture into the air through evaporation. They are referred to as air washers because the water in the discs trap some airborne particles in the water reservoir.
- Ultrasonic Humidifiers - high frequency oscillations are created by a membrane contacting the reservoir water. These oscillations produce a micro-fine water mist which is blown into the room by a small fan where it then evaporates immediately.
- Steam Humidifiers - water is heated to the boiling point where it turns to steam vapor. The steam is allowed to rise from the unit without the aid of a motorized fan.
Problems with Conventional Humidifiers
Comfort - units with powerful fans to force air through them are noisy and can be disruptive while sleeping or conversing. Many times, you have to use a high fan setting to get good humidification and the higher the fan speed the higher the noise. Additionally, you may be uncomfortable sitting near a unit that is blowing moist room temperature air as this will feel cool to the body.
Performance - Units that use fans to push air across a wet surface to cause evaporation lose their effectiveness as the room humidification increases. The higher the water vapor differential between the incoming air and the wick or disc, the greater the water vapor will be released from that surface. As the relative humidity of the room increases, the water vapor differential decreases and the slower moisture is released into the room. This means you will need to run the unit at a higher speed or for longer periods to get the humidification effectiveness at a higher room relative humidity. Humidifier units that produce steam will lose their effectiveness as the heating elements get covered with scale build-up.
Mold and Bacteria Growth - the air is full of living microorganisms. Anytime there is warm, standing water, a favorable environment is created for the growth of bacteria, mold, fungi, etc. Unless some measure is taken to control the growth of microorganisms, they can be distributed into the room air by the humidifier. The problem exists primarily in water absorbing wicks and water reservoirs. Many products use an anti-bacterial impregnated plastic or coated wicks and chemical anti-bacterial solutions added to the water to control microorganism growth. Coated plastics may prevent growth on the plastic, but has minimal impact on the standing water. Coatings on wicks wear off or become ineffective as particle buildup on the wicks prevents direct contact with the microorganisms. Chemicals added to water will be evaporated with the water to be released into the room air.
White Dust - minerals present in all water such as calcium and magnesium, are released into the air with the water vapor. These minerals precipitate out of the water vapor as it evaporates and can leave a white dust on room furnishings. Some humidifier manufacturers use mineral absorption pads, which only have a limited capacity and effectiveness to capture minerals.
Operating Costs and Maintenance - maintenance and operating costs should be a major consideration when purchasing a humidifier. For a humidifier to work effectively, it must be maintained regularly. If it is difficult to clean and maintain, you will either not use it or it will not provide good humidification performance. The true cost of a humidifier is not just the purchase cost, but the cost to operate it and provide any necessary maintenance components. Units that boil water to produce steam require a powerful heating element that can use 350-450 watts of energy. These units can also develop heavy scaling over the heating element due to water minerals and require frequent and difficult cleaning. Other units that use water absorbing wicks get clogged and require frequent changes as the wick acts like an air filter by trapping airborne particles as the fan pushes air through them. |
