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Humidifier

A humidifier is a house hold appliance that increases humidity (moisture) in a single room or in the entire home. There are humidifiers which are commonly used to increase moisture within one room and the there are the one’s which connect to your HVAC system.

Anatomy of a humidifier

The most basic humidifier consists of three basic parts: a reservoir, Wick and Fan.

Reservoir

The reservoir can come in various shapes and sizes and without this the humidifier would not be able to produce the moisture required.

Wick

The wick absorbs the water from the reservoir and acts as a filter. This type of humidifier is self regulating; as the humidity increases the water vapour will decrease and if the humidity drops the water vapour will increase. You will need to change the wick in the humidifiers otherwise they will stop working. The way to monitor this is to check the water level in the reservoir tank, if it stays at the same level you need to change the wick.

Fan

The fan blows air into the wick, thus aiding in the evaporation of the water within the wick.

Other types of humidifiers

Other types of humidifiers include:

Vaporizer steam humidifier/warm mist humidifier

This boil’s the water which releases steam and moisture into the air. This humidifier can be used for administering medical assistance to those with coughs or colds. It is noisy and sounds like boiling water. Although the product is cheaper its running costs are high due to the consumption of electricity used to heat the water.

Impeller humidifier – cool mist humidifier

This works by a rotating disc flinging water at a diffuser, which breaks the water into fine droplets that float into the air.

Ultrasonic humidifier

A metal diaphragm vibrates at an ultrasonic frequency causing water droplets to exit the humidifier and create a cool fog.

Although silent the ultrasonic humidifier needs to be cleaned on a regular basis to stop bacteria being projected into the air.

The impeller and ultrasonic humidifiers do not selectively put water in the air; they also add suspended material in the water to the air such as micro organisms and minerals. If distilled water is used in these humidifiers then the risk is greatly reduced, but no water is absolutely pure. The use of filters also reduces the amount of material but the EPA warns “the ability of these devices to remove minerals may vary widely”. Depending on the volume, this dust may have negative health results. Wick humidifiers trap the mineral deposits within the wick.

Forced air humidifiers

Buildings which contain a forced air furnace the humidifier should be built in to the furnace, as they provide comfort, health and static electricity benefits to the occupants. They are also used to maintain artefacts and wooden furniture in museums as these can be very sensitive to dry conditions. Museums often monitor temperature and humidity around the most valuable antiques. These humidifiers may also provide a substantial energy saving as the effects may make people feel warmer than they actual are. This type of unit is called a bypass humidifier, because they are connected between the heated and cool air return ducts, by using the pressure difference between the ducts, causes some heat to by pass through the humidifier and again return to the furnace.

The humidifier should be disconnected during the summer months if an air conditioning unit is to be used.

There are two basic styles of humidifiers:

Drum style

Water is brought directly to the reservoir (a pan) via a pipe which is attached to the furnace. The level of water in the pan is regulated by a float valve, similar to the tank float in a toilet. The wick is a foam pad attached to a motor in the centre of a drum. When the hot air enters the drum via the one end it is forced to leave through the sides of the drum. When the hygrostat calls for humidity, the motor is turned on causing the drum to slowly rotate through the pan of water and thus preventing the foam pad drying out.

Advantages

Low cost. The maintenance is inexpensive (drum style pads are cheap and readily available).

Disadvantages

They require an inspection at least once a month to check cleanliness and pad condition.

Water evaporation when humidification is not required (due to the pan of water being exposed to high velocity air stream).

Mould growth in the pan full of water (this problem is exacerbated by the large quantity of air, inevitably carrying mould spores, passing through the humidifier whether in use or not).

Drum style humidifiers must be turned off at the water supply during summer months, to reduce the chance of mould growth. They should also be used with high quality furnace filters. The MERV rating as high as possible should ensure small numbers of mould spores do not reach the humidifiers pan, during winter when the water supply to the humidifier is turned on.

Flow through style

A pipe brings the water directly to an electrically controlled valve at the top of the humidifier. Air passes through an aluminium biscuit, often called a pad, the term biscuit is used so there is less confusion with the foamy form. The biscuit is similar to a piece of extremely coarse steel wool. The biscuit is coated in matte ceramic, resulting in a large area within a small space. When the hygrostat calls for it the valve opens and causes a spray of water to land on the biscuit. Hot air is then passed through the biscuit, which then causes the water to evaporate and the vapour is then carried throughout the building.

Advantages

Low Maintenance the only thing you need to replace is the biscuit when it is clogged with dust or mineral deposits.

Lack of a pan prevents stagnant water to serve as a breeding ground for mould as with a drum style.

No incidental humidification caused by a constant replenished pan of water in a high velocity air stream.

Reduced requirement for expensive air filters (MERV 3 for simple equipment protection, though a MERV 7 or above should be used for indoor air quality reasons).

Replacement of the biscuit is necessary when it becomes clogged with dust or mineral deposits (annually or there a bouts. Depending on the quality of the air filter and the water supply).

Disadvantages

Manufacturer and model specific replacement biscuits versus the relatively generic drum style pads.

The requirement for a drain provision (inevitably some water will pass through the biscuits without being evaporated; the quantity is tiny and the difficulty of providing a drain is becoming a moot point since most modern high-efficiency gas furnaces require an available drain to which the humidifier is easily attached).

Risks

Using a humidifier can help dust mites and mould to breed which can cause problems for young children and the elderly. The relative humidity should not rise above 55%.

Micro ban technology is now being used in the new humidifiers which prevents mould and bacteria growing within the humidifier.