Humidifiers are appliances used to increase moisture in indoor spaces. There are point-of-use humidifiers, which are commonly used to humidify a single room, and whole-house or furnace humidifiers, which connect to a home’s HVAC system to provide humidity to the entire house.

Hindol Bhattacharya, Sales & Marketing Manager at Best Pro, which represents cooling and dehumidification systems provider, Advantix, in the region, explains that “improper humidity levels (either too high or too low) can cause discomfort for people, and can damage many kinds of equipment and materials”.

Humidification can be approached by two processes — he says — isothermal humidification and adiabatic humidification.

In isothermal humidification, water is heated and dissipates as steam to be dispersed in the air. This process requires a source of energy to heat the water.

The adiabatic humidification process involves the direct evaporation of water in the air without the addition of energy from the outside. The water is finely atomised to maximise the heat exchange surface and then introduced into the environment. “Fogging systems use compressed air to atomise water and create a stream of microscopic water particles which appears as fog,” Bhattacharya points out. “The water particles quickly change from liquid to gas as they absorb heat from the surrounding air. It is a constant enthalpy process and air decreases its temperature.”

Humidifiers’ main industrial applications include greenhouses, manufacturing, dust suppression systems, cold storage & ripening rooms, textiles and hatcheries, Bhattacharya explains.

Dehumidifiers, on the other hand, are designed to reduce the level of humidity in the air, usually for health reasons.

“A very humid climate like that prevailing in the Middle East can cause people to feel uncomfortable, producing excessive sweating that can’t evaporate in the already saturated air,” Bhattacharya says.

Humid air can lead to condensation and provides a fertile condition for growth of mould and mildew. Higher humidity also provides a breeding ground for pests like moths, fleas, cockroaches, mites and lice. Bacteria causing Legionnaire’s disease also can thrive in moist conditions. Furthermore, humid air circulation in closed air conditioned spaces leads to a deterioration in the Indoor Air Quality (IAQ).

By their operation, dehumidifiers produce an excess of water which has been removed from the conditioned air. This water must be collected and disposed of. Some dehumidifier designs dispose of excess water in a vapour, rather than liquid form. Dehumidifiers are also used in industrial climatic chambers, to control relative humidity within certain rooms to stay at levels conducive to processing of products.

According to John Magaway, Sales Manager-Business Area Air Treatment at Munters UAE, a global provider of dehumidification equipment, last year, the approximate sales volume of the GCC dehumidifiers market amounted to €2 million.

The most common types available on the market are refrigerant and desiccant dehumidifiers.

Refrigeration-based dehumidifiers work by passing air over a cooling coil which cools air to its dew point. This causes the moisture to condense out of the air, leaving it dry, explains Bhattacharya. However, the air leaving the coil at this point is too cold and must usually be re-heated to space conditions.

If tight control over relative humidity is desired, the sorption-based dehumidification systems must be considered for such applications.

Desiccants in either solid or liquid form have a natural affinity for moisture. Desiccant materials attract moisture based on differences in vapour pressure. Desiccant dehumidifiers include solid desiccant or the desiccant wheel systems and the liquid desiccant systems.

“Because the amount of water that can be contained in the air is a function of the temperature and pressure of that air, the next step is to look at ways to remove moisture by changing the temperature or pressure,” says Atul Pahune, Branch Manager ̶ MENA Region at Bry-Air, a division of Bry-Air Asia, which offers moisture control solutions for a wide array of applications.

As he explains, lowering air temperature decreases the air’s ability to hold moisture. Thus, the air can be made drier by cooling it. However, he claims, cooling air just to dry it is usually not practical.

“An exception might be when cool air is needed anyhow, that air’s dryness satisfies the required moisture conditions, and enough conditioned air is available,” Pahune says. “Normally, this method is reserved for applications where outdoor air is being dried to levels only slightly lower than the incoming ambient — that is to say, the system air.”

To remove large amounts of water by cooling the air, over-cooling and subsequent reheating air required.

However, in his view, such procedures typically have problems with operation and maintenance, as well as cycle and control.

Therefore, the method is unsuitable for producing large quantities of dry air.

Another limitation to this technique is the freezing point of water. When air is dried via refrigeration, the cooling surfaces of the coils may reach sub-freezing temperatures. This causes ice to form, which, in turn, reduces the efficiency of the cooling system. So anti-icing devices or duel systems and defrost cycles may be required.

He believes that the most straightforward way to obtain dry air is to use desiccants which are adsorbents or materials that have a natural affinity for water.

“A desiccant is able to take up the additional moisture given up by the air without changing its size or shape,” Pahune explains.

He adds that the air stream can pass through a desiccant and become significantly drier without elaborate cooling, compression, cooling water, or other complex systems or controls. After the drying task is complete, the desiccant is regenerated through heat and is ready to dry more air.

The main industrial applications for desiccant dehumidifiers include food processing, pharmaceuticals and commercial applications such as swimming pools, libraries, etc.

From a technical point of view, dehumidifiers should be able to constantly deliver very low dew point and consume little energy, Pahune points out.

Indeed, he mentions energy consumption and low dew point, as the main criteria that his clients take into account when selecting a certain brand, along with easy installation, operations and maintenance, high efficiency and reliability, 24/7 post-sale service support and successful installations for various applications.

He claims that Bry-Air dehumidifiers, which comply with CE standards, use only a relatively small amount of desiccant at any one time and constantly regenerate it as part of a continuous cycle. These devices are manufactured in two designs and different sizes, from very small to very large, to meet various dry air requirements.

As Best Pro’s Bhattacharya points out, given that all humidifiers work by converting water to vapour, the quality of supply water has the greatest impact on maintenance requirements.

“Untreated tap water contains minerals such as magnesium, calcium, and iron that make water ‘hard’,” he says. “These minerals clog boiling chambers, wetted media pads, and atomising nozzles. Adiabatic systems using untreated water disperse minerals into air causing white dust fallout, which can contaminate furnishings and processes as well as cause inhalation hazards.”

He believes that using treated, softened water can mitigate many of these issues. “Systems using properly processed de-mineralised water have virtually no supply water maintenance issues,” he observes.

As he explains, refrigeration-based dehumidification systems need special attention to maintenance. “Coils and drain pans should be cleaned from time to time to ensure they are not clogged and free from dirt which provides a breeding ground for mould and mildew,” he points out.

He adds that solid desiccant/desiccant wheel systems have their own maintenance issues such as cleaning of wheel periodically to clear it of contaminants/deposits, reactivation heaters that might break down, needing periodic replacement, periodic post cooling coil maintenance and service, performance degradation over time due to continuous heating and cooling of the desiccant wheel. Replacement of the desiccant wheel is costly, accounting for about 50% of the system cost.

Liquid Desiccant systems, on the other hand, are relatively easier to operate and maintain. Still, it is necessary to filter the liquid desiccant every five years, as well as cleaning the filters periodically as one would in a AHU.

“There are no wet coils, no drain pans to clean. The air leaves the system cool and dry. The liquid desiccant works as an air scrubber, removing suspended particulates. The hygroscopic salt solution also destroys up to 91% bacteria and other microorganisms in a single pass, thereby delivering healthy Indoor Air Quality,” Bhattacharya says.

Munters’ Magaway points out that desiccant dehumidifier’s performance is mostly affected by dust or tiny foreign particles infiltrating the desiccant rotor inside the unit, which has narrow channels and is constructed in honey-comb pattern.

Once the channel is clogged, then the air passage will be blocked, thus affecting the performance. “It is very important to observe regular filter inspection and maintenance,” he says.

Another issue concerning desiccant dehumidifiers is the available power at site.

“Normally, if not planned originally, dehumidifiers are add-on equipment in the factory and only considered when the customer encounters problems with humidity that A/C Unit alone cannot solve,” Magaway explains.

Desiccant dehumidifiers are equipped with a reactivation heater for desiccant regeneration.

Given that refrigeration-based dehumidifiers use a portable unit, the installation issues are not as significant.

Bhattacharya points out that determining the best type of home or office humidifier to purchase is based on application requirements. General parameters to keep in mind when selecting a humidifier are the size of the area in which the humidifier is required to work, and how much maintenance is involved. “The humidifiers which leave a lower mineral residue are the ones preferred,” he says.

With regard to dehumidifiers, he observes: “Dehumidifiers should be able to remove moisture and maintain space conditions effectively. Maintenance should be simple and easy to carry out. Energy consumption should be compared.”

In his view, one of key installation issues for humidifiers and dehumidifiers is that clearances and access spaces are not available as required. “This leads to servicing difficulties at site later on. Proper care should be taken to ensure manufacturer-recommended service clearances are available.”

Bhattacharya emphasises that, although there aren’t currently any specific standards which have been implemented for humidifiers and desiccant dehumidifiers, it’s important to check if the manufacturer has ISO Quality Standards certification.

Furthermore, refrigeration-based dehumidifiers/air handlers must have AHRI certification for cooling coil performance, AMCA ratings for fans, etc., while indoor pool dehumidifiers are currently rated in accordance with the new standard 910-2011: Performance Rating of Indoor Pool Dehumidifiers.