Achieving optimum humidification with minimum cost of ownership requires choosing the best type of humidifier for the specific needs of the project. Lindsey Henderson of Axair Climate explains the key criteria
IT’S an unfortunate fact that the benefits of controlling humidity in the workplace are often under-appreciated and under-valued – unfortunate because failing to control humidity compromises the health and comfort of the workforce. So it is very important to include humidification in projects and it’s just as important to choose the most suitable humidifier.

However, there are a number of different ways to humidify air, and a wide range of products to do it with. So, arriving at the best solution with the right balance of performance and cost of ownership means taking a look at a number of important criteria.

Of course, the first consideration must be how much moisture, in the form of steam or cold vapour, will need to be added to the air to achieve the required level of humidification. Humidifiers vary greatly in their capacity so this first criterion may narrow the field somewhat. For example, resistance boilers will not supply more than 80kg/hr of steam, while electrode boilers can provide up to 180kg/hr and gas boilers up to 240kg/hr. Of course, there is always the option of installing more than one humidifier if space and budgetary considerations allow.

Adiabatic humidifiers offer much higher capacities, theoretically almost infinite, though constraints such as capital cost, particularly for ultrasonic models, and duct dimensions will come into play. While the ability of the kit to deliver the required levels of humidification is clearly the most important consideration, the cost of ownership must come a close second. Again, there are several issues to consider.

For instance, in hard water areas the potential for limescale formation cannot be ignored. Demineralised or reverse osmosis water is recommended for all spray adiabatic humidifiers but modern designs of evaporative adiabatic humidifiers can be used with tap water to greatly reduce running costs.

The performance of resistance and gas boilers will not be affected by water quality but use of normal mains water will increase scale formation in hard water areas so demineralised water is often recommended. In contrast, electrode boilers cannot be used with demineralised water because they use the electrical resistance of the water to generate heat.

In some projects, therefore, it may be deemed necessary to install demineralisation or reverse osmosis plant to treat the water before it reaches the humidifier.

However, there are now resistance boilers on the market that incorporate a patented scale management system that eliminates problems of scale, even when tap water is used. Such units have the potential to greatly reduce both the capital and running costs of humidification projects. When scale is controlled effectively, or avoided through the use of demineralised water, the maintenance of all of these humidifiers is relatively low.

With adiabatic coolers, where the water is not heated, the maintenance regime must also include anti-bacterial measures, which must be built into the humidifier. For instance, one hybrid system that combines low pressure nozzles with a post evaporator also incorporates a silver ionisation mechanism to eliminate bacteria from the water.

Energy consumption will clearly make a significant contribution to overall running costs and, again, this varies between the different types of humidifier.

Theoretically, it takes 0.73kW to produce 1kg of steam though there will be distribution and other losses that might add as much as a further 20% to the energy consumption. Gas boiler humidifiers are less efficient, by a few percent, than electrode or resistance boilers but as the cost of gas is currently lower this does not have serious implications for running costs.

All forms of adiabatic humidification use less energy than self-generating steam humidifiers, though there is quite a lot of variation within the adiabatic category. For instance, low pressure nozzles use pressurised air to atomise the water so energy is consumed by the air compressor. High pressure nozzles, on the other hand, take the energy for atomisation from the high pressure water, so here the high pressure pumps is the main consumer of energy. Ultrasonic humidifiers, on the other hand, have higher electrical energy consumption than other adiabatic systems, due to the low efficiency of the generators.

Evaporative adiabatic humidifiers offer the lowest energy consumption and their ability to use any cold water supply without increasing maintenance requirements makes them an ideal choice for new and retrofit projects where energy consumption, carbon footprint and cost of ownership are important specification considerations.

With all adiabatic humidifiers, there is also the opportunity for ‘free’ adiabatic cooling which can be used to supplement any existing cooling plant and reduce running costs even further.

Just from considering these main points it becomes clear that, despite its apparent simplicity, humidification is very much a specialist area.

Axair Climate

0121 705 7601