Getting to grips with humidity control

While good humidity control is important in all indoor spaces, achieving this can be particularly challenging in certain industrial applications. This is because not only must the relative humidity (RH) be conducive to the health of both the workforce and the building fabric, in many cases it must also meet certain criteria to support manufacturing and other processes.

The most commonly experienced problem with humidity control in industrial/commercial environments is that the RH is too low. This can make the eyes become dry and itchy, especially for contact lens wearers, and respiratory surfaces start to dry out, leading to dehydration.

In parallel, low humidity can cause drying out of stored materials and potentially affect machinery, resulting in disruption of the manufacturing process. As a consequence of these factors, there are very good reasons for including humidification in new build projects and potentially retrofitting it to existing buildings.

In such cases, choosing the right type of humidification system is essential in terms of providing the right amount of moisture and maintaining the required RH. Account must also be taken of additional factors such as energy consumption, maintenance requirements and where to locate the humidification plant (particularly if plant room space is limited).

In many cases the best solution will be to heat water to produce steam and there are several ways of doing this, so the selection needs to be influenced by the specific requirements of project. For example, we recently worked with a specialist packaging tester where the humidity was controlled by electrode steam boilers. These were experiencing regular scaling and were unable to maintain the required humidity without extensive maintenance. A more cost-effective alternative proved to be resistive steam humidifiers served with demineralised water.

However, there is clearly an energy cost to heating water. As a rule of thumb, it takes 0.73kW of heat to produce 1kg of steam, though distribution and other losses might add as much as a further 20%.

A lower energy alternative to heating water is to spray water through nozzles, so that the water is atomised and absorbed into the air (adiabatic humidification). The water may be sprayed – at low or high pressure - into ductwork or directly into the space being humidified. Such systems also need to incorporate anti-bacterial measures such as ultra violet disinfection combined with demineralised or reverse osmosis water.

All forms of adiabatic humidification use less energy than self-generating steam humidifiers, though there is some variation. Low pressure nozzles use pressurised air so energy is consumed by the air compressor. High pressure nozzles take the energy for atomisation from high pressure water, so here the high pressure pump is the main energy consumer.

Achieving effective humidity control while minimising lifecycle costs was a consideration for bespoke cardboard tube packaging manufacturer Visican; there were problems with paper curl and static electricity resulting from low humidity in both the storeroom and the factory. The solution proved to be an adiabatic humidification system introducing water to the factory and store room through high pressure nozzles to maintain an RH of 55%.

A similar solution was used for a manufacturer of injection-moulded plastic drink bottles, again delivering moisture through fan -assisted nozzle heads, each configured to suit the area being served and to ensure effective humidification without risk of wetting or condensation on machines and products.

In both cases use of adiabatic humidification delivered additional benefits through the cooling effects produced by evaporating water, which reduced the need for mechanical cooling in the spaces.

As a company that supplies all types of humidity control we don’t have a particular axe to grind. The important thing is to recognise is that effective humidification isn’t as simple as it may at first seem, so it makes sense to team up with companies that have both the experience and the product range to offer the most appropriate solution.