Maintaining effective control of humidity is essential in industrial environments for both occupants and manufacturing processes. John Barker of Humidity Solutions explains
It is well accepted that humidity control is essential in maintaining the health and comfort of the workforce, as well as protecting the integrity of stored materials and the reliability of the manufacturing process.
When there are problems with humidity control in industrial environments it is usually because the RH is too low. This can make eyes dry and itchy and cause dehydration. Low RH is also linked with Sick Building Syndrome, the intensity of chemical pollution in buildings and a higher survival rate for certain viruses.
Additionally, low RH may cause materials to dry out very quickly. Timber, for instance, is prone to shrinkage, defamation and cracks in a low humidity environment.
Moreover, low RH makes occupants feel colder, so they turn the heating up to compensate; though raising temperature reduces RH even further. Conversely, RH at the upper end of the acceptable range will make the space feel 2-3°C warmer so that heating can be turned down.
For all of these reasons, it makes commercial sense to include humidity control in new build projects and to consider retrofitting it to existing buildings. Good humidity control will keep the RH between 40% and 60% and, as noted above, the requirement will usually be to increase humidity using a humidification system.
In such cases, choosing the right type of humidification system is essential. Account must be taken of factors such as energy consumption, maintenance requirements and where to locate the humidification plant (particularly if plant room space is limited).
Traditionally, the solution has been to heat water to produce steam that is then introduced to the ventilation system. However, high pressure, low energy systems using cold water are becoming increasingly popular in industrial applications.
There are several ways of generating steam for humidification and it’s important to be aware of the characteristics of each. For example, electrode boilers will not supply more than 90kg/hr. of steam, while resistive generators can provide up to 120kg/hr for a single unit and modular gas-fired humidifiers will deliver up to 400kg/hr. A modular configuration of gas-fired humidifiers (as with modular boilers) enables the system to respond to varying humidification requirements very efficiently.
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%. The method of heating is therefore important and gas-fired humidifiers will generally offer higher efficiency than mains electricity.
Gas fired units may also prove less costly to install because electric humidifiers have heavy cabling requirements.
In hard water areas the potential for limescale formation cannot be ignored and demineralised water is often recommended. For example, when a specialist packaging tester was experiencing regular scaling problems with electrode steam boilers, a more cost-effective alternative proved to be resistive steam humidifiers served with demineralised water.
Low energy, high pressure
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 and can be combined with demineralised or reverse osmosis water.
All forms of adiabatic humidification use less energy than self-generating steam humidifiers. 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, although very low.
Achieving effective humidity control while minimising lifecycle costs was a consideration for bespoke cardboard tube packaging manufacturer Visican, where 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 without risk of wetting or condensation on machines and products.
In both cases the 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.
Given all of the factors discussed here, it is clear that achieving acceptable humidity control depends on addressing a number of variables within each project. For that reason, it makes sense to team up with companies that have a comprehensive range of different humidity solutions and the expertise to apply them to optimum effect.
Further information: www.humiditysolutions.co.uk