Debbie Batchelor, Sales Manager, Condair
Level of humidity and fluctuation? Different applications require different levels of humidity control. The most common application for a HVAC consultant will be the office environment’s requirement of between 40-60%rH (relative humidity). At this level people are comfortable and static buildup is reduced. Manufacturing industries may require a more specific level of humidity control. For instance, printers need to control humidity to a tighter 50-60%rH and textile manufacturers will need a higher 65-75%rH. Some pharmaceutical applications need an even tighter ±2%rH.
If an application requires tight control of humidity then the humidifier selection will be restricted to systems that give very fast responses to a drop or increase in humidity, like resistive steam or spray units. Water treatment may also be required to improve the consistency of performance.
Running time/shut down? If a humidification system is going to be used 24/7, then the number and type of humidifiers will need to reflect this. A critical system that needs to be constantly delivering a certain level of humidity must include run and standby humidifiers as every humidifier in the world needs to be shut down occasionally for maintenance.
Running costs/environmental impact? Running costs vary widely with different types of humidifiers. Some steam systems can use 150 times more energy than an efficient evaporative humidifier and require six times more to be spent on them in servicing and spare parts. The initial purchase cost is a lot less for the steam system but an error in the initial product selection can cost the client (and the environment) dearly over the life of the unit.
Consideration should also be given to using some evaporative humidifiers to reduce the running costs associated with the building’s cooling system. This can reduce the running costs associated with DX chillers and reduce the building’s overall carbon footprint.
Energy types and availability? This is a critical question as it’s not unheard of for contractors to arrive on site to install equipment only to find that the amount of electricity required to run a humidification system is not available. For really large duties, the energy requirements of using an electrical system can become prohibitive and either evaporative, spray or gas humidifiers may be a more viable option for the end-user.
Water quality and maintenance? Water quality and maintenance are intrinsically linked when dealing with humidifiers as poor water quality inevitably leads to a higher servicing requirement. The minerals left behind in the humidifier when the water is either boiled or evaporated into an atmosphere need to be dealt with.
If the water has a high mineral content but a high level of maintenance is unacceptable, water treatment should also be specified. This can take the form of reverse osmosis filters and water softeners to help improve the quality of the water and reduce the level and frequency of servicing.
Evaporation distance required? For humidifiers providing moisture to ducts or AHU systems, the humidifier must be able to evaporate the moisture into the airstream before it meets physical obstructions, like duct corners, otherwise this will cause condensation. If the available evaporation distance is short, specialist steam lances can be used, which give evaporation in under 60cms, or evaporative humidifiers specified, which provide instant evaporation.
Where to locate humidifiers? If access to the location is restrictive, certain humidifiers may be easier to install than others. Also, if a unit is located in an awkward position, servicing may be difficult or sometimes impossible. Mounting height should also be considered.
Budgets and advice Asking these questions helps paint a clearer picture of the end-user’s ideal requirements. However, the “ideal” obviously has to be balanced against the available budget. While trying to reach this balance it is always worthwhile drawing up a matrix of capital cost vs running cost as budgets are often set without this in mind. A higher investment in the initial equipment than the proposed budget can often be in the client’s best interests.