As end users look for ways to reduce overheads without compromising on indoor comfort a low energy approach to humidification makes a lot of sense. Roger Palamarczuk of Walter Meier (Climate UK) explains.
IN THE current economic conditions end users are looking to building services specifiers and contractors to do more than just design and install systems, they are also looking for options that will help them cut costs.

And this goes beyond capital costs as many organisations are also motivated by their environmental impact and are looking for low energy consumption and low cost of ownership.

Humidification is a case in point. Whereas this was once considered as something that could be dropped from a project to save money, the importance of humidity control in maintaining a comfortable and productive indoor environment is now increasingly recognised.

Clearly, the best way to address all of these issues is to arrive at an effective humidification solution that offers a sensible capital cost, low energy consumption and minimal running costs.

In our experience, modern adiabatic humidifiers using cold water meet all of these criteria – while adding the bonus of ‘free cooling’ from evaporating water into the air.

At this point, many older readers may hold up their hands in horror at the prospect. Certainly, years ago, there were issues with the potential for these systems to spread micro-organisms, dust and allergens – requiring intensive maintenance regimes to mitigate the risk.

With modern technologies, though, this is no longer a concern. New systems, which have been developed to address the very issues described above, incorporate a number of features that were absent from older systems.

As the potential source of any problems, the water is the first logical area to address. Using fully demineralised water is a good starting point and, as this costs more than tap water, the system also needs to use the water efficiently. Low maintenance anti-bacterial measures are still necessary, of course and silver ions have proved to be ideal for this purpose.

Tried and tested in a wide range of applications over many years, the silver ions enter the cells of micro-organisms, block key metabolic processes and kill them.

Another benefit is that the dosage of silver ions in adiabatic humidifiers can be precisely matched to the flow rate by using electrolysis.

These principles were put to the test at a hospital in Zurich. Following extensive testing of the Condair Dual 2 adiabatic humidifier, where bacteria levels were found to be well below the 100 bacteria/m3 specified for humidified supply air, the hospital is now using these units for humidifying operating theatres.

Another important issue is the efficiency of water vaporisation, to eliminate the risk of creating potentially hazardous pools of water. Research has shown that use of molecular, low pressure (4-6bar) nozzles with ceramic orifices, arranged on a mesh grid is a very efficient approach. This is because it creates an homogenous spray mist that immediately starts to evaporate in the air flow.

Unlike classic nozzle systems, which require a long absorption distance and a droplet separator, this arrangement functions very efficiently with a short absorption distance, which increases efficiency and reduces water consumption.

In situations where the humidifier is a stand alone unit, the efficiency of the evaporation can be further increased by passing the air flow over highly porous, adjacently-arranged 50mm thick ceramic plates located 80cm downstream. Any remaining spray mist is deposited on the plates, and then evaporated by the energy of the passing air.

This arrangement serves to optimise the use of the water as well as raising efficiency levels to over 90%. It also facilitates rapid drying when spraying is switched off – a further safeguard against hygiene hazards.

In distributed systems humidifying several areas of a building, a central high pressure system fed by partially de-mineralised water can serve atomising nozzles.

The pulsation pressure from the system will produce ultra-fine atomising at the swirl nozzles, with no need for compressed air, releasing a mist that evaporates into the air to increase humidity and cool the air at the same time.

As compressed air is not required, these systems are also very quiet and hygiene is taken care of by silver ionisation within the centrally installed system.

The result is that humidification is localised, rather than being applied to the entire air supply, so that the needs of each space can be addressed very precisely by using different types of atomising nozzles and tailored control strategies.

At the European headquarters of Gallaher Group, for example, this ‘direct-room’ approach has been applied to four floors of office space, each measuring 3000m2. Each floor is fitted with 18 wall-mounted Draabe TurboFog nozzles to provide a constant relative humidity of 50%, monitored by hygrostats mounted in each space.

Similar benefits can be applied to industrial settings. Blaupunkt, for instance, has replaced steam humidification systems with distributed TurboFog systems to prevent build up of electrostatic charges in several of its manufacturing facilities.

Of course, it would be wrong to suggest that adiabatic systems are the best humidification solution for every application. As with any building services system the equipment needs to be selected to suit the needs of the project.

However, I would recommend that adiabatic humidification is given the consideration it deserves during the design process, taking account of the advances made with these systems in recent years.

Walter Meier (Climate UK) 0871 663 0664