16 Humidification


Sponsored by Evaporation is cool


Staying cool with minimum energy consumption is an attractive proposition for all building operators. John Barker of Humidity Solutions explains how evaporative humidifiers have an increasingly important role to play.


BEING COOL isn’t just an aspiration of younger people – it is also a key ingredient of maintaining a comfortable indoor environment when ambient temperatures are high. However, traditional methods of cooling using refrigerants are not only energy-hungry, they also have significant environmental implications.


As a result, there is growing interest in alternative methods for cooling buildings that don’t carry the same cost and environmental burdens. And, as is often the case, newer technologies and improved engineering practices can help to enhance the performance of well-established processes.


A case in point is adiabatic


humidification, which uses the evaporation of water to raise humidity levels while also providing cooling as a result of energy being taken from the air to evaporate the water (latent heat of vaporisation). This cooling effect of evaporation has been used in buildings in hot climates for thousands of years and there is growing interest in using modern adiabatic humidifiers in today’s building services systems, even in more temperate climates.


This is the result of two key factors. The first of these is that the cooling effect of adiabatic humidification can eliminate, or mitigate, the need for mechanical cooling, thereby reducing energy consumption and carbon emissions.


Second is the increased recognition of the importance of effective humidity control which, in the UK, is generally focused on raising humidity levels in workplaces. The negative impacts of low humidity on health and productivity are now well-understood and building operators are more disposed to invest in humidification.


To that end, there are two key ways to introduce adiabatic humidification to a building. The first is to integrate it with the ventilation system. The second is to introduce the water vapour directly into the space. Both methods can potentially be applied to new buildings or retrofitted to existing buildings.


Integrating with ventilation


A significant benefit of integrated adiabatic humidification with a ventilation system is that it enables the adiabatic cooling effects to be combined with free cooling using outside air. For example, we have recently supplied adiabatic humidifiers to two air handling unit (AHU) manufacturers for


A supplement to ACR News May 2014


use in AHUs designed specifically for cooling data centres. This is a particularly demanding application and illustrates the potentially high cooling capacity that can be delivered by this combination. In this scenario the evaporative humidifier is incorporated into the AHU after the pre-heating coil and before the cooling coil. It can then be used to supplement the free cooling to achieve the level of cooling required.


Typically in a UK data centre, free cooling will provide the required cooling for around 90% of the year, with supplementary adiabatic cooling for the remaining 10%.


Crucially, the evaporative distance is very short to avoid condensation in the AHU and ductwork and the evaporative humidifier is highly efficient so that minimum energy is required to deliver the additional cooling.


Also, given that so much energy is consumed by existing buildings, a further benefit is that this type of evaporative humidifier can be retrofitted into an air duct system very easily, simply by provision of a duct section enlargement to ensure correct air velocity.


These units can also be supplied in modules to build a ‘humidification bank’ of the required size, with flow rates of more than 100,000m3/h.


This is greatly facilitated by using a software selection tool that gives a list of results for a specific air inlet condition and allows the AHU manufacturer or specifier to select the best solution for each specific case.


Humidity control with a bonus With adiabatic cooling systems, as described above, the primary purpose is to achieve low energy cooling while the humidity control aspects may be a secondary benefit. In other situations, humidification may be the priority with the additional free cooling from evaporation as a bonus.


When introducing humidification to an existing building the most effective and energy-efficient method is to inject water vapour directly into the space. There are several options available but most have serious limitations. For example, ultrasonic humidifiers and atmospheric steam generators within the space are unsightly and occupy valuable floor space, while wetted media above the ceiling require extra ductwork and diffusers. An alternative that avoids these issues is a pressurised water system that uses cold water with compact multi-directional fan assisted nozzles, so that the water is atomised and absorbed into the air. The fact that cold water is used means there is no additional heating energy, though a high pressure pump is required to achieve the required atomisation within a very short distance.


In both of the scenarios described, the key is to make use of the most appropriate humidifier to achieve the required result – whether low energy cooling or improved humidity control is the primary objective. Getting it right and taking full advantage of the latest technologies requires specialist knowledge and the right humidity control partner.


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