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Why Evaporative Cooling Works! 24/01/2017

Evaporative cooling concepts are being successfully employed globally in some of the world’s most prestigious projects. Over the last 10-15 years in the UK alone there are literally thousands of successful installations.  Despite this, there are still many who are sceptical or due to a lack of knowledge don’t understand the fundamentals of system design to employ this technology successfully and benefit from the significant energy savings this technology can bring. However, it can be argued that the evaporative cooling industry has done a pretty poor job of educating the wider HVAC industry on the design considerations and selection of evaporative cooling concepts and system types.

Fundamentally, to cool a building you need to supply air at a lower temperature than the required internal condition and of sufficient volume to cater for the calculated heat gains. For example, if we decide we don’t want to exceed 25°c in the summer internally and our system is designed to supply the correct air volume at a temperature of 17°c, then the building is sufficiently cooled and comfort is achieved.

The building doesn’t care how we cool the air to the desired temperature, we can use DX, Chilled water, fresh air, PCM, evaporative cooling etc.. As long as we supply air at the correct design temperature and air volume then the building is adequately cooled. A recent study of a project near Gatwick Airport, showed evaporative cooling concepts can be used to cool the air to 17°c and lower for 99% of the year with a worst-case supply air temp of 18°c. So, if the project allowed for evaporative cooling there is no need for a chiller or DX and COP of +10 and SEER of +40 can easily be achieved with lower capital cost.

Evaporative cooling concepts are sometimes misunderstood. It is true that direct evaporative cooling increases the moisture content of the supply air and this may or may not be an issue dependent upon application. However, there are more concepts of evaporative cooling to consider than just direct. They include indirect (no moisture added), a combination of indirect and direct for maximum performance and hybrid where indirect and DX or Chilled water can be used simultaneously. Typically in the UK this approach leads to a 50% reduction in mechanical plant size.

Installation of hybrid evaporative cooling system

Ultimately, evaporative cooling can meet the cooling demands of any building in the UK in the most efficient manner possible, although whether it is the right choice, is project dependant. However, there are thousands of successful projects in the UK ranging from large scale factory and warehouse cooling, offices, retail, education facilities and data centres.

Every engineer has a responsibility with any HVAC design to produce the most efficient and sustainable solution possible, given the particular practical and budget constraints they are faced with. If natural or mechanical ventilation can be utilised to cool a building, then clearly this is most efficient. However, a building with any real level of heat gain needs “mechanical” cooling. Before we jump to traditional Chilled water/DX system types there is the whole science of evaporative cooling to consider, where COP’s of +10 and SEER of +40 can easily be achieved with no compromise on performance.

The various system types and nuisance of design are too detailed to cover in this short blog but hopefully this brief overview is beneficial for the specifier to ask the question and consider the potential of evaporative cooling.

Cosaf Environments have 20 years experience of designing and installing evaporative cooling solutions in the UK and globally, which is why we would be pleased to share our expertise with you on any project.

Call us today to arrange a consultation on 0845 873 0660 or send us an email to


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