In Queensland’s hot, humid climate cooling coils provide opportunity for microbial growth and dissemination of microorganisms and their by-products throughout a building. As air entering the building passes through the coil it deposits dust on the coil fins. This dust, combined with condensation and moisture that are produced by the normal running of the cooling coils are at risk of biofilm growth.
Fungal contamination of cooling coils is also a common problem. Fungal spores can be released into the airflow from coils and contaminate downstream air conditioning components and the building air.
It’s important to start good cleaning procedures, as soon as coils are put into operation.
When you look at an installed cooling coil you’re only visualising a section of the surface area that the air passes over, dust and biofilm generally builds up in the centre of the unit in the direction that the air passes over. If coils are cleaned only upon a visual dust build-up it’s likely you’ve got a contamination issue and your cooling system isn’t running efficiently.
Filtration efficiency, hours of operation, use of building and location all need to be considered when determining how often individual installations will require cleaning. Regular inspection is recommended to determine the time frame for cleaning and sanitising of coils.
We don’t recommend that you clean coils yourself, but you should inspect coils on a regular basis to make sure they look clean. A visual inspection will give you a decent general indication of when you need to clean them, but if you’re managing a site that serves critical environments (like a hospital, dentist office or a lab) you’ll want to take a more technical approach to maintain good air quality. Measurement of the differences in temperature entering and leaving the coil and comparing this to your benchmark of optimal temperature differentials will help.
At a minimum, we recommend conducting a visual inspection of your cooling coils at least once a month. The Australian Standard AS/NZS3666.2:2011 Air Handling & Water Systems of Buildings – Microbial Control stipulates that coils in the air handling system should be inspected monthly and cleaned when necessary.
There’s actually a bit of contention in the HVAC industry about how often coils need to be cleaned – currently there’s no minimum requirement for cleaning. There are industry bodies, government, and businesses that are hosting discussions around the best way to determine minimum requirements.
The honest answer is, there’s no easy solution. Every building is different, every HVAC system is different and on top of that are different types of coils in your HVAC system. All these interconnected elements are also taking air in from different outdoor conditions and serving different indoor spaces, which may have different requirements. So, there are a lot of variables that can make it quite a complex task to offer a standard solution to fit everyone.
AIRAH, the independent industry association for Air is also in the process of updating Design Application Manuals to assist with HVAC&R Maintenance, and those are due to be released later this year. You may find AIRAH’s publications useful in determining your coil cleaning schedule.