Bryair decided to conduct an experiment before Christmas. Seeing as we have been heavily pushing UVC for improving Indoor Air Quality, it would have been massively hypocritical if we at Bryair had not installed any UVC within our office. Our AC system has had UVC installed since August 2020 and we have continued with regular maintenance procedures on both units every three months, ensuring the filters are kept clean.

We have a split AC system with two Cassette units installed within the ceiling void. These cassette units are in the same room and are spaced only 3.5m apart.

I do not know if you guys are like me, in that seeing is believing! The fact is I have been totally behind UVC and the Virus destroying properties. In the back of my mind, I have always had that niggling feeling “it’s just manmade light”.

  • How is manmade light providing all these benefits?
  • How does manmade light make me more productive, whilst in the office?
  • How is it improving my health?
  • How does it affect the energy bills, that drastically? It is just a manmade light!

It is now that I must rely on the information that has been provided to me and trust the science.

Do not get me wrong, I am fully behind the fact UVC offers all these health benefits as well as saving money by reducing energy bills. I was in the office when the UVC was installed and I saw that familiar UVC coloured light as can be seen in fig 1 above. But once the cassette was closed, that is it. I no longer see anything happening.

If we had someone to come out and wipe a cloth around in the cassette unit and saw this happening every day, no questions would be asked, we would all be happy that our coils were completely clean. I am also convinced, that, if that were happening there would-be questions that should be asked but are not.

  • How clean are they?
  • Are they doing a thorough job?
  • Are the tools used adequate to perform the task?
  • Is the cleaning spray toxic?

Lots of different questions that could get asked, but are not, simply because we can see the action.

Seeing is believing, right!!

This brings me nicely back to our experiment. The decision was made to perform the experiment within our office. We decided we would turn the UVC off in one of our cassette units in November. We then purchased some contact plate petri dishes and conducted a swab test in January. Each of the contact plates was pushed into the coil fins of the cassette units in the office and sealed up and left over the weekend.

Monday morning comes around, as they always do, and I look at the contact plates.


As you look at fig 2 below, the nice clean petri dish on the left was the one swabbed on the unit with UVC and the one on the right where you can clearly see mould growing was swabbed on the non UVC cassette.

Two and a half days after performing the swab tests the result is conclusive. The contact plates have now been sent off to a lab to analyse what the mould contains (results of that test to follow). But what this does prove is that what an amazing job UVC does. Seeing is believing!

Inhaling mould fragments or spores can inflame the airways, causing nasal congestion, wheezing, chest tightness, coughing and throat irritation. Prolonged exposure to high levels of mould can reduce lung function and cause chronic health problems such as asthma. How many people within the office already suffer from Asthma? Just for information, the coil fins are already the other side of the already installed filters, meaning the air filtered around the indoor space is containing what you can clearly see in the right-hand petri dish! This includes all airborne viruses.

Evidence of mould forming on coils is evidence that a biofilm has formed on the coil. The mould doubles inside of 4 – 6 hours and easily multiplies into a Billion organisms in 12 days. As long as the mould is alive it will keep growing. This biofilm continues to make the HVAC system less and less efficient as the biofilm grows, even a biofilm on the coil which is only 0.15mm in thickness, will reduce the efficiency of the AC unit and will require an extra 11% of energy to drive the unit to the same settings. As the units are not performing as well the settings on the control units are often turned up to achieve the same thermal comfort which again takes even more energy to obtain the same results.

Installing UVC within the HVAC systems provide better Health and Wellbeing, increased employee productivity, less sick days, equipment sustainability, obtain BREEAM® credits, reduce Carbon Footprint and save money on energy bills which have over the past 10 years risen sharply and will continue to do so as the government strive towards a carbon net zero by 2050.

Seeing is Believing!!

Please contact Bryair Mechanical () for further information and see how we can help improve your IAQ.