By Michael Young

Temperature, humidity and Covid 19 – what do they have in common?

Also read: How geographical location and application can affect the design of an HVAC system: Part 1

I had an interesting discussion on a Linkedin group to learn how the HVAC industry is currently dealing with the Covid-19 pandemic.

The discussion moved from filtration, to the use of UV-C lamps, to 100% fresh ambient air flushing of an entire building. After delivering my fair share of recommendations, one person reached out to me and asked about the impact of using a 100% fresh air system as a viable solution.

The discussion actually turned into a full- blown interview with many questions being asked and I thought I would share the results of this interview with you in this month’s publication.

Q: Michael, what do you think is the best option to deal with the Covid-19 pandemic?

A: I consulted with some publications from the ASHRAE website and unfortunately there is no clear way forward. Right now, the industry is implementing the use of primary and secondary filters as one solution. Use of UV-C lamps is another solution while the final solution is to provide 100% fresh air flushing of the room. I personally feel that 100% fresh air flushing is not the best option.

Q: Why would you say 100% fresh air flushing of a building is not the right way forward?

A: Well, when we flush 100% fresh air into a building, we need to condition all the air to a specific setpoint. So, if we were dealing with a very hot and humid climate we would have to sensibly cool and dehumidify the air in summer conditions. For winter operations, we would have to heat and possibly humidify the air depending once again on the ambient winter conditions.

Q: Why is dehumidification so important and what impact does it have on the design of the cooling system?

A: To dehumidify the air, we first need to sensibly cool the air to a temperature that is below its wet bulb temperature. In some instances, the dew point temperature is so low that you can’t introduce the air into a room as occupants within the room will complain that the air is too cold. So, we will need to first dehumidify the air then reheat it to a temperature that is comfortable.

Q: Does this not this result in more energy being used?

A: Absolutely; so when working with a 100% fresh air system, sensible, latent and possibly heating loads increase. This results in a cooling system that consumes more high cost energy.

Q: In your opinion, should we not introduce fresh air into our HVAC system?

A: We must introduce fresh air in accordance with SANS 10400 standards and according to the application. For comfort cooling such as offices and gyms, consult with SANS 10400 standards. If you are positively pressurising a room for a data centre, then you will have to introduce fresh air to maintain a 5Pa pressure difference. So, I would recommend that fresh air be introduced according to the desired outcome and application.

It was great sharing this interview with you. Join us next month where we will discuss how ambient air conditions can generate critical alarms within your HVAC system. You won’t want to miss it!

Wishing you a successful month ahead and chat soon.

 Michael can be contacted on or 073 171 2311 for any questions or HVAC training needs. 


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