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GRANT LAIDLAW
Grant Laidlaw is currently the owner of the Air Conditioning and Refrigeration Academy( ACRA) in Edenvale. He holds a Bachelor of Business Administration and an associate degree in educational administration. He has a National Technical Diploma and completed an apprenticeship with Transnet. He has dual-trades status: refrigeration and electrical. He has been involved with SAIRAC for over two decades and served on the Johannesburg committee as chairman and was also president between 2015 and 2018. Currently he is the SAIRAC national treasurer.
WELCOME TO THE SOLUTIONS PAGE
By Grant Laidlaw
Many people ask for assistance in understanding theoretical and practical aspects of the industry. I will endeavour to enlighten. We are going back to basics as I have questions coming in that indicate that the basic understanding necessary to work in industry is not in place.
Ben sent in the following:“ Sir, can you please explain the evaporative coolers. How do these coolers work? Thank you.”
Hi Ben, yes, it is important to understand how evaporative coolers operate as they are somewhat different to airconditioning units.
In essence we pass air over a pad that has been saturated with water into the space to be cooled. The water evaporates, and in order to do so, heat energy is absorbed from the air; this then cools the supply air.
An evaporative cooler works on what is known as adiabatic cooling:
• An adiabatic process is one in which there is no heat gained or lost in the process, such as the evaporative cooling process
• In the process, heat is changed from one form to another( sensible heat to latent heat) but there is no overall change to the total heat in the process
• Temperatures change but the total heat does not
An important aspect when dealing with evaporative cooling is air flow. You must make sure that all the air entering the space to be cooled is able to exit freely. Failure to achieve this will result in an inefficient system with higher humidity levels in the space being cooled. Air flow is the quantity of air moving through the system and space to be conditioned. Typically, air flow is measured in litres / sec( l / sec) or cubic meters / hour( cm / h or m3 / h), or cubic meters / sec( m3 / s)
Air flow should not be confused with air velocity, which is the rate at which the air is travelling through the system.
In the case of evaporative cooling human comfort factors are important:
RACA Journal I February 2026
• A human being ' s thermal sensation is mainly related to the thermal balance of his or her body as a whole. It is NOT only about temperature and humidity.
• This balance is influenced by physical activity and clothing, as well as the environmental parameters: air temperature, mean radiant temperature, air velocity and air humidity.
• When these factors have been estimated or measured, the thermal sensation for the body as a whole can be predicted by calculating the predicted mean.
• The predicted mean is an index that predicts the mean value of the votes of a large group of persons on the seven-point thermal sensation scale table based on the heat balance of the human body.
+ 3 Hot + 2 Warm + 1 Slightly warm 0 Neutral-1 Slightly cool-2 Cool-3 Cold Seven-point thermal sensation scale.
Let us consider what is meant by comfort: Climate control is largely about establishing a comfortable environment for people. When people are comfortable, they are more productive, more tolerant, more healthy, more amiable, more reliable, etc. This translates into a more pleasant social atmosphere in some cases, and more productivity( and hence profits) in other cases.
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All images supplied by Grant Laidlaw