www . refrigerationandaircon . co . za RACA Journal I March 2025 37
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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 .
Deon writes : Hi Grant . We ran into a situation where a client wanted air conditioning and ventilation . This caused confusion . When running a hideaway air conditioning unit , the evaporator fan circulates air through the room to the return , then the evaporator filters and cools the air . The system then distributes the clean , cool air into the room , ventilating the room . Could you help here please ? Thank you .
Hi Deon . While it is true that the air conditioning system does clean and cool the air , the issue is more complex than this . In addition to cleaning and cooling one has to maintain the quality of the air . We are primarily referring to oxygen levels , humidity , odour and contaminant levels . In your example the people in the room use the oxygen when breathing and release carbon dioxide . As your unit is only recirculating the same air , over time the oxygen levels decrease , and carbon dioxide levels increase . Odour levels may increase . The air becomes stale . This is an unhealthy situation with people becoming drowsy , getting headaches and experiencing general fatigue . What is needed to rectify this situation is fresh air ventilation from outdoors .
Fresh ventilation air replaces oxygen , removes the carbon dioxide , contaminants and odours . In fact , most correctly designed buildings will have a minimum fresh air intake of 10 %. ASHRAE has published recommended tables for fresh air rates expressed in air changes per hour . An office for example should have around six air changes per hour . In other words , the ventilation system should supply fresh air six times the volume of the room every hour .
This is a common situation with unitary air conditioning systems installed without regard to fresh air intake . Installers simply rely on natural ventilation through open doors and windows . In certain circumstances this becomes more critical . In a boardroom , for instance , there may be several people present who close doors and windows for a meeting that spans several hours . The air will rapidly become ‘ stale ’ in this situation .
Hideaway units , as well as cassette units , often have the facility to install fresh air intake and this should be used . In this way you will be able to condition the air as well as maintain air quality . Remember as you are now adding extra air into the room there will be slightly positive pressure . This is advantageous as the fresh air is filtered and dust will not enter the room . Due to the higher pressure in the room , air tends to leak out , preventing dusty air from entering . At the same time remember that you must ensure that the air has some path to exit the room . Small door grills or even undercut doors should suffice .
DEEP DIVE INTO VENTILATION Let us have a deeper look at ventilation . As you noted , the terms ‘ ventilation ’ and ‘ air conditioning ’ are sometimes confused . All air conditioning systems should incorporate a ventilation system of some form . The essential requirement of a ventilation system is to replace the contaminated air in a particular area with fresh outdoor air .
The purpose of ventilation is to freshen up the air inside buildings in order to achieve and maintain good air quality and thermal comfort . Ventilation also has important psychological aspects , which can be illustrated by the feeling of being in control , having odour management and creating a link to nature .
The quality of indoor air influences humans in several ways :
• Comfort : the pleasantness of the air is immediately felt when a person enters a building
• Health : breathing poor indoor air with lowered oxygen and increased carbon dioxide levels can have negative health effects
• Performance : high-quality indoor air can improve mental performance and general well-being
• Nature : fresh air creates a link to the outdoor environment , and fresh air through windows is a valued aspect of ventilation
www . refrigerationandaircon . co . za RACA Journal I March 2025 37