www . refrigerationandaircon . co . za RACA Journal I November 2023 29
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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
Given that this month ’ s feature topic is chillers , one of the themes to emerge from the feature was a lack of adequate skills . Grant Laidlaw kindly agreed to address this topic .
All images supplied by Grant Laidlaw
Many people ask for assistance in the understanding of 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 .
Hi Grant . Thanks for all the information , I would like to ask , can you explain what is a dry cooler ? We do not understand how this works , as there is no water spraying in the unit . How does this relate to a chiller system ? Kyle .
Hi Kyle , let us look at the dry cooler and then a basic chiller operation .
Looking at the dry cooler , yes you are correct , dry coolers do not necessarily spray water to achieve the required cooling effect . A dry cooler is a cooling device that uses air to achieve the cooling effect and is based on the principles of sensible heat rejection .
A dry cooler on the roof of a data centre .
For a dry cooler , thermal exchange is performed by drawing in external ambient air and passing it over tubes containing a cooling fluid ( typically water or water-glycol mixture ). To ensure efficient process cooling , a suitable difference in temperatures between the cooling medium and the air within the dry cooler must be maintained . A minimum difference of 5 ° C is usually sufficient . The cooled fluid is then circulated through a heat exchanger attached to an associated process . The excess heat transferred to the cooling fluid is then returned to the dry cooler and the cycle is restarted .
The outdoor unit differs from a cooling tower in that a cooling tower uses the latent heat of evaporation to cool the condenser water whereas the dry cooler simply blows cool ambient air over tubes that contain brine . The brine is contained in a closed loop circuit . The outdoor component is the dry cooler which rejects heat to the ambient air .
ADVANTAGES OF USING A DRY COOLER
• Easy installation and start-up
• Convenient separation of components allows operators to save vital floor space for other equipment
• Overall low operating costs after initial installation
• Dry coolers do not require a constant water supply , therefore supply and disposal concerns are non-existent
• The generated heat can be channelled directly into other processes , reducing energy waste and improving overall efficiency
• Dry coolers can be programmed to operate year-round , even in environments with low temperatures
DISADVANTAGES OF USING A DRY COOLER
• Additional costs of add-on components increase the total set-up expenditure
• Regular monitoring – or an automated chiller monitoring system – is required to ensure cooling fluid levels do not drop below required levels
DRY BULB TEMPERATURE In order for cooling towers and dry coolers to work , the temperature of the water in the system needs to be hotter than
www . refrigerationandaircon . co . za RACA Journal I November 2023 29