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the air temperature . Remember one of our basic laws states that heat always moves from a warmer body to a cooler body . However , air temperature has two parts : dry bulb temperature and wet bulb temperature .
Dry bulb temperature is the actual temperature – the temperature that the thermometer reads . This is the temperature we refer to when talking about the weather .
Wet bulb temperature , on the other hand , is the temperature a thermometer would read if it was wet and had air moving over it . Wet bulb temperature is affected by the humidity in the air and will always be lower than the dry bulb temperature , except when the relative humidity is at 100 %.
Cooling towers work as long as the wet bulb temperature is lower than the temperature of the liquid running through it – a condition that is achievable in most of the country throughout the year .
Dry coolers work off the dry bulb temperature , meaning the outdoor temperature needs to be lower than what cooling towers require for effective heat transfer . As such , dry coolers are not as effective year-round as cooling towers .
However , dry coolers are easier to maintain because the water is not exposed to air ( closed loop ), and they do not require water testing . Cooling towers are susceptible to degradation through fouling ( getting clogged up ), scaling ( water-deposit build-ups ), corrosion ( gradual breakdown due to the environment ), and require testing for the prevention of Legionnaire ’ s disease .
Occasionally , water sprays are used to increase the cooling effect by spraying the coil surfaces , thus providing additional capacity , utilising the water ’ s latent heat of evaporation . Kyle , let us move on to the basic operation of a chiller . Artificial refrigeration was demonstrated for the first time by William Cullen of Glasgow University in Scotland , in the year 1748 . Thereafter , a continuous process of liquefying large volumes of gas was invented by the German engineer Carl von Linde , in the year of 1876 . This invention eventually made chilling and refrigeration possible on a domestic and industrial scale and laid the groundwork for the development of the modern refrigeration industry .
In 1921 , the first centrifugal water chiller was patented by an inventor named Willis Carrier . Before this time , chillers used a reciprocating compressor to move the refrigerant through the system . The main part of a centrifugal chiller is the centrifugal compressor . In a 1929 speech , Willis Carrier reminded his audience that " twenty-five years ago ' air conditioning ' was an unknown quantity either in theory or practice .” He also made a forecast of the future when he said , " air conditioning and cooling for summer may become a necessity rather than a luxury , and we will look
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RACA Journal I November 2023 www . refrigerationandaircon . co . za