RACA Journal November 2023 | Page 33

Support upon present times as marking the end of that ' dark age ' in which there was but relatively little cooling for human comfort .”

Looking at how this all works we find , putting it simply , industrial chillers cool ( chill ) process fluids . Process fluids ( typically water or a water / glycol brine mix ) are used to cool people , machinery , equipment , food and such like . The process fluid ( chilled water ) absorbs heat from what is being cooled and then travels through the chiller where the heat is removed from the fluid and transferred to the ambient air in various different ways .

Chillers are highly diverse in their application . They are used in industry for cooling processes , in the food industry , hospitals , shopping centres , office buildings and metal finishing plants . Their use extends to injection moulding processes , as well as cooling spaces in buildings , among others .

Chillers are sometimes preferred over traditional split systems or package units because water conducts heat better than air . This is also why water-cooled chillers are known for being more consistent and efficient in their performance and for having a longer lifespan than their air-cooled counterparts .

TWO MAIN TYPES OF CHILLERS : WATER- COOLED AND AIR-COOLED

• Water-cooled chillers are common in medium and larger facilities , such as airports , hospitals and hotels . On the condensing side of the chiller , a condensing water circuit removes heat from the refrigerant in the condenser . The condenser water is pumped to the cooling tower which in turn passes the heat to the ambient air . The cooler water returns to the condenser to complete the circuit . Because the condensing water is exposed to the outside air , contaminates and sunlight – we use the term ‘ open loop ’.

• Air-cooled chillers utilising air-cooled condensers are more prevalent in small to medium sized facilities , where space and water may be limited . The costs to install and maintain these chillers are lower than that of their water-cooled counterparts that use condenser water and cooling towers or possibly evaporative condensers .

The chiller is generally located in the basement area within a plant room , which houses the chilled water pumps , as well as the condenser water pumps . The chilled water is pumped throughout the building via insulated steel piping normally rising up into each area that requires cooling from the system . In these areas there are air handlers that distribute the cooled air via ducts and diffusers depending on the way the air conditioning system has been designed and installed . Chilled water circuits are normally closed loop circuits .

The third circuit is the refrigeration circuit . The refrigeration circuit transfers heat from the chilled water circuit to the condenser water circuit . and completes the chiller described .

The refrigeration circuit is the most technical part of how a chiller works . The refrigeration cycle uses the principles of thermodynamics to efficiently move heat from one area where it isn ’ t wanted , to another . In the case of chillers , heat is taken from the fluid being chilled and transferred to the ambient air .

No matter the type of chiller , the main components are always the same for the unit to operate as per designed . The main components are similar in function to many air-conditioning and refrigeration systems .

TO REFRESH

• The compressor : The refrigeration cycle begins with the compressor , which takes low-pressure low to mediumtemperature refrigerant in gas form from the evaporator and compresses it into a high-pressure high-temperature gas feeding it to the condenser .

• Condenser : This gas then flows through coils in the condenser . While in the condenser , air will flow over the coils or water will surround the refrigerant pipes and draw the heat from the refrigerant . As the refrigerant loses heat , it will begin to condense until all of the gas has condensed into a liquid where it now travels as a liquid to the expansion device .

• Expansion device : After leaving the condenser , the liquid goes through the expansion device which restricts the flow of refrigerant . When the high-pressure liquid goes through the expansion device , it enters the evaporator as a low-pressure low temperature mixture of liquid and vapour .

• The evaporator : The evaporator is where the refrigerant starts evaporating back into a gas . When the refrigerant evaporates it gets very cold and will absorb heat . It is in the evaporator that the chilled water will interact with the cold refrigerant . Heat is removed from the chilled water and transferred to the refrigerant . The refrigerant gas will return to the compressor and the cycle begins again .

Kyle , this concludes a basic description of the operation of a chiller and a dry cooler – hope that this helps with your understanding .

Thanks to everybody for the overwhelming response . I receive on average over sixty questions per month and cannot publish all of them . But keep them coming , as I may answer you directly .

Looking forward to hearing from you . RACA

Grant Laidlaw