Feature only chilled water circulating pumps are needed , they offer a lower first cost , and on the operational aspect have reduced maintenance needs . On the cons side , as Russell mentioned previously , they are less efficient and have a higher running costs ,” adds Roelofse .
• Water cooled chillers Water-cooled chillers will , in general , consume less energy than their air-cooled counterparts . Water is generally inexpensive and the overall cost of ownership of a watercooled plant is generally less .
“ Exactly how much cheaper depends on facility type , and the size and manner in which it is operated . Water chillers are more versatile in that they can be customised to suit special applications ( such as special cooling mediums , voltages , tubes , water boxes ). A perceived downside of water-cooled chillers is that their cooling towers require some love and care to ensure efficient operation ( water treatment ),” says Hattingh .
Redundancy , however , comes at a price – the cost of downtime has to be weighed up against the additional capital-spend required
Water-cooled chillers find applications in buildings , process plants , factories , mines and food and beverage facilities . Engineers shooting for ‘ green ’ points often try to steer clear of water-cooled chillers . The choice of water-cooled over aircooled is really an owner decision as they need to decide what is important for them . First cost versus ownership cost . Saving water versus saving electricity .
“ A water-cooled chiller system ’ s primary advantage is the improved energy efficiency as mentioned – obtained by water cooling . One also has the advantage of positioning the plant ( excluding cooling towers ) in basement plant rooms , which is often an architectural preference . However , its main drawback is that it consumes water . This is a limiting factor in many applications nowadays , particularly in our water-scarce country . For the same reason , as well as legionella risks , water-consuming systems are also discouraged in green star buildings ,” du Plessis continues .
Roelofse adds , “ On the contrary to air cooled chiller ’ s simple pipe runs , water cooled chiller pipe runs tend to involve a more complicated installation with both chilled water and condenser water piping runs , they carry a higher first cost and increased maintenance through the water treatment of the condenser water circuit .”
• Hybrid chillers Hybrid chillers offer the simplicity of an air-cooled installation with the added bonus of reduced running costs . Water quality can seriously reduce the reliability of the system and in some cases lead to equipment damage ( high mineral content tends to clog spray nozzles and deposit on condenser coil surfaces ). These systems are retrofitted in most cases , and few chiller OEMs supply these as standard .
• Absorption chillers Absorption chillers can provide large amounts of cooling at a greatly reduced running cost ( despite higher water consumption ). They have few running parts and are fairly robust . They are however not as responsive to changes in load as their vapour compression counterparts – meaning if tight temperature control is required these chillers would be less ideal .
“ Absorption chiller systems have very high efficiencies due to the absorption cycle being fundamentally different to the vapour-compression cycle . However , these types of chillers usually only become feasible at very large cooling capacities due to their size , complexity and cost . It is therefore more frequently applied in industrial settings , and in most cases found not to be feasible for typical commercial applications . Furthermore , perceived safety risks such as ammonia leakages adds to the potential disadvantages of these chillers ,” notes du Plessis .
CHILLERS AND HYBRID-TYPE INSTALLATIONS Hybrid installations , comprising air-cooled and water-cooled chillers , are sometimes considered in order to minimise operational risk .
“ In South Africa , electrical outages are common , but can be overcome with generators . Water supply issues , although less common , are an occurrence some end users have to factor in to ensure 24-hour operability . Water cannot be generated on site , so air-cooled chillers may be supplied as back ups for critical areas ( such as data centres and broadcasting facilities ). Redundancy , however , comes at a price – the cost of downtime has to be weighed up against the additional capital-spend required ,” Hattingh says .
Du Plessis adds , “ There are naturally various methods of hybridisation that can be considered to increase efficiency , but these must always be viewed within context . An example includes heat recovery from chillers used as heat source for domestic hot water to minimise energy , which will typically only be found feasible in applications where there is a constant hot water demand , such as hotels .”
“ Heating of water is achieved through the recovery of heat from the compression cycle ( partial and total recovery percentages ), and a mix of cooling only chillers , heat pumps and / or multipurpose units are other ways hybrid type systems can be created ,”, says Roelofse .
Continued on page 25
www . hvacronline . co . za RACA Journal I March 2021 23