Water Cooled Chiller vs Air Cooled Chiller in HVAC System
Initial cost of air cooled chillers is lower than
water cooled chillers as air cooled systems don’t require cooling
towers,condenser water pumps and associated HVAC components.
Small systems are almost always air-cooled since
the extra requirements of water treatment and maintenance are capital intensive
and will not be offset quickly by the lower operating costs. Larger HVACwater chillers are almost always water cooled .HVAC engineers and technicians
feel easy with maintenance free or less maintenance equipment.
Water cooled chillers may be preferred because
ofbetter heat transfer properties of
water as compared to air cooled chillers.The primary advantage of water is that
the film coefficient is 10-100 times better with water than air.Film
coefficient controls heat transfer with given constant area and temperature
difference.
Water-cooled HVAC units make less noise and give more
cooling per square foot.While air cooled chillers have comparatively less
cooling per square foot and are more noisy HVAC machines.Noisy machines are
annoying especially for occupants of nearest offices or zones.
While comparing air and water cooled chillers, an overall
system cost (both running and installed) has to be worked out. Size of
HVAC unit matters when selecting the water cooled chiller or air cooled
chiller.SmallerHVAC units are usually air cooled, larger are water cooled.
HVAC engineers have to evaluate air cooled and
water cooled chillers keeping in mind various factors.Refrigeration engineer
has to consider the ambient conditions (wet bulb and dry bulb), number of hours
of operation, part load pattern and cost of maintenance etc.
HVAC experts have no single answer to when asked “water
cooled chiller is better or air cooled chiller?”. The fact is that “It all depends”.
Water-cooled chillers will normally condense at an average lower pressure than
air-cooled chillers. This is because the water temperature will
usually be less than the air temperature.If your condenser is operating at
lower pressure then it is directly reflected and translated into lower
operating costs or KW /TR(Ton of refrigeration).
The difference between the wet-bulb temperature
and the dry-bulb temperature gives the available difference between the
condensing temperatures of water-cooled and air-cooled condensers
respectively.
Cooling towers and/or evaporative condensers have
main disadvantage of maintenance and water treatment costs. This running cost
is not present in air cooled chillers.
Despite the advantages of lower IKW/TR of a
water-cooled system or water cooled chillers, sometimes, air-cooled systems are
preferred for various applications.
For example in 24 hour application of HVAC chillers,the
night time dry bulb temperature are generally much lower than the day time dry
bulb temperature, as compared to the difference in wet bulb temperature between
day and night. This advantage is best capitalized by an air-cooled
system or air cooled chillers.
Other examples could be where the wet bulb
temperatures are very high, especially coastal areas.
When comparing water cooled and air cooled chiller,scarcity of water and hence cost of water is
another issue which is a point to be considered while deciding on the
system. This happens in many countries .
Space is also of importance in some applications.
Air cooled chillers can utilize open space, such as a parking lot, roof or
ground level area. Although smaller in size but Water cooled chillers require a
mechanical room and cooling towers.
Air recirculation is very important for air
cooled chillers.Any obstruction in the circulation of air near water chillers
would adversely affect the performance of air cooled chillers.Air cooled
chillers can have problems with recirculation if there are walls higher than
the unit or too many units to close together. If there is a situation where
outside walls are required for building code and the unit will not be receiving
enough fresh air, then a water cooled application may be the best option.
Water cooled chillers have longer life,higher efficiency,large capacity and also refrigerant containment.While looking on disadvantatges of air cooled chillers,they have lower efficiency,comparatively short life span and available in
low capacity range.
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