When comparing air-cooled and water-cooled chillers, the overall system cost (operation and installation) must be calculated. The size of the HVAC unit is important when choosing a water-cooled chiller or an air-cooled chiller. Smaller HVAC units are typically air-cooled and larger ones are water-cooled.
HVAC engineers must evaluate air-cooled and water-cooled chillers taking into account a variety of factors. Refrigeration engineers must consider environmental conditions (wet and dry bulb), operating hours, part-load patterns, and maintenance costs.
The difference between wet bulb and dry bulb temperatures gives the available difference between the condensing temperatures of water-cooled and air-cooled condensers respectively.
The main disadvantages of cooling towers and/or evaporative condensers are maintenance and water treatment costs. Such operating costs do not exist for air-cooled chillers.
Although water-cooled systems or water-cooled chillers offer the advantage of lower IKW/TR, sometimes air-cooled systems are better suited for a variety of applications.
Water Cooled Chiller
For example, in a 24-hour HVAC chiller application, the dry bulb temperature at night is usually much lower than the dry bulb temperature during the day compared to the difference in wet bulb temperature between day and night. Air-cooled systems or air-cooled chillers can take full advantage of this. Other examples may be where wet bulb temperatures are very high, especially in coastal areas.
The scarcity of water and the cost of water is another issue to consider when comparing water-cooled and air-cooled chillers, and this is an issue that needs to be considered when deciding on a system. This happens in many countries.
In some applications, space is also important. Air-cooled chillers can utilize open spaces such as parking lots, rooftops or ground level areas. Although smaller in size, water-cooled chillers require mechanical chambers and cooling towers.
When asked, "Is a water-cooled chiller or an air-cooled chiller better?" HVAC experts do not have a single answer.
Air Cooled Chiller
Water-cooled chillers typically have lower condensing pressures than air-cooled chillers. This is because the water temperature is usually lower than the air temperature. If your condenser is operating at a lower pressure, then it will directly reflect and translate into lower operating costs or KW/TR (tons of cooling).
Air-cooled chillers have a condenser that is cooled by ambient air. Air-cooled chillers are preferred for small or medium installations, but recent quality improvements in their construction allow the use of modular types, also suitable for large installations. Air-cooled chillers are preferred, especially if there is not enough water available or if water is very expensive.
The initial cost of air-cooled chillers is lower than water-cooled chillers because air-cooled systems do not require cooling towers, condensate pumps and associated HVAC components.
Smaller systems are almost always air-cooled because the additional requirements for water treatment and maintenance are capital intensive and are not quickly offset by lower operating costs. Larger HVAC chillers are almost always water-cooled, and HVAC engineers and technicians feel comfortable with maintenance-free or less maintenance equipment.
Water-cooled chillers have a water-cooled condenser connected to a cooling tower and are usually suitable for medium and large installations where sufficient water is available. They are also preferred where stable system performance independent of ambient temperature is required (industrial air conditioning, digital system air conditioning, etc.) .
Water-cooled chillers are probably preferred because of the better heat transfer properties of water compared to air-cooled chillers. The main advantage of water is that the film coefficient of water is 10-100 times better than that of air. The film coefficient controls the heat transfer area and temperature difference for a given constant.
Water-cooled HVAC units are quieter and provide more cooling per square foot. Air-cooled chillers, on the other hand, provide relatively little cooling per square foot, and HVAC machines are noisier. Noisy machines are annoying, especially to the occupants of the nearest office or area.
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