Chillers, Part 3: Air-Cooled or Water-Cooled?

Heat Transfer

Chillers, Part 3: Air-Cooled or Water-Cooled?

Chiller Essentials explained that chillers circulate cooling water through process equipment to remove heat. When that cooling water returns to the chiller, it transfers the heat away from the chiller to the environment using a refrigerant loop and either an air- or water-cooled condenser.

  • Air-cooled condensers resemble the “radiators” that cool automobile engines. They use a motorized blower to force air across a grid of refrigerant lines. Unless they are specially designed for high-ambient conditions, air-cooled condensers require ambient temperatures of 95°F (35°C) or below to operate effectively.
  • Water-cooled condensers perform the same function as air-cooled condensers, but require two steps, rather than one, to complete heat transfer.First, heat moves from refrigerant vapor into the condenser water. Then the warm condenser water is pumped to a cooling tower where the process heat is ultimately discharged to the atmosphere.

Should your chillers be air-cooled or water-cooled?

If minimizing operating costs is of paramount concern and the processor can invest in systems and facilities for a long period, a water-cooled chiller system may well be the best choice. The condenser cooling provided by a recirculating cooling-tower system is less costly than the electrically driven fan used on an air-cooled condenser. In fact, tower water cooling can actually be used in place of chiller cooling during cold weather or if process-water temperatures below 85°F (29°C) are not required.

However, water cooling involves a higher initial investment, since these systems require both a chiller and a circulating tower system, which in turn will require additional pumps, piping, and tanks. In addition, all water-cooling systems consume significant amounts of water due to evaporation, purging, and bleeding. So, if water cost, quality and conservation are of concern, an air-cooled chiller may be the better choice.

Air-cooled chillers cost significantly less per ton than water-cooled systems primarily because they require fewer components to build and operate and require less support equipment and plumbing. Installation of an air-cooled chiller is faster and easier than that of a water-cooled chiller. Installation of an air-cooled chiller requires three things: a chiller location, electrical service, and process water pump and piping connections.

While central air-cooled chillers are typically located outside, most portable air-cooled chillers are located indoors, where they send a stream of warm air directly from the condenser fan to the plant floor. This may be undesirable except during cool weather when the warm airflow produced by the condenser fan can supplement a plant’s space heating system. Where chiller space is limited or ambient temperatures are high, air-cooled condensers can be located outdoors, remote from the main chiller, to conserve space or improve condenser performance.