Chillers generate chilled water which is used to provide air conditioning in buildings. All building generate a lot of unwanted heat, common sources being solar heat gain from glazing or occupants, lighting and equipment. A Chiller is a heat transfer device that uses a refrigeration cycle to transfer heat between two fluids. There are two main kinds of chillers commonly used in building services:

Air-Cooled Chillers

Air-cooled chillers are equipped with condensers that utilize ambient air to reduce refrigerant temperatures. Fans are used to force the air over tubing containing refrigerant and therefore remove heat from it. The cycle then removes heat from a water loop which is distributed through a building providing cooling where it is needed. The entire chiller is located outside so that heat can be rejection to atmosphere.

Water-Cooled Chillers

Water-cooled chillers take advantage of the high heat capacity of water to facilitate refrigerant chilling. There are two water loops used, one for distributing cooling around the building and one to transfer waste heat to the atmosphere via a cooling tower. Pumping is required for both the primary and condenser water loops and the only piece of equipment that is external is the cooling tower.

Key considerations:

  • Air-cooled chillers require additional roof space as they must be fully external to operate.

  • In terms of costs, there are fewer components in an air-cooled chiller plant, often leading to reduced initial costs of the plant.

  • Water-cooled chillers perform at higher efficiency, however require both internal and external equipment, along with additional pumping.

  • Water-cooled chillers introduce an additional water use to a building through the water lost of evaporation and blow down at the cooling tower.

  • In locations where water is scarce or regulation around legionnaire disease is strict, air cooled chillers maybe a better option.

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