Two cooling methods, one principle
Water-cooled and air-cooled chillers share the same refrigeration cycle; they differ only in how the condenser is cooled. Water-cooled units use shell-and-tube condensers with water, while air-cooled units use finned coils cooled directly by air, removing the need for cooling towers, pumps and piping.
Investment and running cost
- Capital cost: air-cooled needs fewer auxiliaries, so its initial investment is lower than water-cooled.
- Energy: at full load the air-cooled condenser runs hotter and the compressor draws more power, yet real loads fluctuate with outdoor temperature, so annual electricity is close.
- Maintenance: air-cooled needs only unit servicing, whereas water-cooled also demands cooling-tower and pump upkeep, raising cost.
Air-source heat pumps
Air-cooled heat pumps can also supply heat, but efficiency drops in extreme weather and they may fail below about -8°C, with extra defrost loss and a local heat-island effect. Water-cooled pays back its premium only after very long annual runtimes.