Air-Cooled vs. Water-Cooled Chillers: Choosing the Right Type

Both chiller types do the same fundamental job — removing heat from water that then circulates through a building's cooling system — but they reject that heat to the outside environment in different ways, and the difference has real, practical consequences for installation cost, ongoing efficiency, and maintenance.

Air-cooled chillers

An air-cooled chiller uses large fans to blow ambient air across condenser coils, rejecting heat directly to the atmosphere. The whole unit — compressor, condenser, and fans — sits in one outdoor package, typically on a rooftop or a ground-level pad outside the building. This makes installation simpler and generally cheaper: no cooling tower, no condenser water piping loop, no water treatment system to maintain. The tradeoff is lower efficiency in hot weather, since the fans are rejecting heat into air that's already warm — performance degrades as ambient temperature rises, which matters in genuinely hot climates during peak summer conditions.

Water-cooled chillers

A water-cooled chiller rejects heat to a separate condenser water loop, which runs to a cooling tower (usually on the roof) where the heat is released to the atmosphere through evaporation. This is inherently more efficient than air-cooled rejection, particularly in hot climates, because evaporative cooling can bring the condenser water closer to the wet-bulb temperature rather than the higher dry-bulb air temperature an air-cooled unit is working against. The tradeoffs are real: a cooling tower, condenser water pumps, and water treatment to prevent scaling and bacterial growth (including Legionella risk, which requires an active maintenance program) add both installation cost and ongoing operational responsibility.

Making the choice

For smaller buildings, or projects where rooftop space and mechanical room space are both limited, air-cooled is usually the practical choice — simpler installation, no water treatment program to manage, and adequate efficiency for the load. For larger buildings with substantial, sustained cooling loads — where the efficiency gain compounds into real energy cost savings over the chiller's service life — water-cooled is usually worth the additional installation complexity and the ongoing water treatment commitment, provided there's actually space and budget for a cooling tower and the maintenance program it requires.

Climate matters more than building size for this decision in genuinely hot regions: even a mid-size building may benefit from water-cooled chillers if summer conditions are severe enough that air-cooled efficiency drops significantly during the exact hours cooling demand peaks.

Once you've settled on a chiller type, see our broader HVAC system selection guide, or browse NAD's current chiller range directly.