Air cooled chiller consists of an evaporator and a fan section as a condenser. The compressor type in air-cooled chillers are either screw (helical rotary) type or scroll type. These chillers are available in 10 to 500 ton capacity. Air cooled chillers are more efficient at low ambient temperatures and low wet bulb temperatures. Some manufacturers offer these chillers with VFDs but most of the manufacturers are using Hot Gas Bypass, Unloading Valves, Variable Primary Flow (VPF) system or Digital Compressors for load control. In any of the mentioned control schemes, the chillers’ load can be varied between, 5% to 100% (for example 5, 15, 33, 48, 52, 67, 81, 87, 100%). The common refrigerant for Scroll type compressor is R- 410A, and for Screw type compressor is R-134a. Air cooled chillers efficiency should meet ASHRAE 90.1 minimum energy efficiency requirements.
Water has more thermal mass than air therefore the on-and-off cycling of the air-cooled chiller compressor doesn’t cause as much fluctuation in the supply air temperature, in addition, air-cooled chillers have a much greater “turndown” capability and they are better able to match part-load cooling conditions than roof top units (These factors enable air-cooled chillers to provide better humidity and temperature control, which translates into greater occupant comfort and better efficiency.
Scroll compressors are not repairable and thus can only be replaced. On the other hand Screw type (helical rotary) compressors can be repaired and renovated.