A water cooled aftercooler is a tube-in-shell arrangement whereby compressed air heat is exchanged with the cooled water. If sized correctly, the compressed air temperature can be cooled to within 5°C of the cooled water supply (if the chilled water is at 5°C, the compressed air temperature can be cooled to within 10°C, achieving a relatively cheap low dew point). This after cooler takes up little space, can be fitted vertically or horizontally, almost entirely maintenance free and does not use electrical power.
An airblast after cooler works (& looks like) a radiator by exchanging heat between the compressed air to the ambient air. A correctly sized and operating after cooler reduces the temperature of the compressed air to within approximately 10°C of the ambient temperature (if the temperature surrounding the after cooler is 30°C, the after cooler will drop the compressed air temperature to within 40°C).
This after cooler is a relatively low maintenance item but care must be taken in keeping the fins free of dirt build-up. The fan motor requires an electrical power supply but some after coolers are available with pneumatically driven fan motors.