Aftercoolers For Air Compressors

Why Your Air Compressor Needs an Aftercooler

Compressed Air is full of energy, and as a result, it gives off heat. This means compressed air will always be hot when it exits the compression chamber. If you do not already have one, you need an aftercooler here. Think you can get by without one? Then, you best be prepared for the heat.

Typical Compressor Average Outlet Temperatures:

• Oil-Injected Rotary Screw         200°F
• Oil-Free Rotary Screw              350°F
• 2-Stage Reciprocating              300°F

High-temperature air is typically not usable in air-operated equipment, as heat detrimentally impacts equipment lubrication and sealing materials. Hot air is filled with large quantities of moisture vapor. As it condenses and stays in the airstream, problems like rust, scale build-up, potential freezing, and washing out of lubricant can happen.

Types Of Aftercoolers

There are two different types of aftercoolers for air compressors. Systems will either have an air-cooled or water-cooled aftercooler. 

Air-Powered Aftercoolers

Air-cooled aftercoolers use ambient air to cool the hot compressed air. Compressed air enters the air-cooled aftercooler and travels through either a spiral-fin tube coil or a plate-fin coil design, while ambient air is forced over the cooler by a motor-driven fan. The cooler ambient air removes heat from the compressed air.

Most air-cooled aftercoolers are sized to cool the compressed air to within 15°F to 20°F of ambient cooling air temperature, also called approach temperature. As the compressed air cools, up to 75% of the water vapor condenses into a liquid that should be removed.

Water-Powered Aftercoolers

Water-cooled aftercoolers are similar to air-cooled aftercoolers but are often used in stationary compressor installations, where cooling water is available. There are a few advantages to using water as the cooling media:

• Water has minimal seasonal fluctuation in temperature
• Cold water is cost-effective and available in large volumes
• Cold water can efficiently approach the ambient air temperature, which eliminates condensation downstream

Water-cooled aftercoolers typically have an approach temperature between 10°F and 15°F, which is also beneficial when cooler air is required. 

To be properly sized, aftercoolers need three crucial variables: CFM, PSI, and Temperature. The first two, CFM and PSI, are relatively straightforward. You want them to align with your compressor measurements. The last variable and the real determinant factor for size is the difference in compressed air temperature after compression and the desired ending temperature. The greater the difference in these temperatures, the larger an aftercooler you will need.

Need help sizing your after cooler? Feel free to give us a call and talk to one of our support technicians.