Free cooling is an economical method of using low external air temperatures and an air cooled heat exchanger to satisfy a cooling load. It is a smart method of providing effective cooling in addition to, or in place of, a chiller.


An air cooled heat exchanger is installed either in series or parallel with a chiller system’s evaporator. Electrical controls open a diverting valve to divert water from the chiller to the air cooled heat exchanger when the ambient temperature reaches the programmed set point. The diverting valve will divert water back to the chiller when temperatures are 1-2 degrees above the set point. Both the chiller and air cooled heat exchanger will turn on and automatically start cooling based on the temperature set point of the chilled water supplying the process. The free cooling system can run automatically when required, saving energy at full and partial loads.

Winter Operation. In winter, or any time the ambient air temperature is 5°-10°F below the process supply water temperature design, the water is chilled solely by the air cooled heat exchanger. This allows the chillers’ compressors to stop operating, saving significant amounts of energy. The only electrical power used in winter operation is for the air cooled heat exchanger fans.

Mid-Season Operation. Any time the ambient air temperature is 1°-2°F below the process return water temperature, the water is partially cooled through the air cooled heat exchanger then flows through the chillers to achieve the required set point temperature. The percentage of free cooling achieved mid-season is dependent on seasonal temperatures and cooling load.

High Ambient Temperature. When the ambient air temperature is equal to or greater than the process return water temperature, free cooling is not available. Whenever this occurs, the system’s three way valve will bypass the air cooled heat exchanger and direct the fluid flow through the chiller to be cooled to the required temperature.


The benefits of free cooling are significant if setup properly.

Less Wear and Tear. Free cooling extends the life expectancy of the chiller because it reduces the operational hours of the compressor and other internal components. This reduces maintenance and overall life cycle costs.

Energy and Cost Savings. The primary means of free cooling is via outside air, which is free. This reduces the overall power costs because the chiller is off. Because chillers can expend vast amounts of energy during peak load times, the ability to shut them off, or reduce the amount of chilling required, will save energy and money. Energy savings can be as much as 70% which means payback for a new system can be in as little as 12 months.

Protects against Low Suction Pressure Shutdown.  Having an air cooled heat exchanger to take over your cooling needs in colder temperatures also protects against nuisance chiller shut downs caused by low temperatures.  When designing free cooling into a system the customer does not have to purchase any additional “low ambient controls”, which also provides cost savings.

Whether designing into new applications or adding to an existing one, a free cooling arrangement can be a smart, economical element. To find out more about free cooling, or our other solutions, contact us at: sales@fluidcoolingsystems.com