What’s the Difference Between Water-Cooled and Air-Cooled Chillers?

Two main types of industrial chillers exist: water-cooled and air-cooled. Though both chiller types cool industrial process fluids, how the system rejects the extracted heat differs. The needs of the overall refrigeration system therefore determine the best chiller model. Understanding these various strengths makes choosing a proper system design easier.

Chiller Operation Overview

All industrial chillers have the same basic components: evaporator, compressor, expansion device and condenser. They utilize a closed loop refrigeration circuit to cool a fluid (typically water or a water/glycol mixture). The compressor circulates the refrigerant through the closed loop, from condenser to expansion device to the evaporator and, finally, back to the compressor.  As the refrigerant flows through the circuit, the expansion device, usually a valve or a capillary tube, meters it. The evaporator extracts the heat, lowering the fluid temperature and raising the refrigerant temperature. The closed loop system means that the extracted heat must be expelled elsewhere from the system. This role falls to the condenser.  Refrigerant heated by the evaporator fluid and the compressor, enters the condenser. How the condenser cools the refrigerant determines the key difference between water-cooled and air-cooled chillers.

Differences in the Condenser

Air-cooled chillers have condensers that use ambient air to cool hot refrigerant. They are similar in construction to the radiator on a car or the outdoor portion of a home air conditioner.  Refrigerant flows through a series of tubes mechanically assembled with an array of closely spaced fins.  A fan blows ambient air through the fins and over the outside of the tubes, cooling the refrigerant flowing inside. The excess heat is released to the air and can be recovered for use elsewhere in the facility.

Contrastingly, water-cooled chillers use water to cool the refrigerant in the condenser. Water-cooled condensers are typically tube-in-tube, tube-in-shell, or plate-type heat exchangers in which water from a cooling tower or other water source cools the refrigerant.  The refrigerant and cooling water do not come in direct contact with each other, rather they flow in separate passageways within the heat exchanger which are in close contact for efficient heat transfer. The water flows over the refrigerant tubes and absorbs the excess heat, thus lowering the refrigerant to the necessary temperature for use in the system.

Environmental Installation considerations

Though a great deal of variety exists within both air-cooled and water-cooled chillers, some general installation rules do apply. Knowing the ultimate arrangement of a system can help to guide your chiller choice. For each of the following situations, the most practical chiller type is described.

Indoor areas:

Both air-cooled and water-cooled chillers are installable indoors. However, the chiller type will dictate the room’s arrangement. Indoor air-cooled chillers need ventilation to the outside. Sufficient fresh make-up air allows for the maintenance of a suitable temperature within the space. Water-cooled chillers do not require ventilation or fresh make-up air. They are almost exclusively installed indoors. Since they use water for cooling, the water conducts the heat out of the room, eventually exhausted to ambient, often via a cooling tower.

Outdoor Areas:

Almost all outdoor installations will be air-cooled chillers . In these installations, the heat rejected at the condenser simply dissipates into the ambient air. Outdoor installations require properly configured electrical control panels, based on the expected range of environmental conditions.

High Temperature Environments:

Water-cooled chillers work great in high temperature environments since they do not rely on ambient air for cooling.  Thus, they can be placed in hot mechanical rooms or in spaces with minimal ventilation.

Small Spaces:

The condenser on water-cooled chillers is more compact than an equivalently sized air-cooled unit.  This can result in an overall smaller unit, especially in the case of high capacity chillers. However, the entire refrigeration system will still require sufficient space.

Water-scarce areas:

Use an air-cooled unit. The cooling medium, ambient air, does not require any connections. Nor does a chiller with an air-cooled condenser need a cooling tower. These installations have lower overall environmental concerns surrounding water treatment and removal. An air-cooled chiller should be the best choice for water conservation.

Cost considerations

As with any equipment purchase, price will be a consideration. However, the difference in initial cost between an air-cooled and a water-cooled chiller may be misleading. Instead, it is important to factor in all lifetime costs to create the most accurate comparison.

With indoor installation of an air-cooled chiller, costs associated with duct work, fans, and controls for maintaining proper air temperature in the room may exist. Energy consumption costs may be higher for these chiller models due to its basic operating design.

Often times water-cooled units have a lower initial price. However, they generally have more operational costs, and will typically require the installation of a cooling tower. When using a cooling tower in conjunction with a water-cooled chiller, additional costs may accrue from the regular monitoring of water quality, treatment of the water, and the operation of fans and pumps. However, water-cooled chillers allow the refrigeration system to operate at lower head pressure, making them more efficient and less costly to operate than air-cooled chillers.

Factors such as water costs, efficiency ratings, and electricity can dramatically change the lifetime price of a chiller.

Which one do I choose?

If you are uncertain about how to select the right chiller for your system, our cooling engineering experts are always available to help.  Use these sizing factors to gain quick insight into what your system requires.

If after all these considerations, you still cannot make a decision, focus on cooling capacity. Use the process itself to determine the required cooling amount. This is the number one factor in determining the proper chiller size for your system.

Choosing between water-cooled and air-cooled chillers is not an easy process.  However, with the right support and expertise, working through your system’s individual needs will lead to the best equipment purchase for YOU.