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Air-To-Water Cooler

Closed Air Circuit Water Cooled cooler

Short for “Closed Air Circuit Water Cooled” coolers, CACW coolers are ideal for cooling generators and large electrical motors, no matter the environment.

These products pass water at a lower-than-ambient temperature through an element, providing cooling to a generator or motor. They are also known as TEWAC (“Totally Enclosed Water to Air-Cooled”) coolers.

The advantage of CACW or TEWAC cooling is the closed-circuit design, from which they get their name. This prevents dirt particles and liquids from entering the primary cooling circuit, extending the cooling element’s life and reducing downtime of your equipment.

Improve the reliability of your equipment with this robust, closed-circuit cooling system.

The usage of air-to-water coolers

To understand the usage of air to water coolers, let’s first consider how generators and similar machines are cooled in general. All rotating machines (that is, electrical motors and generators) need an airstream to cool the equipment rotor and stator.

CACW designed and manufactured by Sterling Thermal TechnologySmall electric motors simply have cooling fins on the outside of the motor frame, but larger machines generate much more heat. Direct cooling of the individual components is required.

This direct cooling (or “primary cooling”) is provided by passing air through passages within the machine air circuit. Most of the time, a fan on the machine shaft is used to create this air circulation.

However, in many situations, air alone is a poor heat transfer medium. This is where water-cooling comes in. A CACW generator or motor heat exchanger is installed to facilitate the secondary cooling of the airstream to enhance the heat transfer rate. This significantly increases the cooling system efficiency.

CACW for renewables designed and manufactured by Sterling Thermal Technology
CACW for renewables

With a full understanding of the processes involved, we, at Sterling Thermal Technology, can design and manufacture heat exchangers that meet our customer’s needs.

Learn more about partnering with Sterling TT.

Key benefits of CACW/TEWAC coolers

The most compact cooling option for large electrical machines

CACW coolers can use any available water supply, including river or sea water. However, some filtration or pre-treatment might be required. Closed circuit cooling which is already on the site can also be used.

A closed-circuit design

We can provide levels of protection against solid and liquid ingress up to IP56.

Allows for increased equipment availability

We can build in cooler redundancy to ensure a very high degree of availability of the cooled equipment.

Can be made from robust materials

Transformer oil water cooler- Double tube -Design and manufacture by Sterling Thermal Technology
Double tube

Reducing erosion and corrosion increases equipment life, so we use robust materials. Additionally, we can include double (safety) tube arrangements to protect the machine in case of tube failure.

Important design considerations for CACW coolers

Sterling Thermal Technology is a leader in the design and manufacture of bespoke heat exchangers, including CACW coolers. We know that every installation is different. Below are some of the variables we would consider when designing a new product with a customer:

  • Generator construction: single or double tube.
  • Redundancy requirements for series and/or parallel operating arrangements.
  • Restrictions to the available air side pressure drop.
  • Limitations on the cooling water flow or permitted temperature rise of the water stream. Local Regulations can limit the rise allowed on water before discharging back to the sea or to an inland watercourse.

A CACW cooler can be designed with double tubes to avoid downtime. 

Double Tube Rotating Machine Coolers

Double tube electrical machine coolers are a specific type of CACW cooler. Double tube heat exchangers allow continued operation for a limited period in the event of an inner tube failure, avoiding installing a redundant unit. 

If the tube is in contact with the water fail, the double tube feature ensures the leaking water is directed outside the cooler enclosure to a leak detection system. This gives the operator the opportunity to plan an intervention without immediately shutting down the machine or process.

Flexible & bespoke 

CACW casing and element for oil and gas application manufactured by Sterling Thermal TechnologyOur flexible heat exchanger software offers lots of design options to suit all applications and restraints. We can call upon a wide range of options to meet your thermal and mechanical specifications for the overall equipment requirement.

Whether you are an original equipment manufacturer or an end-user, we can help with your heat exchanger needs. We can address the most stringent requirements with our design capabilities, system quality and production facilities. In addition, we are ASME Boiler and Pressure Vessel certified and produce both ’U’ & ‘UM’ stamped equipment. Contact us today.


If you feel you need another type of heat exchanger, visit our products and services page or contact us.

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