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Efficient cooling for generators and large electrical motors in any climate

A closed air circuit water cooled (CACW) cooler removes the excess heat generated by large electric motors and generators. Water at a suitable temperature, typically below the general ambient, is passed through the element to provide cooling. The closed circuit prevent dirt particles and liquids from entering the primary cooling circuit, ensuring the lifetime of the equipment is extended and optimised.

Key benefits

  1. Compact – A CACW cooler is the most compact cooling option for large electrical machines. Any available water supply can be used including river or sea water (potentially with some filtration or pre-treatment). Closed circuit cooling from cooling towers or other secondary cooling systems already available on the site can also be used.

  2. Equipment availability – Cooler redundancy can be built in to ensure a very high degree of availability of the cooled equipment.

  3. Levels of protection against solid and liquid ingress up to IP56 can be provided.

  4. Robust – Materials can be selected to reduce erosion and corrosion and increase equipment life. Double (safety) tube arrangements to protect the machine in case of tube failure are an option.

How closed air circuit water coolers (CACW) work

All electrical motors and generators need an airstream to cool the equipment rotor and stator. Small electric motors simply have cooling fins on the outside of the motor frame. Larger machines generate much more heat and direct cooling of the individual components is required.

Direct (primary) cooling is provided by passing air through passages within the machine air circuit. A fan on the machine shaft is used for air circulation in the majority of applications. A separate cooling fan is installed when necessary to establish a consistent airflow. Air alone is a poor heat transfer medium. A CACW cooler installed to facilitate the secondary cooling of the airstream enhances the heat transfer rate, which significantly increases the cooling system efficiency.

Every installation is different. Below are some design considerations.

  • 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).

Our flexible optimising 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.

Sterling Thermal Technology can address the most stringent requirements with our design capability, quality system and production facility. We are ASME Boiler and Pressure Vessel certified and produce both ’U’ & ‘UM’ stamped equipment.

CACW designed and manufactured by Sterling Thermal Technology

CACW cooler

CACW - casing and element

CACW – casing and element


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

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We have used CACW coolers for a number of different generator installations. The service from Sterling Thermal Technology has been excellent and their products have always met our expectations.

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