WAZIPOINT Engineering Science & Technology: How Chiller Motor works for Long Time keeping Cool

Sunday, August 27, 2023

How Chiller Motor works for Long Time keeping Cool

Hermetic Motor Cooling
Fig: Hermetic Motor  Cooling System

How Chiller Motor works for a Long Timekeeping Cool

How chiller motor keeps cooling is an important issue because chiller normally works continuously and need to keep cooling; so how chiller motor keeps cooling. 

A motor is used to rotate the impeller(s). A direct-drive motor is connected directly to the impeller shaft and the impeller rotates at the same speed as the motor. 

A gear-drive motor transfers its energy to the impeller shaft using a set of gears. This allows the impeller to rotate at a higher speed than the motor. 

Find the low voltage motor wiring system in another post.

The direct-drive motor requires fewer bearings and does not incur gear losses. Additionally, since the compressor rotates at a slower speed, it can be much quieter.

Direct-drive compressors are, however, only practical in centrifugal chillers that use low-pressure refrigerants.

Another important difference in compressor motors is the issue of hermetic versus open. 

A hermetic motor is totally enclosed within the chiller’s refrigeration system. An open motor is mounted externally—outside of the chiller’s refrigeration system—and uses a coupling to connect the motor and compressor shafts.

The heat generated by the hermetic motor is absorbed by liquid refrigerant that flows around, through, and over the motor. The heat must be rejected by the chiller’s condenser.


The heat generated by the open motor is rejected to the air drawn in from the equipment room. This heat must still be rejected from the equipment room, either by mechanical ventilation or, if the room is conditioned, the building’s cooling system. In some designs, this air is simply drawn into the motor housing by the rotating motor shaft. 

The vent passages tend to get dirty and clog, resulting in higher operating temperatures and hot spots that adversely affect motor efficiency and reliability. Other designs, such as totally-enclosed fan-cooled (TEFC) and totally-enclosed air-over (TEAO), use a separate fan with a protective housing to cool the motor.

Hermetic compressor motors eliminate the need for the shaft couplings and external shaft seals that are associated with open motors. 

The coupling needs precise alignment, and these seals are a prime source of oil and refrigerant leaks. On the other hand, if a motor burns out, a hermetic chiller will require thorough cleaning, while a chiller with an open motor will not.



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