There are two options for motors for water cooled chillers, Open Drive and Hermetic Drive. An open drive has an electric motor that is air cooled by the ambient air. A hermetic drive has an electric motor that is hermetically sealed and cooled with refrigerant. With having experience repairing and maintaining both open drive and hermetic drive machines, each arrangement has its advantages and disadvantages.
Open drive water cooled chillers have the possibility to be driven by other means such as steam turbine, gas motor, or gas turbine, etc. These machines can be converted to alternative refrigerants; the motors do not rely on refrigerant for cooling. Open drive electrical motors can have electrical power diversity, capable of handling high voltages, which will reduce a facilities transformer needs. The electrical motor will have more windings, though, due to higher operating temperatures thus adding motor heat to the space. Repairs can be made to the electrical motor since the motor is accessible. There is a mechanical seal for the compressor shaft that connects to the motor shaft, this mechanical seal will leak in due time. This, as we have all experienced, is in line with the old quote, “More moving parts and more points of connections creates the possibility of more probable failures in time.”
Hermetic drive chillers have electrical motors that are cooled with refrigerant; this allows for reduced motor winding and minimal heat dissipated to the space. The electrical motor heat will be transferred from the refrigerant to the condenser water. Hermetic drive chillers do not have shaft coupling of the motor to the compressor or mechanical seal, which creates a lesser chance for failure. These chillers have placement versatility, i.e. they can be placed outdoors, because the motor is sealed and not cooled by ambient temperatures.
