Variable-speed screw chillers from Johnson Controls achieve major performance benefits

Johnson Controls, York, Chiller

A 40% improvement in real-world efficiency compared with current products is achieved by a new range of air-cooled chillers from Johnson Controls. These air-cooled chillers have screw compressors with variable-speed drives and use R134a refrigerant. Their design EER is up to 3.4, and they can be configured to deliver an integrated part-load (ESTEER) of up to 4.8. Cooling capacities range from 525 to 970 kW.

These chillers have micro-channel condenser coils made of a single material to avoid galvanic corrosion. Coils and headers are brazed as one piece to minimise leaks. Fins do not over­hang, so they cannot be damaged. Efficient heat transfer reduces footprint and reduces refrigerant charge by up to 50%.

The shell-and-tube evaporator is a hybrid falling-film type heat exchanger with a balance of flooded and falling-film technology to optimise efficiency and minimise refrigerant charge.

Variable-speed drives for the twin-screw compressors halve the number of moving parts compared with fixed-speed compressors and slide valves for capacity control.

Each compressor has its own refrigeration circuit with over 60% fewer brazed joints thanks to the use of computer-controlled bending machines, resulting in a reliable and leak-resistant system.

The use of variable-speed drives reduces sound levels by up to 16 dB(A) at off-design conditions. A variety of sound-attenuation options is available for design conditions.

Each chiller is shipped as a complete factory package ready for field installation.

The E-Link Gateway provide a versatile connection between Johnson Controls and open/standard protocols.

For more information on this story, click here:  May 2011, 168
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