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

Published: May 2011

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