Centrifugal chillers are best described as units with which combination of tonnage and operating pressure?

• A. Low tonnage, high pressure machines
• B. High efficiency, high pressure machines
• C. High tonnage, low pressure machines
• D. Medium tonnage, medium pressure machines

Answer: (C)

Centrifugal chillers are built to deliver very large cooling loads, so they provide high tonnage. Their design uses a high-speed impeller to move refrigerant in large volumes, which makes the system efficient at transferring heat when the capacity is big. To keep that heat rejection efficient, they operate with a relatively low pressure rise across the compressor and rely on cooling towers or water-cooled condensers, resulting in lower condenser (operating) pressures compared to other chillers at similar capacities. So the best description is high tonnage, low pressure machines.