Intro to Chillers : Chiller Compressors

 Chiller Compressor Designs:

• Centrifugal Compressors:
  • Types: Low-pressure (operating in a vacuum on one side) and high-pressure.
  • Usage: Large capacity chillers above 100 tons.
  • Design: Impeller spins at high RPM to compress refrigerant vapors.
• Screw Compressors:
  • Characteristics: High pressure with capacity control via slide valves or variable frequency drives.
• Reciprocating and Scroll Compressors:
  • Usage: High-pressure water chillers with multiple compressors due to smaller capacity.
  • Design: Reciprocating compressors have cylinders that can operate at reduced capacity using unloaders. Scroll compressors use multiple units for capacity control.

Centrifugal Chiller Operation:

• Components:
  • Evaporator: Absorbs heat from water passing through the tubes.
  • Condenser: Condenses refrigerant vapors to liquid.
  • Impeller: Compresses vapors, discharging them around the perimeter.
• Process:
  • Suction vapors enter the impeller, are compressed, and discharged to the condenser.
  • Liquid refrigerant returns from the condenser to the evaporator.
  • Evaporator maintains proper liquid refrigerant level above water tubes for effective heat absorption.

Water Circuits for Centrifugal Chillers:

• Chilled Water Circuit:
  • Flow: Warm water returns from remote coils, cooled by evaporator, and sent back at a lower temperature.
  • Approach Temperature: Difference between evaporating temperature (e.g., 40°F) and chilled water supply temperature (e.g., 45°F). Indicates heat transfer efficiency and need for cleaning if the temperature difference increases.
• Condenser Water Circuit:
  • Flow: Condensed refrigerant vapor releases heat to cooler water, which returns to the cooling tower.
  • Condenser Approach Temperature: Difference between condensing temperature (e.g., 105°F) and leaving water temperature (e.g., 95°F). High approach temperature indicates need for cleaning.

Cooling Tower Operation:

• Process: Water is atomized and air is blown across it, causing evaporation and heat absorption from the remaining water.
• Efficiency: Evaporative cooling conserves a large portion of the water for reuse, lowering the temperature of water returning from the cooling tower.