Refrigeration Operator B cheat sheet
Refrigeration Operator B · Keep the key ideas within reach.
Refrigeration Systems and Components
Four core components of a vapour-compression system: compressor, condenser, metering device (expansion valve or capillary/cap tube), and evaporator; the compressor raises pressure and temperature, the condenser rejects heat, the metering device drops pressure, and the evaporator absorbs heat.
Compressor types and typical applications: reciprocating for small-to-medium capacity and high pressure ratios; scroll for mid-range packaged and split systems; screw for large industrial loads; centrifugal for very large capacities and low compression ratios.
Condenser heat rejection equals evaporator load plus compressor work: Q_cond = Q_evap + W_comp. Air-cooled condensers reject roughly 1.2 to 1.3 times evaporator load; water-cooled and evaporative types are typically closer to 1.15 to 1.25.
Evaporator superheat is the difference between suction line temperature and saturated suction temperature at the same pressure; thermostatic expansion valves are set to maintain a stable superheat, commonly 5 to 10 K (about 9 to 18 °F) at the evaporator outlet.
Subcooling is the difference between saturated condensing temperature and liquid line temperature; liquid subcooling improves metering device performance and prevents flash gas at the valve inlet.
Liquid receivers store refrigerant and accommodate charge variation; they must be sized so the system can hold the full charge during pump-down and service.
Oil management: compressors require oil return; oil separators, oil level controls, and proper suction line velocity (typically 4 to 7 m/s in horizontal suction lines) prevent oil logging in evaporators.
Pressure-enthalpy (P-h) diagram: the four processes are compression (isentropic ideal), condensation (constant pressure), expansion (isenthalpic through the metering device), and evaporation (constant pressure).