Commercial and Industrial Refrigeration Systems and Components
Commercial and Industrial Refrigeration Systems and Components tests your knowledge of equipment larger than a single condensing unit: walk-ins, supermarket racks, secondary loops, cascade and ammonia plants. Expect items on component function, defrost, head pressure control, oil management, and code-required safety devices.
System types
- Distributed and parallel-rack supermarket systems share a common suction header and condenser; each circuit has its own EPR valve and case controller.
- CO2 transcritical booster systems run above the critical point on the high side, using a gas cooler instead of a condenser plus a flash tank and high-pressure valve.
- Industrial ammonia plants use reciprocating or screw compressors with liquid overfeed or pumped recirculation, and strict machinery-room separation.
Components
- Evaporators: forced-air unit coolers, gravity coils, plate and shell-and-tube.
- An EPR (evaporator pressure regulator) holds a minimum evaporator pressure; a CPR (crankcase pressure regulator) protects the compressor motor from overload during pulldown.
- Oil separators, oil reservoirs, oil-level controls and equalizing lines keep compressors lubricated across a rack.
- Head pressure control by flooded condenser, fan cycling or variable speed keeps pressure up in cold weather.
- Defrost: off-cycle, electric, hot gas or reverse cycle, terminated by temperature or pressure rather than time alone.
Safety devices
Relief valves sized and piped per CSA B52, high-pressure cutouts, low-pressure pump-down, oil-pressure switches, refrigerant detectors and machine-room ventilation.
Worked example: EPR setting
A chilled walk-in on R-22 must hold a 26°F (−3.3°C) coil. From the PT chart, R-22 at 26°F is about 50 psig. The EPR is set to maintain 50 psig on its evaporator side; as load falls, the valve throttles rather than letting coil temperature drop further.
Traps
- Terminating defrost on time alone with a temperature sensor that never triggers.
- Ignoring receiver liquid seal and subcooling in winter.
- Confusing the EPR (evaporator protection) with the CPR (compressor protection).
- Forgetting that hot-gas defrost needs a check valve and that the suction line must carry the extra load.