Key Points:
Commercial Refrigeration Systems:
- Focus: Walk-in cooler.
- Comparison: Similarities and differences with residential air conditioning systems.
Refrigerant:
- Same R22 refrigerant used.
- Condenser located outdoors with same ambient conditions, resulting in identical condensing pressures and temperatures.
Indoor Space Temperature:
- Lower temperatures in commercial coolers compared to residential settings.
- Results in lower evaporator pressures and temperatures.
System Components:
- Liquid Receiver: Located between the condenser and metering device.
- Thermostatic Expansion Valve (TEV): Replaces fixed orifice metering device. Adjusts refrigerant flow based on evaporator outlet temperature.
System Operation:
- High Side Vapor: Leaving compressor with high side pressure of 278 PSIG and saturation temperature of 125°F.
- Superheating and Desuperheating: Initial refrigerant temperature 175°F, cooled to saturation temperature of 125°F, then further cooled (subcooled) to 115°F.
Liquid Receiver:
- Stores subcooled liquid refrigerant.
- Features a shut-off valve and a liquid line to the metering device.
Thermostatic Expansion Valve (TEV):
- Adjusts refrigerant flow based on evaporator outlet temperature.
- Balances opening force from evaporator temperature with back pressure and spring pressure.
Box Temperature:
- Example: 35°F air blowing over evaporator.
- Requires refrigerant with saturation temperature below 35°F for effective evaporation.
- Evaporator operates at 49 PSIG and 25°F saturation temperature, achieving 10°F superheat.
System Design Temperatures:
- Consistent evaporator and condenser temperatures across different refrigerants.
- Residential A/C: 40°F evaporator and 125°F condenser.
- Walk-in Cooler: 25°F evaporator and 125°F condenser.
Refrigerants:
- Various refrigerants (excluding R12) can be used, with different pressures but same temperatures.
- Important to remember design temperatures rather than multiple saturation pressures.
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