Refrigeration Cycle Lecture Notes

Components of the Refrigeration Cycle

• Outdoor Unit: Contains the compressor and condensing coil.
• Indoor Unit: Consists of the evaporator and metering device.

Types of Metering Devices

• Fixed Orifice Metering Device
  • Simple device with a fixed hole (orifice) that restricts flow.
  • Must match the one provided with the outdoor unit for proper pressure matching.
  • Preferred for its simplicity and lack of moving parts.
  • Charging involves focusing on superheat.

Superheat and Subcooling

• Superheat Calculation
  • Formula: Actual suction line temperature - Suction saturated temperature = Superheated vapor.
  • Important in systems with fixed orifice devices.
  • Example: Suction line temperature = 86°F, Suction saturated = 62.8°F, Superheat = 38.5°F.

Factors Affecting Superheat

• Outdoor Temperature: Higher temperature increases pressure, affecting refrigerant flow.
• Indoor Temperature & Humidity
  • Wet-bulb temperature accounts for sensible and latent heat.
  • Measured with a digital psychrometer.

Calculating Target Superheat

• Method 1: Formula
  • Target Superheat = ((Indoor Wet Bulb Temperature x 3) - Outdoor Temperature - 80) / 2.
  • Example with 71°F indoor wet bulb and 98°F outdoor: Target Superheat = 17.5.
• Method 2: Superheat Chart
  • Uses return air wet bulb and outdoor dry bulb temperatures.
  • Cross-reference temperatures on chart to find target.
• Method 3: Super Cool App
  • An app that calculates superheat using inputted data.

Interpretations

• High Superheat
  • Indicates a starved evaporator (not enough refrigerant).
  • Example: Actual superheat of 38.5°F vs target of 17.5°F.
• Low Superheat
  • Indicates a flooded evaporator (too much refrigerant).

Airflow Considerations

• Ensure proper airflow before adjusting superheat or subcooling.
• System presented has adequate airflow, indicating refrigerant adjustments may be necessary.

Conclusion

• Fixed orifice metering devices require careful calculation and adjustment of superheat to ensure efficient operation.
• Conditions influence ideal superheat values, necessitating periodic recalibration.