Introduction to Walk-In Freezers : Defrost Cycle

 1. Purpose of Defrost Cycle:

• Removes ice from the evaporator coil.
• Ice buildup on the coil blocks airflow, reducing freezer efficiency.
• Periodic defrosting ensures proper operation.

2. Defrost Methods:

• Electric Defrost:

  • Uses a heating element attached to the evaporator coil.
  • Energized heating element melts ice during the defrost cycle.
  • Controlled by a defrost clock and a termination thermostat.
  • Termination thermostat turns off defrost cycle when ice is melted.
  • Fail-safe timer starts refrigeration system if termination switch fails.
  • Common in commercial refrigeration, cheaper, easier to install, but slower.

• Hot Gas Defrost:

  • Uses superheated discharge gas from the compressor as a heat source.
  • Hot gas flows through a solenoid valve (hot gas solenoid valve) to the evaporator.
  • More energy-efficient, heats coil precisely, less thermal energy dispersion.
  • Requires complex piping installation.
  • Addition of a suction line accumulator prevents condensed refrigerant from entering the compressor.
  • Terminates defrost cycle when coil temperature rises to around 50°F.

3. Defrost Cycle Control:

• Defrost Timer:
  • Initiates defrost cycle, can be a dial or circuit board with an integrated timer.
  • Older timers start cycles on schedule regardless of ice conditions.
  • Modern timers progress only when the compressor is active to save energy.
• Demand Defrost:
  • More efficient than scheduled defrost.
  • Measures temperature to determine if defrost is needed.
  • Ends defrost cycle when ice is melted, conserving energy.

4. Importance:

• Defrosting reduces ice restriction in airflow, increasing energy efficiency.
• Monitoring and control systems cut unnecessary defrost cycles, conserving energy.
• Demand defrost cycles are more efficient, starting only when needed.