HVAC System Operations Explained

Aug 1, 2024

Notes on HVAC Systems in Commercial Buildings

Overview of Connected Units

  • Multiple units can be connected within a commercial building.
  • Each unit can provide either heating or cooling, with some providing one while others provide the opposite simultaneously.

Branch Controllers

  • Each indoor unit is connected to a branch controller.
  • The branch controller contains valves to direct refrigerant flow for heating or cooling.
  • Three pipes run to each branch controller:
    • Suction line: carries superheated gas.
    • Liquid line: provides cooling.
    • Hot gas line: provides heating.

Compressor Functionality

  • A variable speed compressor is located outside.

Cooling Mode

  • The compressor sends hot refrigerant to the outdoor unit to reject heat.
  • It flows through:
    • Expansion valve before reaching indoor units for cooling.
    • Indoor units collect unwanted heat and return refrigerant to the compressor.

Heating Mode

  • The compressor sends hot gas to indoor units for heating.
  • The gas flows to the outdoor unit through an expansion valve to absorb heat from ambient air.
  • The cycle continues as gas is compressed to usable temperature and pressure.

Mixed Mode Operation

  • In mixed mode, hot discharge goes to:
    • Indoor units requiring heating.
    • Outdoor units requiring cooling.
  • Indoor units providing heating send refrigerant to those needing cooling.

System Operations in Different Modes

  • Full Cooling Mode:
    • All indoor units collect heat.
    • All outdoor units reject heat.
  • Full Heating Mode:
    • All outdoor units collect heat.
    • All indoor units reject heat.
  • Mixed Mode:
    • If two indoor units require heating and two require cooling with equal loads, outdoor units are not used; thermal energy is transferred between units.
    • The compressor still operates to circulate refrigerant.

Unequal Heating and Cooling Loads

  • If heating and cooling loads are unequal (e.g., three units heating and one cooling):
    • Outdoor units must operate to collect additional thermal energy.
    • A single cooling unit may not suffice for heating demands.

Conclusion

  • Understanding the operation of HVAC systems is crucial for effective heating and cooling.
  • Further learning resources are available through recommended videos and social media channels.