HVAC System Automation Basics

Automatic Mode

• The automatic mode is controlled by a zone controller (computer)
• The zone controller receives desired temperature requests from the selector
• The temperature range for selection is 18 °C (64 °F) to 30 °C (86 °F)
• Zone temperature is measured by temperature sensors in the cabin
• The zone controller calculates the required supply duct temperature to reach desired temperature
• This is called the duct temperature demand
• The zone controller selects the coolest duct temperature demand
• This defines the necessary pack outlet temperature (pack temperature demand)
• The pack controllers use this signal to control pack operation
• If duct temperature demands are identical, the coolest demand for the pack temperature regulation comes from the passenger cabin zones
• This is because the air entering the mixing unit must be cooler than the air needed for the cockpit supply duct due to recirculated warm cabin air.
• The zone controller needs temperature feedback from the mixing unit to account for the recirculated air effect.
• When the cockpit supply duct temperature becomes the coolest demand, the zone controller can use a temperature feedback from the cockpit duct to improve regulation.

Trim Air Control System

• Hot trim air is added to the supply duct when the zone temperature demand is higher than the actual temperature
• The trim air valve controls the amount of hot trim air added
• The valve's position is adjusted based on the difference between the desired duct temperature and the actual duct temperature
• This difference is measured by a temperature sensor in the duct
• A damping circuit prevents temperature fluctuations and overshooting by using the rate of change in the duct temperature signal
• The damping circuit can use a special sensor called an anticipator to measure the rate of temperature change

Explore the fundamentals of automatic HVAC systems controlled by a zone controller. This quiz delves into how desired temperature requests are managed, the importance of supply duct temperature, and the interaction between temperature sensors and pack controllers. Test your knowledge of temperature demands and operational processes in climate control.