Building Automation and Environmental Control
Building Automation and Environmental Control tests HVAC plant control, indoor environmental quality, energy performance and integration with fire and life-safety systems. The exam expects psychrometric reasoning and sequence-level control knowledge, not just BMS point lists.
Core rules and concepts
- A building automation system uses DDC controllers, sensors, actuators and a supervisory layer. BACnet, Modbus, KNX and LonWorks are common protocols; BACnet is widely used for HVAC and fire alarm integration.
- Psychrometrics links dry-bulb, wet-bulb, dew point, relative humidity and enthalpy. Cooling coils handle sensible and latent load; a coil that is wet removes moisture, while a dry coil does not. Do not size cooling from dry-bulb temperature alone.
- Comfort criteria follow ASHRAE 55; ventilation follows ASHRAE 62.1 or local codes. In Hong Kong, the Buildings Energy Efficiency Ordinance Cap. 610 and EMSD requirements drive design and commissioning documentation.
- Common sequences include AHU supply-air-temperature control, duct static-pressure reset, VAV box control, economiser changeover, chiller staging and condenser-water reset. Resets save energy but must respect minimum ventilation and humidity limits.
- Fire and smoke modes override normal control: stair pressurisation, smoke extraction, damper closure and AHU shutdown. Interfaces must be hardwired or otherwise proven, tested and documented with the Fire Services Department requirements.
- Sensors must be located in representative conditions; return-air sensors can mask local overheating and CO2 sensors need calibration.
Worked example
An AHU supplies 0.5 m3/s at 12 °C to a room at 24 °C. Using Q ≈ 1.2 × V × ΔT, Q = 1.2 × 0.5 × 12 = 7.2 kW sensible cooling. If the room latent load is significant, the coil must also remove moisture, so the total cooling load is higher. The reasoning: airflow and temperature difference give sensible capacity only; check the apparatus dew point and condensate behaviour before selecting the coil.
Traps
Sizing from dry-bulb alone; setting minimum outside air below code; allowing simultaneous heating and cooling; placing sensors in dead zones; and treating a BMS graphic as proof of fire-mode operation.