🔍 Key Concepts

• Identify which control loop uses the room thermostat (space thermostat) versus a duct thermostat in the diagram. • Understand that in a dual-duct multiple zone system, the hot and cold air ducts are usually conditioned to fairly constant temperatures, and individual rooms are adjusted locally. • Trace what each coil (preheater, cooling coil, reheater) is controlling: duct temperature or room/zone temperature.

💭 Think About

• Follow the line from the room thermostat symbol in the space back to the equipment: what component or device does it actually move or signal? • Ask yourself which elements (preheat coil, cooling coil, reheat coil, or mixing dampers) would normally serve the entire system, and which element is typically adjusted for each individual room or zone. • Look closely at the hot and cold duct paths at the mixing box: how does the diagram show the hot and cold air being combined before entering the room?

✅ Before You Answer

• Verify which device is labeled as the room thermostat (T) in the legend and where it connects in the schematic. • Confirm whether the steam valves for the preheat and reheat coils and the chilled‑water valve are controlled by duct thermostats or by the room thermostat. • Make sure you can see how the dual-duct mixing unit (M) operates and what signal it receives to adjust either airflow proportion or coil flow.