🔍 Key Concepts

• Follow the air path from the supply fan through the cooling coil, reheater, and into the cold and hot ducts leading to the rooms. • Identify what the room thermostat (T) actually controls versus what the duct thermostat (T) and pneumatic relays/valves control. • Understand the role of the dual duct air mixing unit (M) in a class "G" dual duct system: it mixes hot and cold deck air for each stateroom.

💭 Think About

• Look at the right side of the diagram: which device is located in or near the room, and what component does its signal go to? • Which thermostat is sensing duct temperature, and which is sensing room (space) temperature? How does that affect what each one is controlling? • Does the reheater coil directly change the room temperature of each individual stateroom, or does it simply set the temperature of one of the supply ducts feeding multiple rooms?

✅ Before You Answer

• Trace the control line from the room thermostat (T) and see whether it goes to the dual duct mixing unit (M) or to the steam reheater valve. • Check which thermostat is labeled as Master (M) or Sub‑Master (SM) and note what piece of equipment each one controls. • Verify whether the reheat coil R(S) is in a single duct or arranged in parallel with the cooling coil, and whether it is upstream or downstream of the duct split into hot and cold decks.