🔍 Key Concepts

• Trace the chilled water and steam lines to see what actually produces cooling and heating in this system. • Note how the room thermostat (T), sub-master (SM), and master (M) are connected pneumatically to valves, dampers, and the dual duct air mixing unit (M). • Review how recirculated air vs. outside air affects the heat load on an air conditioning system.

💭 Think About

• Look at the cooling section: does this diagram show a self-contained Freon (refrigerant) unit, or does it show a chilled-water coil supplied from somewhere else? What does that imply about choice A? • Follow the control lines from the room thermostat: do they go directly to a steam valve, to the preheater, or to the mixing box that blends hot and cold air? • Think about heat load: if you bring in more already-conditioned recirculated air instead of hot (or cold) outside air, does the refrigeration system work harder or less?

✅ Before You Answer

• Verify which component actually cools the air: is it a Freon evaporator or a chilled water coil (C)? • Confirm which thermostat or controller is tied to the preheater steam valve versus the reheater steam valve and the dual duct mixing unit. • Check whether increasing recirculated air would increase or decrease the temperature difference the system must overcome, and therefore the cooling/heating load.