Understanding Air Handling Units: From Basics to Real-World Application

A: The correct choice achieves isolation on power loss, matching NO dampers with spring return to closed. A assumes purge logic that isn't shown on the P&ID. B describes a fail-safe pairing you’d expect with opposed blades but conflicts with both marked NO. D ignores the spring designation implied by the NO callout on the damper symbols.

A: The correct choice lands near the fan law estimate: (20,000 cfm × 3 in.w.g)/(6356 × 0.55) ≈ 17 kW before motor losses. A drops a digit and smells like confusing brake horsepower with electrical input. C overstates by assuming pressure scales linearly into the tens of kW at this airflow. D ignores that airflow volume, not just pressure, drives power.

A: The correct choice addresses the unprotected risk: loss of freeze protection lets cold air hit the preheat coil until water freezes and expands. A is a controls tuning issue, not a freeze outcome. B targets the wrong coil since chilled water is typically isolated in winter. D mixes an unrelated life-safety function with a mechanical freeze device.

A: The correct choice achieves clarity on maintenance intent: combined taps hide which bank is loading. A gets the direction wrong because combined drop is higher, not lower. C might happen but isn’t inherent to the tap location. D confuses ventilation code with filtration instrumentation.