VAV with terminal reheat vs standard VAV

One-line orientation

VAV with terminal reheat adds a heating coil at each VAV box to allow per-zone temperature precision — the exam tests knowing this wastes energy and when that tradeoff is justified.

Key points

• Standard VAV recap: varies the volume of centrally cooled air sent to each zone; each zone thermostat modulates a damper. Efficient for variable cooling loads; no local heating capability at the terminal.

• VAV with terminal reheat: adds a heating coil (electric resistance or hot-water) inside each VAV box. The central AHU still supplies cool air; the reheat coil raises the air temperature locally before it enters the zone.

• Operation: the system supplies cool air to every zone simultaneously. Zones that need cooling receive it by increasing airflow; zones that need heating (or need less cooling) receive reheated air from the local coil.

• Energy penalty: the system cools air centrally and then reheats it locally — both processes consume energy. This simultaneous heating-and-cooling loop is an inherent inefficiency and is the reason the system is flagged in energy codes.

• When justified: choose VAV reheat when zones need minimum ventilation airflow and local heating. This is common in hospitals, laboratories, clean rooms, and other spaces that need tight local control.

Confusions / comparison

	Standard VAV	VAV with terminal reheat
Terminal unit	Damper only	Damper + heating coil
Zone temperature control	Cooling only (throttle airflow)	Cooling and heating per zone
Energy efficiency	High	Lower — simultaneous heat/cool
First cost	Lower	Higher (coils + controls)
Best application	Variable-load office/commercial	Hospitals, labs, precision spaces

Related

→ HVAC: single vs multi-zone (VAV reheat is a multi-zone sub-type) · dual-duct system (another energy-intensive precision-control approach) · HVAC distribution systems (all-air context for VAV family).