This Variable volume box has three modes of operation: a cooling mode with variable flow rates designed to meet a temperature set point; a dead-band mode whereby the set point is satisfied and flow is at a minimum value to meet ventilation requirements; and a reheating mode when the zone requires heat. including reheat coil VAV unit , manual vent , air inlet , ball valve , strainer and blow off valve , supply air , union , drain valve VAV stands for Variable Air Volume. In its simplest form, VAV systems use varying airflow at a constant temperature to heat and cool buildings. This is opposite of a CAV (or Constant Air Volume) system, which supplies consistent air flow at varying temperatures to heat or cool a space. for more details of Variable volume box download this file.