VAV terminal units have been widely used for space comfort conditioning over the last 30 plus years. There are many variations on what you will find for boxes from simple shutoff boxes to those with reheat, and either series or parallel fan powered units. VAV boxes provide a great solution for control of comfort with good efficiency and reasonable initial cost.
When dealing with existing buildings, it is not surprising to find a variety of VAV terminals. The age, condition, and controls used on these terminals can vary dramatically — from near-new and in great shape to completely failed. Ideally, we like to see VAV boxes be part of the BAS and to be equipped with pressure-independent DDC controls. This leads to the retrofit of boxes that have older pneumatic or electronic controls. There are many benefits to retrofitting to new DDC. Benefits include: