VAV Parallel Box

[MrMojito]

I am wondering why the fan in this box only turns on when the HVAC system is in heating mode?

 

[willard3]

Is this a reheat system?

 

[MrMojito]

Yes it is.

 

[willard3]

A bunch of questions follow from the first:
Is the control system pneumatic or electric?
Where are the thermostats?
How are resets controlled?
What is the climate of the building?

I could go on and on.....you have not given adequate information even to pose the question.

 

[imok2]

Intermittent fan powered boxes are also known as fan powered induction boxes, parallel fan powered boxes, primary bypass fan powered boxes, and powered induction units (PIU). They provide VAV to the conditioned space when cooling and constant volume when heating.

 

[panduru]

good one, imok2