Application Note: Controlling a FPVAV with Multiple Stages of Reheat

Problem:

It's common to see VAVs with fans and/or multiple stages of heating.  The SmartNode only has two relay outputs.  So using 75F, how would we control the equipment in the scenario that there are more than two relay outputs needed?

Solution:

Using an Analog to Adjustable Relay Device, we are able to configure the VAV zone with the modulating reheat setting.  The SmartNode will use Analog Output 2 to provide a configurable output signal.  The device will then take this analog signal and stage the relays as configured.

Notes:

• 75F designs and supplies our solutions with an ACI analog sequencer board, model number ATL-DB-10%.
• The example above is for 3 stages of electric reheat.  If the application calls for more or less, the potentiometers will need to be adjusted accordingly.
• Each relay is rated for 2A.  If contactors for reheat exceed 2A, isolation relays will need to be added.

Instructions:

The example below is for a FPVAV with 3 stages of electric reheat:

Wiring detail for the SmartNode:

Wiring and setup detail for the sequencer board: