Completing a box auto zero - EasyIO - LIT-12014127 - EASYIO-FW-VAV - FV-VAV - 1.0

EasyIO FW-VAV Application Note

Brand
EasyIO
Product name
FV-VAV
Document type
Application Note
Document number
LIT-12014127
Version
1.0
Revision date
2024-04-09
Product status
Active
Language
English

About this task

When you have a non-zero reading during a zero flow condition, the main AHU is off, the local VAV box fan is deactivated, and the damper is at zero position, perform a flow sensor auto zero.

Figure 1. Calibrated flow sensor with a zero flow offset

When you take into account the differential pressure, a calibrated flow offers a 3-point scaling factor: from the zero flow to the minimum flow, from the minimum flow to the maximum flow, and from the maximum flow to the K-factor.

To prepare the VAV box Auto Zero procedure, complete the following steps:

Procedure

  1. Shut down the main AHU unit or remove the high and low pressure tubes from the controller.
  2. Toggle the Auto Zero Trigger point (Config_AutoZeroTrigger) (BV11) to true for 2 seconds and return it to false.

Results

The Auto Zero mode starts and automatically performs the following actions:

  • Deactivates the local VAV box fan, if applicable
  • Drives the VAV damper to the zero position for the configured actuator drive time (Config_DamperDriveTime_Seconds ) (AV43) + 25 seconds
  • Zeros the differential pressure (DP) flow sensor
  • Returns the VAV to Auto and exits the Auto Zero mode