VAV Controller—Variable Air Volume (VAV) Controller 73
The position accuracy of the VAV box damper is dependent upon the
actuator stroke time entered. It is important that the true damper actuator
stroke time be entered. The listed actuator times of 1, 2, or 5.5 minutes are
for 90 degrees of rotational travel. If a VAV box has 45 or 60 degrees of
travel, the stroke time must be adjusted. Multiply the listed stroke time by
0.5 for 45 degrees of travel by 0.667 for 60 degrees of rotation.
Drive times that are inaccurate cause the controller to calculate a software
damper position that is not synchronous to the actual damper position.
This error is particularly noticeable at the very end of the travel when the
controller thinks the damper is fully closed, but is physically open. If a box
has 45 or 60 degree travel, it is highly recommended that the entered stroke
time used in HVAC PRO for Windows be tested under field conditions to
verify that the box can be driven fully closed and open.
For simplicity, program a Zone Terminal to access only those values
required for testing and balancing processes. For each box configuration
style, determine which parameters the test and balance will require. Build
a controller display file for each configuration. Up to three display files
can be combined into one ZT load file. For example, a single duct box with
reheat might require the values shown in Table 33.
Table 33: Parameters for Balancing a
Single Duct Box with Reheat
Parameter name Function Purpose
Supply Setpt
view display present flow setpoint
Supply Flow
view display present flow rate
Supply Box Area
view & adjust verify & correct box inlet area
Supply Mult
view & adjust calibration of flow measurement
Supply Delta P
view secondary information
Damper Command
view secondary information
Occ Clg Max
view & adjust verify & correct flow setpoint
Occ Clg Min
view & adjust verify & correct flow setpoint
Occ Htg Min
view & adjust verify & correct flow setpoint
Occ Htg Max
view & adjust verify & correct flow setpoint
Occ Setpt
view & adjust change present control point
Occupied Status
view verify mode
Once you load the base configuration files into each controller, the
balancing contractor can use a Zone Terminal to officially set the CFM
schedules.
87F88F89FIncremental
Damper
Actuator Stroke
Time
90F91F92FZone Terminal
Setup for
Balancing
Contractors
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