Auto-Zone Control Systems Auto-Zone Plus Systems Installation & Operation (Version 03A) - Manual (Page 24)

Section 1 Auto-Zone Plus
1-20 Design Guide
Whenever possible, use a single bypass damper and round duct for the bypass. If space
limitations or total airflow requires it, multiple bypass dampers can be controlled in
parallel.
For proper control of the Bypass Damper the static pressure sensor location is very
important. See Figure 1-5: Locating the Static Pressure Sensor for proper mounting
locations.
Step #6 - VFD Considerations
When using a VFD instead of a bypass damper for static pressure control, it is important
to consider the minimum fan speed that will still allow for proper airflow across the
electric heating element or gas fired heat exchanger. You should consult the HVAC unit’s
selection and design information regarding the minimum airflow that is allowed to
prevent damage to the heat exchanger in the case of gas fired equipment and prevent
nuisance tripping of the thermal safety devices when you are using an electric heater.
The VFD Controller on your HVAC unit must be configured so that the airflow never
falls below the minimum required by the heat exchanger. The WattMaster controller will
only modulate the VFD to control the fan speed in response to the static pressure setpoint
that you have set.
Also the wiring supplying the 0-10 VDC signal between the Zone Manager and the VFD
should be 18 gauge minimum 2 conductor twisted pair with shield to help prevent signal
feedback to the Zone Manager. This wire is available from WattMaster as part number
WR-LL-WG-18 or you can use Belden #82760 or equivalent wire.
For proper control of the VFD, the Static Pressure Sensor location is very important. See
Figure 1-5: Locating the Static Pressure Sensor for proper mounting locations.