Auto-Zone Control Systems Auto-Zone Basic Systems Installation & Operation (Version 02C) - Manual (Page 18)

Section 1 Auto-Zone Basic
1-12 Design Guide
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. Refer to Figure 1-3: Locating the Static Pressure Sensor for Bypass
Damper Control below for proper mounting locations.
Preferred Location
If the trunk ducts are properly sized
for minimum pressure drop, the
location of the static pickup probe is
not particularly critical. It should
ideally be located at right angles to
the airflow in a straight section of the
supply duct approximately ⅔
the
distance of the total length of the
supply duct. Also, the probe should
be located not less than 3 duct
diameters downstream and 2 duct
diameters upstream of any elbow or
takeoff.
Fan
RA Sensor
SA Sensor
3D
Min.
2D
Min.
Return Air Duct
S
upp
ly
Air
Duct
SP Pickup
Bypass Damper
SP Sensor
Less Than Ideal, But
Acceptable
Since the "ideal" location is often
difficult to find in an installation, a
location in the main trunk where
the tip is not in a "negative
pressure area" (e.g. just
downstream of the inside curve of
an elbow) or an area where the
tube opening is directly impacted
by the velocity of the supply air is
acceptable.
Fan
RA Sensor
SA Sensor
Return Air Duct
Supply Air Duct
SP Pickup
Bypass Damper
SP Sensor
Least Desirable, But
Acceptable
If the supply duct comes directly
from the unit and immediately
splits in opposite directions, the
pressure pickup should be located
ahead of the split or as close to it
as possible, even if the bypass
damper(s) are located downstream
of the split.
Fan
RA Sensor
SA Sensor
Return Air Duct
Supply Air Duct
Tubing To Be Equal
Length And Size
Bypass Damper
SP Sensor SP Pickups
Figure 1-3: Locating the Static Pressure Sensor for Bypass Damper Control