Auto-Zone Control Systems Auto-Zone Plus Systems Installation & Operation (Version 03A) - Manual (Page 25)

Auto-Zone Plus Section 1
Design Guide 1-21
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
2/3 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.
Supply
Fan
Supply Air
Temp. Sensor
3D
Min.
2D
Min.
Supply Air
Duct
Static Pressure
Pickup Probe
Bypass
Damper
Static Pressure
Sensor
Return Air Duct
Return Air
Temp. 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.
Another option is to use (2) Static
Pressure Probes and tie them together
with a tee. Use equal lengths of tubing
for each sensor and run the third leg of
the tee back to the Static Pressure
Sensor. This will average the pressure
readings of the two duct runs.
Tubing To Be Equal
Length And Size
Tee
Supply
Fan
Supply Air
Temp. Sensor
Static Pressure
Pickup Probes
Bypass
Damper
Static Pressure
Sensor
Supply Air
Duct
Return Air Duct
Return Air
Temp. Sensor
Least Desirable, But Acceptable
If the supply duct comes directly from
the unit and immediately splits in
opposite directions without a curved
duct split, the pressure pickup should be
located ahead of the split, or as close to
it as possible to it, even if the bypass
damper(s) are located downstream of the
split.
Return Air Duct
Supply
Fan
Return Air
Temp. Sensor
Supply Air
Temp. Sensor
Supply Air
Duct
Static Pressure
Pickup Probe
Bypass
Damper
Static Pressure
Sensor
Figure 1-5: Locating the Static Pressure Sensor