Flow Tracking System With Mixing Box Static Pressure Control - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

INDOOR AIR QUALITY FUNDAMENTALS
FLOW TRACKING SYSTEM WITH MIXING
BOX STATIC PRESSURE CONTROL
Figure 5 is the same as the Flow Tracking System except for
the addition of a method of controlling the amount of outdoor
air. The outdoor air is controlled by maintaining a constant
negative static pressure in the mixed air. The pressure sensor is
referenced across the outdoor air damper which is maintained
at a variable minimum position until the economizer calls for
EA
OA OA
TEMPER- DAMPER
ATURE
RETURN
AND RELIEF
DAMPER
Fig. 5. HVAC Flow Tracking with Differential Pressure Control of OA.
RETURN FAN
RA FAN
STATUS
OA
STATIC MA
TEMPER-
PRESSURE
ATURE
additional outdoor air. During non-economizer periods the EA/
RA dampers modulate to maintain static pressure constant at
the filter inlet. This is accomplished by separating the control
of the outdoor air damper from the control of the return and
relief dampers. Note that the OA damper minimum position
and the MA static pressure setpoint must be determined in
conjunction with the air balancing contractor. Refer to VAV
AHU WITH RETURN FAN AND FLOW TRACKING in the
Air Handling System Control Applications section.
CT VSD
RA RA FLOW
RA FAN
RA
TEMPER- SIGNAL
SPEED
FAN
ATURE
SUPPLY FAN
CT
VSD
SA FAN
HEATING COOLING SA
SPEED
VALVE VALVE FAN
SA FAN
STATUS
ENGINEERING MANUAL OF AUTOMATIC CONTROL
166
RA
F
SA
F
SA
SA
ROOM
TEMPER-
PRESSURE
TEMPER-
ATURE
ATURE
SA FLOW
SIGNAL
AFTER
HOURS
M10487