ENGINEERING MANUAL OF AUTOMATIC CONTROL
INDOOR AIR QUALITY FUNDAMENTALS
167
ROOFTOP UNIT CONTROL SYSTEM
Figure 6 shows a typical packaged rooftop VAV system
similar to the pervious system but with humidification and
without a return fan. Differential pressure mixed air control is
well suited to roof top applications which usually do not have
sufficient ductwork for flow station outdoor air measurement.
Without the return fan and with a two position exhaust fan it
is difficult to ensure air balance in the building.
Fig. 6. Typical Rooftop HVAC System.
OA
SA
RA
EA
M10488
SUPPLY FAN
EXHAUST FAN
CT
RA
TEMPERATURE
MA
TEMPER-
ATURE
HEATING
STAGE
COOLING
VALVE
SA
FAN
SA FAN
STATUS
HUMIDIFIER
VALVE
SA
TEMPER-
ATURE
SA
RELATIVE
HUMIDITY
ROOM
TEMPER-
ATURE
EXHAUST
FAN
STATUS
SA
PRESSURE
AFTER
HOURS
OA
TEMPER-
ATURE
OA
DAMPER
RETURN
AND RELIEF
DAMPER
STATIC
PRESSURE
OPERATOR INTERFACE
Modern Building Management Systems (BMS) utilizing
distributed direct digital controllers and personnel computer based
local area networks are installed in many buildings. Full utilization
of a BMS greatly simplifies the operations and maintenance tasks
and provides prompt alert of IAQ problems. By furnishing quality
of information knowledgeable operators and engineers can easily
visualize the system, comprehend the current status, and determine
the nature of any problem.
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