Basic Documentation

Room Pressurization Control Application Guide
SUPPLY
TERMINAL
ROOM
CONTROLLER
FUME
HOOD
CONTROLLERS
ROOM
GENERAL
EXHAUST
CFM
CFM
CFM
CFM
STATIC PRESSURE
ROOM STATIC
PRESSURE SENSOR
LAB0196R1
Figure 5. Direct Pressure Control Arrangement for a Chemical Laboratory Room.
The Room Controller also monitors the room static pressure via the Room Static Pressure
Sensor and controls the total room supply airflow to maintain the required room static
pressure set point.
If the room static pressure is less than the set point, the controller reduces the supply airflow
to increase the difference between the room supply and total room exhaust airflow’s and,
thus, increase the room’s negative static pressure.
If the room static pressure is greater than the set point, the controller increases the supply
airflow to decrease the difference between the room supply and total room exhaust airflow’s
and, thus, decrease the room’s negative static pressure
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.
With a VAV ventilation system there may be times, particularly during the cooling season,
when the room will require more supply airflow to maintain the desired room temperature
than the amount needed to maintain the required room static pressure. In such instances, the
Room Controller will increase the amount of supply airflow to maintain the desired room
temperature while simultaneously increasing the room general exhaust as necessary so that
the room static pressure remains constant.
In a VAV laboratory room served by a single supply duct that also has a Room General
Exhaust, the many functions of the Room Controller include:
• Maintaining the proper amount of room general exhaust to ensure that the required
minimum room ventilation rate
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is always maintained.
9
In negatively pressurized rooms the supply airflow needs to be less then the total room exhaust airflow. In positively
pressurized rooms the supply airflow needs to be greater than the total room exhaust airflow.
10
In negatively pressurized rooms the ACH rate is determined by the total room exhaust airflow. In positively pressurized rooms
the ACH rate is determined by total room supply airflow.
22 Siemens Building Technologies, Inc.