Basic Documentation
Table Of Contents
- About this Application Guide
- Chapter 1–Introduction
- Chapter 2–Goals of the Laboratory Environment
- Chapter 3–Unique Ventilation Needs of a Laboratory Facility
- Chapter 4–Ventilation Systems Classification
- Chapter 5–Laboratory Facility Exhaust Systems
- Chapter 6–Laboratory Containment Units - Ventilation
- Chapter 7–Room Ventilation, Makeup Air, and Pressurization Control Systems
- Chapter 8–Laboratory Temperature and Humidity Control Systems
- Chapter 9–Laboratory Emergencies - Ventilation System Response
- Chapter 10–Laboratory Ventilation System - Validation
- Chapter 11–Laboratory Ventilation System - Commissioning
- Glossary
- Index
Chapter 7–Room Ventilation, Makeup Air, and Pressurization Control Systems
This control approach essentially combines the room differential pressure sensor of
Figure 12 with the airflow tracking method of Figure 13, and is referred to as
cascaded static pressure control. The net result would provide the benefits of both
direct pressure control and flow tracking. The control scenario is essentially that of
airflow tracking; however a wall mounted pressure sensor is used so that the room
controller can periodically read the actual differential pressure and if need be, adjust
the airflow tracking differential as needed. As a result of this arrangement, the airflow
tracking value does not remain fixed from the time the room is initially balanced, but
will be periodically reset (perhaps based on an ongoing 5-minute average) to
maintain precise static pressure control. This cascaded control arrangement will
therefore compensate for static pressure variations that might otherwise occur due to
outside temperature, wind velocity and direction, and other potential internal and
external building effects.
CFM
SUPPLY TERMINAL
ROOM
CONTROLLER
VARIABLE
VOLUME
FUME HOODS
EXHAUST
ROOM
GENERAL
EXHAUST
CFM
CFM
CFM
VESTIBULE
CFM
FUME HOOD
CONTROLLERS
Figure 14. Room Dual Pressurization Control by Airflow Tracking.
An additional benefit of a cascaded control arrangement is that the room differential
sensor enables providing local indication and also remote monitoring of the specific
static pressure difference between the laboratory room and the adjacent area.
Dual Pressurization of Laboratories
In some instances, it is necessary to ensure that a laboratory room does not become
contaminated by airborne impurities emanating from adjacent areas. Common
examples include animal surgery rooms and laboratories with microelectronics that
must maintain a clean environment and would be adversely affected by an inward
airflow. When the room atmosphere presents no danger to adjacent areas, positive
room pressurization can be maintained by either the control methods described
previously (airflow tracking generally being the preferred method).
70 Siemens Building Technologies, Inc.