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
Containment Units
DAMPER
EXHAUST AIRFLOW SENSOR
SASH POSITION
SENSOR
VAV
FUME HOOD
CONTROLLER
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OPERATOR
DISPLAY PANEL
EXHAUST
ROOM AIR
Figure 9. VAV Fume Hood Face Velocity Control Arrangement.
A two-position constant volume bypass fume hood requires a control element
in the fume hood exhaust to reduce the exhaust during the unoccupied
period. In addition, a sash closure switch or some equivalent means of
control interlock must be added to ensure that the sash is closed before a
reduction in exhaust airflow can be made. Note that the control of a two-
position constant volume ventilation system also requires a volumetric
reduction control arrangement on the ventilation system’s primary air
handling units. This enables reducing the makeup air to the laboratory rooms
whenever the fume hood exhaust is reduced to maintain a proper balance in
the room airflow.
Due to its relative simplicity, a conversion to a two-position constant volume
ventilation system is very applicable for retrofit applications where a full
conversion to VAV is not practical.
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In new facilities VAV laboratory
ventilation systems may be a better investment in terms of maximizing
energy savings and also ensuring better fume hood containment. In either
case, the networking and communicating capability of digital controllers that
are used for VAV and two position CAV applications enables implementing a
centralized monitoring system for a facility’s laboratory ventilation systems.
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Renovating an existing facility ventilation system to obtain VAV operation typically requires changing out a substantial
portion of the ductwork along with installing the necessary airflow measurement and control devices. This may not be
practical or feasible in some facilities depending upon the investment that must be made and of course the potential
savings that can be attained.
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Central monitoring enables a systematic way to maintain data of ventilation system performance which assists in
regulatory agency record keeping requirements.
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