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 4–Ventilation Systems Classification
As the air passes through the laboratory room it provides the required room ventilation (ACH)
rate. In cases where the room has chemical fume hoods, biological safety cabinets that are
exhausted outdoors, or other types of exhaust needs, the supply air also provides the
makeup air for the amount exhausted from these containment units. After passing through
the room and/or the containment units, the air is exhausted out of the laboratory facility by the
exhaust system.
Most codes do not permit the recirculation of any laboratory exhaust air as return air for
ventilation purposes. Those codes that do permit this require removal of all contaminants
from the exhaust air. Because of the difficulty of ensuring all contaminants are removed and
the potential high costs likely to be involved, air exhausted from laboratory rooms is not
normally reused or re-introduced into the ventilation system.
ROOM TERMINAL UNIT
LABORATORY ROOM
REHEAT
COOLING HUMIDIFICATION
FILTERING
OUTSIDE AIR
EXHAUST
S Y S T E M
HEATI NG
SUPPLY
FAN
C A V F U M E H O OD S
GENERAL
EXHAUST
PRIMARY AIR HANDLING UNIT
Figure 1. CAV Ventilation System Applied to Ventilate a Chemical Laboratory Room.
In the case of a laboratory room with CAV fume hoods, (see Figure 1), some air leaves by
means of the general exhaust provision in the room ceiling; however, most of the room air
actually leaves by through the fume hoods since CAV fume hoods exhaust a relatively large
amount of air. The amount of makeup air brought into the room that is necessary to replace
the air exhausted by the fume hoods often exceeds the amount of air necessary to provide
the required number of room air changes per hour. Therefore, ventilation system designers
must be sure to determine the makeup air requirements for the fume hoods as well as any
other containment units or specialized exhausts that will be in the laboratory room. The
amount of ventilation air to be supplied to the room must be sufficient to makeup air for the
totalized exhaust of the room and not just meet the required room ventilation rate.
14 Siemens Building Technologies, Inc.