Basic Documentation

0
10
20
30
40
50
60
70
80
90
CAV-1 CAV-2
100
LAF-1 LAF-2
VAV
OC UN OC UN OC UN OC UN OC UN
0
10
20
30
40
50
60
70
80
90
CAV-1 CAV-2
100
LAF-1 LAF-2
VAV
OC UN OC UN OC UN OC UN OC UN
Figure 1. Comparative Energy Consumption Characteristics for Laboratory Ventilation Systems
During the OC (Occupied) and UN (Unoccupied) Times of the Day.
Low Air Flow (LAF) 1 & 2-Position
LAF 1 & 2-Position ventilation systems are basically
CAV systems that achieve a lower ventilation airflow
in conjunction due to the use of Low Air Flow
1
chemical fume hoods. Like the CAV system, a LAF
system can be implemented as a 1-Position or 2-
Position type of system. Since it is basically a CAV
type of system, it is not overly difficult to design, but
it does require some amount of associated airflow
control to ensure proper and safe operation. Also,
because it is critical to ensure that the proper level of
airflow is maintained, LAF systems require
significant vigilance by support personnel. Low Air
Flow fume hoods generally have a considerably
higher initial cost than conventional fume hoods,
which is an important factor in considering the
overall life cycle cost. As with the other types of
systems, an LAF type of system can be an optimum
choice in certain applications.
Page 2 of 10 Siemens Industry, Inc.
Document No. 149-980
1. Low Air Flow fume hoods typically consume about 60% of
the airflow of conventional CAV fume hoods. However, the
concept of LAF fume hoods is relatively new and has not yet
received wide acceptance within the industry, nor have they
established a history of satisfactory implementation and
performance.
Variable Air Volume (VAV)
A VAV ventilation system is intended to provide just
the right amount of airflow through a laboratory room
and its fume hoods 24 hours a day and 7 days a
week. It requires a careful ventilation system design
and a sophisticated airflow control system. It also
requires knowledgeable staff personnel to monitor
and operate the VAV system. The major benefit of
the VAV system is that it is the most energy efficient
since it can reduce energy usage whenever a fume
hood sash is not fully open. In other words, it has the
potential to reduce energy consumption continually
and not just when a laboratory room is unoccupied.
VAV also provides much operational flexibility since
fume hood face velocity and other ventilation
parameters can be easily reset as needed. A VAV
system can also achieve a lower ventilation related
room sound level since it keeps the airflow at the
minimal level. In many instances the VAV ventilation
system is the optimum type of system due to the
potential energy savings and operational flexibility.