Basic Documentation

Siemens Industry, Inc. Page 3 of 10
Document No. 149-980
Ventilation System Functions
Regardless of the type of ventilation system they
must all fulfill five requirements:
1. Maintain necessary fume hood exhaust
airflow.
2. Provide sufficient room makeup airflow to
balance off the fume hood exhaust and
other exhausts.
3. Maintain sufficient total room exhaust airflow
to achieve the room's minimum ventilation
rate in air changes per hour
2
.
4. Maintain enough total room exhaust airflow
to allow sufficient supply airflow for
maintaining the room ambient temperature
and humidity
2
.
5. Maintain the required differential between
the room's supply airflow and total room
exhaust airflow to attain the required
negative or positive static pressurization
3
relationship between the room and adjacent
areas.
2. In rooms having only one or two small fume hoods a room
general exhaust may also be required to attain sufficient total
room exhaust airflow for this purpose.
3. Chemical laboratory rooms normally are required to be
negatively pressurized to prevent room air from migrating out
to non-laboratory areas. In some instances laboratory rooms
require positive pressurization to prevent contamination from
adjoining spaces. In such instances, an entry vestibule can
be provided and maintained at a negative static pressure to
prevent undesired transfer of laboratory room air to non-
laboratory areas and vice-versa.
Table 1 lists the advantages and disadvantages of
each type of system and provides general guidance
for the type of system most suited for different types
of laboratory facilities. All of the ventilation systems
listed in Table 1 can be designed and controlled to
meet the ventilation system function
s listed above.
The major differences lie in the cost effectiveness
and suitability of each ventilation system for the
specific application. The commentary that follows
provides details on the recommendations listed in
Table 1. Later in this document there are guidelines
for determinin
g the actual potential energy
consumption for the different types of ventilation
systems.