Basic Documentation

Chapter 2–Goals of the Laboratory Environment
Room Ventilation Rates
Standards, codes, and various regulatory agencies have established minimum requirements
for most laboratory ventilation functions. The first one that we’ll discuss is the minimum room
ventilation rate that must be provided to attain an acceptable overall laboratory room
environment. Virtually all regulatory agencies and standards address this issue and require
that laboratory rooms have a room ventilation rate that substantially exceeds the rate
required for non-laboratory occupancies.
However, there is no way of reliably knowing specifically what chemical or airborne
substances will be present and at what concentration in a given laboratory room. Further,
laboratory rooms can be subjected to unpredictable combinations of airborne agents, thus
resulting in a still more complex and indeterminate situation. For these reasons, no
scientifically based process exists at this time to specifically determine the appropriate
ventilation rate necessary for a given laboratory room. Therefore, there are variations
between the requirements of different regulatory agencies and standards organizations.
The American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE),
a preeminent standards organization with regard to ventilation, has established and
published minimum ventilation rate recommendations for an extensive list of different
occupancies including various laboratory rooms. However, before reviewing these
recommendations, it is important that the reader understand how a room’s ventilation rate is
determined.
Ventilation Air
The ventilation air that is provided to a room is sometimes called the room supply air or room
makeup air. Regardless of what it’s called, it is typically comprised of two components, the
first being the fresh air or outside air. Ventilation rates for rooms that do not normally involve
chemical fumes (for example, offices, auditoriums, libraries, classrooms, etc.) are primarily
based on supplying a sufficient amount of fresh air per occupant. The basic intent is to
ensure sufficient breathing air and thus prevent the carbon dioxide (CO
2
) level from
becoming too high. In most cases, a maximum occupancy is established based on the size,
type and purpose of a room and the ventilation rate can therefore be determined based on
providing a certain amount of cubic feet per minute (cfm) per person.
The second component that must also be addressed when designing a ventilation system is
determining the total amount of room supply air needed to maintain the required room
ambient temperature and humidity. If a room has a relatively low occupancy, the low amount
of fresh outside air required to satisfy the ventilation component might not be able to also
maintain room ambient comfort. The common solution for non-laboratory room applications is
to satisfy the total room supply air requirements by recirculating some of the air that is being
exhausted from the room and combining it with the required amount of fresh air for
ventilation.
4 Siemens Building Technologies, Inc.