Another important aspect of the change
in the current air change standards and
guidelines is the move away from a prescriptive approach to a more performance-based
approach. In fact, the ANSI/AIHA Z9.5-2012
Laboratory Ventilation Standard states that
“An air exchange rate (air changes per hour)
cannot be specified that will meet all con-
ditions.” Similarly the ACGIH (American
Conference of Governmental Industrial
Hygienists) Industrial Ventilation Handbook
states that “ …‘Air changes per hour’ or ‘air
changes per minute’ is a poor basis for venti-
lation criteria where environmental control
of hazards, heat and/or odors is required. The
required ventilation depends on the problem,
not on the size of the room in which it occurs.”
The 2011 version of NFPA 45 Standard on
Fire Protection for Labs Using Chemicals has
also changed its language on air change rates
By Gordon P. Sharp
Guidelines and standards for minimum air change rates in labs and vivariums have changed over the last few years.
More than 10 years ago, minimum air change
rates were commonly set prescriptively at 8 to
12 air changes per hour (ACH). However, with
increasing concerns over rising energy costs, the
pendulum on air change rates swung to lower
prescriptive rates to 6 ACH. More recently, the
pendulum has begun to swing back, with recent
research showing that a significant increase in
dilution and clearing performance is achieved
by increasing air change rates from 6 ACH to
a minimum of 8 ACH, but with diminishing
returns above 12 ACH. As Chapter 16 (Labs)
of the 2011 Edition of the ASHRAE HVAC
Applications Handbook states, “…This information indicates that minimum ventilation
rates at the lower end of the 6 to 12 ACH range
may not be appropriate for all labs”.
• The lab has two wings in an L-shape configuration, separating the office function from
the lab. This allowed a separated air system
for the lab so the common areas and offices
incorporate natural ventilation (Figure 1).
• The design’s primary feature keeps sun
off of the walls of the lab while allowing
diffusion of daylight into the lab. The roof
has a wide overhang that works in concert
with an open CMU sunscreen common to
Mozambique. Figure 1, Target 1(T-1).
• The sunscreen enclosure creates a natural
utility distribution corridor, keeping utility
distribution outside of the lab spaces. Figure
1, Target 9 (T- 9).
• A clearstory enclosed in translucent panel
admits light with reduced heat with a light
shelf that bounces light into the adjacent
instrument lab. Figure 1, Target 2 (T- 2).
• Soffit forming the plenum also directs light
to diffuse through interior glazing. Figure 1,
Target 7 (T- 7), Target 8 (T- 8).
• The lab ventilation system is designed as a
single-pass supply with digital scroll compressor to operate efficiently during part-load conditions. Air supply and exhaust is
controlled by a VAV system. Figure 1, Target
3 (T- 3), Target 5 (T- 5).
• Natural ventilation will be incorporated into
the lab design to remove heat. The operable
windows are designed to operate based on outdoor and indoor conditions. Occupancy sensors were implemented to control the amount
of ventilation and lightening to minimize energy consumption. The section shows how the
clearstory collects heat for direct ventilation to
the exterior. Figure 1, Target 2 (T- 2).
• The roof surface is designed to shed water
and designed as a cool roof. Figure 1, Target
6 (T- 6), Target 10 (T- 10).
1. Tropical climates present extremes of heat,
humidity and glare. A good design uses
passive sustainability techniques in order to
reduce the stress on the technology maintaining an acceptable interior environment.
2. Along with the challenges of designing in a
tropical climate, there are also advantages.
AECOM didn’t need to worry about freezing temperatures that allowed freedom
to place piping outside of the controlled
environment. The sunscreen formed a utility distribution corridor that promotes an
efficient design. Also, personnel are accustomed to warmer interior temperatures.
3. Control the sun. Creative approaches to
building massing, plan arrangement and
exterior wall design provides passive solutions to shielding the lab from exterior heat.
4. A simple technology such as open CMU
blocks once used in this country provides
an opportunity for a sophisticated expres-
sion that admits diffuse light and shielding
the wall from heat transference.
5. Natural ventilation is problematic in a
lab because of air control. However, plan
arrangement makes it feasible to incorporate natural ventilation in the sizable common and office areas.
Thomas Serruto is an Associate Principal at AE-
COM with a specialty in lab design that has exten-
sive experience in complex, time-critical projects
and possesses a thorough knowledge of all phases of
the design and construction process for labs. tom.
firstname.lastname@example.org. David Tash is a principal
at AECOM, based in the firm’s National Capital
Office in Arlington, Vir., where he manages the
healthcare and life sciences engineering practice
at the 250-person office. He is also the AECOM
North America Lab & Pharmaceutical Market
Sector leader. email@example.com.
continued on page 34
Figure 1: Southeast view of pharmaceutical NQCL laboratory in Maputo, Mozambique and building section showing sustainable characteristics of the design
A review of recent changes in current lab ACH
rate standards, guidelines