area to create distinct sensor signals
used for traditional monitoring and
control. Typically, 20 to 30 areas can be
sampled with one set of sensors approximately every 15 minutes, depending on
the requirements for those spaces.
A variety of different types of sensors
can be used to analyze the air samples
for multiple air parameters. Figure 1
shows an example of the architecture of
the multiplexed sensing system used to
implement the study.
This multiplexed sensing concept
reduced the number of sensors needed to
implement this methodology by a factor of
nearly 30. It also improved the accuracy of
different contaminant or parameter measurements. For controlling the lab room
space airflow and IEQ it is usually best
to look at the contaminant levels in the
room differentially, subtracting the contaminants in the supply airflow from the
exhaust or room levels. Any sensor offset
drift error will be the same for both measurements, since the sensor is the same for
both measurements. That means the offset
drift error of each is cancelled out.
LABS ARE CLEAN
Study results, shown on Figure 2, con-
cluded that labs are typically “clean” of
most chemical contaminants about 99.2
percent of the time. This suggests that
facilities will save energy by operating at
reduced minimum air change rates the
majority of the time with respect to the
Figure 3 shows the average TVOC
level percentages for multiple lab sites.
Even at the site with the greatest amount
of TVOC activity, the dynamic control
concept can still save energy about 97
percent of the time.
Particles are another parameter that
can cause an increase in the minimum
air change rate. This could be due to a
reaction that goes out of control, an acid
spill that causes an evolution of smoke,
or perhaps an aerosol into the lab room.
The graph on Figure 4 shows the percentage of time that small particle levels
exceed the threshold at various lab sites.
The average lab room (shown by the
dotted black line) is above the 1 million
particles per cubic foot (PCF) threshold
about 0.5 percent of the time, an average
of only about 30 minutes per week.
The information indicates that airflow
should be increased based on a particle
event from a low of nearly zero percent
of the time to about 1. 5 percent of the
time. If one adds this to the time TVOCs
are above the control threshold, it adds
up to a need for increased airflow for
only an average of 1. 2 percent of the
time, an average of up to about 5 hours
LOWER FLOW RATES
TVOC and particle events that require
high ventilation rates occur only a few hours a
week. Minimum air change rates of between
2 to 4 ACH are adequate to handle either
TVOCs or particle events from 97 percent to
more than 99.0 percent of the time. The study
indicates that facilities can use much lower
flow rates with an automatic demand-based
ACH rate control system.
One example is the Aircuity 2.0 platform, which was designed for research
laboratory facilities looking to significantly reduce energy costs, monitor
space conditions and occupant behavior,
and achieve quantifiable savings that
can be reinvested in research. The web
and desktop apps give laboratory facility
managers implementing airside efficiency actionable insights, transparency, and
accountability. Moving beyond simple
data trends, the platform offers deep
analytics of cost and energy savings,
indoor environmental quality responses, and occupant behaviors. The user
Figure 3 shows the average TVOC level percentages for multiple lab sites.