ASHRAE Journal - February 2010 - 32

EQ 3.2 credit for flush-out of an office building after construction, which is Sensor Suite based on certain EPA and Washington Information Knowledge Center Management state requirements. This is a conservative CO Server CO2 threshold when used with labs for control Internet RH of air changes since the study data in this TVOCs Particles article shows primarily infrequent shortWeb User Interface term exposures of VOC events versus a BACnet Air Data Interface Router constant level of VOCs from off-gassing of construction materials. Typical values for the particle level Web Accessible Reports threshold are about 1 million pcf or particles per cubic foot (35.3 million particles/ m3), and similarly this particle requireRoom ment was also set with guidance from Sensor the LEED EQ 3.2 credit’s average value threshold for flush-out after construction, which is about 1.6 million pcf (56.5 million particles/m3). Setting the minimum Figure 1: Facility-wide multiplexed sensing architecture. control threshold level at 1 million pcf (35.3 million particles/m3), again provides a slightly more also can be used to sense the lab and vivarium rooms for other conservative threshold level for the lab ach control approach. control and monitoring purposes. One approach to economically and reliably sense environmental conditions in many labs and vivarium rooms of Methodology of the Study and Data Analysis a facility is to use a novel sensing architecture known as In addition to being used for control purposes, the multimultiplexed sensing. With this approach, one central set of plexed sensing system of Figure 1 also sends its sensing data to sensors is used in a multiplexed fashion to sense not one but a password-protected Web site to be archived and made available many different rooms or areas. Instead of placing multiple for review and analysis purposes by facilities and other qualified sensors in each room, this networked system routes packets, personnel. One use of this information is to assess the environor samples of air, sequentially in a multiplexed fashion to a mental and energy savings impact of demand-based control of shared set of sensors. air changes in a specific facility. To get a broader view of the Every 40 to 50 seconds a sample of air from different areas efficacy of this concept across not just one, but many facilities, is routed through a common air sampling backbone consisting a comprehensive research study was undertaken to analyze of a hollow structured cable to the centralized set of sensors the archived data from many different lab and vivarium sites. (known as a sensor suite) for measurement. These sequential This study was conducted using environmental data from 18 measurements are then “de-multiplexed” for each sampled area different lab and vivarium sites across the U.S. and Canada. Of to create distinct sensor signals that can be used for monitoring these sites, six were from the East Coast, seven from the Central and control. Typically, 15 to 20 areas can be sampled with one U.S., three from the West Coast, and two from Canada. These set of sensors approximately every 15 minutes, which theoretical sites consisted primarily of life sciences and biology-related and empirical spill testing7 has shown meets the time require- areas, as well as a smaller amount of chemistry and physical ments for the safe, demand-based control of these spaces. sciences lab areas. Three of the above sites involved animal This multiplexed sensing approach (Figure 1) can measure facilities that were broken out as a separate group. Almost all of many different air parameters. For laboratories, the use of a PID the lab facilities involved spaces with a moderate or low density type of TVOC sensor is beneficial for accurately detecting hun- of fume hoods. In total, more than 300 lab and vivarium rooms dreds of commonly used laboratory chemicals that can volatize were involved in the study, representing a large cross-section and become a safety concern. Additionally, other nonorganic of different lab room environments. compounds (such as ammonia, which is of interest in vivarium Approximately 1.5 million operating hours of lab data and rooms) can be detected with a PID sensor. Other TVOC sensors about 100,000 hours of vivarium data were analyzed. If only such as metal oxide (MOS) sensors are used in addition to the one lab room was studied versus more than 300, the number PID sensor for broader detection of chemical contaminants. of operating hours would have spanned over 18 decades. The Combining these sensors with a laser-based particle counter data from the various sites was for different lengths of time allows the identification of particles, which can be used as a depending on when the site came online. Data was analyzed proxy for animal allergens in a vivarium, as well as for detect- for lab operation in a range starting in the early fall of 2006 ing aerosol vapors and smoke particles in a lab room. Carbon and continuing until early January 2009. In total, more than 20 dioxide sensors and accurate dew-point or humidity sensors million sensor values were collected and analyzed including 32 ASHRAE Journal ashrae.org February 2010

ASHRAE Journal - February 2010

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