Lab research facilities are energy-intense building types due to the vast amounts of 100 percent outside air required. With today’s concerns over high energy expenses, reducing carbon footprints, and efforts to make facilities green and provide better indoor environments, reducing both new and existing lab and vivarium facility energy expenses has become a critical challenge. The primary reason behind many labs’ high energy expenses is the minimum ventilation or air change requirements that often dominate the amount of outside air required by these facilities. To date, very little objective data has been available on the environmental and energy savings impact of both reducing and varying air change rates. To address this gap, a major research study was conducted that generated a significant amount of objective data on the indoor environmental quality (IEQ) conditions of labs and vivariums that are using the dynamic control of air change rate.
Opportunity for optimization
The study is believed to be the largest one done of laboratory and vivarium IEQ conditions, covering over 1.5 million hours of lab operation from over 300 lab areas at 18 different facilities. In total, over 20 million sensor values were collected and analyzed, including data on total VOCs (TVOCs), particles of a size range of 0.3 to 2.5 microns, carbon dioxide, and dew point (absolute humidity). These sites consisted primarily of life sciences- and biology-related areas, as well as a smaller amount of chemistry and physical sciences lab areas.
In addition to dramatically reducing the number of sensors needed to implement this concept by a factor of nearly 30, this multiplexed sensing concept can measure different contaminant or parameter levels much more accurately. Typically, for controlling the lab room space airflow and IEQ , it is 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 offset drift error of the sensor will be the same for both measurements, since the sensor is the same for both measurements and the offset drift error of each is cancelled out.
Another parameter that can cause an increase in the minimum air change rate is particles in the lab. This could be due to a reaction that goes out of control, or an acid spill that causes an evolution of smoke, or an aerosol in the lab room. Figure 3 shows a graph of the average level of 0.3- to 2.5-micron particle counts (PM2.5) that exceeded a background level of the lab room’s supply air for all the different sites of the study.
The fourth figure depicts that the average lab room (dotted black line) is above the 1 million per cubic foot threshold almost 0.5 percent of the time, or about 30 minutes a week, on average. The individual sites show a range of values from near zero up to about 1.5 percent of the time that airflow should be increased based on a particle event. If this amount of time is added to the time that TVOCs are above the control threshold, this adds up to only 1.2 percent of the time, on average. In other words, minimum air change rates of between two and four ACH can be achieved from 97 percent to in excess of 99 percent of the time due to the presence of either TVOC or particle events occurring up to about five hours a week, on average.
American Industrial Hygiene Association (AIHA). 2012. Laboratory ventilation. ANSI/AIHA Standard Z9.5-2012. American Industrial Hygiene Association, Fairfax, VA.
American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE). (2011). ASHRAE handbook - HVAC applications, Chapter 16, Laboratories (pp. 16.1 to 16.22), Atlanta, GA: ASHRAE, Inc.
Like this article? Click here to subscribe to free newsletters from Lab Manager