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Diagram showing the components of a DCV system, including sensors, an air data router, and an information management server that communicates with the building management system via BACnet. Images courtesy of Aircuity
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The growth of sustainable building, even over the past year, has been unprecedented. From new construction to retrofits, all construction—especially on our nation’s college and university campuses—has a strong green element to it these days. No matter the type of facility—administrative offices, science buildings, sports arenas—schools are looking for ways to improve sustainability, lower energy costs and limit their carbon footprints.
As organizations strive to find new approaches to making their facilities green, one area recently gaining significant attention is building ventilation. This issue has more often been discussed in terms of providing a safe and comfortable environment that enhances user productivity. This is even more important in lab facilities, where protections need to be built into any ventilation system since procedures generate unwanted chemicals or contaminants that can get into the breathing air.
Taking the cue from commercial construction, the owners of R&D facilities have begun to see the real energy and cost advantages to changing the way their buildings are ventilated. Administrators and managers had long been afraid to touch these systems, fearing safety compromises.
Typical lab ventilation systems work on the principle that there should be continuous high levels of airflow, just in case contaminants are present. However, numerous studies have shown that the demand for full design airflow to dilute contaminants occurs very infrequently. One study that analyzed more than 1.5 million aggregate hours across multiple lab facilities showed that the design airflow was only needed 2% of the time. In other words, it is very rare for there to be a need for full, constant ventilation. Providing full airflow for the other 98% of the time only results in wasted energy, since perfectly clean air is merely replaced with equally clean supply air.
Smarter flow with demand control
A smarter approach to regulating ventilation is to make sure that the ventilation is based on actual demand or usage. With a demand control ventilation (DCV) approach, advanced technology continuously measures the indoor environmental quality and then varies the amount of air brought into the lab throughout the day.
DCV implementations respond not only to changes in carbon dioxide levels, but also to the real-time levels of multiple contaminants in a space. A multi-parameter DCV approach enables the system to not only save energy when occupancy levels are low and the air is “clean” but also to increase the fresh air supply when needed to dilute contaminants. When they are present, ventilation runs at higher levels. When the system determines that the air is free of contaminants, airflow through the space can be greatly reduced, resulting in a significant and meaningful reduction in energy.
DCV in action at Cal Poly
The Center for Science and Mathematics at the California Polytechnical Institute, San Luis Obispo, recently received an award at the California Sustainability Conference for a design that included a number of green features. The school was recognized for its lab HVAC design, which not only reduced its energy costs and improved its carbon footprint, but also reduced the first cost of the new building.
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Air from lab areas is drawn to a sensor suite, measuring such common parameters as CO and CO2, as well as relative humidity, total volatile organic compounds (TVOCs), and particles.
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The HVAC design combined the use of chilled beams to handle the thermal load with a DCV system (OptiNet, provided by Aircuity Inc.), which allows lab dilution air to be varied based on contaminant levels. The system uses advanced environmental analysis technologies to determine when the ventilation in individual labs should run at full design levels by monitoring the air for contaminants generated by normal procedures or spills.
The school’s advanced air sampling system, combined with lab-grade measurement instruments, carefully analyzes the air within the individual spaces. Each space is monitored for volatile organic compounds (VOCs), particulate levels, carbon dioxide (CO2) and moisture levels using multiple instruments and sensing technologies. The analysis leads to a signal being sent to the laboratory airflow controller, which adjusts general ventilation to appropriate levels while continuing to maintain the necessary room pressure relationships and providing make up air to hoods as they are opened.
In simple terms, the system says “contaminants present—increase the airflow,” or “clean lab air—run at reduced levels.”
Reducing “first cost”—an added benefit
Cal Poly also realized an additional benefit: lowering the overall capital cost of the project. The reduction in “first cost” comes from the fact that there will never be an instance when all of the facility’s labs are demanding new airflow at the same time. While each individual lab is designed to handle a high volume of air such as 10 or 12 air changes per hour (ACH), the primary components do not need to be sized to supply such levels to the entire building all at once. This leads to smaller primary fans and smaller main distribution ducts; even the building penthouse is smaller.
Ted Hyman, FAIA, a partner with ZGF Architects LLP, Los Angeles, mentioned during the panel discussion following the award presentation that the design team was able to eliminate 1 ft from the floor-to-floor height, in turn reducing the entire height of the building and thus the construction cost. Engineer Peter Rumsey of the Integral Group, PE and fellow of ASHRAE, mentioned that the OptiNet system was added to the design as part of the value engineering process. Evaluations showed that including this technology to manage ventilation based on demand resulted in an overall reduction of $715,000 to the first cost.
In summary, not only are there substantial energy and carbon-footprint reductions to be realized from improving a lab facility’s ventilation system, but these reductions can also be achieved in a way that also reduces both the first cost of the building and the ongoing costs of maintaining a healthy, safe and productive environment.
Robert Brierley is the COO and president of the smart airside-efficiency company Aircuity Inc., Newton, Mass. (www.aircuity.com). The company’s proprietary technology is the linchpin of the OptiNet DCV system discussed in this article.
Published in Laboratory Design newsletter: Vol. 15, No. 11, November, 2010
