Combining Dynamic Air Change Rate Sensing with VAV Exhaust Fan Control to Minimize HVAC Energy Consumption in Laboratories

Brad Cochran, CPP, Inc.
Gordon Sharp, Aircuity, Inc.

Many laboratory facilities have transitioned from CAV to VAV lab systems to improve their sustainability. However, do these current systems go far enough or can further improvements be made to make the systems more energy efficient and safer?

The concept of applying dynamic air change rate control to labs has been discussed at past Labs21 conferences. This demand based approach uses sensors to lower room air change rates when laboratory air is "clean" and raises the laboratory airflow when contaminants are sensed in the laboratory space. This concept can cut the average consumption of outside air in a laboratory by over 50 percent, significantly reducing the laboratory's HVAC energy requirements.

While current design strategies for laboratory exhaust fans often employ a VAV system, the systems still may operate at volume flow rates that are in excess of the lab's actual air flow exhaust requirements. The higher volume flow rates are used to prevent re-entrainment of potential laboratory exhaust stream contaminants, even when the exhaust air is "clean."

This presentation will introduce a new and innovative approach to substantially reduce exhaust fan energy consumption without compromising safety. This approach borrows a chapter from the dynamic air changes per hour (ACH) rate control concept by applying demand-based contaminant sensing and control to the exhaust fan systems. With this concept the exhaust fans typically operate at a minimum flow rate to achieve reasonable dilution levels and significantly reduced energy consumption. When a chemical and particulate sensing system detects sufficient levels of contaminants in the exhaust stream, the fan exhaust volume flow rates are increased to a maximum design level reduce re-entrainment of the exhaust at nearby air intakes. Because these systems infrequently operate at these high volume flow rates, they can be designed to higher performance standards that might be practical with a conventional CAV or VAV system.

Two case studies will be presented on the potential energy saving benefits achievable with this design approach. This will include over a year of exhaust stream monitoring data from a lab facility in Texas to demonstrate the frequency and characteristics of actual sensed events that might have required the maximum fan operating mode and the associated energy savings from running at reduced flow rates during the remaining hours of the year.

In summary, a new approach to lab exhaust fan control will be presented that changes the paradigm of lab exhaust fan design and operation. This concept promotes the principles of the Labs21 Approach to laboratory design by reducing the environmental impact of laboratories via increased energy savings and reduced first cost while maintaining or even improving occupant safety.

Biographies:

Brad Cochran, a CPP, Inc. associate, has over 15 years of experience conducting wind-tunnel and numerical modeling studies related to laboratory exhaust design. Brad has managed projects for such clients as Northwestern University, the University of California at Los Angeles, Irvine, Davis, and Berkeley; the National Institutes of Health; University of Texas Medical Center; Loyola University; Bayer; and many others. While employed at CPP, Inc. he has been instrumental in the development, and the U.S. Environmental Protection Agency's (EPA) subsequent approval, of the Equivalent Building Dimension concept. This concept provides greater accuracy in estimating concentrations due to building downwash using EPA's ISC model. He has conducted numerous wind-tunnel dispersion studies of Good Engineering Practice stack height, building ventilation, and site-specific evaluations of environmental impact. Brad has helped develop a new algorithm to describe plume trajectories under sea breeze conditions. Before arriving at CPP, Brad was involved in pollution diffusion studies for the Lawrence Livermore National Laboratories, erosion and threshold velocity studies under reduced pressure conditions at the NASA Ames Research Facility, and was involved in various pedestrian-level wind studies for an environmental group in San Francisco, California while obtaining a Master of Science degree in aeronautical sciences at the University of California at Davis. Brad has both a Bachelor of Science and Master of Science in mechanical engineering and an Master of Business Administration from Regis University.

Gordon Sharp has over 25 years of wide-ranging entrepreneurial experience and more than 20 U.S. patents to his name. From 1979 to 1985, he was vice president and co-founder of IMEC Corporation, a motor controls technology company from which he created a spin-off company called the Phoenix Controls Corporation. As president, CEO, and founder of Phoenix Controls, Gordon led the development of a $25 million venture capital-backed company. Phoenix Controls is a world leader in laboratory airflow controls that, under Gordon's leadership, was honored for three consecutive years by INC magazine as one of the 500 fastest growing private companies in America.

In early 1998, Phoenix Controls was acquired by Honeywell, Inc. Thereafter, in addition to participating in restructuring the Honeywell Home and Buildings Solutions business, Gordon led the development of a Honeywell business unit now known as Aircuity. In January of 2000, Aircuity became an independent, venture capital-backed company and today is the leading manufacturer of energy- and environment-sensing and information systems to optimize building ventilation for energy-efficient performance without sacrificing occupant comfort or health.

Gordon is the chairman and founder of Aircuity and a graduate of the Massachusetts Institute of Technology with bachelor's and master's degrees in electrical engineering. He is a member of the ANSI Z9.5 Laboratory Ventilation Standard committee and a member of the board of directors of the International Institute for Sustainable Laboratories, a nonprofit foundation, and the official cosponsor of the Labs21 2008 Annual Conference.

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