A Study of Factors Affecting Fume Hood Energy Consumption

Joseph S. Marian, Jr., American Auto-Matrix

Introduction

It is well known throughout the HVAC industry that laboratories and fume hoods are generally the largest consumers of energy in a facility. Volumes of information have been written and many studies have been performed outlining the substantial amounts of energy that laboratories and fume hoods consume over the lifetime of their operation. Various industry estimates put the energy consumed by a single fume hood in a year to be 1 to 3.5 times that of the average residential home. In most cases, the air required for the operation of the fume hood is totally exhausted out of the ventilation system due to the hazardous particles and/or gasses it may contain. This forces new makeup air to be introduced into the system, which requires a considerable amount of energy to condition. In regular HVAC ventilation systems designed for comfort, the system is typically designed so that a percentage of the air required by the system is “recycled” and the tempered return air is not being wasted to the atmosphere, thereby keeping energy costs lower.  

The continuous operation of laboratory and fume hood exhaust fans and the speed at which they operate to maintain the desired static pressures and volumetric flow rates, is also an area where a reduction in energy consumption can be realized. Many laboratory and fume hood exhaust fans in industrial or research facilities operate 24 hours a day, seven days a week.  The ability to lower the design static pressure setpoints and employ various control strategies of these continuously operating laboratories and fume hoods, equates to potentially lower fan operating speeds and exhausted CFM. 

Since recycling exhaust air and intermittent HVAC equipment operation are not luxuries afforded in the operation of many laboratories and fume hoods, it is necessary to take into account some specific areas when designing or retrofitting a laboratory and fume hood exhaust system.   

1. Laboratory and fume hood HVAC operational system static pressure requirements.  
2. Fume hood exhaust duct size.  
3. VAV vs. CAV operation of the fume hood exhaust. 
4. Control air valve selection. 

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Biography

Joseph S. Marian, Jr., is the director of application engineering and critical environments product manager for American Auto-Matrix. Mr. Marian has extensive experience in RHVAC controls, where he has held a broad range of positions, including technical trainer, product manager, application engineer, and systems integrator. Mr. Marian was a sergeant with the U.S. Air Force, where he was responsible for maintaining critical RHVAC and power generation systems for the Minute Man nuclear weapons system.