Laboratory ventilation design plays an outsized role in the planning of educational institutions. Though safety is the primary purpose of any laboratory fume hood, there is an ever increasing demand for hoods to also have a reduced impact on the environment, as well as a lower cost to operate.
These demands are understandable, considering a single traditional 6-foot fume hood operating at a 100 feet per minute (fpm) face velocity, with the sash fully open, will consume 70,800 cubic feet of valuable tempered air every hour. That’s air that the institution has already paid to heat or cool, and in some cases sanitize and treat for humidity. That same fume hood costs approximately $8,260 per year to operate. In the typical laboratory, the fume hood is the largest consumer of energy and can expend more energy annually than three average American households.
The need for more energy efficient fume hoods has resulted in the implementation of various energy reducing developments for fume hoods, such as high performance fume hoods, variable air volume (VAV) mechanical systems, and ductless fume hoods. Knowing all of the available options is one thing, but determining the right option for a specific facility can seem like a daunting task. The following sections offer an overview of each of these options and the effect they can have on energy reduction.
High Performance Fume Hoods
One of the most powerful tools to reduce energy consumption is the implementation of high performance hoods in the laboratory. The purpose of a high performance fume hood is to provide the highest level of containment at the lowest possible cost to operate. Synonyms for this type of hood include low velocity or high efficiency hoods. These types of fume hoods rely on containment-enhancing features such as specialized baffles, aerodynamic shapes at the front of the fume hood, and many others.
These features contribute to the ability of the fume hood to contain very well with dramatically reduced airflows. When compared to conventional fume hoods, which are typically operated at a 100 fpm face velocity, high performance hoods provide as good (or better) containment at face velocities as low as 60 fpm. SEFA (Scientific Equipment and Furniture Association) defines the containment requirements of a high performance hood to be tested at face velocities no greater than 60 feet per minute (fpm) while maintaining a full open sash of 25 inches or greater. This ability to contain at high levels at reduced face velocities means less air needs to be exhausted through the fume hood, thus providing a direct reduction in energy consumption associated with a HVAC system.
Variable Air Volume (VAV) Systems
Variable Air Volume (VAV) systems feature whole-building ventilation automation. These systems go far beyond controlling the airflow through a fume hood.
Modern VAV systems simultaneously maintain the safest minimum fume hood face velocities regardless of sash position. They can also ensure minimum room air changes per hour are met, hold specific laboratory pressurization, and maintain the desired temperature and humidity. In short, these systems maximize comfort and safety while minimizing the energy consumption by cutting the demand for air as the fume hood sash closes, consequently minimizing operating cost.
Unfortunately, there is no energy consumption/operating cost benefit to a VAV system unless the operator of the fume hood closes the sash, reducing the demand for tempered air. For this reason, automated sash closure systems are often used in conjunction with VAV systems. These systems typically use an occupation sensor which, when no motion is sensed for a set period of time, tells the fume hood sash to close automatically, resulting in the reduction of air being exhausted. When no one is detected for the entire pre-selected delay time, the sash will close.
Pairing a VAV system with an automatic sash closure system will ensure that the sash is closed when the area is unoccupied, and encourage minimal sash openings when occupied, thus taking advantage of every possible opportunity to reduce the air volume demand. The result, especially when coupled with a high performance fume hood, is a dramatic reduction in energy consumption and noticeable savings.
Ductless Fume Hoods
As the name implies, ductless fume hoods are not connected to an exhaust system. These hoods utilize specialized carbon filters to trap vapors and fumes before air is recirculated to the room. The filters are usually made of specially-treated activated carbon media that treat or adsorb chemical fumes, including certain organic solvents, ammonia, acids and formaldehyde. Since these enclosures recirculate filtered air back into the laboratory, all of the valuable tempered air that is in the building, stays in the building. The benefit to the HVAC system is clear here. With the elimination of exhaust air associated with the fume hood comes the elimination of supply air associated with the fume hood.
To continue to ensure the safety of laboratory personnel, these hoods often have a built-in mechanism to alert the user of unsafe concentrations of chemicals detected in the exhaust area of the filters. For this reason, there are some applications that aren’t compatible with carbon filtration, but these applications are typically reviewed by the manufacturer prior to the fume hood being purchased. In an approved, compatible application, these hoods can be an excellent solution for any building attempting to reduce the energy costs associated with their lab spaces.
Finding Answers
Make safety first in your laboratory planning. The safety of your personnel, lab technicians and others in your lab should always be the guiding principle in laboratory design. With that focus on safety in mind, ensure that your lab planning team consults ventilation experts with the best available expertise in lab ventilation safety and efficiency.
