Total Exhaust Biosafety Cabinet Upgrade at Research Facility Provides Significant Energy Savings

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Courtesy of The Baker Company

When Harvard’s Biology Research Infrastructure (BRI) facility opened in 2006, they required four biological safety cabinets to provide primary containment during animal procedures. In the selection process, workspace containment and isolation requirements, operation modes for non-use periods and maintenance, building integration, and the energy burden to the building system were all considered. Choosing a cabinet that provided the level of safety required while at the same time offering energy-efficiency was of utmost importance. Ultimately, four Class II Type B2 (total exhaust) biosafety cabinets were installed.

In October 2007, Harvard joined 32 institutions across the country to participate in the Billion Dollar Green Challenge. The program, which invites colleges, universities and other nonprofit organizations to invest a total of one billion dollars in energy-efficiency upgrades, creates revolving funds that can be used for energy-efficiency projects that reduce energy consumption on campuses. The money saved is reinvested in future projects.

Energy efficiency has been a focus for BRI since it opened, and with these funds available, the Manager and Director of Animal Facilities decided to consider upgrading the facility’s five-year-old biosafety cabinets to more energy-efficient models. Type B2 cabinets exhaust 100% of the downflow and intake air into a facility’s HVAC system through a hard duct connection and require a relatively high amount of energy to operate. In the past five years, innovative improvements to cabinet technology have resulted in significant reductions in energy consumption.

Following a risk assessment, an investigation of building control integration, and a return on investment study, BRI determined it could save almost $3,000 in energy costs per cabinet, per year by replacing the original Class II Type B2 cabinets.

Risk Assessment
A portion of the BRI facility is a Biosafety Level 2 laboratory, and much of the work done there is postdoctoral research. Use of isoflurane is prevalent, along with the use of paraformaldehyde when perfusions are performed.

Because these gases are present, the risk assessment determined that Class II Type B2 total exhaust biological safety cabinets were the appropriate engineering control for the vivarium. The airflow in a Class II Type A2 cabinet is not well suited for work involving large quantities of vapors. Because of its recirculating airflow pattern, the concentration of hazardous vapors within the cabinet can increase to potentially unsafe levels.

A total of four biosafety cabinets were required - two were installed in a lab space for perfusions and two were installed in an animal holding suite for use in sterile procedures.

Building Integration
Class II Type B2 cabinets provide no air recirculation within the work area and must be hard-connected to an HVAC system. The HVAC system supplies air to the lab and provides sufficient exhaust airflow and static pressure to maintain proper biosafety cabinet operation. When a total exhaust cabinet drives the number of air changes required, it can add significantly to power consumption.

When originally installed, the static pressure of the biosafety cabinets was reduced by removing the exhaust filters. This lowered the work required to exhaust the air, and helped reduce energy consumption.

Because the exhaust filters were removed, the units were technically no longer classified as biosafety cabinets; however, the cabinets met the needs determined by the risk assessment. Both containment and building integration requirements would be maintained, and an exhaust dispersion study showed adequate dilution of the effluent. The cabinets were labeled to advise operators that no exhaust HEPA filters were present.

Flexibility of design and ease of building integration were important considerations for the new cabinets. The existing cabinets exhaust from the top right-hand side of the cabinets, and the new cabinets exhaust from the center. To open up the hard ceiling and move the duct work would add significant cost to the project. The manufacturer was able to customize the new cabinets to match the existing exhaust drops. This makes installation much easier and less expensive because no renovation is required.

Data Collection For Energy Comparison
When the facility’s director began looking for new energyefficient cabinets to replace the existing ones, he began trending airflow data to and from the four cabinets. Based on the volume of air being supplied to the lab, each cabinet, which typically ran for 12 hours a day and was turned off for 12 hours, exhausted a total of $5,863 of conditioned air.

This data was added to the other energy consumption costs associated with the biosafety cabinets, and then compared to the requirements of the new biosafety cabinets. Results showed that the facility would decrease operating costs by about $3,000 per cabinet, per year after the upgrade (see Energy Consumption Comparison Model).

Energy Balance In Biosafety Cabinets
To reduce energy consumption of a total exhaust biosafety cabinet, both the plug load of the cabinet and the energy used by the HVAC system must be considered. The HVAC system requires energy to supply and exhaust air, which is affected by the volume of air required and static pressure.

The new total exhaust biosafety cabinets to be installed at the BRI facility reduce energy consumption by lowering all three of these requirements: plug load, volume of air exhausted, and static pressure.

An energy consumption comparison model was created to calculate the savings that BRI could realize by installing the new biosafety cabinets. Trend exhaust data for the existing cabinets was provided by BRI and compared to the energy requirements for the updated biosafety cabinet design.

A. Conditioned Air Energy Costs
The cost to condition and supply the make-up air to the lab is calculated by multiplying the amount of flow (CFM) required by the lab’s average cost per CFM. As seen in the chart, this is the most significant energy cost (and opportunity for savings) for the biosafety cabinets at BRI. The new biosafety cabinets take advantage of an optimized airflow and low-flow mode to achieve these results.

B. Cabinet Plug Load
The cost of cabinet power is simply the total watts (volts x amps) necessary to run the unit’s motor / blower converted to kilowatt hours (kWh) per year (W / 1000 × 24 hours × 365 days). In this comparison, the local electricity rate ($0.15 / kW/hour) was used. An energy-efficient motor / blower system allows the new biosafety cabinets to realize these savings.

C. Exhaust System Power
The building exhaust system needs to provide sufficient exhaust airflow and static pressure to maintain proper cabinet operation. Fan Affinity Laws were used to calculate the power (measured in horsepower) required for a facility to exhaust a biosafety cabinet using the cabinet’s exhaust flow rate (CFM) and static pressure, as well as the fan efficiency. The cost was calculated using the local electricity rate ($0.15 / kW/hour).

BRI will continue to trend data, which will be compared to the base-line established for this comparison, so that actual savings can be determined. Estimated payback of the system is expected to be about three years. This is based on the Energy Consumption Comparison Model discussed here, capital equipment costs, and installation costs (minimized due to the exhaust position customization) of the new cabinets. The Harvard BRI facility submitted the project to the NSTAR Retrofit Program, a program from the local electricity company that provides rebates and cost sharing funds for projects that reduce energy consumption at existing facilities, and the project was approved.

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