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Fume Exhaust Systems, Hood Technologies and Controls: Energy Conservation and Design Considerations for New and Retrofit Projects

James J. Walker, PE, Fred Hutchinson Cancer Research Center

Fume exhaust systems consume large amounts of energy and are expensive to build or modify. It's important to understand all aspects of the new one being proposed or one currently in place. Most centralized exhaust systems are fairly typical in design, but there are many options available to reduce energy consumption either in a new facility or as retrofit projects. Centralized fume exhaust system conservation projects implemented at Fred Hutchinson Cancer Center include Variable Geometry Damper, System Static Pressure Reductions, and Bypass Air Reductions. These will be discussed in addition to other options. The application of constant volume, variable volume and low flow hoods will be examined. Low flow hoods may or may not save energy in your facility, but other considerations such as infrastructure may be the deciding factor. Fume hood exhaust air valves are more critical for some hood designs than others. Which system is right for your application? Lab room pressurization control will be addressed including supply air offset and actual room pressure sensing strategies.

Findings:

When considering fume exhaust systems and related equipment or changes to an existing system, the designer should first consider whether the labs served are fume hood driven or air change driven with respect to airflow. There may be no energy saving advantage for low flow hoods in a lab that is driven by air change rates. Does the owner have the training and staff available to keep more sophisticated systems operating as designed?

In existing facilities, the owner's engineering staff needs to be consulted to verify calculations and assumptions. Evaluate the overall building energy impact of specific systems considered rather than that from individual equipment options. Complicated systems must be commissioned prior to turnover to owner and need to be recommissioned over the life of the system to assure that they are still operating safely and saving energy. Energy conserving systems are often installed without clear means of savings verification by the owner. Instrumentation, sensors and the ability to trend data will assure that the system is successful. Flexibility needs to be considered in the design since systems typically operate differently than the designer's assumptions.

Labs21 Connection:

The unique approach of the Fred Hutchinson Cancer Research Center is to seize the initiative for energy conservation for new and retrofit design from the consulting world. Planning and Engineering functions at the Center for over 12 years have far exceeded energy codes and state of the art design when it comes to energy conservation. The Center has been a proving ground for many new conservation concepts. The drive for excellence in conservation comes from within.

Specifically, our fume exhaust systems and upgrades have been consistent with the Labs 21 Approach in many ways. Fume exhaust systems and modifications have always been pursued first with user safety in mind. Our in house Environmental Health and Safety staff has always been involved in each process and outside environmental consultants are brought in when necessary. Consideration to the whole building is given rather than just at the equipment or lab level. Retrofit projects are always monitored both before and afterwards to compare actual savings with calculations. In order to do this effectively, measurables such as airflow, static pressure, amperage, motor speed and fume concentrations must first be identified for tracking purposes. Our pursuit of conservation extends beyond our internal organization through educational programs such as innovative signage at fume hoods, the use of building operations manuals for new building occupants and articles on conservation in our company newspaper.

Biography:

James Walker, PE, has a B.S. in Mechanical Engineering from Seattle University. He has over 25 years of professional experience as a mechanical engineer in manufacturing, consulting engineering and facilities engineering. As a consulting engineer working for a top 15 AE firm, he specialized in energy conservation starting in 1982 and continuing over a 15 year period. His work involved energy surveys of over 110 commercial and institutional facilities to identify cost effective, energy saving measures and follow up retrofit design.

Mr. Walker is currently employed by the Fred Hutchinson Cancer Research Center in Seattle as the Facilities Engineer where he has served for 8 years. He is heavily involved with the implementation of water, gas and electrical conservation projects and bringing cutting edge conservation technology into practice.

 

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