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Improvement and optimization of laboratory exhaust systems

Gang Wang, University of Nebraska - Lincoln


Constant speed fan single stack exhaust systems are widely used in laboratory buildings. Makeup air is always introduced at the inlet of the exhaust fan to maintain constant fan airflow and stack exit velocity when building exhaust airflow changes. The exhaust systems have either more negative duct static pressure or high fan airflow under partial loads. As a result, the exhaust systems have high energy consumption and considerable noise problems. ^ Several measures were developed to improve system performance. The damper measure adds a modulating damper in the main duct to reduce excessive fan head and maintain a constant duct static pressure. The VFD measure adds a variable frequency drive (VFD) on the exhaust fan to balance the fan head with the reduced system pressure drop and maintain a constant duct static pressure. The multiple-stack measure uses multiple stacks, in lieu of a single stack, to reduce the fan airflow with a constant stack exit velocity. Overall, a system with both VFD and multi-stack measures can achieve the best system performance. ^ In multi-stack and VFD exhaust systems, annual fan electricity consumption is affected by the system pressure drop distribution, the building exhaust airflow time pattern and the multiple stack capacities. In order to achieve the best system performance, optimization methods for the stack design were developed for the new system design and the existing system retrofit, respectively. ^ Finally, a demonstration project was conducted on a laboratory exhaust system. A double-stack assembly was installed atop the single stack and a VFD was installed on the exhaust fan. The measurements show that all critical parameters were controlled. The stack exit velocity maintains a safe level when the building airflow changes. The fan peak demand reduction is 49% and the fan energy savings is 55% compared to the original system. The project payback period is 3.7 years. Moreover, the duct static pressure is reduced to a reasonable level, which provides fume hoods with the required face velocity and also avoids noise. ^

Subject Area

Engineering, Civil|Engineering, Mechanical

Recommended Citation

Wang, Gang, "Improvement and optimization of laboratory exhaust systems" (2005). ETD collection for University of Nebraska - Lincoln. AAI3201784.