A Successful Laboratory Exhaust Stack Retrofit at Georgia State University

Mark Hallman, Rowan Williams Davies & Irwin, Inc.

Aging laboratory buildings can be problematic where energy use and occupant safety are concerned. Such buildings often have several individual fume hood exhaust stacks installed on rooftops, each discharging a small volume of exhaust from a particular fume hood. These exhausts can suffer from higher energy use due to having less flexibility in reducing discharge flow during times of low building occupancy, and having less efficient fans than some current models. Additionally, exhaust discharge momentum is reduced in a low-flow stack, resulting in the dispersion of exhaust being more heavily influenced by local wind flow patterns. This influence impedes exhaust dispersion and can pose occupant safety concerns due to exhaust re-entrainment, wherein chemical exhaust is drawn back into the building via the air intakes.

Whenever it is feasible to do so, retrofitting existing small exhausts into fewer and larger manifolded exhausts is an excellent way to realize improvements in building energy use and occupant safety. A successful retrofit of this nature was recently completed at Georgia State University’s Natural Science Center. This retrofit involved the conversion of an existing exhaust system with more than 100 individual exhaust stacks into a combined, manifolded exhaust system. Johnson, Spellman & Associates, Inc. led the mechanical design of the retrofit project, and Rowan Williams Davies & Irwin Inc. conducted a dispersion modeling assessment of the new exhaust system design.

The dispersion modeling assessment demonstrated an overall net decrease in re-entrainment risk with the new exhausts, for both full design flow and reduced flow conditions. Furthermore, the building owner now has the ability to decrease the general exhaust airflow rate during times of low building occupancy and to decrease airflow at individual fume hoods during times of non-use, thus reducing fan power and cooling/re-heat energy. The decreased re-entrainment risk is attributed to increased momentum from the larger volume of exhaust being discharged from the manifolded stack and the additional internal dilution that occurs in the mixing plenum prior to discharge.

This presentation will review the Natural Science Center retrofit in detail, quantifying the improvements in energy use and exhaust dispersion that will enhance overall building efficiency and reduce risks to occupant health. Designers attending the presentation can likely apply similar concepts when retrofitting other aging laboratory exhaust systems.

Biography:

Mark Hallman is a technical coordinator providing exhaust dispersion consulting services with Rowan Williams Davies & Irwin Inc. He has provided consulting services on exhaust and intake designs for a variety of new and existing facilities in the university laboratory and healthcare sectors, including the Georgia State University Natural Science Building laboratory exhaust retrofit project.

When consulting on projects, Mr. Hallman looks to provide advice on exhaust designs that can maximize energy efficiency without compromising the safety or comfort of building occupants.

Mr. Hallman has a background in environmental engineering and has recently earned his LEED® Green Associate accreditation.