Engineered Systems - September 2008 - (Page 67)

structure was not designed to support the required HVAC equipment, so an internal equipment mezzanine that extended up through the roof was constructed. The new “superstructure,” as it was affectionately called, supports the boiler room, two 100% OA central air handlers, electrical distribution gear, transformers, and all the VFDs for both the air handlers and exhaust fans. In addition, the roof portion houses two Strobic Air Tri-Stack™ exhaust fans mounted on a structural plenum, a general exhaust utility set fan, and six environmental room condensing units with space left on the roof platform for future exhaust fans and/or other equipment. Because vibration isolation was a key consideration for the air handlers and the exhaust fans, in order to limit the noise and vibration transmittance into the occupied lab spaces below, vibration isolators and sound attenuators were attached to all units. LABORATORY CONTROLS In addition to acoustical considerations, climate and IAQ for the laboratory area were key as well. As such, VAV Phoenix Laboratory valves and controls were utilized to maintain space temperature and pressurization. The system modulates down from design airflow to minimum required ach while maintaining a predetermined volumetric offset between the supply and exhaust to maintain room pressurization. Furthermore, minimum face velocity requirements are maintained for numerous fume hoods located throughout the labs. In the interest of saving energy, dual-pull occupancy sensors in every room control both the lighting and HVAC system. As for the latter, a special sequence of operations was written to enable the system to operate in occupied and unoccupied modes. When unoccupied, overall ventilation can be decreased by more than 40%, with the fume hood face velocity decreasing from 100 to 60 fpm. The system’s emergency mode enables all the air valves to close to their minimum position, but still maintain a negative pressure in all the labs for safe occupant egress in the event of an emergency. The controls were also tested and balanced in their emergency mode to ensure that proper door forces will be maintained. The laboratory control system ties into an existing Siemens BMS, via a gateway, allowing facility personnel to operate the laboratory controls from anywhere on their campus-wide network. FIGURE 1. Internal equipment mezzanine showing AHUs. (Photo ©2008 Brady Architectural Photography.) on the ambient conditions. Although a unique setup, the pit turned out to be a great location in terms of security, distance from delivery truck routes, and noise control. In addition to the existing storm water sump pit, an extra condensate sump pit, complete with a duplex pumping system and controls, was installed for chiller condensate removal. As a result, there is sufficient space remaining in the pit for two more chillers and one standby generator if needed in the future. EXISTING CONDITIONS Yet another space challenge was dealing with the warehouse’s high bay area, which meant more than 15 ft of ceiling space. While the other extreme involved trying to design laboratory space underneath a pre-existing second story mezzanine with less than 18 in. of ceiling space to work with. Although 15 ft of ceiling space sounds like a designer’s dream, when one is dealing with hanging ductwork and pipes in a large, open space under California’s strict seismic requirements, it is no picnic. Fortunately, 3-D modeling lent much assistance to the process of identifying hangar locations, seismic bracing, and clash detection. The modeling process enabled the design team to keep main ductwork and piping as high as possible, limiting the seismic bracing requirements, while keeping branch ductwork and piping low to maintain accessibility to important system components such as supply and exhaust valves, piping isolation valves, and electrical pull boxes. As for the lab’s tight ceiling space, again 3-D modeling was used to coordinate duct crossings, utility drop points, valve accessibility and, of course, fire sprinkler piping and head locations. With less than 18 in. of ceiling space, every inch counted. Duct sizing and routing played an important role in getting all the required services to fit inside such a tight space. Still another structural limitation was the fact that the existing roof FIGURE 2. Lab underneath first floor mezzanine. (Photo ©2008 Brady Architectural Photography.) w w w. esmag a zin e. c o m 67 http://www.esmagazine.com

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Engineered Systems - September 2008 Contents Editor's Note HVAC Challenge Back2Basics Case In Point Commissioning Building Automation HVACR Designer Tips Application Checklist LEED®, Or Get (It) Out Of The Way? BACnet Supplement Race To Market Steam Humidification In Pharmaceutical Facilities Outside Air, Inside Data Centers Forecast: Increasingly Cloudy And Under Control Products Computers & Software Literature Glossary Classifieds Advertiser Index Tomorrow's Environment

Engineered Systems - September 2008

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