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Facility Design Guidelines - Facilities Management - University of ...

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BSRV 4.4.6 DISTRIBUTION, GENERAL EXHAUST<br />

Ventilation systems in health care facilities shall comply with ASHRAE 170<br />

Plenum returns are not permitted above suspended acoustic tile ceilings. Plenum<br />

returns may by allowed in fully enclosed s<strong>of</strong>fits for normal return air. Exhaust air must<br />

be fully ducted.<br />

Individual exhaust fans in janitor’s closets or single toilet restrooms shall not be used<br />

where central systems are available or reasonably achieved. If such individual exhausts<br />

are used, they shall be equipped with timers or occupancy sensors to turn fans <strong>of</strong>f after<br />

an approved period <strong>of</strong> time.<br />

Outlets <strong>of</strong> multiple exhaust fans shall not be manifolded together unless backdraft<br />

protection is provided.<br />

All ro<strong>of</strong> top exhaust systems shall be vertical up discharge. Centrifugal fans with a<br />

vertical discharge are suitable for most lab exhaust; high dilution exhaust fans shall not<br />

be used unless approved on a case by case basis. Outlets <strong>of</strong> ro<strong>of</strong>top exhaust fans for lab<br />

exhaust and other noxious exhaust shall be at least 7 feet above the top <strong>of</strong> the fan and<br />

at least 10 feet above the ro<strong>of</strong>; this requirement applies to induced flow type fans as<br />

well as fans with straight stacks. Where exhaust fans have inlet bypass openings below<br />

the fan, the bottom <strong>of</strong> the bypass openings shall be above any nearby screens and<br />

obstructions and at least 7 feet above the ro<strong>of</strong>.<br />

Fans shall be sized so as to meet exhaust volumes, stack exit velocity and pressurization<br />

under all expected operating conditions.<br />

Fans shall be positioned so as to allow ready access to all fans, motors, belts, drives,<br />

isolation dampers controls and attached duct work. Fans shall have adequate space for<br />

removal and replacement <strong>of</strong> fan and/or fan parts.<br />

The discharge velocity from the stacks <strong>of</strong> lab exhaust and other noxious exhaust shall be<br />

at least 3,000 fpm and the plume shall be high enough to clear nearby obstructions; this<br />

requirement applies to induced flow type fans as well as fans with straight stacks.<br />

Wind engineering evaluations must be conducted where fume hood or other toxic or<br />

potentially noxious exhaust has the potential to have an adverse impact on nearby air<br />

intakes or other sensitive locations.<br />

To avoid re-entrainment <strong>of</strong> hazardous or noxious sources <strong>of</strong> exhaust air into the building<br />

or into adjacent buildings’ air intakes and other sensitive locations, wind tunnel testing<br />

or other modeling must be performed to ensure adequate dispersion <strong>of</strong> the exhaust<br />

sources.<br />

Large installations or installations close to fresh air intakes or community receptors<br />

must be modeled (wind engineering evaluations) to determine best locations and stack<br />

height needed for effective dispersion <strong>of</strong> contaminants. Wind tunnel testing may allow<br />

BSRV 4 HEATING, VENTILATION, AND AIR CONDITIONING 198

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