720
Design Rationale: Services
6. Floor Area Required for Equipment
More floor area will be required for equipment, but this increase is
mitigated by two factors:
a. Area required for supply air shafts is eliminated.
b. Added area is distributed over all floors, reducing building height
while increasing site coverage.
7. Air Intake per Floor
a. Assuming one air-handling unit per service module, air intake per
floor reduces ducting. When local conditions disallow intake per
floor, the mechanical room will be replaced by a supply duct from a
roof-mounted fan unit.
b. The opening required for removal and replacement of the air-
handling unit is always large enough for the required fresh air intake.
724.1.5
Return/Exhaust Systems
For the general return/exhaust system a plenum can be used.
Pro:
1. Elimination of exhaust/return trunk and branch ducts reduces HVC
system cost by approximately 70 cents per square foot.
2. The ceiling required for a walk-on platform and acoustical barrier is
easily sealed to provide air tightness.
3. The elimination of the exhaust/return ductwork eases access to other
service distribution components.
4. Toilet, isolation room, fume hood, and other special exhaust air is
separately ducted to an exhaust shaft to the roof.
5. The usual drawback of return plenums an accumulation of dust
which spills down through accessible-ceiling panels is virtually
eliminated because vertical access through the platform-ceiling can be
limited to hatches in non-critical rooms.
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