June 2006
HVAC
342.1 Supply Systems: The major alterna-
tives for supply are low or medium pressure,
variable air volume (VAV) systems with terminal
reheat. The close humidity control required for
certain areas in the hospital may be difficult to
achieve unless cooling/dehumidification is em-
ployed at the unit.
Where climatic conditions require, a mixed sys-
VA Medical Center
tem which combines hot water convectors for
building perimeter auxiliary heating with a single San Diego, CA, 1971
duct system for heating and cooling could be a (not VAHBS, used interstitial space)
prime variation.
342.2 Return and Exhaust Systems: The systems must be capable of handling from 25 to
100% outside air. Both return and exhaust shall be extracted through the service zone by fully
ducted systems. The return air fans shall be placed in the service bay mechanical rooms.
Ducts for special exhaust systems will be required in various service modules. Exhaust ducts
shall be routed to shaft(s) in the service bay and then to fans on the roof. General exhaust will
handle a range of conditions from individual toilets to large areas such as isolation suites and
shall be ducted through the service bay to fans on the roof.
343.1.1 Sub zones: Flexible duct within subzones S-4 or S-5 shall be limited to 3 feet for
each run. Flex duct within subzone S-7 shall be limited to 5 feet. Return/exhaust system ple-
nums are not allowed.
343.1.3. Return or exhaust plenum: Are not allowed.
344.6 Accessibility: Hydronic components, such as control valves, strainers and other de-
vices requiring periodic service, shall be located above the interstitial platform approximately 14
inches to allow a catch basin to be used when servicing that component.
344.4 Fire Safety: No exhaust or return plenums are allowed.
Fire dampers are required on vertical exhaust ducts that penetrate the floor assembly separat-
ing service bays. Fire dampers are not required in ductwork penetrating the one hour wall sepa-
rating the service bay from the interstitial service zone. Fire dampers are not required for duct-
work that penetrates the interstitial platform (subject to the limits of the Fire Performance Tests
for the floor/ceiling assembly).
In many cases, current codes will require fewer (or no) fire or smoke separations in the intersti-
tial service zone than envisioned in the Red Book. However, ductwork systems serving distinct
(different) smoke or fire zones in the functional zone shall not be "cross-connected" in the inter-
stitial service zone.
SUPPLEMENT TO RESEARCH STUDY REPORT
VA HOSPITAL BUILDING SYSTEM
SECTION 4-12
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