720
Design Rationale: Services
724.1.3
Air Velocity
Low- or medium-velocity systems are considered most appropriate in the
Prototype Design. The S3 subzone at a depth of 36" in a 10,000 square
foot service module will handle low-velocity ductwork. Low-velocity
distribution requires less energy to move the air, and greatly reduces the
noise generation problems found in high-velocity systems. High-velocity
systems are considered inappropriate except with dual-duct systems
where the mixing box can reduce velocity and noise in the system. The
need for extra care in construction to avoid leakage and the limited
contractor experience in some areas of the country would also limit their
application.
724.1.4
Fan Units: Satellite versus Central Fan Room
1. Adaptability
Satellite air-handling units may be changed to respond to changes in
the areas which they serve without disrupting the operation of other
functional areas. Breakdowns affect only local areas.
2. Quality Control
Large central fan systems must be site-fabricated. Units of the size
contemplated are assembled in the factory and trucked to the site for
installation. Since VA hospitals are constructed in every part of the
country, it is not always possible to find mechanical contractors
experienced enough to guarantee top-quality on-site assembly of large
central fan systems. The packaged units offer predictable quality.
3. First Cost
In addition to predictable quality, factory-fabricated units offer
predictable first cost. Several factors also tend to reduce the first cost
of systems composed of small satellite units, compared to large central
fan systems.
a. Vertical supply air shafts are eliminated, as well as the pressure-
reducing devices to the take-offs at each floor.
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