340
Heating-Ventilating-Cooling: Design Criteria
344
DESIGN CRITERIA
344.1
HVC LOAD DISTRIBUTION
In order to systematically handle the HVC subsystem it is necessary to
make assumptions about the general load distribution pattern in a hospital.
The variables of air quality and return/exhaust alternatives are discussed
later, but the first consideration is the supply load.
Hospitals will vary in c.f.m. per square foot required because of climate,
configuration, etc., but the overall pattern of distribution is likely to remain
the same. Figure 340-4 illustrates the pattern found in the design of one
hospital which is considered typical.
In general, a majority of spaces and departments will require 6 to 8 air
changes per hour which requires 1 to 1.5 c.f.m. per square foot with a ten-
foot floor-to-ceiling height. Several departments will require up to 15 air
changes, or 2.5 c.f.m. per square foot; some individual rooms, such as
operating rooms, will also go as high as 30 air changes, or 5 c.f.m., but
this would average down considerably over the total area that one fan unit
would be serving, to about 2.5 c.f.m. As shown on Figure 340-4, laundries
and kitchens will tend to considerably exceed these figures, therefore
space modules handling these functions will probably require non typical
air systems and fan units.
In recent years, there has been a tendency to boost the number of air
changes as well as increased filtration required throughout the hospital to
improve asepsis, maintain pressure differentials more adequately and
speed up the response of the system to room temperature change. These
higher values, sometimes quoted from 10 to 20, and even up to 30 air
changes, would increase the figures quoted above and have to be taken
into account in the design assumptions.
344.2
SERVICE MODULE REQUIREMENTS
A major factor in sizing service modules is the capacity of available pre-
packaged air-handling units. Figure 340-5 is a diagram of the c.f.m. per
square foot capacity of three typical units plotted against various service
module sizes. The 35,000 c.f.m. unit is about the largest packaged unit
available.
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