06-06
B. SUPPORT AREAS: If an all air system is selected to serve the
support areas, the supply air volume for the occupied areas shall
be calculated to meet the internal heat gain from all sources but
not less than 4 air changes per hour.
With variable air volume
(VAV) systems, the supply air volume, during part load conditions,
shall be established to ensure stable performance of the supply,
and more so the return air fans.
The reasons for this requirement
are:
1. The VA selected sequence of operation for the VAV systems
requires that a constant difference in m3/ min (CFM), amounting
to the outdoor air quantity for the air handling system, shall
be maintained between the supply and return air fans at all
times.
If the supply air fan volume is allowed to drop to a
very low value, the corresponding return air volume shall be
even lower as the return air fan has to maintain a constant
difference in m3/min (CFM) with respect to the supply air
volume at all times. Under this condition, the supply (and
particularly the return) air fans could fall in an unstable
region where the fan operation is not recommended by the
equipment manufacturers.
2. The supply and return air fans of the VAV systems are generally
equipped with variable speed drives.
If these drives are
allowed to run at very low speeds for a long period of time,
the fan motors will tend to overheat and cause damage to the
winding insulation.
2.4 OUTSIDE AIR REQUIREMENTS
A. ANIMAL RESEARCH AREA: All air supplied to the animal research
areas shall be 100% outdoor air.
B. SUPPORT AREAS:
1. General:
The outdoor air for ventilation shall be computed in
accordance with ASHRAE 62/1989; however, how it is actually
supplied to the occupied spaces would depend upon the type of
HVAC system as explained in 2.4B2 and 2.4B3, below. The outdoor
air quantity shall be increased, if required, to meet the space
exhaust requirements or to meet the manufacturer's
recommendations when radiant ceiling panel cooling system is
used.
2. All Air Systems: With an all air system, the outdoor air is
mixed with return air, and the supply air is distributed on the
basis of the cooling load requirements.
Since the distribution
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