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 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
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
SUPPLY AIR CHANGES
Offices and Conference Rooms ................. 4
Patient Rooms ............................... 4
Corridors .................................... 2
2.4 OUTSIDE AIR REQUIREMENTS
A. For areas where the outdoor air requirements is less than 100% of the
supply air, the minimum outdoor air shall be based on the
recommendations contained in the ASHRAE Standard 62-1989, Table 2,
with additional specific requirements as listed below.
B. For the patient bedrooms and offices, any one of the following HVAC
systems can be used:
1. All air systems with minimum outdoor air.
2. Terminal heating and cooling units, such as, fan coil units or
radiant ceiling panels system.
C. The amount of outdoor air and how it is actually supplied to the
occupied spaces would depend upon the type of system used, as
1. When the fan coil units or radiant ceiling panels are used, a
central ventilation unit supplies conditioned air to the spaces.
With this arrangement, the source of outdoor air being external to
the principle cooling and heating equipment, it is possible to
ensure the predetermined and exact amount of outdoor air for