Space Ventilation. Minimum total and outside air change rates
shall be as indicated at Appendix A; Computed on a per-occupant basis,
minimum outside air ventilation shall meet the worst-case requirements of
either appendix A, or ASHRAE Standard 62-89. Higher air change rates may be
required to meet air conditioning or makeup air requirements as supported
by engineering calculations. See 8.16 of this Section for additional
guidance and requirements.
Ambient Design Dry and Wet Bulb. The HVAC cooling design for
medical facilities shall generally be based on the 2.5 percent dry bulb
(DB) temperature and the corresponding 2.5 percent mean coincident wet bulb
(MCWB) temperature, and heating design upon the 97.5% DB, as provided in
reference 8i. Exceptions include Critical Care and Sensitive spaces, where
special environmental requirements demand more precise temperature or
humidity control, or both, at all times (see below). In addition, designs
for facilities in humid climates should examine BIN weather data for the
locale to determine if the 2.5% MCWB temperature is reasonable for that
project; Use of a higher design wet bulb temperature may be warranted for
facilities utilizing large quantities of outside air, or cooling towers,
where the 2.5% MCWB temperature is exceeded for a significant number of
occupied hours during the cooling season.
Critical Care Spaces. Critical Care Spaces are identified in
Section 10, Electrical, of this Military Handbook. HVAC cooling design for
critical hospital areas shall be based on the 1 percent dry bulb
temperature with corresponding 1 percent MCWB temperature. The heating
design shall be based upon the 99% winter dry bulb temperature.
Sensitive Spaces. Sensitive areas include Automated Data
Processing (Computer) rooms, Radiology and MRI computer rooms, selected
laboratories (see below), and Telephone Switch Room. Other rooms housing
sensitive electronic or other equipment or processes may be designated as
Sensitive Areas on an individual project basis. Design ambient
temperatures shall generally be the 1% DB/1% MCWB (summer), and 99% DB
(winter). Each application should consider using 2.5% DB/2.5% MCWB
(summer), and 97.5% DB (winter) design conditions for less critical
equipment/process air conditioning requirements.
Laboratories. Space design temperatures for laboratories are
indicated at Appendix A, generally 26C. However, designers shall be
responsible to coordinate with the equipment designer and user to establish
whether temperature-sensitive equipment is expected to be utilized in a
laboratory space. When such equipment requires, for proper operability or
to meet warranty limitations, an ambient temperature lower than can be
maintained by the HVAC/Control System when set at 26C, the designer shall
coordinate with the Design Agent to establish a reasonable lower design
temperature for that space.
Temperature during Smoke Control Operation. When a supply air
system is required to operate on 100% outside air during smoke mode
operation, the system shall be designed with sufficient heating capacity to
maintain a minimum of 45 degrees at the air handling unit discharge under
the 99% winter design conditions.