MIL-HDBK-1003/3
APPENDIX C (Continued)
when moving away from the air handling unit toward the VAV
terminal units, until no diversity is taken at the distant VAV
terminal runouts.
C-2.04
Design and specify for both peak and part load
conditions. Submit design calculations verifying that careful
consideration has been given to the following areas:
a) Consider the psychrometric performance of the
cooling coil (taking into account the method of capacity control)
during difficult off peak conditions when the room sensible heat
ratio can be significantly reduced. Select appropriately
difficult off peak conditions for analysis. At a minimum, show
how the system will perform when sensible load due to solar is
lost while latent loads remain constant. This is not necessary
in dry climates. The VAV system may operate with 100 percent
outside air during warm-up or on maximum heating days.
b) When selecting a fan for a VAV system, submit
design calculations verifying the system has been analyzed at the
following three points: (1) normal peak load (including
diversity), (2) maximum cooling load (no diversity with VAV box
dampers open), and (3) minimum cooling load (with VAV boxes at
the minimum flow condition). The supply fan should be
scheduled/specified (cfm and pressure) to satisfactorily meet all
three of these operating points. Submit design calculations and
a typical fan performance curve showing all of these points
plotted. A fan should never be selected which will become
unstable or overload anywhere on its operating curve.
c) Consider limiting the size of VAV air handling
units to 10,000 cfm for flexibility and ease of maintenance.
Plan for units to serve zones with different exposures to achieve
unit diversity.
d) VAV terminal boxes should be sized with both
maximum and minimum flows in mind. Schedules should indicate
cfm, neck velocity, pressure drop, and noise criteria at both
maximum and minimum flow (refer to par. C-2.11).
e) For air distribution devices, the minimum allowable
"throw" should be scheduled for both maximum and minimum flow
conditions.
f) If an outside air injection fan is used to maintain
minimum ventilation, select a fan with a "steep" fan curve which
will maintain a relatively constant flow regardless of mixing box
176
Previous Page
