APPENDIX C (Continued)
changeover. The warm-up cycle would be as follows: in the
morning the air handling unit is turned on (typically by the same
device that turned the unit off for setback). A central hot
water coil in the AHU is activated, and the thermostats are
signaled to warm-up action. During the warm-up the interior zone
thermostats thus open up the air dampers to warm up the space to
the thermostat setpoint. After the warm-up period, the
thermostats are signaled to return to normal action for cooling
and the AHU hot water coil is deactivated.
The designer should be aware that pneumatic damper
actuators provided are often inadequately sized and are not
capable of performing their specified duty. Paying special
attention to submittals in this area or specifying pilot
positioners could help avoid many problems.
Note that use of air troffer lighting return may reduce
design air volume to an undesirable low air distribution level
(in non-fan-powered systems).
Modulate the capacity of the supply fan, giving
attention to the method chosen. Be aware that all of the
available methods, including variable speed, inlet guide vanes,
controllable pitch vane axial, and even discharge dampers, have
problems in Navy VAV systems. Feedback: Inlet guide vanes are
often found to be inoperable due to poor maintenance. They are
not the trouble-free devices that the designers think they are.
It is recommended that supply air fans under 10 horsepower be
forward curved fans with inlet guide vanes. Supply fans larger
drive (VFD). When designing a system with a VFD, the following
guides may be of help.
Sequence of Operation.
For suggested sequence of
operations, refer to par. 8.5.
procedures, refer to pars. 8.6 and 8.6.7 which specifically
address VAV systems.
Operation and Maintenance Personnel Training. It is
suggested that training sessions of operation and maintenance