APPENDIX C (Continued)
on the drawings than you allow in the specifications. Seek
self-balancing by having equal lengths of flexible ducts instead
of long and short runs on the same system.
When designing VAV systems, do not use flex duct
upstream of the terminal VAV box (i.e., between the air handling
unit and the VAV box). Use flex duct only to make terminal runs
to diffuser boots and limit applications to straight runs of no
more than 5 feet. Hard duct 90 degree elbows should be used to
connect the flex duct to the diffuser boot. Do not use flex duct
Many zones in Navy buildings do not need heating.
These include zones in a building in a cooling only climate or
completely interior zones in any climate. In these situations, a
recommended control sequence is as follows: the air handling unit
supplies a constant cold temperature (say 55 degrees F) air.
Each VAV box modulates from maximum position (fully open) to
minimum position (fully closed) through the control range of the
in interior zones, in light of IAQ concerns, is that the people
load plus lights in an interior zone are substantial, usually
amounting to 50 percent of the zone load or more. This is true
for perimeter zones in a cooling only climate also, but to a
lesser extent. So, if people are present, and thus the lights
are on, the load will be above the minimum anyway.
the minimum is not needed. If the people are gone and the lights
are out, the load may fall below where a ventilation determined
limit would come into play, but since the people are gone, no
ventilation is needed.
For zones that need heating, there are two recommended
situations. For the very cold climate when the peak heating load
on the exterior wall is greater than 400 Btuh per linear foot of
wall (including infiltration), a separate skin heating system may
be used consisting of baseboard hot water convectors.
Two-position electric spring-return control valves should be
installed in each zone. Thus each perimeter zone will be served
by a VAV terminal unit for cooling and a corresponding section of
hot water convector for heating. The zone thermostat should
control both the VAV damper actuator and hot water valve actuator
in sequence at the cooling and heating setpoint. The VAV damper
should have a mechanical minimum position for ventilation air
which would be field set during the testing and balancing phase