MIL-HDBK-1003/3
APPENDIX C (Continued)
the operating and maintenance personnel. It is recommended that
electronic controls be used with as simple a sequence as
possible.
d) DDC. DDC is the state-of-art of control systems
and is in common use throughout the industry. Navy DDC systems
are distributed (have controllers located near the equipment
being controlled) and usually include a means for the operator to
diagnose HVAC operation from a remote location. A DDC system is
the system of choice for Naval projects if the facility operating
and maintenance personnel are qualified in DDC systems or, at
least, are willing to take the recommended training and make a
sincere effort to properly use DDC. The designer should not
overdesign the DDC system, should make it simple, and as user
friendly as possible. It is critical that quality DDC sensors be
used which have long term (5 years) stability to minimize
maintenance and calibration while providing accurate conditions.
DDC systems may incorporate energy management strategies in
addition to normal control functions with little or no additional
cost.
C-2.00
Do's and Don'ts
C-2.01
Do not oversize the system. Do not add safety factors
in load calculations. The calculation methods already have an
adequate safety factor included. Feedback: Many Navy VAV
systems are significantly oversized. This not only costs more,
but it handicaps the system in performing the already difficult
task of providing comfort under difficult part load conditions
commonly seen in humid, coastal environments where many Navy
installations are located. Because of the inherent diversity
factor in VAV systems, they are more "forgiving" of capacity
shortages than are constant volume systems.
C-2.02
Use computerized load calculations based on the ASHRAE
transfer function method. The manual use of the total equivalent
temperature difference/time averaging (TETD/TA) method or the
cooling load temperature difference/cooling load factor
(CLTD/CLF) methods are not as accurate and require engineering
judgment which typically leads to unnecessary conservatism.
C-2.03
Design for diversity. Select central air handling
equipment and heating/refrigeration systems for "block" loads.
Spread diversity appropriately through the supply ducts, taking
full diversity at the air handling unit, and lessening diversity
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