5.1.2 Matching Definitive Designs to Load Demands. Develop design concepts
that satisfy electric loads in the most economic manner. Select the
definitive design with necessary modifications in accordance with the best
design concept. Use economic analysis methodology as addressed in Section 2
in accordance with life-cycle cost analysis methodology in NAVFAC P-442,
Economic Analysis Handbook. Evaluate all plausible deviations from the
selected definitive design using the same economic analysis methodology.
However, NAVFACENGCOM Headquarters approval will be required for all designs
deviating radically from the definitive design.
5.1.3 Definitive Design Plant Capacities. Definitive designs provide for
three initial engine-generator bays for prime duty and two initial bays for
standby/emergency duty plants. A future engine-generator bay is indicated
for all designs. Most plants will need to be expanded to satisfy future
electric loads. The definitive designs provide only for a single operating
unit; additional units are required to meet NAVFACENGCOM minimum reliability
needs. Provision of a single operating unit is not usually economical.
Selection of unit capacities must consider varying electric demands. Plant
capacity must be selected to satisfy reliability criteria once the unit
capacity has been established.
Criteria for Unit and Plant Capacities.
5.2.1 Number of Units. The number of units selected for any plant should
provide for the required reliability and flexibility of plant operations.
The minimum number of units needed to satisfy these requirements usually
results in the most economical and satisfactory installation. Utilization
of different sized engine-generator units in a plant must be authorized by
5.2.2 Reliability. Spare units are required to ensure system reliability.
Minimum reliability requirements are related to duty types and criticality
220.127.116.11 Prime Duty. Two spare units are required, one for scheduled
maintenance and one for standby or spinning reserve.
18.104.22.168 Standby Duty. One spare unit is required for scheduled
maintenance. Another unit may be required for spinning reserve when
22.214.171.124 Emergency Duty. No spare is required in Continental United States
(CONUS); one spare unit is required for plants outside of CONUS.
5.2.3 Flexibility. To provide for future growth, the firm capacity (total
capacity less spare capacity) shall be no less than 125 percent of the
maximum estimated electric demand. For an economical operation, individual
generating units should be operated at least 50 percent of their rated
capacities to satisfy minimum or average demand. Consider providing a split
bus (tie circuit breaker) to permit partial plant operation in the event of
a bus failure.