Page 398 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Governmental Facility—Mission Critical 371

that shows these assets spread around (Facilities with the prospect of an appropriate
thermal load are identified in bold lines.). Further, Fig. 23-1 provides a schematic of
countywide critical operations: The risk mitigation plan required in Section 708.64 of
the 2008 National Electric Code should encompass many emergency management
assets within single building premises as well as assets that are widely scattered but
networked together as a single operation. Single point of failure risk is reduced but a
network of distributed COPS assets increases the capital costs.
While Article 708 only requires a 3-day supply of fuel, urban planners and engi-
neers should contemplate the development of COPS cities with a 30-day major regional
contingency as a benchmark. Proximity to primary and secondary fuel supplies is
essential. Since cooling water is needed to generate energy; and energy is needed to
deliver water, the availability of water needs to be a factor in the risk equations. These
benchmarks are similar to 10- and 100-year benchmarks civil engineers use to design
storm water infrastructure.

The Energy Conservation Objective
Among energy professionals, concern about fuel cost and stability in any CHP scheme
is never far below the surface. Spot market phenomena in gas and electricity—the so-
called “spark spread”—can seriously unbalance the energy budget of many local gov-
ernment agencies in a single 15-minute outage or extreme weather day.
The most cost-effective cogeneration systems operate at full output 24/7, though
they may only generate a portion of the total electric and thermal need—commonly in
the range of 50 to 80 percent. Capital and operation and maintenance (O&M) costs per
unit output increases as the facility size decreases, lowering the natural gas prices
required for breakeven with electricity. The thermal load factor determines the amount
of electricity that can be produced assuming the cogeneration unit operates to supply
base load thermal demand.
CHP-COPS can be used by the emergency management facility as a peak-shaving
distributed resource of its own. The capacity of the prime mover can be scaled to the
demand profile of the COPS, and the demand of other electrical loads in the facility.
One financial strategy involves consuming kilowatthours (energy) from the macrogrid
but reducing kilowatt demand (power) with the local microgrid. This arrangement can
be cost-effective when the microgrid produces only 2 to 3 percent of the kilowatthour
needs but significantly reduces kilowatt demand.
How significant? One rule of thumb is that any more than 20 to 25 percent of the
COPS demand for peak reduction purposes may not be economically justifiable.
(Because on-site kilowatthours are more expensive than macrogrid, central station kilo-
watthours)
COPS Integration with District Heating
A district energy system for government center critical operations power can meet
economic goals that individual building installations usually cannot. District energy
systems can use a variety of fuels such as oil and natural gas, whichever is most
competitive at the time. Central management of operations and maintenance offers
economy of scale and the lowest delivered cost and emissions impact.
In some cost structures, the normal and alternate supply is a combination of fired
and unfired boilers, steam and gas turbines, prime-rated diesel gen-sets that provide