Page 340 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Sustaining CHP Operations 313

In addition to the parasitic loads, system losses must also be evaluated, including
• Electrical distribution system
• Steam distribution system
• Condensate return system
• Hot water system
• Chilled water system
With operating costs and losses known, appropriate billing rates can be developed.
The bill itself should be easy for consumers to follow and should include relevant met-
rics to indicate efficiency such as kilowatthour per square foot, utility usage for the
same time period in previous years.

Operating Strategies
The number and type of possible plant operating strategies usually depends on the
CHP plant size versus facility electric and thermal loads; the nature and type of avail-
able CHP plant equipment options; the number and size of various CHP units avail-
able; and the available CHP plant features such as duct burners. A modern,
technologically advanced, robust, fast-acting, adaptive control system capable of calcu-
lations and automated decision making can be very helpful, if not essential, in imple-
menting various operating strategies. While it is beyond the scope of this chapter to
discuss/detail every operating strategy of a CHP plant, this section attempts to provide
overall guidance on how to think about and how to develop appropriate sustainable
operating strategies for the site-specific CHP plant.
Operating strategies will depend upon the CHP plant size versus facility electric
and thermal loads, with thermal loads understood to include all heating, cooling, and
thermal-to-power loads. For example, if the CHP plant has been sized to be base loaded
electrically and thermally 100 percent of the time, the operating strategies will solely be
focused on maximizing equipment and system efficiencies, as previously described,
and minimizing plant parasitic losses in order to help minimize CHP fuel consumption.
On the other hand, the CHP plant may be sized to track facility thermal loads such that
declining thermal loads will require decisions regarding thermal use, power produc-
tion, and related prime mover operation. Furthermore, plant operating strategies
depend on the nature and type of available equipment options, and a matrix of all avail-
able equipment options, may need to be developed. The matrix should show all plant
equipment options listing each and every equipment/system choice. For example,
equipment/system choices might include: operate one engine-generator, operate two
engine-generators, fire the duct-burner, operate the turbine inlet cooling system, oper-
ate the steam powered chiller(s), operate the electric-drive chiller(s), operate the steam
turbine generator(s), and transfer heat either directly or via plant heat exchangers to
various thermal loads with each load or system heat exchanger listed as a separate line
item in the matrix. The matrix should include the available number of units, the num-
ber of CHP modules, the number of chillers, the number of pumps for each system
along with marginal operating costs, values, and even relative values (e.g., on-peak
operational savings or cost) that can help determine good equipment choices/operating
strategies.