Page 365 - Sustainable On-Site CHP Systems Design, Construction, and Operations

338 Ca s e S t u d y 2

control system determines the best operating strategy on an hourly basis. This opti-
mizer considers the electric load, heating and cooling loads, grid electricity and fuel
prices, equipment characteristics, and weather data to determine how to best meet
these loads using the CHP equipment, electric grid power, and the auxiliary heating
and cooling equipment. The optimization software guides the plant operations staff by
recommending set points for the turbine generator and other major equipment. The
economic performance (i.e., cost savings) provided by the CHP optimizer software is a
function of the energy prices, energy loads, and equipment characteristics of the site.
Simulations of this software have shown an estimated annual energy cost savings of
approximately 5 percent over the typical, nonintegrated operating strategy. In practice,
the actual annual performance will vary as energy prices and energy loads fluctuate.
Ft. Bragg central plant operations and overall post energy management functions are
managed from a central Energy Information Center.
Overall, the post has a maximum peak demand of approximately 110 MW, with
most of the electrical power being purchased from a local electric utility. The CHP sys-
tem’s electric power generating capacity of up to 5 MW can be combined with approxi-
mately 8 MW of diesel generator capacity on the post to manage energy costs and
provide a measure of energy security. These on-site generating assets provide an energy
security benefit in that they can be used to serve critical loads on the post in the event
of a disruption on the electrical grid.

Measured Performance
This project included a period of detailed performance monitoring of the CHP system,
covering the period of June 2004 through August 2005. A system block diagram show-
ing the performance analysis boundaries is shown in Fig. 20-3. In the following sections,
the CHP system is referred to as an integrated energy system (IES).

Energy Delivery
A high-level summary of energy delivery for the monitoring period is shown in
Fig. 20-4 and Table 20-1. Runtime and generation results (as well as all other mea-
surements) during the 2004 summer season were affected by periods of downtime
due to extended commissioning activity and delays in acquiring an emissions operat-
ing permit. Also note that the duct burner’s start-up in March resulted in a significant
increase in steam production. Reduced demand lowered steam production in the
following month.

Operational Monitoring
A high-level summary of operational results for the monitoring period is shown in
Fig. 20-5 and Table 20-2. The definition of system efficiency is taken as (useful
energy output)/(total energy input from fuel). The IES system energy efficiency is
based on the lower heating value (LHV) of the fuel input. Energy efficiency calcu-
lations were made in accordance with “Distributed Generation Combined Heat
and Power Long-Term Monitoring Protocols” Interim Version, October 29, 2004,