Page 334 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Sustaining CHP Operations 307

Note that fuel cost is also minimized by maximizing plant operating efficiency and
minimizing energy use per unit of production (e.g., Btu/kWh, kW/ton) which is
affected by a variety of factors as discussed under “Operating Strategies” in this chap-
ter. Labor costs can also be a significant cost of operating a CHP plant if, for example,
full-time licensed steam plant operators are required.
Maximizing the ROI many times involves properly metering and billing for CHP
plant–generated services. Therefore, CHP plant management and staff need to under-
stand the basics of the number, functions, and types of usage meters and how the infor-
mation on those meters is translated onto costumer utility bills, as applicable.

CHP Data Gathering
As noted, one of the critical requirements for a sustainable CHP plant is the ability to
gather sufficient information/data in order to (1) properly meter and bill for CHP ser-
vices, and (2) monitor and trend performance in order to help maximize performance.
The first step begins with data gathering, which can be automated as part of the plant
control system.

Metering
CHP systems are often part of a district energy system, and, in many cases, costumers are
billed for their electricity and thermal usage. Meters are typically used to measure the
amount of usage of electricity, steam, condensate, heating hot water, domestic hot water,
and chilled water, for example. Measurement of electricity typically includes both a mea-
surement for usage and for demand. Electricity meters are not only required for each
individual building, but also required to capture generator output, parasitic losses, pur-
chased power, power sold to the grid (if applicable), and individual system/equipment
consumption (e.g., chiller power in order to measure kW/ton). As with many types of
fluid meters, steam meters need to be located with the proper upstream and downstream
straight-run diameters to function properly. Steam meters need to record total produc-
tion, parasitic losses, as well as individual building consumption. Condensate meters
should also be installed, and customers charged on their net consumption (Btu) obtained
by computing the total energy consumed equal to the energy (enthalpy) supplied in the
steam minus the energy returned in the condensate. In this way, condensate that is not
returned to the CHP plant is accounted for and charged. Finally, by employing meters
now available with significant technology enhancements, for example, smart meters
compatible with automated billing systems and wireless technology that allow meters to
be read remotely, significant time and costs can be saved.
Monitoring
In addition to metering, the CHP plant’s power output and the various power usages,
the CHP plant control system, as noted, needs to monitor and record total thermal pro-
duction (steam/hot water), all thermal usage, and any chilled water production. The
monitoring and control system should also monitor and record all of the flows and
temperatures and pressures listed in Chap. 17. In addition to alarms and control, the
plant monitoring data should be used to compute equipment and system efficiencies
for use by plant operations to better track CHP operations, to help with plant trouble-
shooting, and to provide CHP plant optimization feedback. Monitoring points and cal-
culated quantities can also be trended to help in plant operating decisions.