Page 326 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Sustaining Operational Ef ficiency of a CHP System 299

values or calculations of derived engineering quantities (e.g., the COP, which is calcu-
lated using data from a number of primary sensors). It can also involve calculation
of moving averages for certain measured quantities. The results of preprocessing are
written back into the database. A set of algorithms, either continuously or periodically,
analyzes both the raw and preprocessed data to generate useful information and post it
back to the database. Users can then review the results or the system can provide alarms
and suggestions to users through the Web browser.

CHP Performance Monitoring and Commissioning Verification
Application Scenarios
In this section, we describe two hypothetical scenarios in which the algorithms pre-
sented in the chapter for CHP system monitoring and CxV are used in the start-up and
operation of a CHP plant. The plant in this scenario uses a small natural gas–fired tur-
bine as the prime mover with heat recovered from the exhaust to produce hot water.
The hot water is used to fire an absorption chiller to provide cooling to a commercial
building. A duct burner fired with natural gas is used to provide supplemental heat to
the absorption chiller to meet building needs when cooling demand exceeds the capacity
provided by the exhaust alone.
The CHP system is rated at 1 MW and produces about 1.7 MW of useful heat,
e th
which is available to the absorption chiller in the form of hot water at 257°F (≈ 125°C).
Chilled water is supplied by the chiller at approximately 45°F (≈ 7°C) for use in cooling
a commercial building. The COP (coefficient of performance) of the absorption chiller is
about 0.70. The local price of natural gas to fuel the turbine and auxiliary duct burner is
about $1.00/therm (≈ $9.50/GJ), and the price of electricity is $0.10/kWh. The value of
the cooling provided (based on comparison to cooling from a vapor-compression air
conditioner and electricity at the price indicated) is approximately $0.035/kWh
th
($10.25/million Btu) of cooling.
A scenario describing the use of monitoring is presented first and is followed by a
scenario illustrating the use of the commissioning verification process.
The monitoring system provides continuous streams of data for the following effi-
ciency and effectiveness metrics:

• Value-weighted energy utilization factor, EUF
VW
• System fuel utilization efficiency, η
F
• Electric generation efficiency, η
EE
• Heat recovery unit effectiveness, ε
HRU
• Absorption chiller coefficient of performance, COP
AbChiller
• Cooling tower efficiency, η
CT
• Cooling tower electric utilization efficiency, η
CT, elec
• Cooling tower pump efficiency, η
Pump
In addition, the system provides real-time monitoring for the following conditions:
• Fuel input rate to the turbine, ρ v LHV
Fuel Fuel,Turbine Fuel
• Auxiliary fuel input to duct burner, v
Fuel,Aux