Page 303 - Sustainable On-Site CHP Systems Design, Construction, and Operations

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This process relies on the monitoring algorithms described next. The CxV algorithms
provide the logic by which measurements on performance are interpreted, relative to
performance expectations, to identify during initial operation of the CHP system
deficiencies in the performance of the system and major individual components. By
verifying the performance of the individual components, deficiencies in overall system
performance can be isolated so that follow-up efforts can be targeted at the offending
components. Some deficiencies may span multiple components of the system. In these
cases, controls for component integration are identified as needing rechecking and fur-
ther commissioning. The outputs of the CxV algorithms are alarms, quantitative indica-
tors of deficiencies, and supporting information to help guide corrective actions.

Component Monitoring
CHP system components can be combined in various ways to create CHP systems (see
Fig. 1-2) and, therefore, these algorithms can be used to monitor the components in
any of these systems.
Prime Movers
The prime mover converts chemical energy in the fuel to rotational mechanical energy,
which then turns an electric generator. As discussed in Chap. 2, small turbines and
reciprocating engines represent the most commonly used prime movers for CHP sys-
tems, especially those with electrical outputs of less than 1 MW. Both of these prime
movers release waste heat in exhaust gases and through their jackets. Jacket losses are
not sufficiently large for most small turbines to warrant heat recovery, but for recipro-
cating engines, water at approximately 180ºF or higher can be recovered by circulation
of cooling water through the engine jacket. For purposes of analysis, the prime mover
and electric generator will be considered as a single component. So the useful energy
output is the electric power (W ), the rate of energy input is the energy content (based
elec
on lower heating value, LHV) of fuel flowing into the prime mover (Q ), and the
Fuel,engine
unused power released from this component is the sum of the heat losses in the exhaust
gases and through the jacket.
Efficiency of Prime Movers
The electrical generation efficiency (η ) for the prime mover/electric generator combina-
EE
tion is
W
η = elec (17-2)
EE Q
Fuel,engine
This is also the electric generation efficiency of entire CHP systems for which there
is no additional electricity production (e.g., by a steam turbine) using heat recovered
from the exhaust gases of the prime mover and no additional fuel input to other com-
ponents for supplemental heating. The rate of energy input to the engine can be
expressed as

Q = m LHV
Fuel,engine Fuel Fuel
=ρ v LHV (17-3)
Fuel Fuel Fuel