Page 320 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Sustaining Operational Ef ficiency of a CHP System 293

Metric Purpose Functional Relation Variables
Fuel Indicate η = ( W elec + Q ) η = fuel utilization
F
th
utilization the overall F Q efficiency
efficiency CHP system Fuel W elec = net electrical
(η ) efficiency in ⎛ ⎞ power output ∗
F
using fuel ⎜∑ W elec, j + ∑ Q th, k ⎟ Q = total useful thermal
th
= ⎝ j k ⎠ energy output of the CHP
∑ Q Fuel, l system
l Q = total rate of fuel
Fuel
use by the CHP system

(see below for other
definitions)
Value- Indicate net value of system outputs EUF = value-weighted
EUF = VW
weighted the overall VW Cost energy utilization factor
energy CHP system Fuel Y = unit value of
elec
utilization efficiency ∑ W Y + ∑ Q Y electricity produced
factor based on = j elec, j elec, j k th, k th, k Y = unit value of useful
th, j
(EUF ) monetary ∑ Q Price thermal energy output
e
VW Fuel, l Fuel,l
value of input l stream j
fuel and Price Fuel, j = price of fuel
output energy for fuel input j to the CHP
system
Cost = total rate of
Fuel
expenditure on fuel for
the system
(see below for other
definitions)
Current rate Indicate the Q = ∑ Q Q = total useful thermal
th
of useful rate of useful th j th, j energy output of the CHP
thermal thermal system
output (Q ) output for Q = useful thermal
th th, j
heating or energy output j of the
cooling by the CHP system
CHP system
=
Current Indicate the W elec ∑ W W elec = net electrical
electric net electric j elec, j power output of the CHP
power output power output system
(W ) from the CHP W = electrical output
elec elec, j
system j from the CHP system

(parasitic uses of electricity
take negative values)
=
Current total Indicate the Q Fuel ∑ Q Q Fuel = total rate of fuel
rate of fuel total rate j Fuel, j use by the CHP system
use (Q ) of fuel use Q = rate of fuel use
Fuel Fuel, j
by the CHP by fuel input j to the CHP
system system

∗ The electricity terms include negative values corresponding to parasitic electricity use by pumps, fans, etc.
TABLE 17-2 Summary of Functional Relations for CHP System-Level Metrics