Decentralized Poly-generation of Energy: Basic Concepts - Design for Micro-Combined Cooling, Heating and Power Systems - page 47

SHP

CHP

100

33

100

15

18

Fig. 6 Energy balance of separate vs. combined production

2.2.2 Fuel Utilization Ef ciency

Fuel utilization ef ned as the ratio of net power output to net

fuel consumption, where net fuel consumption excludes the portion of fuel used for
producing useful heat output. Fuel used to produce useful heat

ciency (FUE)isde

is calculated

assuming that the typical boiler ef ciency, EFF H , is 85 %. FUE can be calculated

with the relationship:

E
Q F

FUE ¼ ð 6 Þ

Q H
EFF H

The difference between the primary energy in the case of separate production
and the primary energy in the case of combined production represents the primary
energy corresponding to the saved fuel.

2.2.3 Primary Energy Saving

Primary energy saving or Percent fuel savings (PES) with combined production is
obtained relating this energy to the primary energy in the case of separate pro-
duction and is calculated with the relation:

0 1

Q F

@ A

PES ¼ 1 100 ð 7 Þ

%

Q H
g Href

E

g Eref þ

Similarly, fuel saving compares the fuel used by the CHP system to a separate
heat and power system. Positive values represent fuel savings, while negative
values indicate that the CHP system is using more fuel than SHP.
Recoverable thermal energy from the various prime movers is available in one or
both of the following two forms, namely hot exhaust gases and hot water.