Civil Engineering Reference
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for the thermal subsystem:
Q
b
¼
Q
þ
Q
hw
ð
9
Þ
where:
E
grid
the quantity of electricity consumed from the grid;
COP
C
the coef
cient of performance of the compression chiller;
Q
b
the heat produced by the boiler
Decentralized energy producing system. In the case of the decentralized system,
two solutions are applied for the supply with electricity:
(a) On-grid (or open) system
This solution produces combined heat and power by using a CHP technology
[
23
,
24
], and cold for air conditioning is generated by means of an absorption
refrigerator making use of the
heat (Fig.
11
). The CHP are sized in
order to satisfy the maximum heat demand, so that they generate power in excess of
customer needs. This excess power is exported to the utility grid.
The characteristics of the CHP prime movers can be effectively and synthetically
described by means of the electrical ef
“
cogenerated
”
ciency and the thermal ef
ciency. For an
absorption refrigerator, the COP
a
can be de
ned as the ratio of the desired cooling
energy output to the relevant input (thermal energy for steam-fed, hot water-fed, or
exhaust-fed absorption chillers).
The energetic balance of this system is:
for the electric subsystem:
E
CHP
¼
E
E
grid
ð
10
Þ
E
grid
Imported/
Exported
electricity
E
Power
Electricity need
E
CHP
C
Cold for space
conditioning
Absorbtion
chiller
Natural gas
CHP unit
Q
CHP
C/COP
a
Heat for space
heating (winter)
Hot water
Q+Q
HW
Heat
Fig. 11 Decentralized on-grid energy producing system
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