Decentralized Poly-generation of Energy: Basic Concepts - Design for Micro-Combined Cooling, Heating and Power Systems - page 52

for the thermal subsystem:

￿

C
COP a

Q CHP ¼

þ

Q hw þ

ð Þ

Q 11

where:
COP a the coef cient of performance of the ad/absorption chiller;

(b) Off-grid (or '' isolated '' ) system

Since they do not involve importing/exporting electricity from/to the utility grid,
small power plants are sized in order to satisfy the maximum customer needs of
electricity. This implies that the amount of

'' ''

cogenerated heat is yes or not suf-

ficient to satisfy energy needs for domestic heating and air conditioning. Heat and
cold demands of the residence can be covered by adding a boiler and an absorption
chiller (Fig. 12 ). Energy balance of the system is the following:

for the electric subsystem:

￿

C 0
COP C

E CHP ¼

þ ð Þ

E 12

for the thermal subsystem:

￿

C 0
COP a

C

Q b þ Q CHP ¼ Q þ Q hw þ ð 13 Þ

E

Power

Electricity need

C'

Compres-
sion chiller

E CHP

Cold for space
conditioning

CHP unit

Natural gas

Absorption
chiller

Q CHP

C-C'

C-C'

Heat for space
heating (winter)
Hot water

Q+Q HW

COP a

Heat

Q b

Condensing
boiler

Fig. 12 Decentralized system with off-grid energy production