Combined Micro-Systems - Design for Micro-Combined Cooling, Heating and Power Systems - page 84

needed is purchased from the utility grid. The thermal energy requirement of the
site may be met by the cogeneration system alone or by additional boiler.

Q CHP ¼ Q CCHP Q ad ð 24 Þ

(e) Mixed-match mode, In certain periods of time, the heat-match mode is fol-
lowed, while in other periods, the electricity-match mode is followed. The
decision is based on considerations such as the load levels, the fuel price and
the electricity tariff at the particular day and time.
(f) Stand-alone mode, (Fig. 20 ). There is complete coverage of the electrical and
thermal loads at any instant of time, with no connection to the grid. This mode
requires the system to have reserve electrical and thermal capacity, so that in
case a unit is out of service for any reason, the remaining units are capable of
covering the electrical and thermal load. This is the most expensive strategy, at
least from the point of view of the initial cost of the system.

The energetic balance equations are:

C 0
COP c

E CHP ¼ E CCHP E ad ¼ E þ E ad ð 25 Þ

C 0
COP a

C

Q CHP ¼ Q CCHP Q ad ¼

þ

Q hw þ

ð Þ

Q Q ad 26

where C ' is cold produced by compression chiller, C is cooling load.

The energy demand
of the residential
building

mCCHP energy production

PV
electricity

Electricity
switch-
board

Electricity
load

Compression
chiller

Combined
heat &
power

Heating
load

Heat

Heat
rejection
unit

Thermally
driven
chiller

Cooling
load

Back-up
heater

Cold

Fig. 20 Stand-alone mode