Combined Micro-Systems - Design for Micro-Combined Cooling, Heating and Power Systems - page 81

The electricity demand of the residence is composed of the electricity intake of
the residence appliances. The electricity production of the CCHP system is the
difference between the electricity demand of the residence and the energy received
from the grid:

E CCHP ¼ E E grid ð 18 Þ

3.2 Operation Modes of the mCHP Unit

In satisfying these demands, the mCHP unit may have various modes of operation.
The mode of operation is characterized by the criterion on which the adjustment of
the electrical and useful thermal output of a trigeneration system is based. The
following operation modes can be applied:

(a) Heat-match mode, where the total thermal energy for the residence is ensured
by the cogeneration unit (Fig. 16 ). As a consequence, the useful thermal
output of a cogeneration system at any instant of time is equal to the thermal
load (without exceeding the capacity of the cogeneration system), that is:

Q CHP ¼ Q CCHP ð 19 Þ

If the generated electricity is higher than the load, excess electricity is sold to the
grid; if it is lower, supplementary electricity is purchased from the grid.

The energy demand
of the residential
building

mCCHP energy production

Electricity
grid

Electricity
switch-
board

Electricity
load

Compression
chiller

Combined
heat &
power

Heating
load

Heat
storage

Thermally
driven
chiller

Heat
rejection
unit

Cooling
load

Cold
storage

Fig. 16 Heat-match mode