Combined Micro-Systems - Design for Micro-Combined Cooling, Heating and Power Systems - page 77

Table 8 The default values
of the power to heat ratio [ 21 ]

Type of the unit Default power

to heat ratio

γ

Combined cycle gas turbine
with heat recovery

0.95

Steam backpressure turbine

0.45

Steam condensing extraction turbine

0.45

Gas turbine with heat recovery

0.55

Internal combustion engine

0.75

If the actual power to heat ratio of a cogeneration unit is not known, the default
values given in Table 8 , may be used.
Cogeneration applications in buildings can be designed to:

satisfy both the electrical and thermal demands,

￿

satisfy the thermal demand and part of the electrical demand,

￿

￿ or satisfy the electrical demand and part of the thermal demand

￿ or, most commonly, satisfy part of the electrical demand and part of the thermal

demand.

In addition, cogeneration in buildings can be designed for peak shaving appli-
cations, i.e., the cogeneration plant is used to reduce either the peak electrical
demand or thermal demand.
In the case of single-family applications, the design of systems poses a signif-
icant technical challenge due to the potential noncoincidence of thermal and elec-
trical loads, necessitating the need for electrical/thermal storage or connection in
parallel to the electrical grid.

3 The mCCHP Systems

3.1 Architecture of the mCCHP Systems

Trigeneration applications in buildings have to satisfy either both the electrical and
the thermal demands, or to satisfy the thermal demand and part of the electrical
demand, or to satisfy the electrical demand and part of the thermal demand.
Architecture of the mCCHP systems depends on the magnitude of the electrical and
thermal loads, whether they match or not, and on the operating strategy.
The trigeneration system can run at part-load conditions, the surplus energy
(electricity or heat) may have to be stored or sold, and de ciencies may have to be

made up by purchasing electricity from other sources such as the electrical grid [ 6 ].
The surplus heat produced may be stored in a thermal storage device, such as a
water tank, or in phase change materials, while surplus electricity may be stored in
electrical storage devices such as batteries or capacitors.