Decentralized Poly-generation of Energy: Basic Concepts - Design for Micro-Combined Cooling, Heating and Power Systems - page 48

Two options for recovering heat from the hot exhaust gases from the prime
movers could be considered:

1. Direct use of the exhaust for providing process heat;
2. Indirect use via heat exchangers for producing hot water. Hot water produced
can be used to meet the needs for space heating. In applications that require
more thermal energy or higher temperatures than that available from power
generation equipment, supplementary heat is supplied using a duct burn .The
possibilities and the level of energy loss recuperation are dependent on the
energy conversion technology for CHP systems.

3 The Trigeneration Concept

Trigeneration is a basic and most popular form of polygeneration. The term
describes an energy conversion process with combined heat, cooling, and power
generation. Today, availability of CHP technologies with good electrical and
excellent overall ef

ciency has been adopted on a small-scale [ 17 ] and even on a
microscale [ 18 ] basis, with suitable applications ranging from residential houses to
schools, restaurants, hotels, and so forth. The trend toward distributed micro-
cogeneration could be signi cant in terms of increasing the local energy source

availability, reducing both the energy dependency [ 19 ] and the vulnerability of the
electrical system to the effects of grid congestions, reducing service interruptions,
blackouts, vandalism or external attacks [ 19 , 20 ] through the formation of self-
healing energy areas [ 21 , 22 ]. The advantage of combined production of heating
and power in a cogeneration (or CHP) system is obvious: the waste heat which is
always produced when electricity is generated using thermodynamic cycles is not
released into the environment but can

be used. Typical use of this heat is to heat buildings or to produce domestic hot
water. Depending on the building site and building standard, the heating season
often lasts for only 6 months or less. But for the economic viability of CHP
systems, it is important that they are used as much as possible. Therefore, other uses
of the waste heat are awakening more interest. One of the possible uses of waste
heat during the nonheating season is cooling. The concept of trigeneration is an
extension of the CHP concept through adding cold producing equipment for the
summer. Classical trigeneration solutions are represented by coupling a CHP prime
mover to an absorption chiller

— as in large-scale centralized power plants —

fired by cogenerated heat. In this scheme, the pro-
duced thermal power is exploited also in the summertime to produce cooling. In this
way, one of the biggest shortcomings that often make cogeneration unpro table,

that is the lack of adequate thermal request throughout the whole year, is made up
for by transforming the cooling demand into thermal demand.
One difference between various CCHP systems resides in the connection mode
of the cold producing device (Fig. 7 ), where: PM-primary mover; EG-electrical
generator; MCP-monitoring control and protection system; PC-personal computer.