Trigeneration

Trigeneration is a combined production of electric power, heat and cold. Technologically, this means combining a cogeneration unit with absorption cooling unit.
In this process, cold is being produced by absorption cooling machine, that consumes heat (and not electric) power.
This is a very efficient, as it provides for utilization of heat in summer, out of the heating season, whereby the unit is used all year round providing good return on investment. There are two main ways to integrate cogeneration system with the cooler; they are compression and absorption.
Absorption cooling unit uses thermochemical (instead of mechanical) compressor for compressing vapor of the cooling agent. Absorption unit uses solution of two working media, where one is cooling agent, and the second one is absorbent. One working body, the cooling agent, must have low boiling temperature and can be dissolved or absorbed by a second working body, the absorbent, which may be either liquid or solid.

Trigeneration diagram

Absorption machine

Another advantage of absorption cooling compared to compressor cooling (besides the ones mentioned above) is that this process uses cheaper heat energy instead of more expensive electric power, which is the case for compressor cooling. Absorption cooling is quiet, simple and very dependable. Disadvantages of absorption cooling compared to compressor cooling is higher costs, bigger size and weight of the installations. Cogeneration systems provide for general efficiency of use of the fuel at the level of 90% (in real life from 86 to 92%), while traditional separate generation of electricity and heat gives only 500-60%. Total losses at production and transportation of the heat and electrical power ranges from 45% (as specified in the norms) to 60% and more (actual) from the input energetic potential of the fuel.
This explains for the growing popularity of decentralized combined sources of electric and heat supply. Such energy units have several advantages, namely: short term of construction, higher reliability of heat supply, lower inertia of thermal regulation and lower losses in the heating networks. Disadvantages include difficulties in placing such units and the issue of transmitting the excess of electric power to central network.

Trigeneration is used in the following areas:
Local air conditioning: to provide air conditioning (cooling) to apartment buildings, houses, commercial property and sometimes industrial facilities by means of communal networks (rather than individual air conditioners).
In such cases absorption coolers (chillers) are used; they are easily integrated with cogeneration equipment. Main reasons for that are: use of heat to produce cold during summer time levels the seasonal need for heat energy; water is used in chiller as cooling agent (instead of harmful chloro- and fluoro-hydrocarbons that are used in traditional individual air conditioners).
Chillers may be located at the cogeneration system or at the location of specific end users. Time limit related to low limit of capacity of absorption chillers available on the market today, makes effective their use in the covered areas from 300-400 sq.m and bigger.

Industrial air conditioning
In some areas of industry, especially in food industry, there is a need in cool water (with temperature of 10-15 C) which is used in production processes. During the summer, the temperature of the river water is 25-30 C (beer brewers use cool water for cooling the end product, dairy factories use it to cool milk, etc.). Producers of frozen food use temperature of -20 to -30 C 24 hours a day 365 days a year.
Each trigeneration project is unique; it is due to external factors (like fuel cost, reliability of suppliers, network tariffs, etc.) and internal factors (like the time profile of the need in heat and electricity, peak loads, level of dependability and quality of power supply).
To make the use of trigeneration system commercially effective, it is necessary to conduct preliminary analysis and undertake the measures to increase energy efficiency of the entire object. Detailed evaluation of the economics of the project plus control of its implementation will provide for economically sound solution.

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