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Top1. Introduction
The economic globalization has been wider over the years and is accompanied by an increase in energy demand and energy consumption. According to the International Energy Agency (IEA), energy consumption has increased dramatically (almost doubled) from 1975 to 2015 (Chen 2018). To traditional response to face the increase in consumption by producing more amount of energy is no longer environmentally, economic and social acceptable. Therefore, new ways to capture energy loses and reuse them in an efficient way is on focus. For example, the gases released in the energy generation processes in the thermoelectric plants, still have energy content. This energy content is normally lost by the chimneys of the plants to the atmosphere in the form of heat. If the heat is harnessed, the efficiency of the processes is improved, and losses are avoided (Feidt, Dupont et al. 2017). Conventionally, the production of heat energy and electricity is carried out in different systems. With the development of cogeneration systems, it is possible to produce electricity and heat through the same process. In the generation of electrical energy, heat is released into the atmosphere, part of which can be used to satisfy the heat needs of consumers. Being a typically decentralized process, Cogeneration allows to satisfy the consumer's heat and electrical needs, guaranteeing a efficiency of 80 to 95% (Consulting). The use of systems that allow the production of heat and electricity separately guarantee a lower efficiency, this is due to the amount of energy that is lost in these systems when compared to Cogeneration systems (to satisfy a determined energy demand, Cogeneration uses a smaller amount of fossil fuels) (Consulting). The technologies normally used in Cogeneration are based on: Alternative Internal Combustion Engine, External Combustion Engine, Steam Turbine, Gas Turbine, Fuel Cells and Hybrid Photovoltaic Thermal Solar Collectors.
The concept of trigeneration is an extension of the working of cogeneration, where exists the production of cold in addition to the production of heat and electricity. Trigeneration systems are implemented when there is a need for cooling equipment such as absorption chillers to produce cold (Baghernejad 2016, Feidt, Dupont et al. 2017). Figure 1 (Feidt, Dupont et al. 2017) presents a diagram referring to the connection of Trigeneration systems with Cogeneration systems.
In Figure 1, the area enclosed by the acronym CHP (Combined Heat and Power) represents the constitution of Cogeneration systems, while the area enclosed by the acronym CCHP (Combined Cooling, Heat and Power) represents the composition of Trigeneration systems. The implementation of Trigeneration systems has several advantages, one of these is based on more efficient, economical and reliable use of primary energy compared to the cogeneration system. This advantage is guaranteed because the heat lost in the prime mover, is recovered through a heat exchanger and used in heating and cooling systems (Baghernejad 2016, Feidt, Dupont et al. 2017). By taking use of this energy, lower energy production is needed, thereby lower social and environmental impacts are present. The technologies used for the Trigeneration Systems are based on Absorption Chillers, Adsorption Chillers, Desiccant Cooling Systems and Ejector Cooling Systems.