Performance Analysis of an Innovative ORC-based Micro-scale CCHP System under Lebanese Conditions

International Journal of Thermodynamics (IJoT) ISSN 1301-9724 / e-ISSN 2146-1511 www.ijoticat.com Vol. 22 (No. 2), pp. 96-103, 2019 doi: 10.5541/ijot.494481 Published online: June 1, 2019 Performance Analysis of an Innovative ORC-based Micro-scale CCHP System under Lebanese Conditions M. JRADI1*, S.B. RIFFAT2 Center for Energy Informatics, The Mærsk Mc-Kinney Moller Institute, University of Southern Denmark, 5230 Odense M, Denmark 2 Institute of Building Technology & Institute of Sustainable Energy, Faculty of Engineering, University of Nottingham, Nottingham, UK *Corresponding Author Email: 1 Received 10 December 2018, Accepted 06 May 2019 Abstract Considering the high demand for cooling, heating and electricity and with more than 300 annual sunny days, an innovative hybrid biomass-solar driven micro-scale tri-generation system is proposed to provide cooling, heating and electricity under Lebanese conditions. The system comprises an organic Rankine cycle-based combined heat and power unit, a liquid desiccant dehumidification unit and a dew point evaporative cooling unit. A complete technical, economic and environmental assessment of the tri-generation system is performed to assess its applicability and feasibility. Employing a 2 kWe ORC-based CHP unit, the useful heat output ranges between 4.2 and 11.75 kW, with an electric power capacity between 0.7 and 1.92 kW. The maximum hourly cooling capacity delivered by the coupled cooling and dehumidification system is attained in August with 8.7 kW. The tri-generation system allows annual savings of 8225 USD on the heating bill, 960 USD on the electricity bill and 950 USD on the cooling bill compared to conventional production technologies. In addition, the CO 2 emissions reduction ranges between 3.1 tons in June and 9.2 tons in March. The results of this study demonstrate the large potential of using such tri-generation systems under the Lebanese conditions compared to the conventional separate energy production technologies. Keywords: Micro-scale tri-generation system, Organic Rankine cycle; Evaporative cooling; Liquid desiccant dehumidification; Techno-economic and environmental analysis. 1. Introduction Achieving a secure and reliable energy production and supply sector is a major concern for every country and thus establishing and developing renewable and alternative energy supply technologies and systems is a priority. Through covering both heating and electricity demands, combined heat and power (CHP) is one of the alternative energy efficient technologies [1] which has been established and developed with a major contribution in the energy production and supply scheme in various countries. CHP systems offer high operation flexibility and reliability with a simultaneous heat and power production and the possibility to be driven by alternative and renewable energy resources including solar thermal energy, biomass combustion heat and waste heat. A standard CHP system allows more rational use of energy resources and is capable of providing different products including hot water, space heating and electricity, with higher efficiency compared to conventional separate production systems [2]. The prime mover is the heart of the CHP system and the responsible for the simultaneous heat and electric power generation. In the recent decades, various prime movers have been considered for CHP applications including gas turbines, reciprocating engines, Stirling-based units, Rankine cycle-driven units and fuel cells. Despite the numerous advantages presented by CHP systems in terms of energy production and supply compared to separate energy production units, such systems have major drawbacks [3] including the dominance of large-scale CHP units and the *Corresponding Author limited number of micro-scale energy efficient CHP systems convenient for residential and building applications. Another disadvantage concerns the drop in the overall CHP system energy efficiency in the summer season when there is no need for heating and the cooling need is very high, making such system unfeasible and inappropriate in areas with hot and temperate climates. To overcome these challenges, a new concept of ‘tri-generation’ [4] was introduced in the recent years, coupling the standard CHP unit with a thermally-driven cooling/refrigeration technology, and thus delivering heating, electricity and cooling as energy products. A tri-generation system generally consists of five main components: prime mover, electricity generator, thermally-driven cooling unit, heat recovery unit and a management and control unit. A typical tri-generation system is presented in Figure 1, where the CHP unit is the heart of the system, with its standard operation and heat and electricity generation. In addition, excess heat generated in the form of flue gases or hot water is employed to drive the cooling technology using heat recovery units, and thus fulfilling the cooling demand. Compared to conventional separate energy production units, tri-generation systems allow various technical, environmental and socio-economic benefits [5] including higher energy production efficiency, lower operational and maintenance costs, less greenhouse gas emissions and higher energy supply reliability and security. Different cooling technologies could be used within the tri-generation system including absorption- and Vol. 22 (No. 2) / 96 adsorption-based cooling, ejector cooling, liquid and solid desiccant cooling [6]. Figure 1. A typical tri-generation system. For micro-scale tri-generation systems serving houses and residential buildings, Rankine- and Stirling-driven units are the two most favorable and feasible prime movers due to their reliable operation, low emissions, relatively high energy efficiencies and the capability to be integrated and driven by renewable energy resources. However, Stirling engines require relatively high-quality heat and is generally accompanied with high investment and operation costs. Thus, Rankine-based units provide an effective technology to fulfil heating and electricity demands of residential applications with an acceptable economic feasibility and energy efficiency. While the conventional water-based Rankine cycle-driven units have been used excessively in various applications in the last decades, such systems are associated with major problems [7] including the high risk of turbine blades erosion, high evaporator pressure and the excessive need for superheating to prevent condensation during the expansion phase. This in turn results into more expensive components, higher investment and operational costs and major safety concerns. Thus, organic Rankine cycle (ORC)-based systems [8,9], using organic working fluids instead of water, have been developed recently and received large interest with a growing block of research and investigations in various energy production and supply applications. Such systems allow eliminating the majority of the problems (...truncated)