Exergy analysis of a solar combined cycle: organic Rankine cycle and absorption cooling system

Lavinia Grosu,Alexandru Dobrovicescu,Andreea Marin,Diogo Queiros-Conde

doi:10.1007/s40095-015-0168-y

Abstract

In this paper, exergy analysis is used to evaluate the performance of a combined cycle: organic Rankine cycle (ORC) and absorption cooling system (ACS) using LiBr–H2O, powered by a solar field with linear concentrators. The goal of this work is to design the cogeneration system able to supply electricity and ambient cooling of an academic building and to find solutions to improve the performance of the global system. Solar ACS is combined with the ORC system—its coefficient of performance depends on the inlet temperature of the generator which is imposed by the outlet of the ORC. Exergetic efficiency and exergy destruction ratio are calculated for the whole system according to the second law of thermodynamics. Exergy analysis of each sub-system leads to the choice of the optimum physical parameters for minimum local exergy destruction ratios. In this way, a different connection of the heat exchangers is proposed in order to assure a maximum heat recovery.

Highlights

The use of renewable energy to power energetic systems leads to the diminution of the pollution and in the same time of the operation cost of the system
In this paper, exergy analysis is used to evaluate the performance of a combined cycle: organic Rankine cycle (ORC) and absorption cooling system (ACS) using LiBr–H2O, powered by a solar field with linear concentrators
The goal of this work is to design the cogeneration system able to supply electricity and ambient cooling of an academic building and to find solutions to improve the performance of the global system

Summary

Introduction

The use of renewable energy to power energetic systems leads to the diminution of the pollution and in the same time of the operation cost of the system. A combined system, organic Rankine cycle (ORC) and an absorption cooling system (ACS) using LiBr/H2O, is studied Both the sub-systems are connected to the same water flow heated at 140 °C on a solar field installed on the rooftop of the building. ORC system uses an organic fluid as working fluid, which in the vapor state drives the turbine to power electricity [8] It is a hopeful system for heat conversion to mechanical power at low temperature, adapted to solar applications. Several fluids were compared in previous works and it was found that R245fa provide interesting performances for a solar system ORC [12, 13] For this fluid, the mechanical power is the higher for the same sun conditions and ambient temperature, which implies the higher thermal efficiency (for the same input energy or fuel). The fuel of the heat exchanger in terms of exergy represents the exergy flow available on the main flow: E_ xRHE ORC 1⁄4 E_ xTQmHHE

À T0 TmH

Results

Conclusion