Fluid selection optimization of a combined cooling, heating and power (CCHP) system for residential applications

Abstract

This research paper mainly deals with a comprehensive techno-economic modeling and multi-objective optimization of a CCHP system for residential application. An internal combustion engine (ICE) proposed as the prime power and a combined organic Rankine cycle (ORC), ejector refrigeration cycle (ERC), and domestic water heater (DWH) is considered to recover the wasted heat from the ICE through exhaust gas and water jacket. Their common working fluids namely R-134a, R-600, R-123, and R-11 are selected in this study. A comprehensive multi-objective optimization is applied to determine the optimal design parameters of the system. Two major objective functions, exergy efficiency that should be maximized and total cost rate of the system to be minimized are considered while satisfying several reasonable constraints. The total cost rate as an objective function consists of purchase equipment costs, fuel cost, and environmental impact cost. Diesel engine capacity, diesel engine part load, expander inlet pressure, expander extraction pressure, extraction ratio, condenser pressure, and evaporator pressure are selected as decision variables. A developed multi-objective genetic algorithm is used as an optimization tool with ability of better optimal results with less computer running time. It is observed that R-11 working fluid is a good candidate from both exergy efficiency and total cost rate point of view. To examine the effect of each decision variable on objective functions, a sensitivity analysis is performed. Finally, the ability of the system is studied to meet the cooling, heating, and electricity demand of a detached house with a defined load in Tehran.