Optimal design, operation and analytical criteria for determining optimal operating modes of a CCHP with fired HRSG, boiler, electric chiller and absorption chiller

The configuration, design and operation strategy are the main factors that can affect the technical, economic and environmental performances of combined cooling, heating and power (CCHP) system. In this paper, the operation of a CCHP system with fired heat recovery steam generator (HRSG), electric chiller, absorption chiller and a boiler is classified into one of three scenarios which are determined by gas turbine size and magnitude of thermal and electric loads. The optimal operating strategies are presented for these scenarios. For scenario with high cooling loads, we derive analytical expressions for calculation of ratio (electricity price/natural gas price) values which delimit three optimal modes for providing cooling demand in summer, thereby enabling selection of optimal operating strategy without numerical optimization. We examine the optimal design of CCHP system in three climate zones based on the proposed strategy. Supplementary firing as well as a higher coefficient of performance (COP) of the absorption chiller increase system efficiency and enable reduction of gas turbine size. Our case studies show that supplementary firing, (for some values of price ratio, absorption chiller COP and climate zone) the electric chiller and/or the boiler are necessary components to achieve optimal system performance. •Analytical criteria for optimal structure and operation of CCHP system are presented.•Use of supplementary firing reduces the optimal size of the gas turbine.•Electric chiller and boiler sizes decrease because of supplementary firing usage.•Optimal structure of CCHP depends on energy prices and COP of the absorption chiller.•Electric chiller is needed for some values of electricity/natural gas price ratios.