Modelling And Operation Optimization Of A Multi-energy Complementary Distributed Heating And Cooling System

With rapid economic development and improvement of living standard, energy demandin China is steadily increasing. As a result, environmental problems caused by the energyconsumption are also become serious. As one of China’s three energy-hungry fields, buildingenergy consumption, a significant fraction of which is used for building heating and cooling,is growing year by year. In the background of energy conservation and sustainabledevelopment, owing to its higher energy efficiency and less emission, combined heating andcooling system is considered as an effective and sustainable solution to ensure heating andcooling. According to the integration of multi-energy complementary and combined heatingand cooling system, this paper designs a multi-energy complementary distributed heating andcooling system, which makes use of wind energy, solar energy, natural gas and electricenergy.Above all, based on the analysis of available energy resources of a combined heating andcooling system and the present development of China’s energy resources utilization, theenergy resources of the distributed heating and cooling system are determined. In addition, themain equipment of the system is selected according to the analysis of its applicability. Fullytaking into account the energy resources utilization and the type of devices, we establish theprocessing scheme of heating subsystem and cooling subsystem, and decide the finalprocessing scheme of the distributed heating and cooling system. Compared with theconventional separation production (SP) system, the system combines heating and cooling.The designed system is operated in the heating mode in winter and operated in the coolingmode in summer. Moreover, unlike traditional combined heating and cooling system, thedesigned system makes joints use of multiply energy resources, including both non-renewableenergy and renewable energy. Therefore, such an integrated energy based system can makethe energy supply sustainable and reliable concurrently.The next, this paper presents a comprehensive model of the distributed heating andcooling system. The model includes distributed heating and cooling station, water supplynetwork and terminal load. The distributed heating and cooling station model includes anoff-grid wind energy system, a solar water heater, a gas-fired water boiler, an electric waterboiler, a reciprocating chiller and an absorption chiller. The water supply network modelincludes pressure drop and temperature drop model. The terminal load model includes loadcalculation, a heating radiator and a fan coil.Afterwards, based on the model built, we also investigate an optimal operating strategy for the designed system, through which the daily running cost of system is optimized in boththe heating and cooling seasons. In order to obtained the optimal operating strategy, twoobjective functions are constructed with complex operating constraints. GSO (Group SearchOptimizer) is used to trace the optimal solution to minimize the running cost while satisfyingvariable constraints. With the optimal operating strategy, the centralized controller of thesystem can give the optimal outlet temperature set points of boilers, the optimal number ofoperating chillers and the optimal flow of pumps at an hourly rate in daily operation. In orderto verify the model and the optimal operating strategy, performance tests have beenundertaken using MATLAB, including parameter settings, simulation results and discussion.The simulation results prove the validity of the model and the strategy. It can be concludedfrom the results that GSO is able to trace the optimal solution. It can be also demonstrated thatthe strategy can determine the optimal set points for the operating devices to minimize therunning cost of the total system, taking into account the cost function and various operatingconstraints.Finally, in order to evaluate the economy and the energy efficiency of the designedsystem, the designed system is compared with the separation production system, from theperspective of running cost and energy consumption. The comparison results confirm that thedesigned system is much more energy and cost effective than the separation productionsystem in daily operation. Based on the comparison result of the running cost of two differentsystems, the investment feasibility of the designed system is further analyzed. The analysisresult shows that the designed system is feasible and applicable, and also has a shorterpayback period.