Experimental Study And Simulation Optimization Of The Heat-Source Tower Based Heat Pump System Based On The Energy Limit

The Yangtze River Basin is hot in summer,cold in winter,and has high humidity throughout the year.In order to solve the problem of winter heating in the Yangtze River Basin,the 13th Five-Year Plan for R&D of"Solutions to HVAC in the Yangtze River Basin"was proposed,which specified the overall project target of annual heating and air conditioning that not exceed 20k Wh/m~2,and the application of heat source tower based heat pump is one of the main ways to achieve the project’s o verall target.This paper takes a heat source tower based heat pump system in an elderly residential area in Changsha as an example,and conducts field tests and data collection for more than one year.Based on the month-by-month measured data and the data of typical day,the heat transfer characteristics of the heat source tower under different operating conditions are analyzed,as well as the energy-saving effects and problems of the heat source tower based heat pump system in actual engineering.The analysis shows that the heat source tower based heat pump system runs stably in practical applications and has a good energy saving effect.However,the analysis found that the system works under“small temperature difference and large flow rate”operating conditions of the source-side heat transfer medium circulation system and the load-side water circulation system in winter and summer,as well as low system operation efficiency under partial load rate.The annual heating and air-conditioning power consumption is 26.64k Wh/m~2,which is still higher than the project’s energy consumption target of 20k Wh/m~2.In order to meet the indoor thermal comfort,and to keep the energy consumption per unit area of heating and air-conditioning in the district within the above-specified energy consumption limit,this paper adopts a combination of active and passive energy-saving optimization strategies through actual measurement analysis and numerical simulation.A comprehensive energy-saving optimization study was performed on the system.The main works are as follows:Firstly,the heat and mass transfer model of the open cross-flow heat source tower is established,and the influence of parameters of the heat source tower inlet(inlet air dry bulb temperature,inlet air relat ive humidity,inlet air flow rate,inlet solution temperature,inlet solution flow,etc.)to the heat transfer performance are analyzed.The study found that the effect of air folw rate on heat transfer effect of the heat source tower is significant.Secon dly,based on the above conclusions,a TRNRSYS transient simulation software was used to establish a heat pump system model for a heat source tower in an elderly residential area in Changsha,and its accuracy was verified through measured data.The average relative error of the inlet temperature of the solution was 5.98%.The maximum relative error of the energy consumption of the system is 6.69%.Based on the goal of HVAC consumption not exceeding 20k Wh/m~2 throughout the year,the temperature difference be tween the supply and return solution,the number of different heat source towers,and the frequency control of heat source tower fans were analyzed.The influence of system energy consumption and the optimal operation plan of the heat source tower based heat pump system were obtained,and the optimization suggestions were put forward from the perspective of system design and operation control.Through comparison,it is concluded that the HVAC power consumption is 22.18k Wh/m~2,using the optimized temperature diffierence of solution,which is 16.74%less energy than the original system(26.64k Wh/m~2).In addition,this paper also analyzes the space for further energy savings of the heat source tower based heat pump system from the perspective of the intermitten t operation mode of the HVAC and the building envelope.Energy Plus was used to simulate and analyze the influence of system energy consumption under different intermittent operating moments,different indoor temperature setting values,and different thermal performance modes of the envelope structure on the residential area of the elderly.The results show that under the intermittent operation optimization mode of the HVAC system in this elderly residential area,the power consumption of HVAC is 22.73k Wh/m~2,which can save energy by about 14.68%compared with the original system;Reasonably setting the indoor temperature value in the intermittent mode,the annual power consumption is 20.24k Wh/m~2,which is 20.82%energy saving compared to the actual intermittent energy use mode of the existing system.Optimizing the thermal insulation structure and thermal performance of the envelope structure under the existing intermittent operation mode and temperature set value,the annual power consumption can be redu ced to 19.47k Wh/m~2,so that the residential area can reach the goal of not exceeding 20k Wh/m~2,which can save energy by about26.90%compared with the original system.In this paper,through field test analysis and simulation optimization research,an optimal operation plan for the central air conditioning system of the heat source tower based heat pump in the intermittent operation mode of residential area in the Yangtze River Basin was obtained.It has laid a theoretical foundation for the efficient operation and popularization and application of central air-conditioning systems of heat source tower based heat pumps in the region in the future.