Study On The Energy-saving Performance Of A New Structured Hybrid Air Conditioning System

Reducing the energy consumption of fresh-air treatment is the key to achieving green and low-energy buildings,and it is also one of the important measures to alleviate energy shortages and achieve the national goals of CO2 emissions peak and neutralize.The development of evaporative cooling and total heat recovery technology provides space for further improvement in the energy conservation research on fresh-air treatment.However,after extensive review,it is found that the existing design of fresh air conditioner and its hybrid air conditioning system still have some issues such as single operation mode,poor climate adaptation,and unstable energy-saving effect.Aiming at the above-mentioned key issues,this research proposes and studies a new structured design of evaporative cooling fresh air conditioner(FAC).Further,a new structured hybrid air conditioning(HAC)system combining the FAC and mechanical vapor compression cycle(MVC)system is also studied.The FAC contains multiple air-to-water heat/mass exchangers,which are connected by pipelines to form a heat exchanger network.By adjusting some pipeline valve,the FAC can switch between different operation modes for adapting to various climates.Based on the collaborative work of FAC and MVC,the HAC system has four operating modes,which can adapt to four typical climates,namely hot-humid,mild-humid,hot-dry,and cold winter climates.The HAC system has the potential of annual energy-saving operation.In order to fully understand and explore the energy consumption performance of the FAC and HAC,the main work carried out in this research includes:Firstly,the FAC was theoretically studied,which has three operating modes(FAC-CDR,FAC-EC and FAC-HH).A dimensionless analysis model of FAC was proposed,which provides an effective tool for performance analysis and optimization design.The internal heat/mass exchanger models(packed bed and finned-coils heat exchanger)were established based on the finite difference method and verified by experimental data.The effect of operating parameters,environmental parameters and structural(characteristic)parameters on the temperature efficiency,cooling/heating capacity and COP of the FAC in different modes was comprehensively analyzed.Secondly,the HAC was theoretically studied,which has three operating modes(HAC-CDH,HAC-DHR,HAC-EC and HAC-HH modes)designed for the abovementioned four typical climates.A complete analysis model of the HAC with four modes was established,which provides an effective tool for performance a nalysis and optimization design.In order to improve the accuracy and reliability of the complete model,the MVC sub-model of each mode was solved iteratively,and the evaporator and condenser were modeled by the finite difference method.Then the MVC model was verified via some experimental data.The effect of operating parameters,environmental parameters and structural(characteristic)parameters on the energy consumption,COP and energy saving rate of the HAC in different modes was comprehensively analyzed.Thirdly,based on TRNSYS software and HAC's calculation model,the energy consumption and energy saving potential of HAC in six typical cities(Urumqi,Beijing,Xi'an,Changsha,Guangzhou and Kunming)were evaluated.And then,the economic feasibility of HAC was evaluated via the static investment payback period.The results show that HAC can adapt to all typical city climates,and the annual energy-saving rate is as high as 52% to 64%.In most cities,the investment payback period for FAC is less than 2 years.Fourthly,based on the energy and exergy analysis methods,a comparative study of FAC and four conventional evaporative coolers was conducted.T he effect of ambient temperature and humidity,number of heat/mass transfer units and fresh air volume on the cooling efficiency,COP,exergy efficiency,exergy efficiency ratio and exergy destruction of the above-mentioned evaporative coolers was analyzed.The performance characteristics of each evaporative cooler under different operating conditions was summarized.The results show that FAC always has the best COP and exergy efficiency ratio,which is more significant under higher ambient temperature conditions.Moreover,under the reference condition,its total exergy destruction is the lowest.The design rationality and performance advantages of FAC were revealed.Finally,the seasonal and annual energy consumption performance of the HAC system and four conventional evaporative cooling hybrid systems were comparatively studied.Through the horizontal comparison between different hybird systems,the climate adaptability characteristics of each hybrid system were summarized.The significant advantages of HAC in climate adaptability and energy saving performance were revealed.This research proposes a brand-new fresh air conditioner and its hybrid airconditioning system,which provides a new idea for solving the issues of poor climate adaptation and high energy consumption of existing air-conditioning systems.Through this exploratory research,the FAC and HAC are comprehensively introduced,mathematically modeled in detail,parametrically analyzed,annually evaluated and comparatively studied.At the theoretical level,this research fully proves that the FAC and HAC have a significant energy-saving potential.Moreover,this research has an important guiding role for subsequent prototype manufacturing,design optimization and product promotion.It is expected to enrich and update the types of air-conditioning equipment in the future,providing consumers with more and better choices.