Optimization Of Air-conditioning System Scheme In Savanna Climate

In public buildings,the energy consumption of air-conditioning system is the major component of building energy consumption,and promoting the energy-saving operation of air-conditioning system is important to achieve building energy efficiency.As one of the important factors affecting the energy consumption of air-conditioning system,the climate not only affects air handling process,but also restricts the selection of the cold source choice of air-conditioning system.The savanna climate is distributed between 10°～20° north-south latitudes,predominantly including the East African Plateau and the southern and northern of Australia.It has obvious climatic characteristics of annual high temperature and distinct dry and wet seasons.The unique climatic characteristics make the design of air-conditioning system in this climate zone have different features from the traditional air conditioning system in China.In this thesis,a United Nations office building in West Africa located in Dakar,belong to the savanna climate zone,is taken as the object building.The preliminary design of the building and air-conditioning system was provided by the French designers,and the scheme optimization and the construction drawing design were carried out by the Chinese designers.Based on the evaluating indicators of system energy efficiency ratio,system energy consumption and annual cost,the suitable air-conditioning system was explored by CFD numerical simulation in the savanna climate area,and the air treatment process was optimized.The main research contents are as follows:Firstly,the annual load dynamic simulation of the building is carried out by using the De ST software.According to the characteristics of the savanna climatic,two sets of cold source schemes were selected,one is the water cooling chiller + dry cooler（water cooling scheme）and the other is the air cooling chiller（air cooling scheme）.According to the different air treatment processes,the whole year was divided into three air conditioning working conditions,and the humidity frequency diagram and enthalpy frequency diagram of air conditioning operation time were plotted.Based on the data of typical meteorological years,the annual operation regulation condition analysis and energy consumption analysis of air conditioning terminal were carried out.Secondly,by analyzing the operation principle of each equipment of the air-conditioning cold source system,the mathematical models of water-cooled chillers and air-cooled chillers were constructed according to the DOE-2 model.The models were then fitted and verified by using sample data.The effects of chilled water outlet temperature,cooling water inlet temperature（water-cooled chiller）,condenser air inlet temperature（air-cooled chiller）and unit load rate on the refrigerating capacity and COP of the unit were analyzed.According to the law of pump similarity,the mathematical model of the pump was constructed and simplified.According to the efficiency-heat transfer unit number method,the mathematical model of dry cooler was established,and the effects of inlet water temperature,cooling water flow rate,inlet and outlet temperature difference of cooling water,and load rate on the heat transfer efficiency of dry cooler were investigated.The energy consumption model and the evaluating index of cold source system were proposed.Afterwards,the simulation modules of each equipment of the cold source system were established and combined by the TRNSYS software.And the dynamic simulation platforms of the cold source system of the water cooling scheme and the air cooling scheme were established respectively.Finally,on the basis of the simulation platform of water cooling and air cooling system built by TRNSYS software,the water cooling scheme was gradually optimized from the aspects of cooling water temperature,cooling water temperature difference and regulation strategy.As a result,the system energy consumption of water cooling scheme was effectively reduced.The system energy consumption and energy efficiency ratio of water cooling scheme and air cooling scheme were compared and analyzed.Taking the annual cost as the evaluating index,the economy of water cooling scheme and air cooling scheme was compared.Driven by China’s “ Silk Road Economic Belt” and “ 21 st Century Maritime Silk Road”framework,the economy of many cities and regions in the savanna climate zone will develop rapidly,and the demand for air-conditioning will increase significantly.More and more abroad projects will be hosted by domestic enterprises.The research results of this thesis not only enrich the design of air-conditioning systems in the climate zone,but also provide a reference for China’s HVAC industry to expand overseas markets and accelerate the internationalization process.