| Low latitude islands locate in extremely hot and humid climates,with extreme climatic characteristics such as high temperature,high humidity and strong solar radiation.The low latitude island's buildings are subject to various types of extreme climate conditions throughout the year,and it is difficult to meet the basic thermal comfort requirements of the human body only by passive technologies such as heat insulation,shading,and natural ventilation technology.The construction of indoor environment relies on cooling and dehumidification equipment system all year round.But the islands are scattered in vast oceans far from the land,where conventional energy is scarce.It would be too costly to use the long-distance transported fuel to power air conditioners.Low latitude islands in extremely hot and humid climates have a good supply of solar energy,and there is a positive synchronous relationship between heat and humidity load and solar energy supply.Therefore,the best way to adjust the thermal environment of buildings is the solar air conditioning system.With solar air conditioning running all year round in extremely hot and humid climates,the solar air conditioning has a high return on investmentyield.China's building thermal design climate zone does not include low latitude islands in extremely hot and humid climates.The current building standards and load calculation methods are based on high latitude areas,which is not applicable to low latitude islands.Therefore,it is necessary to reconstruct the local building cooling load characteristics according to the climatic characteristics of the islands,and the solar cooling and dehumidification system will put forward more calculation parameters,new design principles and methods.Given the limited area of these islands,it is difficult to provide additional solar energy collection sites.The solar energy resources required for air conditioning can only be collected and converted through photovoltaics or heat collectors on the roof of the building.Therefore,the dynamic and contradictory relationships between building cooling load and cooling capacity,electricity consumption and heat consumption,as well as wet load and dehumidification regeneration must be mediated internally through each building's own structure in order to achieve a balance between energy supply and consumption.Based on this,this study focuses on six aspects: cooling load characteristics of low latitude Island,building load reduction strategy,self-sustaining theory and design of solar air conditioning system,performance and matching optimization of solar air conditioning system,experimental research of solar air conditioning system,and efficiency enhancement technology of photovoltaic power generation.The main research contents and conclusions are listed below:(1)The calculation method of building load under various climatic conditions in low latitude island is modified.According to the climate characteristics of high temperature,high humidity and strong radiation of low latitude islands,and the orientation characteristics of small difference between four seasons,large solar altitude angle and small difference between north and south of buildings,the coupled equations of heat and humidity with temperature and humidity as the driving force of heat and humidity transfer are established.The calculation method of building load based on heat and humidity transfer under various climatic conditions of low latitude island is proposed,which improves the lack of existing codes for load calculation of low latitude island.The characteristics of building load and orientation load of low latitude islands are clarified.The overall characteristics of cold load are: the average load is small,the fluctuation is small,the annual duration is long,and the accumulated load is large.The characteristics of orientation load are: the difference between east and west is large,and the difference between north and south is small.Moreover,the influence of radiation,temperature difference,humidity and other factors on building load is clarified.The characteristics of building load composition are: the proportion of relative humidity is the largest,followed by solar radiation,and the proportion of temperature difference is the smallest.(2)Strategies for reducing building load on low latitude islands are proposed.In response to the high building load of low latitude islands,combined with the characteristics of high air temperature and strong radiation in all directions in low latitude areas,developed with passive energy saving technology of building envelope structure heat insulation,ventilation and shading,a comprehensive load reduction strategy of double-layer ventilation and sunshade roof,comprehensive external sunshade and thermal insulation layer is proposed.After calculation,the comprehensive load reduction rate is as high as29.2%.The load reduction strategy can reduce the building load to its maximum extent,which lays a practical foundation for the operation of solar air conditioning system in low latitude islands.(3)Suitability analysis and self-sustaining theory design of solar air conditioning system are conducted.According to the climate characteristics of the extremely hot and humid climates,the suitability of common solar air conditioning systems is analyzed.A solar air conditioning dehumidification combined system of "photovoltaic drive,collector regeneration,air conditioning cooling and independent dehumidification" is proposed,which is suitable for island buildings.The system adopts the coupling operation mode of photovoltaic drive and photothermal regeneration.It realizes the combination of photovoltaic drive,photothermal regeneration,condensation recovery,temperature,and humidity independent control.The whole process of "cooling load characteristics,reduction strategy,energy balance" is proposed as a self-sustainable design method for solar air conditioning buildings.Relying on the building's own collection,conversion and storage of solar energy resources,this study finally realizes the self-sustaining of air conditioning energy consumption through the reasonable matching of cooling load and the dynamic process of refrigeration,as well as dehumidification and regeneration.By establishing a self-sustained energy balance model for solar air conditioning buildings,it is calculated that relying on the building's own area to collect and convert solar energy can meet the self-sustained operation of solar air conditioning systems for nearly five-layer island's buildings.(4)The performance and matching optimization of solar air conditioning independent dehumidification system.The mathematical models of solar air conditioning solution dehumidification system and solar air conditioning rotary dehumidification system are established.The results of MATLAB numerical simulation show that,in solar air conditioning solution dehumidification system,the regeneration temperature and heat increase with the increase of outdoor air humidity.The regeneration temperature and heat decreased with the increase of indoor air relative humidity.The condensing heat recovered by the system increases with the increase of dehumidification capacity.For solar air conditioning rotary dehumidification system,the dehumidification capacity grows with the increase of regeneration temperature and drops with the increase of return air ratio.The cooling capacity grows with the increase of regeneration temperature and drops with the increase of return air ratio.With the increase of the regeneration temperature,the condensation heat of the refrigerator and the preheating temperature of the regeneration air increase.The two combined systems can better match the low temperature heat source for waste heat recovery and effectively reduce the energy consumption of the system,which is suitable for the application in the extremely hot and humid climates.(5)Experimental study on solar air conditioning rotary dehumidification system.In the State Key Laboratory of green building in Western China,a combined system of solar air conditioning and wheel dehumidification was built to test the design and operation performance of the system,including condensation heat recovery,energy balance of power generation and consumption,etc.The test results show that the cooling and dehumidification performance is good.The regeneration temperature of the solar air conditioning system can be increased by 15.3 ? and 90.4 ? respectively through the condenser waste heat recovering and collector heating.In addition,the solar air conditioning system not only realizes energy self-sufficiency,but also generates 7.2% of the remaining electricity.It can be seen that it has a good application significance for the extremely hot and humid climate area where conventional energy is scarce but solar energy resources are abundant.(6)Low latitude Island photovoltaic power generation efficiency technology.Photovoltaic system is an important factor affecting the operation reliability of solar air conditioning system.The high temperature weather in low latitude island will make the photovoltaic temperature rise significantly,resulting in the reduction of power generation efficiency.In order to improve the guarantee rate of solar air conditioning system,the cooling and efficiency of photovoltaic system is studied from the perspective of thermodynamics.A tube plate photovoltaic active cooling system is proposed,and the structure layout and parameters are optimized.Through the establishment of photovoltaic cooling system thermoelectric coupling model,the influence of tube spacing,pipe diameter,tube spacing and flow velocity on photovoltaic cooling effect is analyzed.Numerical simulation shows that when the parameters of tube plate PV cooling system are type C,pipe diameter is 20 mm,tube spacing is 50 mm and flow velocity is 0.10 m/s,the cooling effect is the best.Moreover,according to the optimal configuration,an experimental platform of photovoltaic cooling system is built.The test results show that the photovoltaic cooling system can effectively reduce the photovoltaic surface temperature,which is about 31.4 ? lower than the non-cooling system.Through data fitting,it is found that the conversion efficiency and efficiency of PV show an exponential function relationship with mass flow.It increases and tends to be stable with the increase of mass flow,and gradually reaches the maximum value of 11.9% and 12.4%. |
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