Study On The Energy Performance And Optimal Design Of Semi-transparent A-Si PV Windows

Building energy saving is an important way to reduce energy consumption and realize sustainable development.The window is the key component of heat transfer in building envelope,which is one of the main factors influencing indoor thermal environment and building energy savings.Developing new energy saving window system is of great importance for building energy savings.Photovoltaic(PV)Windows are the use of semi-transparent photovoltaic glass on the building,which utilize the PV material to replace the glass.It cannot only reduce the energy consumption of air conditioning,but also utilize solar power to generate electricity for building use.The PV window has caught the attention of researchers.This paper investigates the energy saving performance of different types of semi-transparent a-Si PV Windows,and optimizes the structures of semi-transparent a-Si PV windows.In order to be concise,PV windows in the research content are referred to semi-transparent a-Si PV windows.PV windows can be divided into single-pane PV Window(SPPVW),PV insulating glass unit(PV IGU)and PV double skin facade(PV DSF)depending on the difference in structure.In this paper,energy saving performance of SPPVW,PV IGU and PV DSF is studied and compared through experiment and simulation.In this paper,the spectral characteristics,heat transfer characteristics and power generation characteristics of semi-transparent a-Si PV modules are measured at first.The PV window simulation model was established based on measured PV module characteristics.Meanwhile,experimental rigs of PV windows are set up to analyze the performance of PV windows.Then the experimental data which are obtained in PV test are used to validate this model.Finally,validated PV window models are used to conduct the performance analysis and optimization design.In this paper,the Sandia model parameters of a-Si PV modules are determined through indoor and outdoor laboratory instruments,and the Sandia models are utilized to calculate the power generation of a-Si PV modules.The structure of SPPVW is simple.It utilizes semi-transparent PV modules to replace glasses.SPPVW can reduce the solar heat gain coefficient(SHGC)of single-layer glass Windows,while increases the thermal resistance of single-layer glass Windows.At the same time,SPPVW can also produce power to supply building.In this paper,the model of SPPVW is established,and the model is validated by experimental data.Then energy saving performance of SPPVW in the Hong Kong region and Changsha region was analyzed by using the validated model.The results showed that in the Hong Kong region,the lowest energy consumption in winter was found to be low-e glazed Windows.Compared with single-glazed windows,SPPVW can save up to 7.3%energy.In Changsha region,the low-e window achieves the best energy saving performance,while the SPPVW has the highest energy consumption.The main reason consists of two aspects,the first is that the SHGC of SPPVW is relatively low,and the heat gain of the building is limited,and the second is that SPPVW have higher U values and higher indoor thermal losses.Therefore,this paper examines the energy performance of PV IGU in the next content.With the air sealed in the cavity,the thermal resistance of the PV windows increase and the heating load of the PV windows in winter could be reduced.This paper studies the energy saving performance of PV IGU by experiment and simulation.The PV IGU consists of PV module and inner glass.Between the PV module and inner glass,there is a sealed air layer in the center,which can improve the insulating performance of the PV IGU.In this paper,PV IGU test rig was established,and the heat transfer,daylighting and power generation performance of the PV IGU were studied.At the same time,this paper also establishes the simulation model of PV IGU to simulate the energy saving performance of the PV IGU.The PV IGU simulation model is developed based on the building energy simulation software EnergyPlus.In the simulation model,the heat transfer model,daylighting model and power generation model are utilized to simulate the heat transfer performance,daylighting performance and power performance simultaneously.The simulation model is validated by the experimental data obtained from the PV IGU test rig.The validated model is used for the optimization design and performance research of the PV IGUs.The results show that,in Hong Kong,the optimized PV IGU which utilize low-e glass as the inner glass has the best energy saving performance.The optimized PV IGU can save 20.8%and 10.7%respectively in energy consumption,compared with insulating glass units and Low-e windows.According to the above research content,it was found that due to the improvement of the thermal resistance,the energy saving performance of PV IGU is very good.Since PV DSF is another kind of PV window which is energy-efficient and possesses the advantages of low SHGC in summer.Thus,this paper compares the energy saving performance between PV IGU and PV DSF.A comparative analysis on heat transfer performance,daylighting performance and power generation performance of PV IGU and PV DSF is performed.The results indicate that the SHGC and U values of the PV DSF and the PV IGU are 0.152 and 0.238,2.535 W/(m2 · K)and 2.281 W/(m2 · K),respectively.During the test period,the average daily energy conversion efficiency of the PV DSF and the PV IGU was 5.7%and 5.6%,respectively.In this paper,the energy saving performance of the PV IGU and PV DSF is analyzed by simulation.Simulation models of the PV IGU and the PV DSF are established and validated by experimental data.Then the energy saving performance of PV IGU and PV DSF in five different climate zones in China was analyzed by using the validated simulation model.The results show that the average energy saving performance of PV IGU and PV DSF is 28.4%and 30%,respectively,compared with the traditional insulating glass unit.If take advantage of the ventilation strategy of PV DSF,make full use of the characteristics of reducing cooling load in summer and increasing the passive heating in winter,PV DSF could achieve better energy saving effect than PV IGU.By analyzing the energy saving performance of different kinds of PV windows,the paper provides guidance on the further development of PV windows and lays the foundation for applying PV windows in actual buildings.