Study On The Influence Of PVT Envelope Structure On Cooling And Heating Loads In Islamabad,Pakistan

Pakistan is the sixth most populous country in the world,and Pakistan is also an energy-scarce country.In recent years,with the growth of Pakistan’s population and industrial areas,Pakistan is facing a severe energy crisis.For a long time,Pakistan’s energy consumption has mainly relied on traditional fossil energy and very little use of renewable energy.However,with the reduction of traditional fossil energy in Pakistan,the increase of fossil energy prices and the pollution of fossil energy to the environment,it is very necessary to develop clean and renewable energy to reduce fossil energy consumption and environmental pollution.Building energy consumption in Pakistan accounts for the vast majority of total energy consumption,so how to reduce building energy consumption is a problem that needs to be solved in Pakistan.Pakistan belongs to the subtropical and semi-arid climate zone,with sufficient solar radiation throughout the year,and the development of solar energy has great potential.The PVT heat pump system can not only generate electricity but also heat,and the comprehensive solar energy utilization rate is high,which provides a new way to reduce building energy consumption in Pakistan.Therefore,this paper takes the PVT envelope structure in Pakistan as an example,aiming at the key issues of the influence characteristics of the PVT envelope structure on the cooling and heating load and thermal performance of the building,and analyzes the research status of the PVT envelope structure.After that,using the methods of theoretical analysis and mathematical modeling,the following researches were carried out:Firstly,the composition of the PVT heat pump system and the heating principle of the PVT heat pump system are analyzed in this paper,and the mathematical model of the PVT heat pump system is established for each component of the PVT heat pump system.A 10 coefficient model of PVT heat pump system performance parameter prediction is proposed,and a PVT heat pump system performance parameter prediction model is established,and the accuracy of the model is verified by experimental data.Secondly,on the basis of establishing the performance parameter prediction model of PVT heat pump system,three different forms of PVT envelope structures(ventilated,ventilated closed and close-fitting)are proposed,and different forms of PVT envelopes are established.The heat transfer model of the structure and the calculation model of the cooling and heating loads were established,which also verified the accuracy of the model.Finally,based on the established heat transfer model of the PVT envelope,a simulation program was developed in MATLAB.Taking the building in Islamabad,Pakistan as an example,the temperature and cooling and heating loads of each layer of the PVT envelope were numerically simulated,and the PVT envelope was analyzed.Influence on building thermal insulation performance,ventilation channel width and envelope inclination on cooling and heating load of PVT envelope.The simulation results show that:(1)The change of the inner surface temperature of the ventilated and ventilated closed PV roofs with the outdoor comprehensive temperature is delayed by 1 to 2 hours compared with ordinary roofs.The time that the inner surface temperature of the close-fitting PV roof changes with the outdoor comprehensive temperature has almost no delay compared with the ordinary roof.The temperature attenuation factor of the ventilated PV roof is the largest,and the ventilated PV roof can better maintain a stable indoor temperature.The existence of PV modules increases the heat transfer resistance and thermal inertia index of the original envelope structure,and the existence of PV modules improves the thermal insulation performance and thermal stability performance of the original envelope structure.(2)The peak cooling loads of ventilated PV and PVT roofs are reduced by42% and 75% respectively compared with ordinary roofs,and the peak heat loads are reduced by 13% compared with ordinary roofs.The ventilation type PVT envelope structure can reduce the envelope structure.(3)Considering the power generation,heating capacity,compressor power consumption and the cooling and heating load of the envelope structure of the PVT heat pump system,the heat pump type PVT ventilation envelope structure is most suitable in Islamabad,Pakistan.(4)Through the simulation of the cooling and heating loads of different channel widths of the ventilated PV enclosure,it is found that the cooling and heating loads decrease with the increase of the channel width,and the optimal width of the ventilation channel is 300 mm.(5)Through the simulation of the cooling and heating loads of the PVT envelope on different inclined planes,it is found that the variation trend of the cooling load with the slope angle and the variation trend of the solar irradiance with the slope angle are the same,and the variation trend of the heat load with the slope angle and the solar radiation The variation trend of illuminance with slope angle is opposite.In Islamabad,Pakistan,the cooling load on the vertical surface is the smallest in summer,and the cooling load on the horizontal surface is the largest.In winter,the heat load on the horizontal surface is the largest,and the heat load on the 60-degree inclined surface is the smallest.