Preparation And Performance Of Phase Change Heat Storage Floor In Solar-heat Pump Radiant Heating System

In the context of worsening global warming,the Chinese government has proposed the target of carbon peak and carbon neutrality.It is necessary for us to develop energy-saving technologies in buildings because their consumptions are important part in energy consumption in China.The application of phase change material(PCM)into building has captured much attention,which not only can bridge the imbalance between supply and demand of building energy,but also enhance the thermal inertia of the building,thereby achieving energy saving.As a kind of organic PCM,paraffin is widely used,safe and reliable.In this paper,a phase change heat storage floor using paraffin as PCM is proposed for building ground radiant heating,and the heating system is heated by the combination of solar energy and heat pump.The paper also studied the impact of phase change heat storage floor on the thermal characteristics of the experimental room through experimental tests and simulations.Different from most methods that embed PCM into the building envelope as a whole package,the phase change heat storage mortar in this paper uses the combination of PCM and building cement.First,a paraffin-expanded graphite composite phase change material(CPCM)with a melting point of 40.5℃ and an enthalpy of 220.5 k J/kg was prepared by melt blending,and the mass content of paraffin was 85 wt%.We mechanically mix the cement powder and CPCM according to a certain mass ratio,and the mass fraction of CPCM in the cement powder is 20 wt%,25 wt%,30 wt%,35 wt% and 40 wt%,and stir to a uniform dry mix powder,and then refer to " Dry-mixed ground mortar for construction" JC/T 2457-2018 preparation process,five phase change heat storage mortars with different CPCM contents were prepared.By testing the comprehensive strength,flexural strength,latent heat of phase change and thermal conductivity,it is determined that the phase change energy storage mortar with a mass fraction of CPCM of 35% has good mechanical properties,as well as high latent heat of phase change and thermal conductivity.Its comprehensive strength and flexural strength are 5.54 MPa and 2.6 MPa,respectively,the latent heat of phase change is 35.1 k J/kg,and the thermal conductivity is 2.056 W/(m·K),which can be used as an envelope structure with both load-bearing and thermal insulation properties.Then,after the leak test and the shape analysis of the microscopic SEM image,it is shown that the prepared phase change energy storage mortar solves the problem of the fluidity of the paraffin after melting.Eventually,through the test of specific heat capacity,thermogravimetric analysis and thermal cycle test,it shows that the prepared phase change heat storage mortar has high specific heat capacity and stable thermal reliability.Next,in order to test the practical application effect of the phase change heat storage floor,a solar-heat pump radiant heating system and a floor heating experimental room were built.Based on the ratio of phase change heat storage mortar,the pilot production method of phase change heat storage floor was studied.A total of 16 pieces were produced and laid in the floor heating experimental room,and another 16 pieces of ordinary mortar floor with the same shape were prepared as a control.The floor heating experimental room was built in a cold climate simulation cabin,which can simulate the outdoor environment in winter.The solar collector and the air source heat pump are used as dual heat sources to heat the room floor through the hot water supply pipe.After tested heating water of 50℃,55℃ and 60℃ in the room,the floor surface and indoor air temperature change of room were studied,and it showed that the use of phase change heat storage floor will reduce the rate of change of floor surface and indoor air temperature.In addition,the increased water supply temperature and the use of phase change heat storage floor can improve the thermal performance of the floor heating experimental room,thereby prolonging the thermal comfort duration of the room.Finally,using the TRNSYS building simulation software to simulate the outdoor environment with the climate conditions in Guangzhou,the solar-heat pump heating system and the floor heating experimental room are simulated and studied.The room structure and size,the thermal performance of the envelope structure,etc are consistent with the actual testing room.Besides,module operating system of the heating system is consistent with actual conditions with the use of the combined heating system of solar energy collector and air heat pump.In order to make the floor heating experimental room have better thermal comfort performance,the floor heating temperature is set to 60℃.The results showed that phase change heat storage floor can reduce indoor temperature fluctuations,improve the thermal comfort of the room,and save the operating energy consumption of the heating system.The operating cost is 15.8% lower than that of the room with ordinary floors.In conclusion,the phase change heat storage floor has not only meet the basic requirements,but also improve thermal comfort performance and reducing energy consumption of buildings.Besides,it has relatively complete production technical specifications,so that it can be applied widely in the future.