Design And Performance Research Of Solar Phase Change Heat Storage Floor

In order to cope with the energy crisis and environmental pollution,and to achieve carbon peaking and carbon neutrality as soon as possible,it is necessary to research and develop clean heating methods as soon as possible to replace the burning of scattered coal for heating in some rural areas.Solar energy is of great significance to its development and utilization as the most easily accessible renewable resource.At the same time,low-temperature hot water floor radiant heating has become the first choice of heating because of comfort and economical efficiency.In this thesis,a solar phase-change heat storage floor heating system is designed and built based on the characteristics of the house,heating requirements,and the solar radiation intensity and geographic location of the Jinan area.The system collects and stores solar radiant heat for heating and combines phase change materials with low-temperature hot water radiant heating floors.The system can effectively solve the problem of mismatch between supply and demand of solar energy in time and pollution caused by the burning of scattered coal.In this thesis,the industrial grade Na₂SO₄ with the mass fraction of 95%was selected as the raw material according to the classification of phase-change materials,the screening principle of phase-change materials and the economic concept,and the phase-change materials were prepared with the solid-water ratio of 1:0.5,1:0.75,1:1,1:1.25 and 1:1.5 with ultra-pure water and the industrial grade Na₂SO₄.And the sample cooling cycle experiment and DSC thermal analysis.The experimental results show that,the melting temperature of the phase change material gradually decreases and the latent heat of phase change first increases and then decreases with the increase of the proportion of water in the sample.And the latent heat of phase change reaches the peak when the solid-water ratio is 1:0.75.1:0.75 is chosen as the optimal solid-water ratio,the melting temperature of the phase change material is 31.52?,and the latent heat of the phase change is182.80 J/g.Nucleating agent A(1wt%,2wt%,3wt%,4wt%and 5wt%)was added to the PCM with the optimal solid-to-water ratio to adjust the undercooling degree,and the samples were subjected to cooling cycle experiment and DSC thermal analysis.The experimental results show that,the addition of nucleating agent A can effectively reduce the degree of subcooling,but the latent heat of phase change gradually decreases with the increasing of the mass fraction of nucleating agent A.In order to ensure the latent heat value of PCM,1wt%was selected as the optimal dosage of nucleating agent A.The latent heat of the phase change material is 175.79 J/g,the melting temperature is 29.04?,and the subcooling degree is 0.1?under the condition of 15?constant temperature cooling,which can be used as the phase change material in the phase change floor.In the designing of the solar heat collecting system,the calculation of the collector's best inclination is 36.67°and the heat collecting area of 33.22 m² combined with the building heating area of 62.304 m²and the design heat load of building heating is 105 W/m².20 flat-plate collectors connected in parallel are used according to the actual use requirement.The volume of the hot water storage tank is determined to be 24000 L(24 m3),and it is covered with insulation materials.The heat exchanger is a detachable plate heat exchanger with a heat exchange area of 5.1 m².In the designing of the pipe network of the solar heat collection system,it is calculated that the total flow of the solar heat collector is 1.1424 m³/h,the inner diameter of the circulation pipe is 44.95mm,and the PP-R hot water pipe of DN50 is selected.In the structural design of the phase change heat storage floor,the heating coil adopts the spiral distribution method,the distance between the pipes is calculated to be 300 mm and the required pipe length of each room can be calculated according to the heating demand.The structure characteristics of the ordinary low-temperature hot water radiant heating floor are retained,and the phase change materials are dispersed and encapsulated in to vacuum sealed bag,and laid on the heating coil as an independent layer.The following results are obtained from the analysis of the operating results of the solar phase change heat storage floor system.(1)The heat collection system has a high heat collection efficiency in sunny weather,and the maximum heat collection efficiency can reach 99.21%of the theoretical heat collection efficiency.(2)In the same sunny weather,the heat collection efficiency of the heat collection system decreases with the decrease of air temperature and the increase of the initial temperature of the water tank.(3)For the common brick and tile structure houses without heat preservation,the indoor temperature of the rooms with phase-change heat storage floors is13.8-21.5?,which is higher than that of the rooms with ordinary low-temperature hot water radiant heating floors,and the temperature difference is up to 2.2?.(4)The phase change heat storage floor has better room temperature control ability compared with the ordinary low-temperature hot water radiation floor.