Experimental Study On Working Performance Of Phase Change Energy Storage Concrete Energy Piles

Since the mid-1990s,the total amount of construction industry consumption in China has increased year by year.Therefore,the development of green energy and the further improvement of building energy efficiency have attracted more and more attention.Energy conservation and emission reduction along with using renewable energy have become new trend for building energy efficiency.Energy pile is a new type of ground source heat pump technology,which can not only reduce the consumption of traditional energy resources,but also reduce CO₂ emission and protect the environment.Reasonable use of phase change material?PCM?with good heat storage performance can improve the indoor ambient temperature,reduce air-conditioning running time,save electricity costs,and reduce building energy consumption.In this research,a new type of PCM concrete energy pile?PCEP?is designed by using phase change materials?PCMs?in energy piles.And through comparing with ordinary concrete energy piles?OCEP?,the temperature thermal response of the two types of piles in saturated sand was studied separately,and then the heat exchange efficiency of the two types of piles in air alone was compared,and the storage of PCEP was verified.Thermal capacity and ability to increase heat transfer efficiency.The main research work and conclusions of this thesis are as follows:Firstly,this study builded an testing system for energy pile model cyclic experiment.The system mainly includes water circulation temperature machine,chiller,water storage tank,water pump,flow meter,model experiment box and energy pile,etc.These devices are connected by flexible water pipes.The author made a quantitative analysis of the operation of each step in the process of estabilishing the system;did a systematic analysis and reasonable solution to the problems;and made a complete summary of the above contents.All the work can ensure the repeatability of the experiments.Secondly,the thermal response to temperature of energy piles in saturated sand were studied through the experimental system.The main research work include two different working conditions:heating condition and cooling condition.The heating condition includes the thermal response of OCEP and PCEP in temperature.The cooling condition mainly studied the thermal response of PCEP in temperature.Under the heating condition,the two energy piles were subjected to cyclic experiments with different cycle times,different flow rates or different inlet temperatures.Under the cooling condition,the PCEP was flowed at different flows.1)The main research issues including the variation of the lateral and vertical temperature of the soil around the pile with time and the comparison of the pile-soil temperature cloud before and after the temperature cycle were studied.2)the water temperature and heat exchange of the energy inlet and outlet of the energy pile with different flow rates and different inlet temperatures were studied.3)the heat exchange efficiency of energy piles with different materials and the heat transfer efficiency of concrete energy piles with phase change energy storage under different working conditions were compared and analyzed.The main results of the experiment show that:?1?The energy pile mainly performs radial heat exchange in saturated sand.The closer the soil is to the pile side,the greater the temperature gradient and the denser the isotherms is;?2?The temperature of the OCEP in the saturated sand mainly influenced the zone of 65cm?3.25 times the diameter of the pile?from the pile side,while the temperature of PCEP mainly affected the zone of 45cm?2.25 times the diameter of the pile?.This result indicates that the PCEP can reduce the influence range of the soil temperature;thereby can reduce the thermal consolidation and deformation of the soil,reduce the settlement of the ground and the pile foundation;?3?Under the same flow rate,the heat exchange rate increased with the increase of the cycle temperature.Under the same flow rate and the same cycle temperature,the initial heat transfer of the PCEP in the cycle experiment was 1.8 times larger than that of the OCEP.This shows that the phase change material can improve the heat transfer performance of the energy pile to certain extent;?4?The heat exchange capacity of PCEP,under heating condition,decreased with the increase of flow rate,while the heat exchange capacity increased with the increase of flow rate under the cooling condition;?5?For the temperature difference between the inlet and outlet of PCEP,under the different flow rates,was gradually decreased with the extension of the heating cycle time,and the larger the flow rate,the more the temperature difference.The decrease attenuation was reduced by 19.6%greater than the cooling conditions.