Optimization Of The Latent Heat Thermal Energy Storage(LHTES)based On Low Temperature Phase Change Material

Fresh air is an important factor to ensure indoor air quality,but outdoor high temperature air in summer and outdoor low temperature air in winter are directly connected to the fresh air treatment unit,which makes the energy consumption of fresh air treatment higher.Therefore,in order to effectively reduce the energy consumption of fresh air,fresh air accumulator can be installed in front of the fresh air handling unit.Based on the fresh air accumulator with renewable energy and low-temperature phase change material,a test-bed of fresh air accumulator with paraffin as internal phase change material was built,and the cold storage and release experiments were carried out.Under the condition of cold storage,the paraffin releases heat to the cooling medium.In the initial stage,the sensible heat is released first,and the temperature gradually decreases;when the paraffin temperature reaches the freezing point,it gradually solidifies and releases latent heat.When the initial temperature of paraffin is 20 ℃,the temperature difference between the inlet and outlet of fresh air can reach 10 ℃;as the paraffin continues to absorb heat,it begins to melt,and the temperature increases,resulting in the temperature difference between the inlet and outlet of fresh air decreasing.In order to explore the heat storage and release law of fresh air accumulator under different working conditions and material conditions,according to the structure design of fresh air accumulator,an experimental platform of fresh air accumulator system was built.Based on the basic structure of fresh air accumulator,a numerical model is established.By comparing the experimental data with the theoretical results,the error is less than 5%,which verifies the correctness of the numerical model.By analyzing the numerical simulation results of fresh air accumulator with paraffin or fatty acid as internal phase change material under 64 working conditions,the law of fresh air inlet temperature and phase change material liquid rate change rate,as well as the change law of phase change material liquid rate and fresh air inlet and outlet temperature difference,can be obtained,so that the fresh air outlet temperature can be predicted according to the hourly fresh air inlet temperature.Based on the heat storage and release law of fresh air accumulator,a simplified calculation method of energy saving of fresh air accumulator is proposed.This method can quickly calculate the energy saving of fresh air accumulator when the inlet temperature of fresh air changes hourly.Based on the calculation results of the simplified calculation method,compared with the numerical simulation results,the error is less than 3%,which verifies the correctness of the method.Through the simplified method,the effects of different phase change materials(paraffin and fatty acid)on the energy saving performance of fresh air accumulator were compared and analyzed.It is found that when the phase change material inside the fresh air accumulator is paraffin,the precooling and preheating performance of the fresh air accumulator is relatively good,and the investment of the fresh air accumulator can be recovered.When the phase change material is fatty acid,the investment of fresh air energy storage device cannot be recovered.Therefore,paraffin is more suitable as phase change filling material in fresh air accumulator.In this paper,the heat storage and release characteristics of phase change material(PCM)in the fresh air accumulator and the performance of the device under the condition of dynamic fresh air inlet temperature change are studied by combining experimental and numerical methods.Based on the research results,the economic analysis of fresh air accumulator with different phase change materials is compared,and a simplified calculation method for energy saving of fresh air accumulator is proposed,so as to provide some reference for the research and design of fresh air accumulator.