Dynamic Water Thermal Energy Extraction Method for Water Pit Thermal Energy Storage Based on Experimental and Developed Mathematical Model

Abstract

For internationally prevalent water Pit Thermal Energy Storage (PTES), the mixing between water layers at different temperatures is an important cause of thermodynamic loss. Conventional stable heat extraction method disturbs stratification and increases thermodynamic loss. This study proposes a dynamic water thermal energy extraction method (DWEM) featuring vertically movable water diffuser to selectively extract temperature-stratified water, enabling demand-adaptive heat extraction. A module of DWEM for PTES was developed to assess its performance in heat supply. Experimental validation used data from a constructed underground thermal storage water tank. The effects of two methods under varying tilt angles, volume equivalence coefficients, PTES-heat pump (HP) coupled systems, and PTES scales are explored. The research shows that the proposed module of DWEM for PTES has RMSE of 1.16 °C, 1.56 °C, 1.38 °C, 1.03 °C, 1.25 °C for measuring points. The average COPs for conventional method and DWEM are 4.25 and 5.22, respectively. For DWEM, the average hourly power consumption was reduced by 19.07%, the average COP was increased by 22.75%, and the total power consumption was reduced by 32.22%. For two methods, the equivalent coefficients of a 90° vertical water body to a water body with an inclination angle of 26.6° are 1.25 and 1.33, respectively. The DWEM stratification coefficient was 5.45 times of conventional method, the exergy destruction could be reduced by 4.84%, and the side heat loss was reduced by up to 54.69%. DWEM can match thermal demand in the PTES system and improve thermal energy utilization.

Keywords: Pit thermal energy storage, Dynamic heat extraction, On demand heating, Inclination angle, Heat transfer mathematical model