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Dynamic Control and Thermal Variation of Underground Thermal Energy Storage System

Author: WangLiHua
Tutor: GaoQing
School: Jilin University
Course: Thermal Power Engineering
Keywords: Underground thermal energy utilization Underground thermal energy storage Loading mode Dynamic control Temperature variation
CLC: TK52
Type: Master's thesis
Year: 2011
Downloads: 38
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Abstract

Eventhough the UTES technology has made great advance, there is no enough research on large scale underground heat transfer system equipped with multi-heat source, especially on the load distribution control combining with time featured energy, such as solar energy, industrial and industrial waste heat and live residual heat. The large scale multi-heat sources model is set up in this paper to find out the optimal dynamic control mode on the energy storage heat transfer to improve the energy storage efficiency. And the energy injection process, and energy protection are studied by different dynamic control mode, such as intermittent dynamic control mode and load distribution dynamic control mode and continuous dynamic control mode.In order to investigate the effect and role of intermittent timing control in underground thermal energy storage (UTES), We introduced semi-day intermittent and full-day intermittent dynamic control mode in this paper.To furthermore investigate the effects of the load intermittent time, there are three modes, i.e. short intermittent, medium intermittent and long intermittent respectively provided. For the load sharing of heat sources of ground heat exchangers, temperature amplitude distribution, intermittent period, rest cycle were employed to achieve the dynamic control of heat transfer. Its forming real-time variable temperature field not only has the obvious effect on the heat injection, but also plays a big influence on the heat protection under the ground with controllable diffusion transfer. Thus, the load sharing promotes UTES, expedites the heat injection and downsizes the loss of heat stored. The average temperature increment, maximum temperature, energy injection and protection, and borderline energy flux in the field were analyzed especially by numerical methods. Results show that the semi-day intermittent mode is more effective than the full-day intermittent mode, and the shorter intermittent period is more favorable. They achieve the higher energy storage quantity, average temperature and maximum temperature. Therefore a reasonable selection of dynamic load mode with intermittent period and temperature distribution is beneficial for efficient heat transfer and effective energy transportation in underground heat exchanger system with multi-heat source. Therefore a reasonable selection of dynamic load mode leads to beneficial and effective energy transfer.In order to reduce the effect of underground-water in underground thermal energy storage (UTES), We analyzed load distribution in underground thermal energy storage (UTES)and introduced load biasing concept in this paper. To furthermore investigate the effects of the groundwater, three kinds of groundwater flowing direction named 0°,30°and 45°as studied. The average temperature increment, maximum temperature, energy injection and protection, and borderline energy flux in the field were analyzed especially by numerical methods. Results show that the load biasing layout mode is more effective than load uniform layout in any flowing case and achieved the higher energy storage quantity. For the load biasing layout mode, the case of 45°flowing direction is is more favorable than the case of 30°flowing direction, the case of 45°flowing direction is worst. Overall the load biasing layout mode achieved the higher energy storage quantity, average temperature and maximum temperature. Therefore a reasonable selection of load distribution is beneficial for efficient heat transfer and effective energy transportation in underground heat exchanger system with multi-heat source.Because the existence of dynamic changing characteristics for actual load, we introduced a continuous dynamic control mode in this paper and described the continuity characteristics of dynamic control mode and its influence to the temperature distribution. Changing the load model through the amplitude, phase and heat load distribution, several different control modes are formed and analyzed. Results show that heat load distribution is of the greatest impact on the temperature distribution and amplitude is second and phase is the smallest.The average temperature increment, maximum temperature, energy injection and protection, and centerline temperature distribution in the field were analyzed especially by numerical methods. Thus for heat load distribution, single-wave loading mode is best and double-wave loading mode is second and uniform loading mode is worst. For big amplitude variation control mode is best and small amplitude variation control mode is second and uniform amplitude control mode is worst.Overall small amplitude variation single-wave loading mode achieved the highest energy storage quantity and uniform amplitude uniform loading mode is lowest. Therefore a reasonable selection of continuous dynamic control mode is beneficial for efficient heat transfer and effective energy transportation in underground heat exchanger system with multi-heat source.The dynamic load mode with intermittent period, continuous period and hole distribution is beneficial for efficient heat transfer and effective energy transportation in underground heat exchanger system with multi-heat source. Therefore a reasonable selection of dynamic load mode leads to beneficial and effective energy transfer.

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