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Modeling of a Hybrid Ground Source Heat Pump System with Solar Thermal Collector and Phase Change Materials

Biglarian, Hassan | 2018

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 50796 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Abbaspour, Majid; Saeedi, Mohammad Hassan
  7. Abstract:
  8. In recent years, ground source heat pumps (GSHPs) have received increasing attention for space heating and cooling, and domestic hot water production due to their high energy performance and low environmental impacts. The most common type of ground heat exchanger used in the GSHP systems is borehole heat exchanger (BHE) that consists of U-shaped tubes placed in the vertical boreholes. In this system, the heat is absorbed from or rejected to the ground by circulation of a fluid through the ground loop. The GSHP systems provide high seasonal performance factors when the ground loads are well balanced over the year. However, most buildings in cold or hot climates have unbalanced loads. When the GSHP is utilized in this condition, the heat absorbed from the ground in the heating mode is not balanced by the heat rejected to the ground in the cooling mode. The thermal imbalance leads to the variation of the average annual ground temperature in the vicinity of the BHE, resulting in the performance degradation of the heat pump over the long-term operation. Therefore, in order to preserve the performance of the heat pump at the design level, larger BHE and more land area would be required which increase the initial costs of the GSHP system. In this study, a novel hybrid GSHP system including solar thermal collectors and a storage tank containing phase change materials has been proposed to reduce the BHE size as well as to improve the heat pump performance for heating dominated buildings. The energy performance of the hybrid system has been evaluated using numerical simulation. Also, a novel numerical model based on a thermal resistance-capacity approach has been proposed to predict the thermal response of the BHE. In addition to high accuracy, the proposed model has very low computational cost. Furthermore, a comprehensive study has been conducted on the effects of different design parameters on the performance of the system. Besides, the hybrid system has been compared with a GSHP system and other conventional systems in terms of energy performance, economic and environmental aspects for a design life of 20 years. The results show that despite the smaller BHE requirement, the hybrid system has higher seasonal performance factor and lower electricity consumption than the GSHP system. Moreover, the proposed system has the lowest carbon dioxide emissions among the investigated systems
  9. Keywords:
  10. Ground Heat Exchanger ; Dynamic Simulation ; Numerical Modeling ; Solar Collectors ; Grounad Source Heat Pump ; Borehole Heat Exchanger

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