• Energy Research

Abstract Due to the lack of conventional energy and fragile ecological environment in the Tibet Plateau at an elevation of over 3000 m, renewable energy utilization is of great significance in environment protection and energy conversation. A field measurement of a groundwater source heat pump (GWSHP), a part of a solar assisted GWSHP heating system of an airport in the Tibet Plateau with the side of solar collectors broken down was conducted in this paper. Meanwhile, the indoor thermal environment in the terminal and dormitory heated by radiant floor was measured. The performance, economy of the GWSHP and indoor thermal environment were analyzed. At last, a comparison between the GWSHP and other heat pumps used in this region was made. The results showed that the coefficient of performance (COP) is about 5.0. Compared to conventional heat sources, the performance of the GWSHP is optimal in regard to both energy conservation and economic efficiency. There was a significant difference observed between the thermal environment in the terminal and dormitory. Accordingly, design considerations and regulation measures are recommended to improve the thermal environment. Compared with heat pumps used for heating in the Tibet Plateau so far, the GWSHP in this paper is better.

Abstract Due to the lack of conventional energy and fragile ecological environment in the Tibet Plateau at an elevation of over 3000 m, renewable energy utilization is of great significance in environment protection and energy conversation. A field measurement of a groundwater source heat pump (GWSHP), a part of a solar assisted GWSHP heating system of an airport in the Tibet Plateau with the side of solar collectors broken down was conducted in this paper. Meanwhile, the indoor thermal environment in the terminal and dormitory heated by radiant floor was measured. The performance, economy of the GWSHP and indoor thermal environment were analyzed. At last, a comparison between the GWSHP and other heat pumps used in this region was made. The results showed that the coefficient of performance (COP) is about 5.0. Compared to conventional heat sources, the performance of the GWSHP is optimal in regard to both energy conservation and economic efficiency. There was a significant difference observed between the thermal environment in the terminal and dormitory. Accordingly, design considerations and regulation measures are recommended to improve the thermal environment. Compared with heat pumps used for heating in the Tibet Plateau so far, the GWSHP in this paper is better.

Abstract Ground-source heat pump (GSHP) systems contribute significantly to the reduction in energy consumption and CO2 emissions. The vast territory, abundant geothermal sources, and different climatic zones of Southwestern and Northwestern China provide significant opportunities for the application of GSHP technologies. In this study, a statistical study was performed to assess the general performances and identify the existing problems of GSHP systems located in the abovementioned areas. Twenty-eight GSHP projects, including groundwater heat pumps, soil-source heat pumps, and surface water heat pumps were selected. Water temperature, energy consumption, coefficient of performance (COP), energy efficiency ratio (EER), and thermodynamic perfectibility were analysed. The energy efficiency of GSHP systems were assessed according to the national standard. In addition, barriers and problems in GSHP applications are discussed herein. It is concluded that the average cooling COPs of SSHP, GWHP and SWHP units are 4.9, 4.7, and 4.2, respectively, with SSHP unit being the highest. The average heating COPs of SSHP, GWHP and SWHP units are 4.3, 4.2, and 4.2, respectively with SSHP unit being the highest. The SSHP has the best performance in both seasons amongst three GSHP types. Furthermore, though 89% of the systems can meet the requirements of national standard, more than 50% of them work at the lowest allowable energy efficiency value. This paper attempts to provide essential clues for the adoption feasibility and technical guidelines of GSHPs in the target areas.

Abstract Ground-source heat pump (GSHP) systems contribute significantly to the reduction in energy consumption and CO2 emissions. The vast territory, abundant geothermal sources, and different climatic zones of Southwestern and Northwestern China provide significant opportunities for the application of GSHP technologies. In this study, a statistical study was performed to assess the general performances and identify the existing problems of GSHP systems located in the abovementioned areas. Twenty-eight GSHP projects, including groundwater heat pumps, soil-source heat pumps, and surface water heat pumps were selected. Water temperature, energy consumption, coefficient of performance (COP), energy efficiency ratio (EER), and thermodynamic perfectibility were analysed. The energy efficiency of GSHP systems were assessed according to the national standard. In addition, barriers and problems in GSHP applications are discussed herein. It is concluded that the average cooling COPs of SSHP, GWHP and SWHP units are 4.9, 4.7, and 4.2, respectively, with SSHP unit being the highest. The average heating COPs of SSHP, GWHP and SWHP units are 4.3, 4.2, and 4.2, respectively with SSHP unit being the highest. The SSHP has the best performance in both seasons amongst three GSHP types. Furthermore, though 89% of the systems can meet the requirements of national standard, more than 50% of them work at the lowest allowable energy efficiency value. This paper attempts to provide essential clues for the adoption feasibility and technical guidelines of GSHPs in the target areas.

Abstract Cylinder helix energy pile (CyHEP) is a new popular ground heat exchanger which have the advantages of large heat exchange rate and low initial cost. However, severe thermal interferences exist in the radial and generatrix directions duo to the limited thermal heat capacity of pile and small ratio between coils pitch and radius of pile. Therefore, a novel truncated cone helix energy pile (CoHEP) is presented to weaken the thermal interferences and improve the heat transfer efficiency. Further, an analytical solution model for CoHEP is proposed based on Green’s function to discuss the dynamic characteristics of thermal interferences and heat transfer performance. A laboratory experiment is carried out to validate the presented model. The results indicate that the generatrix thermal interference in the bottom of the novel energy pile is significantly weakened and the radius thermal interference in the top of the novel energy pile is also weakened. Therefore, the heat transfer of the novel energy pile is enhanced compared with CyHEP and better performance of novel energy pile can be obtained by setting bigger cone angle. Besides, the thermal response characteristics of helix energy piles are discussed under the influences of dynamic load and the results show that the average temperature rise on the pipe wall of CoHEP is lower than that of CyHEP in the period of heat rejections while the average temperature of CoHEP is higher than CyHEP in the period of heat extraction. It is indicated that the energy efficiency of ground source heat pump coupled with CoHEP is higher than that coupled with the popular CyHEP.

Abstract Cylinder helix energy pile (CyHEP) is a new popular ground heat exchanger which have the advantages of large heat exchange rate and low initial cost. However, severe thermal interferences exist in the radial and generatrix directions duo to the limited thermal heat capacity of pile and small ratio between coils pitch and radius of pile. Therefore, a novel truncated cone helix energy pile (CoHEP) is presented to weaken the thermal interferences and improve the heat transfer efficiency. Further, an analytical solution model for CoHEP is proposed based on Green’s function to discuss the dynamic characteristics of thermal interferences and heat transfer performance. A laboratory experiment is carried out to validate the presented model. The results indicate that the generatrix thermal interference in the bottom of the novel energy pile is significantly weakened and the radius thermal interference in the top of the novel energy pile is also weakened. Therefore, the heat transfer of the novel energy pile is enhanced compared with CyHEP and better performance of novel energy pile can be obtained by setting bigger cone angle. Besides, the thermal response characteristics of helix energy piles are discussed under the influences of dynamic load and the results show that the average temperature rise on the pipe wall of CoHEP is lower than that of CyHEP in the period of heat rejections while the average temperature of CoHEP is higher than CyHEP in the period of heat extraction. It is indicated that the energy efficiency of ground source heat pump coupled with CoHEP is higher than that coupled with the popular CyHEP.

With the development of Chinese society, there is an increasing demand for emissions reduction and the stable operation of the power grid. Regional comprehensive energy supply systems have entered the public’s view owing to their advantages of reducing capacity, unified dispatch, improving efficiency, and reducing energy consumption. This paper focuses on a system under construction in Chongqing, which adopts a combined gas tri-supply (combined cooling, heat, and power, CCHP) and dynamic ice storage cooling system as the research object. By establishing a mathematical model for the simulation research, this study examines the start–stop priority sequence of the gas tri-supply subsystem and the heat pump subsystem under the ice storage priority strategy in winter and summer and proposes corresponding optimization solutions. By comparing the annual operating energy consumption of the system, we conclude that the gas tri-supply composite system has good economic efficiency and peak-shaving capability, indicating that regional gas tri-supply composite systems have great application potential in the future. The proposed optimized operation strategy and simulated energy consumption calculation provide theoretical guidance for the construction and operation of both this project and similar projects.

With the development of Chinese society, there is an increasing demand for emissions reduction and the stable operation of the power grid. Regional comprehensive energy supply systems have entered the public’s view owing to their advantages of reducing capacity, unified dispatch, improving efficiency, and reducing energy consumption. This paper focuses on a system under construction in Chongqing, which adopts a combined gas tri-supply (combined cooling, heat, and power, CCHP) and dynamic ice storage cooling system as the research object. By establishing a mathematical model for the simulation research, this study examines the start–stop priority sequence of the gas tri-supply subsystem and the heat pump subsystem under the ice storage priority strategy in winter and summer and proposes corresponding optimization solutions. By comparing the annual operating energy consumption of the system, we conclude that the gas tri-supply composite system has good economic efficiency and peak-shaving capability, indicating that regional gas tri-supply composite systems have great application potential in the future. The proposed optimized operation strategy and simulated energy consumption calculation provide theoretical guidance for the construction and operation of both this project and similar projects.

Abstract Solar chimney coupled with earth-to-air heat exchanger (SCEAHE) can provides fresh air and cooling capacity simultaneously without any electricity consumption. To understand the complex working mechanism of the coupled system, a numerical model has been established and verified to investigate various geometric and climatic parameters related to system performance. It is found that the system has the optimum performance when the pipe length is 60 m and pipe diameter is 0.6 m. Increasing the solar collector length or the chimney height can both increase the system performance. However, the effect of chimney height is not as significant as that of solar collector length. For the same increase in chimney height and solar collector length, the cooling capacity is increased by 51.6% and 77.8%, respectively. The higher the solar intensity, the higher the buoyancy force, airflow rate, outlet air temperature, and cooling capacity. The cooling capacity is increased by 101.4% by increasing solar intensity from 100 W/m2 to 600 W/m2. The higher the outdoor air temperature, the lower the buoyancy force and airflow rate, but the higher the outlet air temperature and cooling capacity. Moreover, the effect of outdoor air temperature on outlet air temperature is more significant than that on airflow rate. When the outdoor air temperature increases from 36 °C to 46 °C, the temperature reduction is increased by 75.8%, while the airflow rate is only decreased by 15.6%. The model developed in this study can be used for design and performance prediction of SCEAHE system.