scholarly journals Simulation Analysis on the Heat Performance of Deep Borehole Heat Exchangers in Medium-Depth Geothermal Heat Pump Systems

Energies ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 754 ◽  
Author(s):  
Jiewen Deng ◽  
Qingpeng Wei ◽  
Shi He ◽  
Mei Liang ◽  
Hui Zhang
Keyword(s):  
Heat Transfer ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Geothermal Energy ◽  
Heat Transfer Performance ◽  
Deep Borehole ◽  
Geothermal Heat ◽  
Temperature Heat ◽  
Geothermal Heat Pump ◽  
Borehole Heat Exchangers

Deep borehole heat exchangers (DBHEs) extract heat from the medium-depth geothermal energy with the depth of 2–3 km and provide high-temperature heat source for the medium-depth geothermal heat pump systems (MD-GHPs). This paper focuses on the heat transfer performance of DBHEs, where field tests and simulation are conducted to analyze the heat transfer process and the influence factors. Results identify that the heat transfer performance is greatly influenced by geothermal properties of the ground, thermal properties and depth of DBHEs and operation parameters, which could be classified into external factors, internal factors and synergic adjustment. In addition, the long-term operation effects are analyzed with the simulation, results show that with inlet water temperature setting at 20 °C and flow rate setting at 6.0 kg/s, the average outlet water temperature only drops 0.99 °C and the average heat extraction drops 9.5% after 20-years operation. Therefore, it demonstrates that the medium-depth geothermal energy can serve as the high-temperature heat source for heat pump systems stably and reliably. The results from this study can be potentially used to guide the system design and optimization of DBHEs.

Comparative analysis of heat transfer performance of coaxial pipe and U-type deep borehole heat exchangers

Geothermics ◽  
2021 ◽  
Vol 96 ◽  
pp. 102220
Author(s):  
Wenke Zhang ◽  
Wenjing Li ◽  
Bjørn R Sørensen ◽  
Ping Cui ◽  
Yi Man ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Comparative Analysis ◽  
Heat Exchangers ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Deep Borehole ◽  
Borehole Heat Exchangers

scholarly journals What Is the Main Difference between Medium-Depth Geothermal Heat Pump Systems and Conventional Shallow-Depth Geothermal Heat Pump Systems? Field Tests and Comparative Study

2019 ◽  
Vol 9 (23) ◽  
pp. 5120 ◽  
Author(s):  
Jiewen Deng ◽  
Qingpeng Wei ◽  
Shi He ◽  
Mei Liang ◽  
Hui Zhang
Keyword(s):  
Heat Pump ◽  
Heat Exchangers ◽  
Field Tests ◽  
Energy Performance ◽  
Heat Pumps ◽  
Geothermal Heat ◽  
Temperature Heat ◽  
Geothermal Heat Pump ◽  
Water Pumps ◽  
Whole Systems

Recently, the medium-depth geothermal heat pump systems (MD-GHPs) have been applied for space heating in China. Theoretically, the MD-GHPs use deep borehole heat exchangers (DBHEs) to extract heat from the medium-depth geothermal energy with the depth of 2~3 km, thus, improving the energy performance of whole systems obviously. This paper conducts field tests of nine conventional shallow-depth geothermal heat pump systems (SD-GHPs) and eight MD-GHPs to analyze the energy performance of heat pump systems, as well as heat transfer performance of ground heat exchangers. Then the comparative studies are carried out to analyze the difference between these two ground coupled heat pump systems. Field test results show that the outlet water temperature of DBHEs in MD-GHP can reach more than 30 °C with heat extraction of 195.2 kW~302.8 kW per DBHE with a depth of 2500 m, which are much higher than that of SD-GHPs. However, the heat pumps and water pumps in the ground side should be specially designed to fit the high-temperature heat source instead of following operation mode of SD-GHPs. Then with variable speed compressor which has high energy efficiency under a wide range of load rate and compressor ratio, and with the ground-side water pumps which efficiently operate under high water resistance and low flow rate, the COP of heat pumps and COPs of whole systems could reach 7.80 and 6.46 separately. Thus, the advantage of high-temperature heat source could be fully utilized to achieve great energy-saving effects.

Heat transfer analysis of U-type deep borehole heat exchangers of geothermal energy

2021 ◽  
Vol 237 ◽  
pp. 110794
Author(s):  
Wenke Zhang ◽  
Jianhua Wang ◽  
Fangfang Zhang ◽  
Wei Lu ◽  
Ping Cui ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Geothermal Energy ◽  
Heat Transfer Analysis ◽  
Deep Borehole ◽  
Borehole Heat Exchangers

scholarly journals Analysis and Comparison of Some Low-Temperature Heat Sources for Heat Pumps

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1853 ◽  
Author(s):  
Pavel Neuberger ◽  
Radomír Adamovský
Keyword(s):  
Heat Transfer ◽  
Low Temperature ◽  
Heat Source ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Ambient Air ◽  
Heat Transfer Fluid ◽  
Heat Sources ◽  
Ground Heat Exchangers ◽  
Temperature Heat

The efficiency of a heat pump energy system is significantly influenced by its low-temperature heat source. This paper presents the results of operational monitoring, analysis and comparison of heat transfer fluid temperatures, outputs and extracted energies at the most widely used low temperature heat sources within 218 days of a heating period. The monitoring involved horizontal ground heat exchangers (HGHEs) of linear and Slinky type, vertical ground heat exchangers (VGHEs) with single and double U-tube exchanger as well as the ambient air. The results of the verification indicated that it was not possible to specify clearly the most advantageous low-temperature heat source that meets the requirements of the efficiency of the heat pump operation. The highest average heat transfer fluid temperatures were achieved at linear HGHE (8.13 ± 4.50 °C) and double U-tube VGHE (8.13 ± 3.12 °C). The highest average specific heat output 59.97 ± 41.80 W/m2 and specific energy extracted from the ground mass 2723.40 ± 1785.58 kJ/m2·day were recorded at single U-tube VGHE. The lowest thermal resistance value of 0.07 K·m2/W, specifying the efficiency of the heat transfer process between the ground mass and the heat transfer fluid, was monitored at linear HGHE. The use of ambient air as a low-temperature heat pump source was considered to be the least advantageous in terms of its temperature parameters.

scholarly journals Seasonal High Temperature Heat Storage with Medium Deep Borehole Heat Exchangers

2015 ◽  
Vol 76 ◽  
pp. 351-360 ◽  
Author(s):  
Kristian Bär ◽  
Wolfram Rühaak ◽  
Bastian Welsch ◽  
Daniel Schulte ◽  
Sebastian Homuth ◽  
...  
Keyword(s):  
High Temperature ◽  
Heat Exchangers ◽  
Heat Storage ◽  
Deep Borehole ◽  
Temperature Heat ◽  
Borehole Heat Exchangers
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