scholarly journals Numerical Investigation on Energy Efficiency of Heat Pump with Tunnel Lining Ground Heat Exchangers under Building Cooling

Buildings ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 611
Author(s):  
Xiaohua Liu ◽  
Chenglin Li ◽  
Guozhu Zhang ◽  
Linfeng Zhang ◽  
Bin Wei
Keyword(s):  
Energy Efficiency ◽  
Numerical Model ◽  
Groundwater Flow ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Coupling Effect ◽  
Pump Energy ◽  
Tunnel Lining ◽  
Outlet Temperature ◽  
Ground Heat Exchangers

For mountain tunnels, ground heat exchangers can be integrated into the tunnel lining to extract geothermal energy for building heating and cooling via a heat pump. In recent decades, many researchers only focused on the thermal performance of tunnel lining GHEs, ignoring the energy efficiency of the heat pump. A numerical model combining the tunnel lining GHEs and heat pump was established to investigate the energy efficiency of the heat pump. The inlet temperature of an absorber pipe was coupled with the cooling load of GHEs in the numerical model, and the numerical results were calibrated using the in situ test data. The energy efficiency ratio (EER) of the heat pump was calculated based on the correlation of the outlet temperature and EER. The heat pump energy efficiencies under different pipe layout types, pipe pitches and pipe lengths were evaluated. The coupling effect of ventilation and groundwater flow on the energy efficiency of heat pump was investigated. The results demonstrate that (i) the absorber pipes arranged along the axial direction of the tunnel have a greater EER than those arranged along the cross direction; (ii) the EER increases exponentially with increasing absorber pipe pitch and length (the influence of the pipe pitch and length on the growth rate of EER fades gradually as wind speed and groundwater flow rate increase); (iii) the influence of groundwater conditions on the energy efficiency of heat pumps is more obvious compared with ventilation conditions. Moreover, abundant groundwater may lead to a negative effect of ventilation on the heat pump energy efficiency. Hence, the coupling effect of ventilation and groundwater flow needs to be considered for the tunnel lining GHEs design.

Heat Transfer Analysis of Groundwater Flow for Ground Heat Exchangers in the Multi-Borehole Field of Ground Source Heat Pump under the Intermittent Operation

2014 ◽  
Vol 548-549 ◽  
pp. 595-600
Author(s):  
Can Can Zhang ◽  
Yue Jin Yu
Keyword(s):  
Groundwater Flow ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Heat Transfer Analysis ◽  
Ground Source Heat Pump ◽  
Pump System ◽  
Heat Pump System ◽  
Ground Heat Exchangers ◽  
Ground Source ◽  
Thermal Interference

In order to analyze the influence of groundwater flow on ground heat exchangers with different arrangements, with a project in Nanjing the access temperature field in the multi-borehole field was simulated after the ground source heat pump system had been performed for a year. Simulation results show that the access temperature is higher in the ground surrounding the borehole than the center of the corresponding borehole, thus forming a thermal barrier surrounding the borehole. Groundwater flow helps relieve temperature imbalance owing to the imbalance of heating and cooling load. The performance of the ground heat exchangers is better in staggered arrangement than in aligned arrangement. In the borehole field, the boreholes upstream have thermal interference on those downstream. And the extent of thermal interference depends on the direction of the groundwater flow when the locations of the boreholes are fixed in the borehole field.

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.

Modeling of vertical ground heat exchangers in the presence of groundwater flow and underground temperature gradient

2019 ◽  
Vol 192 ◽  
pp. 15-30 ◽  
Author(s):  
Iosifina Iosif Stylianou ◽  
Savvas Tassou ◽  
Paul Christodoulides ◽  
Lazaros Aresti ◽  
Georgios Florides
Keyword(s):  
Temperature Gradient ◽  
Groundwater Flow ◽  
Heat Exchangers ◽  
Ground Heat Exchangers ◽  
Vertical Ground

Effect of the Circulation Flow Velocity in Ground Heat Exchangers on System Operation

2014 ◽  
Vol 580-583 ◽  
pp. 2457-2460
Author(s):  
Zi Shu Qi ◽  
Qing Gao ◽  
Yan Liu ◽  
Zhen Hai Gao ◽  
Li Bai
Keyword(s):  
Flow Velocity ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Engineering Practice ◽  
Fluid Temperature ◽  
Circulation Flow ◽  
Pump System ◽  
Heat Pump System ◽  
Computing Platform ◽  
Ground Heat Exchangers

The heat pump system by using earth energy is increasing very rapidly. In this paper, by studying the underground heat exchanger heat transfer mode, the computing platform for ground source heat pump system was established. Through a engineering case, the influence character of the circulation flow velocity in ground heat exchangers on the fluid temperature, the heat pump power consumption, and the length of system were analyzed, which provide an approach for system engineering design and operation prediction, and for the thermodynamic analysis of performance of system year by year and prospective study to guide the engineering practice.

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