The Effects of Groundwater Flow on Vertical-Borehole Ground Source Heat Pump Systems

2014 ◽  
Author(s):  
Ayako Funabiki ◽  
Masahito Oguma ◽  
Taisei Yabuki ◽  
Takao Kakizaki
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Groundwater Flow ◽  
Flow Velocity ◽  
Heat Pump ◽  
High Thermal Conductivity ◽  
Ground Source Heat Pump ◽  
Ground Heat Exchangers ◽  
Ground Source ◽  
Gravel Size

Heat advection by groundwater flow is known to improve the performance of ground heat exchangers (GHEs), but the effect of groundwater advection on performance is not yet fully understood. This study examined how parameters related to groundwater flow, such as aquifer thickness, porosity, lithology, and groundwater flow velocity, affect the performance of a borehole GHE. Under the thin-aquifer condition (10 m, or 10% of the entire GHE length in this study), groundwater flow velocity had the greatest effect on heat flux. With a groundwater flow velocity of at least 10−4 m/s through a low-porosity aquifer filled with gravel with high thermal conductivity, the heat flux of a GHE was as much as 60% higher than that of a non-aquifer GHE. If the aquifer is as thick as 50 m (50% of the entire GHE length), the high thermal conductivity of gravel doubled the heat flux of the GHE with a groundwater flow velocity of at least 10−5 m/s. Thus, not only groundwater flow velocity, but also aquifer thickness and thermal conductivity were important factors. However, groundwater seldom flows at such high velocities, and porosity, gravel size, and aquifer thickness vary regionally. Thus, in the design of ground source heat pump systems, it is not appropriate to assume a large groundwater effect.

Effects of Groundwater Flow on a Ground Source Heat Pump System

2017 ◽  
Vol 9 (2) ◽  
Author(s):  
Ayako Funabiki ◽  
Masahito Oguma
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Groundwater Flow ◽  
Flow Velocity ◽  
Heat Pump ◽  
Numerical Study ◽  
High Thermal Conductivity ◽  
Ground Source Heat Pump ◽  
Pump System ◽  
Ground Source

Heat advection by groundwater flow is known to improve the performance of ground heat exchangers (GHEs), but the effect of groundwater advection on performance is not yet fully understood. This numerical study examined how parameters related to groundwater flow, such as aquifer thickness, porosity, lithology, and groundwater flow velocity, affected the performance of a borehole GHE. Under a thin-aquifer condition (10 m, or 10% of the entire GHE length in this study), groundwater flow velocity had the greatest effect on heat flux. At a groundwater flow velocity of at least 10−4 m/s through a low-porosity aquifer filled with granite gravel with high thermal conductivity, the heat flux of a GHE was as much as 60% higher than that of a GHE in a setting without an aquifer. If the aquifer was as thick as 50 m, the high thermal conductivity of granite gravel doubled the heat flux of the GHE at a groundwater flow velocity of at least 10−5 m/s. Thus, not only groundwater flow velocity but also aquifer thickness and thermal conductivity were important factors. However, groundwater seldom flows at such high velocities, and porosity, gravel size and composition, and aquifer thickness vary regionally. Thus, in the design of ground source heat pump systems, it is not appropriate to assume a large groundwater effect.

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 Ground-Source Heat Pump Systems: The Effects of Variable Trench Separations and Pipe Configurations in Horizontal Ground Heat Exchangers

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3919
Author(s):  
Yu Zhou ◽  
Asal Bidarmaghz ◽  
Nikolas Makasis ◽  
Guillermo Narsilio
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Element Model ◽  
Fluid Temperature ◽  
Ground Source Heat Pump ◽  
Carrier Fluid ◽  
Ground Heat Exchangers ◽  
Ground Source

Ground-source heat pump systems are renewable and highly efficient HVAC systems that utilise the ground to exchange heat via ground heat exchangers (GHEs). This study developed a detailed 3D finite element model for horizontal GHEs by using COMSOL Multiphysics and validated it against a fully instrumented system under the loading conditions of rural industries in NSW, Australia. First, the yearly performance evaluation of the horizontal straight GHEs showed an adequate initial design under the unique loads. This study then evaluated the effects of variable trench separations, GHE configurations, and effective thermal conductivity. Different trench separations that varied between 1.2 and 3.5 m were selected and analysed while considering three different horizontal loop configurations, i.e., the horizontal straight, slinky, and dense slinky loop configurations. These configurations had the same length of pipe in one trench, and the first two had the same trench length as well. The results revealed that when the trench separation became smaller, there was a minor increasing trend (0.5 °C) in the carrier fluid temperature. As for the configuration, the dense slinky loop showed an average that was 1.5 °C lower than those of the horizontal straight and slinky loop (which were about the same). This indicates that, when land is limited, compromises on the trench separation should be made first in lieu of changes in the loop configuration. Lastly, the results showed that although the effective thermal conductivity had an impact on the carrier fluid temperature, this impact was much lower compared to that for the GHE configurations and trench separations.

scholarly journals Effect of Groundwater Flow and Thermal Conductivity on the Ground Source Heat Pump Performance at Bangkok and Hanoi: A Numerical Study

2021 ◽  
Author(s):  
Arif Widiatmojo ◽  
Youhei Uchida ◽  
Isao Takashima
Keyword(s):  
Thermal Conductivity ◽  
Groundwater Flow ◽  
Heat Pump ◽  
Line Source ◽  
Thermal Response ◽  
Ground Source Heat Pump ◽  
Source Method ◽  
Ground Source ◽  
Apparent Thermal Conductivity ◽  
Infinite Line

In recent decades, the fast-growing economies of Southeast Asian countries have increased the regional energy demand per capita. The statistic indicates Southeast Asian electricity consumption grows for almost 6% annually, with space cooling becoming the fastest-growing share of electricity use. The ground source heat pump technology could be one of the solutions to improve energy efficiency. However, currently, there are limited data on how a ground source heat pump could perform in such a climate. The thermal response test is widely used to evaluate the apparent thermal conductivity of the soil surrounding the ground heat exchanger. In common practice, the apparent thermal conductivity can be calculated from the test result using an analytical solution of the infinite line source method. The main limitation of this method is the negligence of the physical effect of convective heat transfer due to groundwater flow. While convection and dispersion of heat are two distinctive phenomena, failure to account for both effects separately could lead to an error, especially in high groundwater flow. This chapter discusses the numerical evaluation of thermal response test results in Bangkok, Thailand, and Hanoi, Vietnam. We applied a moving infinite line source analytical model to evaluate the value of thermal conductivity and groundwater flow velocity. While determining the ground thermal properties in a high accuracy is difficult, the moving infinite line source method fulfills the limitation of the infinite line source method. Further, we evaluated the five-year performance of the ground source heat pump system coupled with two vertical ground heat exchangers in Bangkok and Hanoi. The results suggest the importance of groundwater flow to enhance the thermal performance of the system.

A Model for a Geothermal Well in a Hydraulic Groundwater Flow for Ground Source Heat Pump Systems

2011 ◽  
Author(s):  
Kevin D. Woods ◽  
Alfonso Ortega
Keyword(s):  
Thermal Conductivity ◽  
Analytical Solution ◽  
Groundwater Flow ◽  
Heat Pump ◽  
Temperature Response ◽  
Ambient Air ◽  
Heat Pumps ◽  
Thermal Reservoir ◽  
Geothermal Well ◽  
Ground Source

Heat pumps are mechanical systems that provide heating to a space in the winter, and cooling in the summer. They are increasingly popular because the same system provides both cooling modes, depending on the direction of the cycle upon which they operate. For proper operation, the heat pump must be connected to a constant temperature thermal reservoir which in traditional systems is the ambient air. In ground source heat pumps however, subterranean ground water is used as the thermal reservoir. To access the subterranean groundwater, “geothermal” wells are drilled into the formation. Water from the building heating or cooling system is circulated through the wells thereby promoting heat exchange between the coolant water and the subterranean formation. The potential for higher efficiency heating and cooling has increased the utilization of ground source heating ventilating and air conditioning systems. In addition, their compatibility with a naturally occurring and stable thermal reservoir has increased their use in the design of sustainable or green buildings and man-made environments. Groundwater flow affects the temperature response of thermal wells due to advection of heat by physical movement of groundwater through the aquifer. Research on this subject is scarce in the geothermal literature. This paper presents the derivation of an analytical solution for thermal dispersion by conduction and advection from hydraulic groundwater flow for a “geothermal” well. This analytical solution is validated against asymptotic analytical solutions. The traditional constant linear heat source solution is dependent on the ground formation thermal properties; the most dominant of which is the thermal conductivity. The results show that as hydraulic groundwater flow increases, the influence of the ground formation thermal conductivity on the temperature response of the well diminishes. The diminishing influence is evident in the Peclet number parameter; a comparison of thermal advection from hydraulic groundwater flow to thermal conduction by molecular diffusion.

The experimental study on thermal conductivity of backfill material of ground source heat pump based on iron tailings

2018 ◽  
Vol 174 ◽  
pp. 1-12 ◽  
Author(s):  
Rong Wan ◽  
Dequan Kong ◽  
Jiayuan Kang ◽  
Tianyu Yin ◽  
Jiangfeng Ning ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Experimental Study ◽  
Heat Pump ◽  
Ground Source Heat Pump ◽  
Backfill Material ◽  
Ground Source

Determination of Optimum Design Parameters of Horizontal Parallel Pipe and Vertical U-Tube Ground Heat Exchangers

2009 ◽  
Author(s):  
Hakan Demir ◽  
Ahmet Koyun ◽  
S¸. O¨zgu¨r Atayılmaz
Keyword(s):  
Thermal Conductivity ◽  
Energy Consumption ◽  
Heat Exchanger ◽  
Objective Function ◽  
Heat Exchangers ◽  
Ground Heat Exchanger ◽  
Ground Source Heat Pump ◽  
Soil Thermal Conductivity ◽  
Ground Heat Exchangers ◽  
Ground Source

The most important part of a ground source heat pump (GSHP) is the ground heat exchanger (GHE) that consists of pipes buried in the soil and is used for transferring heat between the soil and the heat exchanger of the ground source heat pump. Soil composition, thermal properties and water content affect the length of ground heat exchanger. Another parameter affects the size of the ground heat exchanger is the shape. There are two basic ground heat exchanger configurations: vertical U-tube and horizontal parallel pipe. There are plenty of works on ground source heat pumps and ground heat exchangers in the literature. Most of the works on ground heat exchangers are based on the heat transfer in the soil and temperature distribution around the coil. Some of the works for thermo-economic optimization of thermal systems are based on thermodynamic cycles. This study covers comparative thermo-economical analysis of horizontal parallel pipe and vertical u-tube ground heat exchangers. An objective function has been defined based on heating capacity, investment and energy consumption costs of ground heat exchanger. Investment and energy consumption costs were taken into account as total cost in the objective function. The effects of the soil thermal conductivity, number of pipes, thermal capacity of ground heat exchanger, pipe diameter and the burial depth on the objective function were examined. The main disadvantage of U-tube ground heat exchanger is higher borehole cost that makes installation cost higher than parallel pipe ground heat exchanger. To make reference functions equal for both type of ground heat exchangers, the borehole cost must be under 20 $/m (now 55 $/m) for a given heating or cooling capacity. The performance of ground heat exchangers depends on the soil characteristics especially the soil thermal conductivity.

A Study on the Calculation Model of Rock Soil Thermal Conductivity in the Design of the Ground Source Heat Pump System

2014 ◽  
Vol 889-890 ◽  
pp. 1347-1352
Author(s):  
Hong Wen Jin ◽  
Qing Shen Fang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Pump ◽  
Soil Layer ◽  
Heat Extraction ◽  
Ground Source Heat Pump ◽  
Soil Thermal Conductivity ◽  
Pump System ◽  
Heat Pump System ◽  
Ground Source

The rock soil thermal conductivity is the most important design parameter for the ground source heat pump system. Based on the equation applied for the heat transfer between the geothermal heat exchanger and its surrounding rock soil, a quasi-three dimensional heat conduction model showing the heat transfer inside the borehole of the U-tube was established to determine the thermal conductivity of the deep-layer rock soil. The results obtained show that the average thermal conductivity got through calculation and actual determination in a tube-embedding region of the ground source heat pump engineering were 1.895 and 1.955W/(m·°C), respectively. The soil layer, which has a great thermal conductivity and a strong integrated heat transfer capability, is suitable for the use of the ground source heat pump system with the tubes embedded underground. The soil layer, with a body temperature of 19 °C and a higher initial temperature, is suitable for the heat extraction from underground in winter. The deviation between the calculation and the determination of the average thermal conductivity in the abovementioned region was 0.06, which could meet the required precision, indicating that the results from the calculation could be used for design.

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