Feasibility Study of Ground Source Heat Pump System Considering Underground Thermal Properties

Abstract

Abstract:A typical ground source heat pump (GSHP) system in South Korea has a ground heat exchanger (GHX) with a length of 100-150 m, which utilizes annually stable underground temperature to meet the loads of cooling, heating and hot water in buildings. However, most GSHP systems have been introduced in heating dominated areas because the system performance advantage is larger compared with air source heat pump system than that in cooling dominated areas. To effectively provide geothermal energy to the building in the limited urban area, it is necessary to install deep GHXs. Despite its large capacity, there are few studies on GSHP system with deep GHX over 300 m. In this study, to estimate the performance of the GSHP system with deep GHX and evaluate its feasibility, numerical simulation was conducted. To quantitatively analyze heat transfer between soil and GHX, the coupled model with GHX model and ground heat and groundwater transfer model was used. Furthermore, the heat exchange rate and the source temperature were calculated according to the operation modes, the length of GHX, and soil conditions such as geothermal gradient and thermal conductivity. As a result, the total heat exchange rate of GHX with a length of 300 m heat exchanger was 12.62 kW, 173% that of a length of 150 m. Finally, it was found that the GSHP system with deep GHX has realistic possibility in good condition of geothermal gradient.

Finite Element Modeling of Geothermal Source of Heat Pump in Long-Term Operation

“…However, the heat source may operate longer, for 30 or even 50 years. Therefore, it is crucial to conduct long-term modelling [18] and measurements of such systems [19]. Ground temperature changes depend on the annual heat imbalance between injected and extracted heat rate [20].…”

A Study on the Effect of Performance Factor on GSHP System through Real-Scale Experiments in Korea

“…It, however, does not provide quantitative values for newly developed systems, such as the shape of the ground heat exchanger and the introduction of the heat storage tank. To address this problem, various studies [5][6][7][8][9][10][11][12][13][14][15][16][17][18] have been conducted using experimental and numerical methods.…”

“…Additionally, they examined the measurement method and the GSHP system performance of the previous studies. Bae et al [14] evaluated the performance of a deep depth ground heat exchanger over 300 m using numerical simulation. The length of 300 m ground heat exchanger has 173% higher heat transfer rate than the length of 150 m ground heat exchanger.…”

“…Performance analysis studies are actively conducted according to performance factors [5][6][7][8][9][10][11][12][13][14][15][16]. However, most of the studies [5,6,8,10,11,14] were conducted through numerical analysis. Most experimental studies have been conducted to verify the suitability of sites by real-scale experiments [17,18].…”

Concepts and characteristics of a U-shaped docking well geothermal heat extraction system

“…Sun et al (2018) proposed a U-shaped closed loop geothermal system, but they didn't consider the impact of the length of the horizontal section. For the middle-deep geothermal resources or dry hot rock geothermal resources, most of the previous studies have focused on two aspects: (1) using concentric casing heat extraction system (Bae et al, 2018;Cho et al, 2016;Jin et al, 2012), but both the flow rate and the heat exchange efficiency were low; (2) drilling multiple deep wells for production and injection of working fluid, using fracturing, acidification and other measures to connect the heat reservoir (Cui et al, 2018;Yanagisawa et al, 2008;Zeng et al, 2013). But the process is complicated, the formation is connected to the geothermal system, the water recovery rate is low, and unfavorable recharge will cause land subsidence.…”