Impact of Boundary Conditions on a Groundwater Heat Pump System Design in a Shallow and Thin Aquifer near the River

Longcang Shu,Peigui Liu,Rui Xiao,Yuezan Tao,Zhonghui Wen

doi:10.3390/su9050797

Longcang Shu, Peigui Liu + Show 3 more

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https://doi.org/10.3390/su9050797

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Journal: Sustainability	Publication Date: May 11, 2017
Citations: 3	License type: CC BY 4.0

Affiliation: Hohai University, Hefei University of Technology

Abstract

The exploitation of shallow geothermal energy through a groundwater heat pump (GWHP) is always limited to thick and deep aquifers containing abundant water with a relatively stable temperature. Unfortunately, aquifers in hilly regions which occupy two thirds of China are usually thin and shallow. The boundary conditions in those hilly areas affect the groundwater flow that is used for geothermal energy production. To quantify the impact of boundary conditions on the shallow geothermal energy development, a shallow and thin aquifer near the Qingyi River in Anhui Province was chosen as a case study, and a three-dimensional heat–water model was developed using FEFLOW. The impact of the boundary conditions on the hydrodynamic and temperature fields of the aquifer was analyzed by using the developed model. Furthermore, the well locations of a pumping-recharging system near the river correspond to three different modes of pumping-recharging well layouts that were optimized based on the changes of pumping water temperature and the maximum drawdown. The simulation results indicated that the influence of atmospheric temperature on groundwater temperature is negligible below a depth of 11 m. When the river level is above 28 m, the optimal scheme of pumping-only was used (without considering recharging wells) with a certain distance from the river. This scheme not only operates efficiently, but also reduces the operation cost.

Highlights

Shallow geothermal energy refers to the low-temperature heat energy in groundwater and rock-soil mass at a certain depth below the surface, where the main energy sources are solar radiation and geocentric heat [1]
A heat–water transfer numerical simulation was developed to study the impact of boundary conditions on the hydrodynamic processes and temperature distribution field in a shallow and thin aquifer near a river
On the premise that the river water temperature has no influence on the pumping water temperature, the average pumping water temperature and maximum drawdown at the end of the summer’s cooling period decrease gradually when the river level rises and the moving distance of the pumping-recharging well group increases

Summary

Introduction

Shallow geothermal energy refers to the low-temperature heat energy in groundwater and rock-soil mass at a certain depth below the surface (e.g., buried within 200 m), where the main energy sources are solar radiation and geocentric heat [1]. The development and utilization of shallow geothermal energy mainly employ the ground source heat pump (GSHP) system. Since the introduction of the theoretical and experimental study of GSHP in the 1990s, the heat pump technology has been developed and employed rapidly in China [7], especially the technology of groundwater heat pumps (GWHPs). The GWHP, among many types of GSHP systems, is one in which energy is extracted from groundwater [8,9,10]. By the year 1999, 100 GWHP projects had been completed in China, and the total heating supply area reached approximately 1 million m2 [11]. GWHP systems have been widely implemented in almost all provinces in China. The number of GWHP systems is over 1500, with more than 1800 million m2 of heating and cooling areas. The data have shown that GWHP is playing an important role in China [12]

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