Fouling and clogging are some of the major water quality problems encountered in open loop ground source heat pump (GSHP) systems and aquifer thermal energy storage (ATES) systems. Here we present a surveillance strategy that can detect if and identify where in the system fouling and clogging might be developing without having to shut off the heat pump. In the presented system design, the test requires a minimum of four temperature sensors and two pressure sensors to describe the performance of the four major heat source system components, namely, the production well, the injection well, the submersible pump and the groundwater heat exchanger. The surveillance procedure involves conducting a step-test with incremental increases in the groundwater flow rate while measuring the pressure and temperature responses in the system components. The performance of the newly constructed installation functions as a baseline for future tests. By conducting the test systematically during operation an altered performance of the system can indicate clogging or fouling issues. Even though the cause of the problem must be identified through other means, the surveillance procedure presented here allows the operator to plan necessary maintenance and avoid critical damage to the heat source system.

Fouling and clogging of groundwater wells and heat exchangers are among the major operational challenges for groundwater heat pump (GWHP) and aquifer thermal energy storage (ATES) systems. This article presents the application of a step-test surveillance procedure developed for early detection of clogging in distinct parts of the GWHP system, tested at Lena Terrace in Melhus Norway. Three versions of the test procedure are presented and demonstrate that the test can be performed with a minimum of four steps, each of 15-min duration, while the GWHP system is actively producing heat. The results prove that the surveillance test can detect changes in the hydraulic resistance of the groundwater circuit and locate clogging problems within all of the relevant system components in the groundwater circuit simultaneously. At the Lena Terrace GWHP system, these tests indicate a gradual increase of hydraulic resistance with time, which verify that clogging issues are continuously developing in the injection well, in the production well, and in the groundwater heat exchanger. Cleaning of the heat exchanger was then performed. This increased the pumping capacity by 8.3% points, but continuous clogging of the injection well and the production well necessitates further maintenance to ensure a reliable operation. It is demonstrated that multidisciplinary competence and experience with GWHP-systems, aquifers, and groundwater wells are needed for the evaluation of the results. These results can therefore serve as a reference for other GWHP systems with similar design configurations.

The utilization of groundwater heat pump systems is increasing in Norway, which are currently widely employed for heating and cooling applications in the town center of Melhus. The investigations of the Melhus installations are detecting gas exsolution as a possible trigger for precipitation reaction that causes incrustation of iron and manganese compounds in the systems. This paper discusses risks associated with gas exsolution and considers gas exsolution triggers in a typical Norwegian groundwater heat pump (GWHP) system configuration. The concept of the solubility grade line (SGL) is developed and suggested as a tool for optimizing the design. Based on SGL analysis and the intention of avoiding gas exsolution during heat production, an alternative system design in the same aquifer is presented and compared. The analyses show that the traditional system design is predisposed to gas clogging risks and prone to vacuum pressures in parts of the system. The alternative design mediates the risks by adjusting the well and piping configuration and by applying a backpressure technique. The results demonstrate how the groundwater heat pump system design can be customized according to local aquifer conditions to avoid gas exsolution during operation. It is recommended that the presented method of analysis should be utilized in dimensioning of systems and included in the monitoring scheme of the systems.

The application of 3D technology for fabrication of artificial porous media samples improves porous media flow studies. The geometrical characteristics of a porous media pore channel: the channel shape, size, porosity, specific surface, expansion ratio, contraction ratio, and the tortuous pathway of the channel can be controlled through advanced additive manufacturing techniques (3D printing), computed tomography imagery (CT imaging) and image analysis methods. These 3D technologies have here been applied to construct and analyze four homogeneous porous media samples with predefined geometrical properties that are otherwise impossible to construct with conventional methods. Uncertainties regarding the geometrical properties are minimized because the 3D-printed porous media samples can be evaluated with CT imaging after fabrication. It is this combination of 3D technology that improves the data acquisition and data interpretation and contributes to new insight into the phenomenon of fluid flow through porous media. The effects of the individual geometrical properties on the fluid flow are then accounted for in permeability experiments in a Hassler flow cell. The results of the experimental work are used to test the theoretical foundation of the Kozeny–Carman equation and the extended version known as the Ergun equation. These equations are developed from analogies to the Hagen–Poiseuille flow equation. Based on the results from the laboratory experiments in this study, an analytical equation based on the analytical Navier–Stokes equations is presented as an alternative to the Hagen–Poiseuille analogy for porous media channels with non-uniform channel geometries. The agreement between experiment and the new equation reveals that the dissipating losses of mechanical energy in porous media flows are not a result of frictional shear alone. The mechanical losses are also a result of pressure dissipation that arise due to the non-uniformity of the channel geometry, which induced spatial variations to the strain rate field and induce acceleration of the velocity field in the flow through the porous medium. It is this acceleration that causes a divergence from linear flow conditions as the Stokes flow criterion (Re ≪ 1) is breached and causes the convective acceleration term to affect the flow behavior. The suggested modifications of theory and the presented experiments prove that the effects of surface roughness (1) do not alter the flow behavior in the Darcy flow regime or (2) in the Forchheimer flow regime. This implies that the flow is still laminar for the Forchheimer flow velocities tested.

This paper presents results from video inspections of groundwater wells in Melhus and Elverum, in Norway. The method has identified iron hydroxides, bacterial growth and sand production as causes of clogging in different wells. Video inspection has proven itself a reliable, inexpensive and quick method for such investigations. The videos supply documentation for the building owner about the well condition. A video inspection should be incorporated as a standard part of the tender document and an integrated part of the maintenance routine. Finally, open loop GSHP and ATES system wells should be designed and manufactured with integrated video inspection options. This will ease the fault detection process and reduce maintenance costs of the system through the lifetime of the wells.

Convective acceleration occurs in porous media flows due to the spatial variations of the nonuniform flow channel geometry of natural pores. This article demonstrates that the influence of convective acceleration in a nonuniform a pore channel is analogous to that of a constricting pipe channel. Their fluid mechanical behaviour can be comparable, provided that their geometrical characteristics are described precisely in the same manner, and from the same point of reference with regards to the fluid velocity in the flow channels. The analogy of the dissipation mechanisms in nonlinear porous media flow to the "minor loss" approach in fluid mechanics of pipes is therefore appropriate. Conventional nonuniform pipe channel geometries obtain dissipation coefficients within the range 0 < C_KL < 0.2. These pipe geometries are relevant reference points for natural porous media, and it is thus expected that most natural pore geometries will obtain values within this range. This assumption holds true for the nine different 3D porous media samples presented here. However, the results show that the rate of change in the pore geometry, and consequently the magnitude of induced convective acceleration, depends on: the area ratio a of the pore channel, the angle of approach θ and the rounding of the pore channel geometry. The rounding of the pore channel reduces the dissipation coefficient, as the rate of change becomes smoother along the channel length. The results also indicate that the pore tortuosity increase the magnitude of nonlinear dissipation, in good agreement with pipe flow behaviour. This knowledge can help improve our interpretation of experimental data and enhance the predictability of porous media equations that incorporate the appropriate dissipation coefficients C_KL as a variable. Article Highlights: The analogy of porous media flow to the "minor loss" approach in fluid mechanics of pipes is appropriate, and the angle of approach θ and the area ratio a of the pore channel govern the magnitude of induced convective acceleration in porous media The rounding of the pore channel geometry reduces the magnitude of induced convective acceleration The tortuosity of a pore influences the dissipation coefficient C_KL and increase the magnitude of induced convective acceleration