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Abstract An accurate estimate of site-specific underground thermal properties from thermal response tests (TRTs) is vital to the efficient and sustainable use of ground source heat pump (GSHP) systems. During a conventional TRT, the ground is perturbed by a heat injection and the response is measured in time. Despite the simplicity of the concept, conventional TRT fails to take into account the ground thermal response to heat extraction, which may affect the reliability of the thermal properties derived. To address the problem, an improved TRT based on both heat injection and extraction was proposed in this study. The improvements were demonstrated with an in-situ test carried out in Taiyuan, China. The measurement results showed that the ground thermal conductivity in Taiyuan was 1.56 W/(m K) and the borehole thermal resistance was 0.22 (m K)/W. The results also showed that, in the case of Taiyuan, ground thermal conductivities derived solely from heat injection test and heat extraction test were, respectively, 7.6% higher and 8.3% lower than that from the improved TRT. Thus, compared with the conventional TRT, the improved TRT consisting of both heat injection and extraction tests can provide test data more accurately reflect the annual performance of GSHP systems. [ABSTRACT FROM AUTHOR]

Based on the duct ground heat storage model on TRNSYS software, a thermal-dissipation-corrected transient model which takes the heat dissipation from ground and testing tube surfaces into consideration is established. An experimental platform is built for in-situ thermal response test (in-situ TRT) in Shandong Province, China. The presented model is verified by in-situ TRT with similar inlet and outlet temperatures of borehole heat exchanger (BHE). Furthermore, the key parameters, such as injected heat power, circulation flowrate, etc. are analyzed to study the influences on identified soil thermal conductivity, borehole thermal resistance and heat flow per unit length of BHE. It is showed that test duration has the largest impact on identified soil thermal conductivity, followed by injected heat power, abandoned initial hours, the circulation flowrate and backfill material conductivity; injected heat power has the largest influence on heat flow per unit length of BHE. [ABSTRACT FROM AUTHOR]

An interface is developed to couple the finite element program FEFLOW with the MATLAB-SIMULINK software. The TCP/IP based data exchange routine allows for a co-simulation of borehole heat exchangers and of HVAC components, so that each subsystem can be modeled in its specialized simulation environment. Hereby, the interaction of the subsystems is taken into account, which leads to a more precise representation of the systems’ dynamic behavior. Furthermore, the concept supports the application of mathematical optimization algorithms that can be utilized to automatically determine several design parameters for an overall improved system performance. [ABSTRACT FROM AUTHOR]

The economic viability of Borehole Heat Exchangers (BHEs) depends on the ability of the ground to exchange heat, and maps of the shallow geothermal potential are therefore useful planning tools for future installations. In this work, we present the assessment of shallow geothermal potential in Cerkno, a mountain town of 5,000 inhabitants in western Slovenia. The recently developed G.POT method was applied, taking into account site-specific ground thermal parameters and usage profiles depending on climate conditions. This work is part of the EU-funded project GRETA, aiming at supporting the diffusion of GSHPs in the Alpine territory. [ABSTRACT FROM AUTHOR]

The heat transfer enhancements of borehole heat exchanger (BHE) have been intensively studied which strongly influences the performance of ground-coupled heat pump (GCHP) systems. In this paper, some typical heat transfer enhancement methods of BHE are reviewed based on BHE designs, grout materials and the influence of artificial groundwater flow. Features and feasibility of different methods have been discussed for the different applications. [ABSTRACT FROM AUTHOR]

The efficiency of Geothermal Heat Pumps (GHPs) strongly depends on the site-specific parameters of the ground, which should therefore be mapped for the rational planning of shallow geothermal installations. In this paper, a case study is presented for the potentiality assessment of low enthalpy geothermal energy in the Province of Cuneo, a district of 6900 km 2 in Piedmont, NW Italy. The available information on the geology, stratigraphy, hydrogeology, climate etc. were processed and mapped, and conclusions were drawn on the geothermal suitability and productivity of different areas of the territory surveyed. [ABSTRACT FROM AUTHOR]

Heating of buildings requires more than 25% of the total end energy consumption in Germany. By storing excess heat from solar panels or thermal power stations of more than 110 °C in summer, a medium deep borehole thermal energy storage (MD-BTES) can be operated on temperature levels above 45 °C. Storage depths of 500 m to 1,500 m below surface avoid conflicts with groundwater use. Groundwater flow is decreasing with depth, making conduction the dominant heat transport process. Feasibility and design criteria of a coupled geothermal-solarthermal case study in crystalline bedrock for an office building are presented and discussed. [ABSTRACT FROM AUTHOR]

At present the U-tube borehole heat exchanger (BHE) used for ground-coupled heat pump (GCHP) system mostly applies 32 mm as outer diameter. In order to compare the heat transfer capacity of this diameter with other nearby standard diameters, the thermal performance of U-tube BHE with four kinds of standard outer diameter were simulated by TRNSYS based on a GCHP system case in Tianjin, heat exchange rate and total BHEs number were calculated under different borehole depth and borehole diameter. The simulation result indicated that under the same borehole depth and borehole diameter, BHEs number was the fewest when the U-tube outer diameter was 25 mm, however the cases used U-tube with 32 mm outer diameter needed the most BHEs to meet the load demand. Furthermore, another single borehole simulation was conducted to show that thicker U-tube wall is the reason that U-tube BHE with 32 mm outer diameter had relatively worse thermal performance due to its larger thermal resistance, which offset the positive effect of bigger heat exchange area. [ABSTRACT FROM AUTHOR]

Ground Source Heat Pumps (GSHP) are economically and environmentally advantageous for the heating and cooling of buildings, provided that the long-term sustainability of the thermal exploitation of the soil is ensured. In particular, the performance of a closed-loop Borehole Heat Exchanger (BHE) strongly depends on the geometrical and physical properties of its components and on the thermo-hydrogeological properties of the surrounding soil. In this work, we present the results of a series of simulations of a double U-pipe Borehole Heat Exchanger, carried out with the finite-element flow and heat transport modelling software FEFLOW to assess the relative influence of these parameters on the operation of a GSHP. The analysis confirms that the length of the borehole is the main design parameter, but the thermal conductivity of the grout, the pipe spacing, the heat carrier fluid and its flow rate also have an important effect on the energy efficiency of the system. The thermal conductivity of the soil is another fundamental variable in the design of a GSHP, and hence it is better to rely on site-specific data, rather than adopting values from the literature. Although most design methods neglect it, the presence of a subsurface flow results in an enhancement of the performance of the system. Thermal dispersion also enhances the efficiency of the system but, since it has not yet been adequately studied, relying on it is not advised for the design of BHE fields. [ABSTRACT FROM AUTHOR]

Abstract: Ground source heat pumps are a valid technology for heating and cooling in residential application, since they allow to have a stable temperature of the heat source/sink by means of ground heat exchangers, generally named as Boreholes. In particular, U- pipe heat exchangers are interesting when working with two-phase fluids, especially during the heating season, when natural circulation might occur. This work presents the model of a borehole heat exchanger working with carbon dioxide as secondary fluid in a U-pipe loop. A closed system of equations is introduced with appropriate correlations for heat transfer and pressure drops, accounting for transient heat conduction due to ground temperature variation. Maps of performance varying the main operating parameters are presented and discussed, showing the potential of the model as tool for sensitivity analysis and as sub- model to find the matching between the heat pump and the borehole heat exchanger. [Copyright &y& Elsevier]

Abstract: An unglazed photovoltaic-thermal (PVT) collector provides a double benefit in a heat pump system compared to a conventional heat pump system with PV and borehole heat exchanger. First, the PV cells in the PVT collector are cooled, leading to lower cell temperatures and a higher PV efficiency. Second, the PVT heat raises the temperature level of the heat pump and the borehole heat exchanger and consequently leads to a higher heat pump system performance. In this context a system was measured with a 39 m2 unglazed PVT collector field. The impact of the solar heat to the heat pump is determined by TRNSYS simulations using energetic weighted temperatures for validation and to quantify the impact of the solar heat. The investigated system revealed a temperature increase of 3K which equals 9% lower electricity consumption. The yearly additional PV yield was determined to 4% by reference measurement of uncooled conventional PV panels. Additionally, system simulations in TRNSYS are presented. [Copyright &y& Elsevier]