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Horizontal ground-couple heat pump (GCHP) system incurs lower installation cost compared with the vertical GCHP system. However, the shallow burial depth makes the heat transfer process susceptible to seasonal variations. This paper analyzes the short-term and annual performance of different geothermal heat exchangers’ (GHEs) configurations and geological conditions by developing 3D finite element models. Field monitored data of ground temperature and thermal property are incorporated. Six common types of GHE configurations are analyzed, from which the most efficient patterns are identified. The annual performance of optimal GCHP pattern integrated with different types of building loads are analyzed. Major conclusions include (1) application of soil temperature harmonic function as commonly done in the current practice will lead to overestimation of thermal build-up effects underground; (2) utilization of local geological data (i.e., field measured ground temperature and soil thermal properties) helps improve the annual performance of horizontal GCHP system; (3) shift of ground temperature is less significant for GCHP operating in heating dominant areas due to balanced heat injection and extraction. This study indicates incorporating local geological data reduce the GHE design length by 25%–60% and therefore is a viable strategy to achieve cost effectiveness. [ABSTRACT FROM AUTHOR]

A novel indirect expansion solar-assisted multi-functional heat pump (IX-SAMHP) system which composes of the multi-functional heat pump system and solar thermal collecting system is proposed and studied in this paper. This system can fulfill space heating, space cooling and water heating with high energy efficiency by utilizing solar energy. For solar water heating mode and solar space heating mode, a dynamic model is presented and validated with the experimental results. The simulation results show good consistency with the experimental data, and the established model is able to predict the system performance at a reasonable accuracy (with the root mean square deviations less than 5%). On this basis, the performances of the IX-SAMHP system are investigated under different parametric conditions. For solar water heating mode, simultaneously operating the solar thermal collecting system and multi-functional heat pump system can be an energy efficiency method. With the solar irradiation rising from 0W/m 2 to 800W/m 2 , the COP increases from 2.35 to 2.57. In solar space heating mode, the effect of the mass flow rate of water in evaporator is investigated. To balance the heating capacity and COP, the mass flow rate of water should be adjusted according to different temperature demands and heat load. [ABSTRACT FROM AUTHOR]

The hybrid ground-coupled heat pump (HGCHP) systems with supplemental heat rejecter/supplier can effectively solve heat imbalance problems in the subsurface, and consequently improve the operation performance of the geothermal systems. For example, solar energy and/or industrial waste heat may be used as stable heat sources for underground heat storage in northern China with higher heating load, and cooling towers are installed to release heat into the air in southern China, where more cooling demand is needed. This paper reviews and discusses different HGCHP systems, which have been applied in China. And based on the heat transfer model of vertical borehole heat exchangers (BHE) for HGCHP systems, physical and mathematical models of multistage series circuits are developed to illustrate the heat transfer process of the underground thermal storage. A set of parameters, such as borehole spacing, heat recharging rate fractions and thermal properties of soils, which affect the thermal performance of the ground heat exchangers are analyzed, and the optimal solutions are discussed for engineering application. [ABSTRACT FROM AUTHOR]

Abstract: In this paper an improvement of the model CaRM (CApacity Resistance Model) is presented to consider the borehole thermal capacitance, both of the filling material of the borehole and of the heat carrier fluid inside the ground heat exchanger. Several models, numerical and analytical, are available in literature for short time step analyses of ground-coupled heat pump systems. According to the modelling for the surrounding ground, the new approach for the inside of the borehole is based on electrical analogy. In this study the double U-tube ground heat exchanger is analyzed. The new model has been validated by means of a commercial software based on the finite elements method as well as measurements of ground response test, using a suitable plant system. In this last comparison, the contribution of the thermal capacitance of the circulating fluid is investigated, since it is frequently neglected in short time step simulations. In both cases, there is agreement between the CaRM results and data from numerical simulations and measurements as well. [Copyright &y& Elsevier]

Abstract: Thermal response test (TRT) is crucial for the determination of the ground thermal conductivity and the evaluation of the thermal performance of borehole heat exchangers (BHEs) of ground source heat pump (GSHP) system. This paper presented a novel constant heating-temperature method (CHTM) for TRT. Further, a type of improved TRT equipment was developed and the mathematical model to deal with test data was presented. Based on the measurement of the natural ground temperature distribution, an in situ TRT case was carried out. The experimental results showed that, compared with the conventional TRT with constant heating-flux method (CHFM), CHTM has an obvious advantage of reducing the time period reaching a steady heat-transfer state between the BHE and its surrounding soils. This improved TRT equipment can effectively operate under both heat-injection and heat-extraction modes, and its test data can accurately reflect the thermal properties of the soils as well as the thermal performance of the BHE under different operation conditions. Finally, the advantages and disadvantages between CHTM and CHFM were compared, which can provide a useful reference for the design of GSHP system. [Copyright &y& Elsevier]