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The popularity of ground source heat pump systems for both heating and cooling has grown significantly over recent years. Ground heat exchangers are usually buried in the ground either vertically in boreholes or horizontally in trenches. Antifreeze fluids in closed-loop systems are commonly used in these plants to protect them from freezing phenomena and also to reduce the total length of the ground exchangers. In fact, the use of antifreeze fluid allows the system to work below 0 °C which implies higher temperature difference between the heat-carrier fluid and the undisturbed ground, consequently the heat flux increases and the total length of the boreholes can be reduced. This study has been set out to investigate three types of layout system: two conventional heat pumps using pure water and water-glycol respectively as the secondary fluid and an innovative heat pump with a flooded evaporator using pure water. The results demonstrated that, for conventional heat pumps with dry evaporator, the use of anti-freeze additives in mild climates is convenient only in grid-shaped borehole fields with a heating-dominant thermal load. In all other cases, the use of pure water decreases the overall operating costs. In addition, flooded evaporator heat pumps using pure water as a secondary fluid on the ground loop proved to be the most cost-effective solution. [ABSTRACT FROM AUTHOR]

Abstract: A reliable evaluation of long-term performance of a heat pump coupled with a borehole heat exchanger (BHE) field is necessary to verify the stability of its heat exchange capability over the time. The BHE field pattern is often assumed to be regular (e.g., rectangular, L-shaped, T-shaped, etc.), or is assumed to be adequately approximated by one of these shapes. Moreover, a planned geothermal system is often designed regardless of the presence of other existing or planned BHE systems. In order to evaluate the validity and the possible limitations of these assumptions commonly made by the designer, a number of 25-year time span simulations have been carried out by means of 2D finite element modeling. In particular, the case of a real 28 BHE field, irregularly shaped and related to a building located in Northern Italy, has been studied together with its 7-by-4 regular grid approximation and a series of 28 BHE fields having different shapes. Besides the real annual thermal load profile characterized by quasi-balanced winter heating and summer cooling, two other profiles characterized by increasingly unbalanced operation have been taken into account. The numerical study shows that (i) the regularly shaped approximation, a common choice in BHE design, seems to be reasonable under the condition that groundwater flow is absent for all the thermal load profiles; (ii) if a strong heating/cooling imbalance occurs, the thermal footprint of a BHE field can be very extensive, preventing the installation of future nearby BHE systems. [Copyright &y& Elsevier]

An empirical method aimed at generating maps of potential of geothermal energy exchange for shallow vertical closed-loop systems is proposed here. The method uses both geological and technological information. In particular, the ground parameters that mainly influence the heat transfer in borehole heat exchangers, the energetic parameters driving efficient operations of geothermal systems and heating and cooling requirements of a typical residential building are taken into account. Spatial modeling is carried out in a Geographic Information System leading to an effective and easy-to-use digital cartographic tool. An application of the method to four regions of southern Italy is also shown. [ABSTRACT FROM AUTHOR]

• The design of a new GSHP system cannot disregard local ground thermal properties. • The ground thermal properties also affect the system long-term energetic performances. • A thermal properties database is proposed for both rocks and unconsolidated sediments. • It integrates and compares literature data with more than 400 direct measurements. When a new ground source heat exchanger field is planned, underground thermal properties input data are necessary for the correct sizing of the geo-exchange system. To support the design, the EU founded Cheap-GSHPs project developed a Decision Support System, that comprises a new database of thermal properties for both rocks and unconsolidated sediments. The thermal properties database has been developed by integrating and comparing data (1) provided by the most important international guidelines, (2) acquired from a wide literature review and (3) obtained from more than 400 direct measurements. The data are mainly thermal conductivity data, hence the convective contribution provided by groundwater flow to heat transfer is not included. This paper presents and analyses the collected database. [ABSTRACT FROM AUTHOR]