WP9 – Published papers
Abstract: The design phase of ground source heat pump systems is an extremely important one as many of the decisions made at that time can affect the system’s energy performance as well as installation and operating costs. The current study examined the interpretation of thermal response testing measurements used to evaluate the equivalent ground thermal conductivity and thus to design the system. All the measurements were taken at the same geological site located in Molinella, Bologna (Italy) where a variety of borehole heat exchangers (BHEs) had been installed and investigated within the project Cheap-GSHPs (Cheap and efficient application of reliable Ground Source Heat exchangers and Pumps) of the European Union’s Horizon 2020 research and innovation program. The measurements were initially analyzed in accordance with the common interpretation based on the first-order approximation of the solution for the infinite line source model and then by utilizing the complete solutions of both the infinite line and cylinder source models. An inverse numerical approach based on a detailed model that considers the current geometry of the BHE and the axial heat transfer as well as the effect of weather on the ground surface was also used. Study findings revealed that the best result was generally obtained using the inverse numerical interpretation.
Abstract: The Molinella test site (Italy) is the open-air laboratory of the UE project “Cheap-GSHPs: Cheap and Efficient Application of Reliable Ground Source Heat Exchangers and Pumps”. Here, innovative helical heat baskets and steel coaxial probes are installed next to the traditional double-U. The tests involve the probes design as well as materials and drilling techniques and machines, therefore the newly developed GSHEs can be directly compared with the traditional ones with respect to technical issues and energetic performances.
The Molinella test site therefore represents a very extraordinary possibility to improve the knowledge of heat transfer processes in shallow geo-exchange systems.
Abstract: Direct measurements of gravel thermal properties are usually quite challenging to be performed in laboratory, due to the very coarse sediments size. As a consequence, the reference thermal values provided by literature for gravels are quite limited and dispersed. A guarded hot plate Taurus Instruments TLP 800, usually used for measuring the thermal conductivity of buildings materials, was slightly modified in order to measure the thermal conductivity of some gravel samples. The tests were performed both in dry and wet conditions. The paper presents the first obtained results.
Abstract: The Cheap-GSHPs EU project is shortly presented in the Italian Journal of Groundwater.
Abstract: Reducing the energy demand of buildings has become one of the key points of the European Union. The issue related to the air conditioning of old and historical buildings is nowadays one of the most important field of operation for the primary energy saving and, at the same time, for the reduction of the CO2 emission. The recent development of heat pump able to rise the supply of high temperature at the condenser side makes this technology suitable for the application also in historical buildings that are characterized by low thermal insulation and high thermal capacitance. In this context, the ground source heat pump systems can be used for both heating and cooling. The aim of this work is to analyze the thermal behavior of two historical buildings located in Italy, in Venice and Florence respectively. Detailed computer simulations of the buildings have been carried out by means of a transient calculation tool TRNSYS. Energy simulations of GSHP systems have been performed and a comparison with a common plant system using a gas boiler for heating and air-to-water chiller for cooling has been carried out
Abstract: The relatively high installation costs for different types of shallow geothermal energy systems are obstacles that have lowered the impact of geothermal solutions in the renewable energy market. In order to reduce planning costs and obtain a lithological overview of geothermal potentials
and drilling conditions, a pan-European geological overview map was created using freely accessible JRC (Joint Research Centre) data and ArcGIS software. JRC data were interpreted and merged together in order to collect information about the expenditure of installing geothermal systems in specific geological set-ups, and thereby select the most economic drilling technique. Within the four-year project of the European Union’s Horizon 2020 Research and Innovation Program, which is known as “Cheap-GSHPs” (the Cheap and efficient application of reliable Ground Source Heat exchangers and Pumps), the most diffused lithologies and corresponding drilling costs were analyzed to provide a 1 km × 1 km raster with the required underground information. The final outline map should be valid throughout Europe, and should respect the INSPIRE (INfrastructure for SPatial InfoRmation in Europe) guidelines.
Abstract: Shallow geothermal energy can be exploited in any location by ground heat exchangers (GHE), which consist of pipes placed either horizontally in trenches or vertically in boreholes in the ground. The cost of the GHE is primarily determined by the pipe cost per unit length and the total required length. For a given type of ground and completion conditions, the main parameter that affects the required length of a GHE is the thermal conductivity of the pipe material. The preferred pipe construction materials are usually high density polyethylene (HDPE) as the plastic with the highest thermal conductivity, in a much lesser extent cross-linked polyethylene (PEX) for relatively higher temperature applications, and even stainless or galvanized steel in some other installations. In this paper, alternative metallic materials with higher thermal conductivity as well as thermoplastics available in market were evaluated for shallow geothermal use. The evaluation was made in terms of expected GHE service life based on literature review of buried piping systems, estimation of the required GHE length per unit energy output by computer simulations and cost estimation using current market prices.
Abstract: Nowadays, the energy price fluctuations and the economic crisis are jeopardizing the development and diffusion of renewable technologies and sources. With the aim of both reducing the overall costs of shallow geothermal systems and improving their installation safety, an European project has took place recently, under the Horizon 2020 EU Framework Programme for Research and Innovation. The acronym of the mentioned project is Cheap-GSHPs, meaning “cheap and efficient application of reliable ground source heat exchangers and pumps”; the Cheap-GSHPs project involves 17 partners among 9 European countries such as Belgium, France, Germany, Greece, Ireland, Italy, Romania, Spain and Switzerland. In order to achieve the planned targets, a holistic approach is adopted, where all involved elements that take part of shallow geothermal activities are here integrated. In order to reduce the specific costs of geothermal installations, some newly designed geometries of heat basket-type ground source heat exchanger (GSHE) are modified drastically to receive a better performance of the geothermal installation. Within the sector of very shallow geothermal systems, these new developments are also tested on six representative demonstration sites around Europe. At the German test site in Northern Bavaria, four heat basket-type GSHEs are installed and equipped with certain monitoring systems (moisture, two different temperature sensors) and various backfilling materials of different grain size classes. The different installations will be tested for 12 months to evaluate the best combination of the newly designed heat basket-type GSHE and corresponding backfilling material mixture.