Investigations and modelling for a practical application of borehole thermal energy storage

This study has been carried out within the H2020 Project RES4LIVE “Energy Smart Livestock Farming towards Zero Fossil Fuel Consumption” (2020-2024, grant agreement 101000785). The project’s objective is to bring into the market integrated cost effective and case sensitive Renewable Energy Sources (RES) solutions towards achieving fossil free livestock farming. In this framework, the replacement of heating systems based on fossil fuels in pig barns represents a fundamental target. Therefore, an integrated system was conceived and designed to provide the thermal energy required for heating the alley connecting ten rooms of a nursery barn, hosting up to 2500 weaners. The integrated system is composed by photovoltaic thermal collectors (PVT), a dual source heat pump (DSHP) and a borehole thermal energy storage (BTES). The system is currently under realization at a pilot study case represented by a swine farm located in Mirandola (MO), partner in the project. The project realization has been subjected to a strict regulatory framework. Moreover, the needed antifreeze quantities are higher than those for standard borehole heat exchangers (BHE) project, in order to allow the solar energy to be stored directly in the ground, without intermediate heat exchangers. Specific constraints have been: maximum storage temperature of 35°C, authorization to intercept the aquifer at very shallow depths, obligation of BHE grouting, definition of a strategy for continuous monitoring of groundwater quality. This contribution aims to present the preliminary investigations conducted for the definition of suitability and potential of the BTES, and the actions taken for assuring environmental protection and long-term sustainability. Specifically, two piezometers 2“wide, 25 m deep and distant each other 40 m, were installed, in a line over direction North-South. They have been located around 50 m far from two existing wells, of the same depth, currently used for the farm’s purposes. Between the two piezometers, two double U, PE100 PN16 DN32, BHE were installed, the first one 10 m deep (crossing the first layer of clay with sandy lens), while the second one 30 m deep (crossing the second layer of fine sand, hosting the shallow aquifer). Two thermal response tests were performed, one per each BHE, while temperature and hydraulic head values were taken in the observation boreholes, by using both fixed recording sensors and movable measurements tools. The data gathered and the results of the tests conducted have been used to select the most suitable working depth for the future BTES field, to quantify the potential for underground thermal storage, to understand the heat dispersion due to groundwater movement and to model the BTES behaviour under various operation scenarios. The conclusions obtained will be applied in the design phase to optimize the integration of PVT, BTES and DSHP. The full BTES system is planned to be installed during summer season 2022.