A borehole solar heat storage system with double circuit and dual source for a swine farm: first year of operation

The present contribution illustrates the energetic results of the first period of operation of an innovative borehole thermal energy storage system (BTES) in Northern Italy. The research is finalized to develop a sustainable heating system for livestock building combining various renewable energy sources. The focus is on a pilot case, a swine farrow-to-nursery farm housing 500 sows and 2500 weaners. In fact, livestock farming is a significant energy-intensive branch of agriculture, which is substantially contributing to greenhouse gas (GHG) emissions. Recognizing the imperative to replace fossil fuels with Renewable Energy Sources (RES), the scientific community is actively exploring retrofitting strategies for existing farms. These strategies aim to create novel equipment based on RES for diverse farming activities. The system developed in the research is comprised by borehole heat exchangers in “double circuit” configuration: the installation in the ground is the usual vertical double U, while the connection lines are separated: the first vertical U is linked to photovoltaic / thermal (PVT) system with a novel standardized solar central for underground energy storage, while the second is linked to a dual source heat pump (DSHP) for heating the livestock building. In swine farming, in particular, ensuring optimal environmental conditions in nursery barns is crucial for the health and proper growth of weaners. However, achieving ideal temperature and humidity levels is challenging in both hot and cold seasons, often necessitating high-energy HVAC systems. The “double circuit” configuration allows to fully exploit the mid-seasons (autumn and spring), where solar radiation and heating needs are both not negligible, thus enhancing the efficiency of the ground source. In summer season, the solar heat storage is prominent, allowing to modify the aquifer temperature in the BTES of several degrees, while in winter season, the heating use is prominent, and the air source is activated to cover the peaks, then the BTES is never thermally depleted. A tailored piezometer monitoring system allows to quantify the heat dissipation in the BTES due to groundwater flow. A smart control system was developed and implemented to monitor energy usage and environmental conditions. The findings underscore that monitoring environmental and energy parameters outdoor and inside buildings is fundamental to collect a database of the energy performances, assess the efficiency of the system and allow remote control of the equipment