Experimental Analysis of the Feasibility of Using the Ground as a Temporary Energy Accumulator
Andrés Meana-Fernández, María José Suárez‐López, David García, Eduardo Blanco, Jesús Ignacio Prieto-García · 2023
With significant percentages of worldwide energy consumption occurring in the building sector, it is intended to reduce energy consumption and, in turn, satisfy the demand with renewable energies.However, renewable energies suffer from high variability, so energy accumulation systems become relevant for adjusting the time gap between energy supply and demand.In recent years, air conditioning facilities with geothermal heat pumps have been on the rise, as they reach higher coefficients of performance (COP) than aerothermal heat pumps.In addition, they provide the opportunity to use the ground as a thermal reservoir.A first analysis of the feasibility of using the ground as a temporary energy accumulator has been performed in this work.To this end, tests have been carried out in an experimental facility with vertical buried pipes to evaluate the evolution of ground temperature after heat injection.Temperature probes were placed on the pipe surface and monitored at 5 different depths, with tests performed in three different months to observe seasonal effects.Dimensional analysis led to the identification of the influencing variables of the problem: depth, tube length, tube diameter, time and soil thermal diffusivity.An apparent thermal diffusivity was defined to characterize the soil from the thermal measurements.The results allowed identifying a subterranean water stream at a particular depth, as well as observing the effects of ambient conditions in the system.It was observed that the upper ground layers were heavily affected by ambient conditions, discouraging their use for thermal energy storage, whereas depths below the ground water table seemed suitable for storing heat efficiently.Differences were found between wet and dry soil, with wet soil better suited for the storage of higher energy amounts, but dry soil better suited for keeping the stored energy for longer periods without further isolation.