Development of a 2D numerical transient model to study geothermal coaxial borehole field heat exchangers

Abstract

A numerical 2D transient model to study geothermal coaxial borehole field heat exchangers under thermal interferences has been built and implanted in MATLAB; it has been compared against two analytical solutions and the numerical code COMSOL where the results has been found identical. A coaxial borehole heat exchanger has been selected regarding to its better performances. The results show that porous grounds are more suitable for these systems, when porosity is 0% the thermal load decreases by 15.725% than the case where porosity is 45%; also, it has been found that after occurrence of phase change in the saturated sub-ground, effective thermal properties changes in a way to make the withdrawn thermal load decreases in a more intense manner, it reduces by 5.36% than the case where the process is not accounted for and this is during the last 843 h since the process start; the last part of the thermal investigations yields that the underground-water flow is favoured for the system performance.