Analysis of the Thermal Potential of an Earth-to-Air Heat Exchanger in the Climatic Conditions of the City of Kyiv

This study aims to analyze the thermal potential of a system with a horizontal Earth-to-Air Heat Exchanger pipeline in the subcontinental climatic conditions of the city of Kyiv, taking into account current global warming trends. To assess the year-round temperature distribution in the soil and along a 43 m long pipeline laid at a depth of 2.5 m, a non-stationary semi-analytical mathematical model was developed, and used for the calculations in the MAPLE environment. The key feature of this model is the integration of the solar-air temperature concept to accurately reflect the significant thermal impact of insolation on the soil surface temperature. The calculations reveal a pronounced thermal inertia of the soil massif, which leads to a phase shift of about 2 months between the peak temperatures of atmospheric air and soil at the depth at which the pipeline is laid. It was found that the system effectively smooths peak heat loads, providing an increase in the supply air temperature by 9-11℃ in winter, as well as a corresponding decrease in temperature by 6-10℃ for cooling in summer. Thermodynamic analysis demonstrates that more than 85% of the available heat potential is realized in the first 30-35 m of the pipeline at an air velocity of 3.8 m/s. In addition, a critical operational risk was identified during the summer cooling period of the supply air — the possible condensation of water vapor on the inner wall of the pipe. This film condensation process accelerates the thermal saturation of the surrounding soil and increases the aerodynamic resistance of the pipeline, which is assessed as a negative phenomenon. To prevent energy losses during transitional seasons, when the temperature gradient is minimal, the implementation of an automated bypass strategy is strongly recommended. In general, the results obtained confirm the feasibility of implementing the studied Earth-to-Air Heat Exchanger configuration to cover the basic energy loads for indoor air conditioning in energy-efficient buildings.