Validation of modified one-dimensional models simulating the thermal behavior of earth-to-air heat exchangers-Comparative analysis of modelling and experimental results

The integration of renewable energy technologies in existing HVAC systems is an approach for decreasing their nominal installed capacity and for increasing their energy efficiency. Earth-to-air heat exchangers are considered as alternative energy systems and consist of pipes, horizontally buried underground, through which ambient air is transported by properly sized fans and draws or dumps heat from/to the ground. Due to the high heat capacity of the ground, underground temperature is lower than the ambient during summer and higher during winter, allowing the air that flows inside the earth-to-air heat exchanger to exploit the temperature difference in order to preheat or precool the air before it is actually used for ventilation. In the present study, two common one-dimensional simulation models are modified and validated with theoretical and experimental data of other studies and compared with other existing numerical models that simulate the behavior of earth-to-air heat exchangers. The criterion for their selection was the simplicity of the calculation procedure, without consideration of too many parameters, so that results can be obtained quickly in order to be used for a preliminary sizing of an earth-to-air heat exchanger. The results indicate that both one-dimensional models exhibit similar accuracy in estimation of the temperature rise during the heating period, but quite different in estimating the temperature drop during the cooling period. One of the models exhibits a deviation of less than 10% compared to the measured values which is similar with the most time demanding and complicated CFD analysis.