Comparison of Earth-Air and Earth-Water Ground Tube Heat Exchangers for Residentialal Application

Earth-air systems are already commonly applied as a passive technique to reduce the overall energy use of buildings by reducing the required cooling or heating demand. However, they often require large surface area for their installation, and make use of large diameter tubes to reduce the pressure drop. As an alternative, waterearth systems are being considered. To explore these two options, one dimensional analytical models were derived. The impact of different design parameters, including tube length, tube diameter, fluid flow rate, etc., have been investigated. For the earth-air system, it is shown that for high Reynolds numbers, the soil resistance is in fact dominating, and as such this should be carefully considered in the design. For the water-earth systems, the addition of a compact heat exchanger to transfer the heat to the air, has a strong impact on the overall performance compared to an earth-air system. To allow for comparable performance, a compact heat exchanger with a high effectiveness is required (0.8 or higher). A strong interaction between the effectiveness of these two heat exchangers was found as the water flow rate varies. For the earth-water heat exchanger, the soil resistance is even more dominant than for the earth-air system