| Abstract |
The use of geothermal heat pump systems in residential and commercial buildings around the world is increasing. The cost of ground heat exchanger due to its high share in the total system cost is a key parameter in deciding whether or not to use the heat pumps. The ground heat exchanger cost reduction is therefore, very important in the economic viability of the geothermal heat pump projects. In this paper, the evaluation of a ground heat exchanger in the form of a spiral tube is done using a 3D numerical model of the heat transfer. Furthermore, the thermal efficiency, analysis is conducted for shallow, wide boreholes. Moreover, the effect of aluminum fins inside the ground (inside the well) is evaluated in order to increase the soil and heat exchanger contact area and rise the system performance. In addition, using fins with a high heat transfer coefficient can increase the overall system efficiency by engaging more soil under the ground. The simulated borehole has 1m diameter and 10m depth. In order to reach and outperform the conventional U-tube ground heat exchangers, the impact of parameters such as fluid velocity, thermal conductivity, pitch and specific heat capacity in backfill material and sounding ground on the performance of the system is investigated. The proposed settings and configurations in this paper leads to an increase of about 30% in the heat transfer rate of the system. This improvement is due to the high thermal conductivity of aluminum fin in the soil. Additionally, the heat transfer rate from the tube to the soil is augmented especially at the end-points of the fins. |