Speaker
Description
Keywords: Ground source heat pumps, borehole thermal resistance, borehole heat exchanger
Abstract
Climate changes and rising energy costs are driving forces for researchers and practitioners to introduce competitive and clean energy supplies. Shallow geothermal energy and ground source heat pumps systems have shown an attractive alternative to common energy sources. The borehole heat exchanger is an efficient and economic tool for extracting geothermal energy within ground source heat pump systems. Recovering a higher temperature for heating or a lower temperature for cooling not only increases the amount of energy required, but it also increases the efficiency of the heating or cooling system. The amount of heat can be transferred between the ground and heat exchanger depends on many factors mainly physical properties of ground such as thermal conductivity and borehole thermal resistance. The layout, cross-section, tube configuration, raw material of the borehole heat exchangers are the most crucial aspects that strongly influenced the effectiveness and lifetime expectancy of the system, which recently attracted numerous attentions. Special care should be taken in hydraulic design of borehole heat exchanger system, particularly laminar flow can occur in the borehole heat exchangers due to usage of heat carrier fluid at low temperature with inadequate flow rate. This can lead to lower heat extraction and rejection rates of the exchanger because of higher thermal resistances. This phenomenon is more dominate for the deeper boreholes since the heat short cut in the up part of the borehole would increase. Furthermore, by increasing flow rate to achieve turbulent flow and satisfactory heat transfer rate can lead to increase the pressure drop of the system and over sizing of circulation pump which leads to impairment of seasonal coefficient of performance at the heat pump.
In this ongoing project, different applications of the borehole heat exchangers is reviewed, then the novel geothermal borehole heat exchangers with appropriate characterization are introduced and investigated.
