Enhancement of shallow ground heat exchanger with phase change material

Heat pumps perform better when coupled with ground as thermal source than with air because of their exploitation of consistent temperatures as opposed to variable external air temperatures. In literature, several studies and applications suggest and analyse the use of phase change materials (PCMs) coupled with single or double U borehole heat exchangers which are frequently drilled around 100m depth. Usually, the PCMs are mixed with the grouting material during the installation. However, this is one of the main issues of coupling PCMs-BHEs. An alternative solution of vertical BHEs is the use of horizontal and shallow GHEs. This type of heat exchanger can be installed easily, without the use of drilling machines and at the same time the installation can be controlled more in detail. On the other hand, GHEs field needs more space for the installation, and it is more affected by the climate. The present work investigates the possibility of using PCMs coupled to shallow patent GHEs. This latter is a vertical flat plate heat exchanger installed at 1-1.5 m under the ground surface. The research also includes the coupling of PCMs directly with the heat exchanger compared to the alternative solution of PCMs added to the backtilling material of the trench where the GHEs are buried. The analysis has been carried out with COMSOL software tool. A simulation model of the system was developed to carry out a parametric analysis. The objective of the simulations is the investigation of the thermal behaviour of the GHEs coupled with the PCM under the cycles of operation of the heat pump