What should the “internal” in the sub-menu concerning thermal resistances in the bore hole be filled with?
A. There are two ways of providing information about the heat transfer properties between the circulating heat transfer fluid and the borehole wall, either by specifying the design and the properties of the materials involved (heat carrier fluid, flow rate, pipe, filling material and contact resistance) or by giving a constant value for the borehole thermal resistance. The thermal short-circuiting between the downward and upward flow channel can cause substantial reduction of the thermal performance of the borehole heat exchanger. The thermal resistance between the upward and downward channel is called the internal thermal resistance. If you the option of calculating the borehole thermal resistance, you will get a reasonable value of the internal thermal resistance as a result. The value of the internal thermal resistance will influence the calculated fluid temperatures only if the box “Account for internal heat transfer” in the menu “Borehole thermal resistance” is checked.
