The optimal parameters technique for the vertical ground heat exchangers of the geothermal heat pump systems

Abstract

A scientifically substantiated methodology for determination the optimal parameters of vertical heat exchangers of a underground circuit of the geothermal heat pump systems (GHPS) by the condition of reaching the maximum integral effect or Net Present Value (NPV) is presented. The calculations have confirmed the maximum economic efficiency of the vertical ground heat exchangers can be achieved when observing the optimal values of two defining parameters: the total length of U-shaped heat-receiving pipe and the consumption of the heat carrier passing on it. The optimal values of these parameters are calculated depending on the type and temperature of the ground, the diameter and grade of polyethylene pipes, the initial temperature of the heat carrier at the inlet, tariffs for heat and electricity, specific capital investments in all elements of the ground exchangers, including earthworks, taking into account the real discount rate and a number of additional initial data. The technique allows, to determine the optimal construction and operating parameters of vertical ground heat exchangers under various climatic conditions and types of ground. Also, this technique makes it possible to quantitatively evaluate the maximum achievable economic efficiency of using underground circuit with vertical U-shaped exchangers for the extraction of low-potential ground heat. The use of given technique is necessary for a real assessment of the feasibility of using GHPS as alternative sources of thermal energy in each case.