In this paper, a method for arriving at an optimum design and operation of a geothermal district heating system equipped with deep downhole heat exchanger and heap pump was introduced. A theoretical heat transfer model at steady state was proposed by ignoring the heat loss of transmission pipeline and the heat storage effect of installed facilities and buildings. It shows that there is an optimum ratio of hot geothermal water flowrate to the cold circulating water flowrate through PHE or the evaporator of heat pump. In addition, based on the heat balance equations, and the given costs of PHE, terminal radiator and heat pump, the installation of those main facilities with a minimum capital investment can be obtained.
Keywords geothermal district heating, deep downhole heat exchanger, heat pump, optimal design, optimal operation