Computational Modeling and Sensitivity Analysis of Horizontal Helical Heat Exchangers for GSHPs

At the very beginning of their use, ground source heat pumps were adopted in cold climate only for heating. Nowadays they find application in countries with a temperate climate like in the Mediterranean area, as they represent a good solution for climatization both for heating and cooling seasons. Ground source heat pumps have economic advantages as well, particularly in energy intensive applications where a very efficient system is required in order to reach good energy and cost performance. The most efficient configuration is the GSHP provided with vertical ground heat exchangers for the excellent heat transfer capabilities of these thermal devices, but it is very expensive because of high ground drilling costs. An alternative configuration is that with horizontal ground heat exchanger, which is cheaper, but less efficient. On the other hand using optimized geometrical configurations to enhance heat transfer capabilities of these systems could assure a good compromise between performance and cost. In this work horizontal helical heat exchangers performance were investigated. This kind of ground heat exchanger was analyzed numerically, with the help of the CFD code Fluent, under different operating conditions and with different geometrical configurations. The dependence of the heat transfer efficiency of the system on the parameters like the spires step, the depth of installation and the water inlet velocity were investigated. A cost analysis was performed as well. The convenience of the installation of this horizontal configuration was also carried out compared with a traditional the single tube horizontal heat exchanger one, already investigated in a previous work.