The Bulgarian Experience in the Thermal Response Tests

Abstract

The heat source part of a Ground Source Heat Pump (GSHP) system, the ground heat exchanger, can be developed as an Aquifer Thermal Energy Storage (ATES) or as a Borehole Thermal Energy Storage (BTES). The hydro-geological restrictions are less for the BTES system, thus it has a bigger potential for application. There are built already some installations of this type in Bulgaria. Unfortunately the owners do not know exactly the values of the ground characteristics. That could bring to big inaccuracies during the project calculations and the construction of the geothermal systems. The knowledge of the underground characteristics is very important to design an installation using BTES. The most effective method to determine the ground thermal characteristics is the Thermal Response Test (TRT), which gives an opportunity for their determination in-situ.

The work presents a review of the experiments carried out by a research team of the Technical University of Sofia, branch Plovdiv. A mobile installation for implementing of Thermal Response Test has been designed and constructed in 2007. A test borehole heat exchanger (BHE) with a depth of 41 m has been constructed in the courtyard of the Technical University of Sofia, branch Plovdiv. Three tests have been performed in 2009 using the constructed mobile installation (namely in January, March and April). The ground thermal conductivity and the borehole thermal resistance have been determined experimentally. The results, obtained by the different tests, are compared and mathematical simulations by use of the TRNSYS 16.1 commercial program are also performed. The tests are the first ones of this type in Bulgaria. The mentioned team believes to have the leading position when a cadastre of the ground thermal properties is created in Bulgaria. The team will support the Balkan Peninsula projects connected with construction of Ground Source Heat Pumps.