During the last year thermal response tests of boreholes in rock were carried out with a mobile test equipment (TED) in several duct stores for heating and/or cooling. Most of the tests were made for the Swedish telephone company TELIA that is constructing a great number of direct cooling systems for their telephone switching stations. The size of these duct systems in the different plants tested, varies from 4 to 60 boreholes, drilled in hard rock - mostly granite and gneiss. This paper summarises results and experience from the measurements.