Environment has become a major concern for society, which awareness of the importance of an environmentally respectful development has been growing during the last decades. Economic reasons have encompassed this transition to a more planet friendly conception of human development. In fact, this transition has been parallel to the growing prices of fossil fuels, facing a clear perspective of a shortage on its availability, insufficient to cope with a growing demand in the near future. Within this context, the role of renewable energies in order to stop depending on fossil fuels and to reduce greenhouse gases emissions has become crucial.   Because of its climate, heating represents a major source of energy consumption in Sweden, accounting for almost 60% of the residential and services sector energy use. Maximizing the efficiency of heating systems and using renewable, environmentally friendly and economically sustainable sources of energy may have an enormous impact on both environment and economy.   In this thesis the use of district heating and ground heat pump for a multi-dwelling building is evaluated, both from the economic and environmental points of view. Both are recognized to be efficient heating systems, allowing important savings of other sources of energy, and respectful with the environment.   An installation combining both district heating and ground heat pump, for a multi-dwelling building in Gävle has been analyzed. Different scenarios have been considered, and results obtained show that when installing a ground heat pump, both economic savings and CO2 emissions reduction are obtained. Annual economic savings account for 16,8% when providing 60% of the thermal energy with the ground heat pump, and considering the investment associated to the recent installation of a new heat pump (in the case studied, boreholes were already drilled), the payback time is 7,4 years. CO2 emissions reduction for a normal year reaches 34%. However, if we look at the wider picture of electricity and heat production from a community (local, regional, national or even international) point of view, several considerations have to be taken into account, which are discussed in the report.

Ground Source Heat Pumps (GHSPs) is a relevant application and around 3 million installations are setting up at the beginning of 2010 (IEA ECES Annex 21). The improvements in GSHPs are currently focused on the optimization of the system and the reduction of costs installations. The thermal conductivity of the ground and thermal resistance of the Borehole Heat Exchanger (BHE) are important design parameters for Borehole Thermal Energy Storage (BTES) systems. The Thermal Response Test (TRT), which has been used up to now in the GHE design, only allows estimating mean values for thermal conductivity of the surrounding ground and borehole resistance. However, the ground thermal conductivity and borehole thermal resistance may present local variation along the borehole depth. For improving conventional TRT, the optical fiber technology is applied to collect information about the temperature profiles in the borehole. Thermal Response Test (TRT) logs the inlet and outlet fluid temperatures; meanwhile, the Distributed Thermal Response Test (DTRT) carries out a profile of the temperature along the borehole depth, in this case with fiber optic cables. This Master of Science Thesis focuses on the comparison and analysis of DTRT measurements in a U-pipe borehole in order to estimate the thermal conductivity and the borehole thermal resistance along the borehole. The comparison and the analysis are carried out by: •Comparing the differences of TRT results depending on the heat power rate considered – constant and by steps-. •Comparing the results from two different resolution Distributed Test Sensing (DTS) equipments: Halo and Sentinel DTS. •Comparing the differences of TRT results as depending on the analytical procedure based on the line source theory: line source model and line source approximation.