This paper presents the results of measuring the final energy consumption for heating and domestic hot water (DHW) preparation and indoor conditions in 15 apartments located in pre-war tenement houses. The measurements were compared to the computed energy consumption. The calculations ware made based on the model calibrated by field measurements. The discrepancies between measurements and calculations were assessed using the energy performance gap (EPG). Calculations were made separately for energy for heating and for DHW preparation. Additionally, the results of EPG calculations for different levels of analysis are presented aiming at assessing the impact of weather, temperature in the surrounding zones and users’ behavior. Users’ behaviors influencing the size of the EPG were divided into typical (energy saving or excessive energy consumption) and forced (energy poverty, response to the apartment’s surroundings, technical limitations. The connection between the heating sources and the heating habits has been clearly observed in the research. The former (typical) behaviors were the origin of the energy gap in the apartments heated with natural gas and district heating. The latter (forced) were the origin of the gap in the apartments heated with mostly electricity and solid fuel (with one exception: one apartment that utilized the district heating).

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In the paper the analysis of the operation of ground-source heat pump with various heat-carrier fluids circulating in boreholes was made. The authors considered several aspects related to the heat-carrier fluid selection (freezing point, heat transfer capabilities, toxicity, pumping costs). The lower heat source analysis had been performed in Earth Energy Designer (EED) software. The analyses’ results reliability was assured by the ground-source model calibration made basing on the measurement data from on-site test stand. Analyses were performed for four heat-carrier fluids (two kinds of propylene glycol solutions – standard and with lower viscosity, water and nanofluid (water + CuO)) and in four variants of thermal load (design and actual loads both with and without active regeneration). It had been concluded that temperature of none of the fluids would drop under 0°C if the system was operated under actual thermal load. For design thermal load there would be a risk of the water freezing but it may be minimized by active regeneration or lower heat source enlargement by 20% (in analyzed case) each rising the mean fluid temperature by around 1.0-1.5 K. The use of other fluid in place of standard propylene glycol solution will give pumping energy savings.