No abstract

Based on the statistical analysis of the time series of data, the infl uence of the change of the Sava River temperature on the changes of the groundwater temperature of the Zagreb and Samobor-Zaprešić aquifers is described. In the analysis, data was used from daily measurements of the Sava River temperature and from the quarterly measurements of the groundwater temperature. Statistical methods of correlation and linear regression were applied and the maximum, mean and minimum groundwater temperatures were analysed. The obtained results are presented in the form of statistical parameters, diagrams and maps of isotherms. This da ta is indispensable for the development of shallow geothermal applications related to open loop groundwater heat pump systems. Since the effi ciency of a heat pump is directly dependent on the source temperature, the presented analyses are necessary for a prefeasibility study of geothermal projects and a comparison between diff erent designs. Furthermore, currently operating projects in the Zagreb and Samobor-Zaprešić area are systematically elaborated, giving a fi rst approximation of energy consumption from this renewable energy resource.

Soil gas measurements of radon (222Rn), CO2, and hydrocarbon concentrations, as well as gamma-ray spectrometry, were conducted at two separate locations to estimate the measurement results for known locations of hydrocarbon accumulations in the subsurface and oil seepage on the surface. The aim of the study was to confirm the applicability of the method for identifying migration pathways (e.g., faults) and to detect possible seepages of hydrocarbons to the surface as well as to investigate possible health issue potential about the soil gas analysis results. Site A investigations were performed with a large number of sampling points to provide sufficient spatial coverage to capture the influence of subsurface lithologic variability as well as the influence of the migration pathway on the measured parameters. For the investigation of site B, sampling points were positioned to reflect the situation between the area above producing hydrocarbon fields and areas with no confirmed accumulation. The results presented show that it is possible to distinguish the near-surface lithology (gamma-ray spectrometry), characterize the migration pathway, and indicate the area of oil seepage at the surface. Areas above the known hydrocarbon accumulations generally have elevated radon concentrations and detectable heavier hydrocarbons with sporadic methane in soil gas, which contrasts with the lower radon levels and lack of detectable heavier hydrocarbons in soil gas in the area with no confirmed hydrocarbon accumulation in the subsurface.

Knowing the soil moisture distribution in the unsaturated zone can improve understanding the water flow through the unsaturated zone and thereby enable the calculation of aquifer recharge, which occurs through precipitation. One part of the Zagreb aquifer recharge occurs through infiltration from precipitation. In order to observe and model infiltration from precipitation through the unsaturated zone, the research polygon was constructed at the Velika Gorica well field, located in the southern part of the Zagreb aquifer, Croatia, where hourly measurements of electric conductivity (EC) and soil moisture content were carried out. EC and soil moisture data are measured by Time Domain Reflectometry (TDR) probes which are placed at different depths in the unsaturated zone. Furthermore, electrical resistivity tomography (ERT) measurements were conducted. Geophysical data, along with moisture and EC data from TDR probes, were used as input data for MoisturEC software, in order to obtain soil moisture distribution along a 2D profile. MoisturEC program offers three options for translating EC data to moisture content data which are all tested in this research. We obtained eight moisture content distributions along the observed profile and concluded that MoisturEC provides reasonable results with input data from geophysical measurements and TDR probe measurements. Soil moisture distribution in the unsaturated zone represents the initial conditions for further unsaturated flow modeling. Understanding the flow in the unsaturated zone enables the quantification of effective infiltration and can improve groundwater management.

The wider Zagreb city area, the capital city of the Republic of Croatia, has signifi cant potential for major implementation of geothermal heat pump systems in not just the residential sector, but in the commercial sector as well. Geothermal heat pumps often cumulatively describe diff erent earth energy heat exchanger installations, from groundwater up to shallow ground horizontal and borehole heat exchanger installations. The Zagreb area is especially favourable for both hydrogeological and thermogeological parameters, which allows for the implementation of diff erent designs for residential and commercial heating and cooling. An analysis of comparative energy and economic advantages of heating and cooling with heat pump systems (air, ground or groundwater) was made for the capital city of Zagreb. Since heat pump systems in residential areas are always a higher-class investment, there is often a need for year-round heating since projects increasingly incorporate outdoor swimming pools. Up till now, many authors investigated a comparison of winter heating energy costs for diff erent heat pump systems. However, outdoor swimming pools sometimes consume as much heating energy during the spring-summer-autumn seasons, as do houses in the autumn-winter-spring seasons. Since air temperatures during the spring-summer seasons are much more favourable than sub-cooled ground or groundwater temperatures, air-source heat pumps when used during the whole year for heating, could off set an economically unfavourable coeffi cient of performance (COP) during the coldest days of winter. On a real residential home, currently in the construction phase, techno-economic analysis was performed comparing the seasonal performance factor (SPF) for different heat pump systems during year-round heating.