Heat pump system effi ciency comparison of diff erent renewable energy sources – A family house case study in the Zagreb city area

The wider Zagreb city area, the capital city of the Republic of Croatia, has significant 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 different 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 different 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 different 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 offset an economically unfavourable coefficient 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.