Marija Živić

Building heating energy demand is influenced by indoor temperature, air exchange, and climatic conditions. This study examines the individual and combined effects of these parameters on a district-heated multi-apartment residential building in Osijek, Croatia. A TRNSYS model was evaluated using measured space-heating consumption for the analysed period from October 2024 to April 2025 and representative TMYx weather data. In the model, air exchange was represented by an effective air-change rate accounting for both uncontrolled air infiltration through the building envelope and natural ventilation associated with occupant window opening. The measured seasonal consumption was 666.16 MWh, while the model predicted 670.61 MWh, resulting in a deviation of 0.67%. The model was then used for a full-factorial analysis including nine indoor temperatures from 18 to 26 °C, nine effective air-change rates from 0.30 to 0.70 h⁻¹, and six Croatian locations, giving 486 simulation scenarios. Under reference conditions, heating demand in Zadar and Split was 44.05% and 50.93% lower than in Osijek/Čepin. Increasing the indoor temperature from 18 to 26 °C increased seasonal demand by 432.63–525.32 MWh, while increasing the effective air-change rate from 0.30 to 0.70 h⁻¹ increased it by 182.67–296.55 MWh. The analysis also showed a positive interaction between indoor temperature and effective air-change rate. For the analysed building, the results can support more sustainable energy use by informing energy-efficient building operation and district-heating demand planning, while the reported numerical sensitivities remain specific to the case-study building.

This study investigates the tariff-oriented operation of residential air-to-water heat pump systems integrated with thermal energy storage under long-term real climatic conditions. In contrast to studies based on short-term simulations or advanced predictive control, this work evaluates a simple rule-based control strategy with a focus on practical applicability. The analysis is based on hourly simulations using measured meteorological data over an eight-year period for multiple locations characterized by continental climatic conditions. Two system configurations were considered: a reference system without thermal energy storage and a storage-integrated system operating under a dual-tariff electricity pricing scheme. The results show that thermal energy storage enables effective load shifting toward lower tariff periods, resulting in consistent electricity cost reductions of 19–23% across all analyzed years and locations. These savings are achieved without significant changes in seasonal performance. However, the economic analysis indicates that the payback period remains relatively long (20 years), exceeding typical thresholds for residential investments under current conditions. Overall, the findings highlight the importance of operational flexibility and demonstrate that simple control strategies can improve the economic performance of residential heat pump systems.

Air-to-water heat pumps (ASHPs) are a key technology for residential heating decarbonization; however, their seasonal performance is highly sensitive to outdoor temperature variability. Although thermal energy storage (TES) is widely recognized as a means of improving system efficiency, reported performance gains vary due to differences in climatic datasets, control strategies, and modeling assumptions. This study presents a systematic multi-year assessment of the impact of a water-based TES tank on the seasonal performance of a residential ASHP under measured microclimatic conditions. Hourly simulations were conducted for a single-family house at three locations in eastern Croatia using eight years (2018–2025) of measured meteorological data. Building characteristics, system configuration, and operating strategy were kept identical to isolate the influence of storage volume. TES integration reduced annual electricity consumption by 4.8–9.1%, with a multi-year average reduction of 7.02%, and consistently increased the seasonal coefficient of performance (SCOP) across all analyzed years and locations. The highest relative improvements occurred under less favorable microclimatic conditions, emphasizing the importance of diurnal temperature distribution rather than seasonal averages alone. A parametric analysis identified an optimal storage volume of approximately 1000–1500 L when both energy and economic indicators are considered. The results demonstrate that stable and reproducible seasonal efficiency gains can be achieved through a simple, non-predictive operating strategy under continental climatic variability.

This paper discusses two different thermo-technical systems for heating and cooling the three-story office building under consideration. Data were collected on natural gas energy consumption over three-year period. The measured data on energy consump...