The thermal performance of windows is an important area of research to reduce the energy consumption of buildings and improve indoor comfort. The application of innovative glazing technologies can improve the energy performance of windows and transparent facades, resulting in significant energy savings. This paper presents research results on the energy performance of electrically heated windows. A comprehensive CFD and experimental analysis of the heat transfer processes in a window space depending on the size, power, and location of an electric heater was performed. The convective gas flows in the gas gaps and in the boundary layer were also analysed, and it is shown that a window with an electric heater can reduce the energy consumption of a room by 10–12%. This study is a pilot study to assess the feasibility and cost-effectiveness of electric local heating of a window or facade to minimise heat loss before full-scale implementation. The results of numerical modelling and experimental studies confirm the potential of the new technologies.

Decarbonising the existing residential sector is a central priority of European energy policy, yet masonry buildings from the early 2000s remain significantly underrepresented in net-zero energy building (NZEB) research. This study addresses this critical gap by evaluating a holistic deep retrofit of a representative single-family house in Cracow, Poland, providing a scalable model for the Central European housing stock. The methodology integrated structural and systemic interventions: eliminating thermal bridges via balcony removal, enhancing the envelope with 0.25 m of mineral wool (λ = 0.036 W/m K), and installing innovative active triple-glazed windows (U_w = 0.85 W/m² K) with integrated electric heating foils. The energy system was transformed by replacing a coal-fired boiler with an 8 kW air-to-water heat pump and a 7 kWp photovoltaic array, complemented by a green roof on the western pitch for passive thermal buffering. Verified results demonstrate a radical reduction in the non-renewable primary energy (EP) index from 224.56 kWh/(m²·a) to 0.00 kWh/(m²·a), achieving full compliance with stringent “WT 2021” standards. Economic analysis reveals that the integrated approach is financially viable, with a simple payback time (SPBT) of 7.1 years when supported by available subsidies. This study concludes that the integration of active glazing, high-performance insulation, and nature-based solutions offers a replicable and economically sound roadmap for transforming legacy housing into zero-emission assets.

This study conducts a comparative empirical evaluation of spatial heat flux distribution, cavity thermofluid dynamics, and primary energy implications in an argon-filled triple-glazed unit (TGU) operating under localized bottom-edge perimeter heating (configuration I) and full-surface planar heating (configuration II) across outdoor temperatures ranging from -25 °C to +5 °C. Empirical boundary-layer measurements from a physical test specimen (A_sample= 0.405 m²) were scaled to a standard architectural reference module (A = 2.5 m²). To establish a dimensionally valid comparison against whole-building regulatory NZEB limits, module energy demands were normalized by gross conditioned floor area using a representative fenestration-to-conditioned-floor-area ratio of 0.2. Results demonstrate that localized perimeter heating acts as an exergy-efficient micro-climate buffer, achieving a 34% reduction in inward heat loss when increasing the foil setpoint from 30 °C to 45 °C and effectively suppressing cold downdraughts while restricting floor-area-normalized primary energy demand to 11.4 kWh/m²∙yr (EP_point = 143 kWh/yr total module demand across an 864 h duty cycle). In contrast, full-surface heating eliminates vertical thermal stratification and achieves spatial temperature homogeneity, but converts the glazing into an active space heater, driving high internal heat flux densities (182.1–234.5 W/m² at -25 °C) and an annual primary energy consumption of 1188 kWh/yr per module (EP_planar = 95.04 kWh/m²∙yr, representing an 8.3-fold increase compared to configuration I (143 kWh/yr total module demand). This 8.3-fold discrepancy confirms that unmodulated full-surface planar heating acts as a high-penalty primary energy load, requiring model predictive control architectures to decouple peak thermal capacity from cumulative primary energy constraints. Exterior glass surface temperatures remain thermally independent of internal heating across both regimes, and argon cavity Rayleigh numbers from 2.5 x 10⁴ to 5 x 10⁴ confirm a stable convective boundary-layer regime. To comply with nearly zero-energy building (NZEB) standards, an intelligent model predictive control strategy should maintain localized perimeter heating as a low-power baseline, dynamically escalating to full-surface heating only during extreme sub-zero climatic conditions.

Tematyka artykułu dotyczy budownictwa energo- oszczędnego, a głównym wyznacznikiem jest współczynnik przenikania ciepła U, który określa zdolność przenikania energii cieplnej przez przegrody budowlane. Przeprowadzono badania istniejącego budynku dwukondygnacyjnego przed termomoder- nizacją oraz po wykonaniu robót termomodernizacyjnych w ce- lu określenia korzyści ekonomicznych i ekologicznych, wynikają- cych z przeprowadzonych robót. Prace termomodernizacyjne obej- mowały: docieplenie przegród zewnętrznych styropianem grafito- wym o współczynniku przewodzenia ciepła λ = 0,30 W/(m•K) i grubości warstwy 20 cm, wymianę kotła węglowego na kocioł gazowy dwufunkcyjny z podgrzewaczem ciepłej wody użytko- wej, wymianę grzejników żeliwnych na grzejniki trójpłytowe stalowe oraz grzejnik drabinkowy w łazience, wymianę okien drewnianych dwuszybowych o współczynniku przenikania cie- pła Uw = 2,60 W/(m2•K) na okna drewniano-aluminiowe o współ- czynniku przenikania ciepła Uw = 0,95 W/(m2•K) z dwukomo- rowym pakietem szyb.