This study evaluates the performance of a flat-plate solar collector thermal system located in Bucharest, Romania, by combining experimental measurements (December 2024–April 2025) with numerical modeling. The system, coupled to a 4000 L tank and using a 30% glycol–water mixture, was monitored for irradiance, wind speed, temperature, flow rate, and humidity. Monthly irradiance averaged 448–584 W/m², and wind speed 2.3–4.3 m/s. Instantaneous efficiency ranged from 25.09% to 73.25% (mean 52.96%), with CUF (capacity utilization factor) ranging between 6.55% and 9.38%. Total heat losses were 4.80–7.79 kW and dominated by top losses (3.60–5.59 kW). The model reproduced the manufacturer’s efficiency curve within 5% for data obtained in the spring, with winter deviations of up to 37% due to weather variability and aged insulation. The results provide reference values for the CUF and loss coefficients of flat-plate collectors in temperate continental climates and can support retrofit and sizing decisions.

This paper presents a banana ripening chamber system for Romania. The system comprises two main parts: the refrigerating unit, with a cooling capacity of 47.5 kW, and a fresh air supply system for ethylene exhaust during the ripening process (1000 m³/h). The proposed solution replaces the classical one-stage vapor compression with R134a. The new solution presented in this study has a proven fruit ripening solution that includes the 3Es; it is eco-friendly (low GWP refrigerant R1234ze(E)), economical, and energy efficient (AHU with heat recovery). The advantage of the new system results from an increasing coefficient of performance, with 7.34% owing to decreasing the power consumption of the compressors. Regarding heat recovery, the annual energy consumption for ventilation is lower, using (annual average) 41% less energy than without heat recovery.

This study develops a transient mathematical model for predicting the outlet air temperature of a modular solar air collector integrating recycled concrete as sensible heat storage. The reference prototype used 18.8 kg of recycled concrete storage, with a volume of 0.01033 m³, density of 1820 kg/m³, and measured thermal conductivity of 0.885 W/(m·K). The model connects absorber, airflow, storage, external convection, and radiative heat-transfer mechanisms using a 600 s time step and measured meteorological boundary conditions. Validation was performed for clear, overcast, and scattered cloud conditions, producing absolute MBE values below 0.38 °C, MAE values of 0.64–1.17 °C, RMSE values of 0.87–1.39 °C, and R² values of 0.83–0.96. The expanded uncertainty of the measured outlet temperature was ±0.58 °C, placing the lowest model error close to the experimental uncertainty level. The results support the use of recycled demolition concrete as a sensible storage medium and provide a modeling framework for subsequent investigation of different storage masses, geometries, airflow rates, and longer multi-day operating periods.

Food-industry refrigeration must simultaneously reduce electricity use, replace high-global-warming-potential refrigerants, and make better use of rejected heat. This systematic review synthesises 101 peer-reviewed publications from 2015 to April 2026. Searches in Web of Science Core Collection, ScienceDirect, Scopus and IEEE Xplore identified 435 records; after deduplication, retrieval and full-text eligibility assessment, 101 publications were included and coded across four overlapping directions: heat recovery and useful heat valorisation (D1), energy efficiency and low global warming potential (GWP) refrigerants (D2), renewable energy sources (D3), and modelling, validation and control (D4). A structured descriptive appraisal considered study design, validation, uncertainty reporting, operating relevance and economic or environmental boundaries. The central research gap is the absence of integrated, experimentally validated studies, as these directions are still pursued largely in isolation rather than combined on a single installation. The urgent priority is therefore a comprehensive demonstration that unites refrigerant substitution, staged heat recovery, renewable-energy and storage integration, and dynamic monitoring and control on an operating food-industry installation, evaluated against a measured baseline across representative periods in each season using technical, energy, economic, environmental and operational indicators that capture the overall efficiency gain of the installation.

The electrification of residential heating through heat pumps represents one of the central directions of the European energy transition; however, evaluating these systems requires moving beyond classical approaches limited to purely energy-based indicators. This paper proposes an integrated 3E analysis (Energy–Economy–Environment) of a hybrid system composed of a split-type air-to-water heat pump (nominal heating capacity of 8 kW, R410A refrigerant) and an on-grid photovoltaic installation with a peak power of 6.02 kWp, installed in a single-family house with a usable floor area of 122.3 m², located in climatic zone II with a conventional winter design outdoor temperature of t_ext = −15 °C. Operational data, collected over two consecutive heating seasons (2024–2025 and 2025–2026) at daily resolution and aggregated monthly, were processed to determine the seasonal performance factor (SPF), the specific heat demand, the operating costs compared with a conventional natural-gas solution, and the climatic impact through the TEWI (Total Equivalent Warming Impact) indicator. The results show SPF values of 3.30–3.51 (±7%, standard uncertainty), a strong correlation between outdoor temperature and COP (at both the monthly and daily levels), average annual savings of approximately 2834 RON compared with the natural-gas solution, and a payback period of 15–16 years. The cumulative climatic impact over the equipment’s lifetime (TEWI ≈ 35.1 t CO₂-eq over 15 years) is offset to a large extent (≈83%) by the emissions avoided through photovoltaic production (≈29.25 t CO₂-eq). The results indicated a higher LCCP (Life Cycle Climate Performance) compared with TEWI, by approximately 4.0%, for the system presented in this paper. The study also identifies limitations associated with the local electricity grid infrastructure, which reduce the exploitation of photovoltaic production during periods of high solar potential, and proposes optimization directions such as battery storage and improvements to the building envelope. The results support the need for multicriteria, 3E/4E-type assessments to underpin decisions on the decarbonization of the residential building sector.