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•A middle-deep CBHE system with different operating modes is presented.•Introduced the module structure of TRNSYS simulation and built the model.•The accuracy of short-term simulation is verified by practical engineering.•Insulation measures should be added when the ground thermal conductivity is high.•Intermittent operation is conducive to improving the specific heat transfer rate. Application of the middle-deep coaxial borehole heat exchanger (CBHE) in building heating has been gradually accepted by the public, and has become one of the emerging technologies to extract geothermal energy. This study aims to provide theoretical references for practical projects by simulating the long-term heat transfer characteristics of CBHEs using TRNSYS software. Firstly, this paper proposes a dual-mode operation strategy based on the dynamic response of thermal loads and constructs the middle-deep CBHE system model using software modules. After comparing inlet and outlet water temperature between data obtained from an actual project and the simulation results to validate the model, the impact of factors including the geothermal gradient, ground thermal conductivity, specific heat transfer rate, and run-time ratio are simulated. Additionally, the variation laws of system performance and the energy efficiency of thermal extraction under different influencing factors are analyzed. The results show that the outlet temperature decreases as the geothermal gradient decreases, and the CBHE system cannot operate normally for a long time when the outlet temperature is low. According to the influence of ground thermal conductivity on inlet and outlet water temperatures, insulation measures should be taken. To ensure long-term stability between ground heat extraction and heat recovery, the specific heat transfer rate of a continuously operating heating system should not exceed 150 W/m. Moreover, intermittent heating can improve the specific heat transfer rate of a single well. The system average coefficient of performance (COP) increases with the increase of the geothermal gradient and the ground thermal conductivity. When the specific heat transfer rate is 350 W/m, the run-time ratio increases from 1/3 to 5/12, and the energy efficiency of thermal extraction decreases from 16.6 % to 11.22 %. [Display omitted]

The research work explores the impact of temperature on Silicon photovoltaic (PV) panels, considering Nigeria as a case study. It is found that high solar radiation in Nigeria increases the surface temperature of PV panels above 25 °C of the optimal operating temperature. The redundant energy gain from solar irradiance creates heat at the rear of solar panels and reduces their efficiency. Cooling mechanisms are therefore needed to increase efficiency. In this study, we demonstrated a unique hybrid system design employing a heat exchanger at the back of the panel, with water circulated through the back of the PV panel to cool the system. The system was simulated using TRNSYS at three locations in Nigeria—Maiduguri, Makurdi, and Port Harcourt. The results of the peak annual electrical power output in Maiduguri give a power yield of 1907 kWh/kWp, which is the highest, due to a high solar radiation average of 727 W/m2 across the year. For Makurdi, the peak annual electrical power output is 1542 kWh/kWp, while for Port Harcourt the peak power output is 1355 kWh/kWp. It was observed that the surface temperature of Polycrystalline Si-PV was decreased from 49.25 °C to 38.38 °C. The electrical power was increased from 1526.83 W to 1566.82 W in a day, and efficiency increased from 13.99% to 15.01%.

This study addresses the performance limitations of standalone desiccant cooling systems in extreme climates by developing and optimizing a solar‐assisted hybrid desiccant evaporative cooling (SHDEC) system specifically for the hot and humid coastal climate of Saudi Arabia. The novel system configuration integrates a solid desiccant wheel, an indirect evaporative cooler (IEC), a heat pump, and a solar–thermal array for regeneration. Through extensive transient TRNSYS simulations and a detailed parametric analysis, key system parameters were optimized. The final SHDEC system achieved a solar fraction (SF) of 69%, maintained comfortable indoor conditions for 88% of the year, and demonstrated a coefficient of performance (COP) of 2.1, which rose to 4.9 when considering only grid‐supplied energy. Key findings from the parametric study identified an 80 m 2 glazed flat plate (FP) collector array, a 4 m 3 thermal storage tank, a 400 mm desiccant rotor, and a 2‐ton heat pump as the optimal configuration. The results confirm the SHDEC system as a highly viable and sustainable alternative to conventional vapor‐compression systems, offering significant energy savings and a path to reduced carbon emissions for cooling‐demanding regions.

Climate change and its negative effects are driving the global shift from fossil fuels to renewable energy sources. To tackle the dependency on traditional energy sources in harsh winter regions and improve heating quality during periods of thermal demand fluctuations, this paper proposes a new distributed heating peak shaving system (DHPS). The system combines municipal heat and clean energy within the secondary network while reducing the return water temperature in the primary network. It comprises solar collectors, electric thermal storage tanks (ETST), and absorption heat pump (AHP) units, integrated into conventional heat exchange stations. The system operates in two modes to manage peak and off-peak loads respectively, with TRNSYS simulation used to evaluate performance across a range of peak-shaving gradients. A multidimensional comprehensive assessment is conducted between the DHPS under optimal peak shaving coefficient ( θ ) conditions and conventional peak clipping boiler (PCB). Results indicate that DHPS achieves a high primary energy ratio (PER) of 1.251 at θ = 0.5, reducing combustion emissions by nearly 40%. The static payback period (PBP) of the system is 3.5 years. When the electricity price drops to 0.275 CNY, its operational costs are comparable to PCB. DHPS caters to the energy characteristics of cold regions where electricity supply exceeds demand. It enables flexible peak shaving while ensuring the complete utilization of clean energy and effectively utilizing waste heat from power plants.

A Photovoltaic Thermal (PVT) collector produces heat and electricity simultaneously. Air-type PVT collector uses air as a transfer medium to take heat from PV back side surface. The performance of the air-type PVT collector is affected by design elements such as PV types, inside structures in heat collecting space (baffle or fins), the shape of the air pathway, etc. In this study, an advanced air-type PVT collector was designed with curved baffles (absorber) to improve thermal performance. Within the air-type PVT collector, PV cells were arranged in an interspaced design, and the curved baffles were located in the collecting space to increase heat efficiently. The absorber received solar radiation directly and was utilized as baffles for improving thermal performance. The air-type PVT collector was fabricated and tested in an outdoor environment considering the climatic conditions of Daejeon, Republic of Korea. In addition, based on experiment parameters and data, the annual thermal and electrical performances of the system were analyzed by simulation modeling using the TRNSYS program. Thermal and electrical efficiencies were 37.1% and 6.4% (according to module area) for outdoor test conditions, respectively. Numerical and experimental results were in good agreement with an error of 4% and 0.24% for thermal and electrical efficiencies, respectively. Annual heat gain was 644 kWh th/year, and generated power was 118 kWh el/year.

To address the poor thermal insulation and freeze resistance of rural outdoor toilets in cold regions—key obstacles to achieving the UN Sustainable Development Goal (SDG) 6.2 and popularizing rural sanitary toilets—this study fills the literature gap of insufficient research on passive solar heating systems tailored for rural toilets in cold climates. Using TRNSYS simulation, Plackett–Burman key factor screening, single-factor experiments, and Box–Behnken response surface methodology, we optimized the system with building envelope thermal parameters and Beijing’s typical meteorological year data as inputs, taking January’s average indoor temperature as the core evaluation index. Results indicated six parameters (solar wall area, air cavity thickness, vent area ratio, vent spacing, exterior wall insulation thickness, and heat-gain window-to-wall ratio) significantly influence indoor temperature (p < 0.05). The optimal configuration was as follows: solar wall area 3.45 m2, window-to-wall ratio 30%, exterior wall insulation thickness 200 mm, vent spacing 1800 mm, air cavity thickness 43 mm, and vent area ratio 5.7%. Post-optimization, the average temperature during the heating season reached 10.81 °C (79.5% higher than baseline), with January’s average, maximum, and minimum temperatures at 7.95 °C, 20.47 °C, and −1.42 °C, respectively. This solution effectively prevents freezing of flushing fixtures due to prolonged low temperatures, providing scientific support for the application of passive rural toilets in China’s cold regions.

This study examines the potential of nanofluids to enhance the thermal efficiency of flat-plate solar water heating systems (SDHW) through numerical modeling using TRNSYS software. Improving the efficiency of such systems is critical for increasing the viability and sustainability of solar thermal technologies, particularly in regions with high solar potential like Türkiye. Three different nanofluids (Al 2 O 3 , TiO 2 , and CuO) were evaluated for their ability to improve heat transfer and system performance. Simulation results revealed that incorporating 0.1% Al 2 O 3 into the working fluid increased the collector outlet temperature from 97 °C (with pure water) to 120 °C, indicating a 23% improvement. Comparable enhancements were observed with TiO 2 and CuO nanofluids. Furthermore, collector efficiency, which typically ranges between 35 and 40% under peak solar conditions, was elevated to approximately 45% with the use of nanofluids. These findings suggest that nanofluids significantly improve thermal performance and energy conversion efficiency in SDHW systems. The results highlight the practical potential of nanofluids in advancing solar thermal technology and promoting cleaner, more efficient renewable energy solutions.

The solar drying of sewage sludge in greenhouses is one of the most used solutions in wastewater treatment plants (WWTPs). However, it presents challenges, particularly in terms of efficiency and drying time. In this context, the present study explores the drying performances of an innovative Combined Solar Greenhouse Dryer (CSGD) for sewage sludge. The system integrates rock bed storage (RBS), a solar air collector (SAC), and a solar greenhouse dryer (SGD). A numerical model, developed using TRNSYS software, predicts the drying kinetics of sewage sludge through hourly dynamic simulations based on the climatic conditions of Marrakesh, Morocco. Experimental validation confirmed the accuracy of the model. The results reveal that integrating the SAC with the SGD during the day and the RBS with the SGD at night significantly enhances the drying efficiency of the sewage sludge. During daylight hours, the SAC generates hot air, reaching maximum temperatures of 64 °C in January and 109 °C in July. Concurrently, the outlet air temperature of the RBS rises notably during the day, corresponding to the charging phase of the storage unit. Moreover, during the night, the RBS air temperature exceeds ambient temperatures by approximately 7–16 °C in January and 11–37 °C in July. This integration leads to a substantial reduction in drying time. The reduction in sewage sludge water content from 4 kg/kg of dry solid (20% dry solid content) to 0.24 kg/kg of dry solid (80% dry solid content) is related to a decrease in the drying time from 121 h to 79 h in cold periods and from 47 h to 27 h in warm periods. The drying process is significantly enhanced within the greenhouse, both during daylight and nocturnal periods. The CSGD system proves to be energy-efficient, offering an effective, high-performance solution for sewage sludge management, while also lowering operational costs for WWTPs. This innovative solar drying system combines a thermal storage bed and a solar collector to enhance drying efficiency, even in the absence of sunlight.

Natural ventilation, combined with a passive cooling system, can provide significant energy savings in the refrigeration of indoor spaces. The performance of these systems is highly dependent on outdoor climatic conditions. The objective of this study was to analyse the feasibility of a passive, downdraught, evaporative cooling system driven by solar chimneys in different climatic zones by using an experimentally validated simulation tool. This tool combined a ventilation model and a thermal model of the dwelling in which an empirical model of a direct evaporative system made of plastic mesh was implemented. For experimental validation of the combined model, sensors were installed in the dwelling and calibrated in the laboratory. The combined model was applied to Spanish and European cities with different climates. In the simulation, values of cooling energy per volume of air ranging between 0.53 Wh/m3 and 0.79 Wh/m3 were obtained for Alicante (hot climate with moderate humidity) and Madrid (hot and dry climate), respectively. In these locations, medium and high applicability was obtained, respectively, in comparison with Burgos (cold climate with moderate humidity) and Bilbao (cold and humid climate), which were low. The evaluation of the reference building in each location allowed establishing a classification in terms of performance, comfort and applicability for each climate.

As new energy-efficient technologies emerge, space and water heating systems are continuously evolving. The latest generation of heating, ventilation, and air conditioning (HVAC) systems in Canada and other countries is shifting away from natural gas heating to cleaner electrical options, such as air-source heat pump water heaters (ASHPWH). While many studies focus on reducing space heating, research on the effectiveness of ASHPWHs in cold climates is limited. This study aims to fill that knowledge gap by analyzing the performance of ASHPWHs in typical home applications across various climates in Canada. An experimental setup was constructed, and TRNSYS modeling was employed to evaluate the techno-economic and environmental performances of these systems in comparison to existing natural gas and conventional electric water heating systems. The findings of this research indicate that ASHPWHs possess the capability to substantially decrease greenhouse gas (GHG) emissions when compared to conventional natural gas-fired water heaters. Despite this significant environmental benefit, ASHPWHs may not be the most cost-effective option due to the prevailing natural gas pricing structure. Nevertheless, there is potential for these systems to become more economically viable in the future, particularly if an appropriate level of carbon pricing mechanisms is implemented.