Search Results (44)

This study explores the impact of using water-Al₂O₃ nanofluids, at different nanoparticle concentrations, in solar thermal collectors for solar cooling applications. Improving the seasonal energy performance of solar cooling systems is a current research priority, and this work investigates whether nanofluids can significantly enhance system efficiency compared to traditional heat transfer fluids. A transient simulation was carried out using a dynamic model developed in TRNSYS (TRANsient SYstem Simulation), evaluating the system performance throughout the cooling season. The results show that in July, under low volumetric flow conditions and with nanoparticle concentrations of 0.6% and 0.3%, the solar fraction reaches a maximum value of 1. Using a nanofluid at 0.6% concentration leads to significantly higher fractional energy savings compared to pure water. Despite increased pumping energy, the overall energy savings—which include the contribution from an auxiliary boiler—exceed 80% when nanofluids are used. This study goes beyond previous work by providing a dynamic, system-level simulation of nanofluid-enhanced solar cooling performance under realistic operating conditions. The findings demonstrate the practical potential of nanofluids as a valid and more energy-efficient alternative in solar thermal applications. Full article

The implementation of renewable energy systems (RESs) in the agricultural sector has significant potential to mitigate the negative effects of fossil fuel-based products on the global climate, reduce operational costs, and enhance crop production. However, the intermittent nature of RESs poses a major challenge to realizing these benefits. To address this, thermal energy storage (TES) and hybrid heat pump (HHP) systems are integrated with RESs to balance the mismatch between thermal energy production and demand. In pursuit of clean energy solutions in the agricultural sector, a 3942 m² greenhouse in Yeoju-si, South Korea, is equipped with 231 solar thermal (ST) collectors, 117 photovoltaic thermal (PVT) collectors, four HHPs, two ground-source heat pumps (GSHPs), a 28,500 m³ borehole TES (BTES) unit, a 1040 m³ tank TES (TTES) unit, and three short-term TES units with capacities of 150 m³, 30 m³, and 30 m³. This study evaluates the long-term performance of the integrated hybrid renewable energy and thermal energy storage systems (HRETESSs) in meeting the greenhouse’s heating and cooling demands. Results indicate that the annual system performance efficiencies range from 25.3% to 68.5% for ST collectors and 31.9% to 72.2% for PVT collectors. The coefficient of performance (COP) during the heating season is 3.3 for GSHPs, 2.5 for HHPs using BTES as a source, and 3.6 for HHPs using TTES as a source. During the cooling season, the COP ranges from 5.3 to 5.7 for GSHPs and 1.84 to 2.83 for ASHPs. Notably, the HRETESS supplied 3.4% of its total heating energy directly from solar energy, 89.3% indirectly via heat pump utilization, and 7.3% is provided by auxiliary heating. This study provides valuable insights into the integration of HRETESSs to maximize greenhouse energy efficiency and supports the development of sustainable agricultural energy solutions, contributing to reduced greenhouse gas emissions and operational costs. Full article

This study presents an experimental analysis of two vacuum solar air collectors designed for residential heating applications. The research was conducted from November 2022 to April 2024 in real operating conditions. This study focused on assessing the thermal performance, energy efficiency, and feasibility of integrating these systems into hybrid heating solutions. The first collector (Solar Dragon 2022) utilized five vacuum tubes and achieved a total thermal energy output of 397.67 kWh over five months, with a peak thermal power of 0.55 kW. The second system (Solar Dragon 2023), equipped with 24 vacuum tubes, demonstrated a significantly higher performance, generating 911.69 kWh over the same period, with a peak thermal power of 1.8 kW. The study also identified challenges related to airflow distribution and excessive outlet air temperatures, reaching up to 84 °C in the modified system, which could negatively impact indoor comfort. The findings highlight the potential of vacuum solar collectors as an auxiliary heating source, particularly in transitional seasons, while emphasizing the need for optimized airflow control and thermal regulation strategies to enhance their practical application. Full article

We show the performance of solar heating by coupling a Solar Water Heating System (SWHS) with an Absorption Heat Transformer (AHT) for annual continuous water heating. Solar Fraction (SF), Solar Heat Gain (SHG), and Auxiliary Heat (Q_aux) were meticulously assessed for three Mexican cities located in the most characteristic climates (Saltillo, Toluca, and Tapachula). This rigorous assessment process ensures the reliability and accuracy of our findings. The potential reduction in net solar collector area (A_c) and storage tank volume (V_t) can be seen by comparing its annual performance to that of a conventional SWHS. Both configurations were designed to deliver the same hot water amount (0.019 kg/s, 1693.4 L/day, heating from 15.8 to 94.4 °C) and simulated using TRNSYS software version 16.01 concerning combinational systems. The results showed that SWHS-AHT achieved superior performance in solar water heating, achieving a higher SF (up to 99.6%) and SHG (up to 1352 kWh/m²-year) compared to the conventional SWHS. On the other hand, the SWHS-AHT achieved similar performance to a conventional SWHS with up to 60% less A_c. For instance, in Tapachula, a SWHS-AHT with an A_c of 150 m² and a V_t of 18 m³ matched the performance of a SWHS with an A_c of 375 m² and a V_t of 15 m³. Notably, both systems required the same Q_aux. Thus, the Q_aux requirement shows that SWHS-AHT is promising for industrial applications in Mexico, offering improved performance and a reduced footprint. Full article

Facing severe climate change, preserving the environment, and promoting sustainable development necessitate innovative global solutions such as waste recycling, extracting value-added by-products, and transitioning from traditional to renewable energy sources. Accordingly, this study aims to repurpose fish waste into valuable, nutritionally rich products and extract essential chemical compounds such as proteins and oils using a newly developed hybrid solar dryer (HSD). This proposed HSD aims to produce thermal energy for drying fish waste through the combined use of solar collectors and solar panels. The HSD, primarily composed of a solar collector, drying chamber, auxiliary heating system, solar panels, battery, pump, heating tank, control panel, and charging unit, has been designed for the effective drying of fish waste. We subjected the fish waste samples to controlled drying at three distinct temperatures: 45, 50, and 55 °C. The results indicated a reduction in moisture content from 75.2% to 24.8% within drying times of 10, 7, and 5 h, respectively, at these temperatures. Moreover, maximum drying rates of 1.10, 1.22, and 1.41 kgH₂O/kg dry material/h were recorded at 45, 50, and 55 °C, respectively. Remarkable energy efficiency was also observed in the HSD’s operation, with savings of 79.2%, 75.8%, and 62.2% at each respective temperature. Notably, with an increase in drying temperature, the microbial load, crude lipid, and moisture content decreased, while the crude protein and ash content increased. The outcomes of this study indicate that the practical, solar-powered HSD can recycle fish waste, enhance its value, and reduce the carbon footprint of processing operations. This sustainable approach, underpinned by renewable energy, offers significant environmental preservation and a reduction in fossil fuel reliance for industrial operations. Full article

Carbon–arsenic-bearing gold ore is a typical complex refractory gold resource. Traditionally, xanthate was often used as a flotation agent to separate gold minerals. But, in this paper, in order to reduce the cost of the agent, kerosene was used as an auxiliary collector, and the gold grade and recovery rate were increased by about 10 g/t and 5.5%, respectively. Through process mineralogy studies of the raw ore, it was found that the ore has an Au grade of 5.68 g/t, most of which is surrounded by sulfide ore, accounting for 79.46%. The main minerals are pyrite, arsenopyrite, and quartz, etc. Their content, shape, particle size distribution, and occurrence state were obtained via microscopic observation and statistical analysis. According to the results of process mineralogy, various flotation conditions were tested, including grinding fineness, kerosene dosage, collector dosage, foaming agent dosage, and the slurry pH value. The optimal chemical system and the process flow of “two roughing, three cleaning and two scavenging” were finally determined, and the concentrate product with a gold grade of 42.83 g/t and recovery of 91.02% was obtained, which verified the feasibility of the kerosene-assisted xanthate flotation of refractory gold. Full article

This paper regards the design and dynamic modelling of a greenhouse coupled with renewable energy technologies to obtain a hybrid renewable energy plant as an optimal solution in the green farm framework. The considered technologies are PV panels, solar thermal collectors, and a biomass auxiliary heater. The system is also coupled with a pyrogasifier, supplied by wood and agricultural waste in the framework of a biocircular economic approach. To supply the investigated user, with a “green farm” located in Castelvolturno (Naples, South of Italy) reducing the energy consumption and operating costs, all of the main components of the plant were suitably designed. The operation of the designed components was simulated by a dynamic simulation model developed by TRNSYS software and validated by means of the literature results. A comprehensive energy, economic, and environmental analysis of the greenhouse is presented. The main results suggest that the investigated renewable plant reduces the total equivalent CO₂ emissions by 148.66 t/y. Considering the current high increases in energy prices as a result of the energy crisis due to the war, the system shows very significant profitability with a simple payback of only 1.7 years. Full article

Evacuated tube heat pipe solar collector as a passive solar water heating system is a simple, reliable, and cost-effective way to capture the sun’s thermal energy to supply hot water to homes. In the proposed system, the manifold is reshaped to a tank and filled with phase change materials (PCM) and porous media, which the PCM acts as a latent heat thermal energy storage medium. In order to increase the heat flux from the heat pipe to the PCM and overcome the low thermal conductivity of the PCM, porous media is used. The porous media is connected to the heat pipe condenser to collect the heat and distribute it uniformly throughout the PCM filling the pores. This design of the manifold acts as a heat storage tank or thermal battery. Another pipe in the tank transfers heat from the PCM to the water. Experiments were conducted in 2 modes: charging/discharging and periodic draw-off. The results demonstrated that this thermal battery design could provide homes with the hot water they require on sunny days, while it needs an auxiliary heater or larger solar collector to provide enough hot water on rainy/cloudy days. Considering the solar radiation fluctuation, the efficiency of the thermal battery is 50% ± 9.3%. The thermal battery can warm up the cold water higher than the operating temperature on a sunny day (more than 120 L per day at 38 °C). Using porous media provides better heat distribution in the PCM. Full article

In this study, a solar single/double-effect switching LiBr-H₂O absorption refrigeration system was investigated to make full use of solar energy and give full play to the advantages of solar refrigeration systems. A corresponding thermodynamic dynamic mathematical model was developed. The operation characteristics of the system operating continuously for one week were analyzed. In order to highlight the advantages of the solar single/double-effect switching absorption refrigeration system, it was compared with other forms of solar refrigeration systems and compression refrigeration systems. The practical application potential of the single/double-effect switching LiBr-H₂O absorption refrigeration system was evaluated from the perspective of economy and environmental effect. The results showed that the system could achieve the switching operation between single-effect mode and double-effect mode under weather conditions of high solar radiation intensity, and the daily cooling efficiency on such days was relatively high. After an auxiliary heater was added, the primary energy savings of the solar single/double-effect switching LiBr-H₂O absorption refrigeration system were 25–52%, depending on the area of the collector and the volume of the storage tank. The solar fraction of the system was about 71.99% for continuous operation during the whole refrigeration season. However, the initial investment cost of the system equipment accounted for 89.66% of the total cost. Compared with the traditional compression refrigeration system, the initial investment cost of the solar single/double-effect switching LiBr-H₂O absorption refrigeration system was higher, but it had a better environmental protection effect. Full article

A solar heating system is designed to reduce energy consumption in a poultry farm. According to the physics and conditions of the indoor environment of the poultry building and the effect of the poultry weather conditions, the amount of 1.37 × 10⁸ kJ/h during the year energy is required for heating. Then, by using double-glazed windows and insulation for the exterior walls of the building in the building architecture section, the amount of energy consumption is drastically reduced, and the required annual gas consumption is equal to 11,833 m³. The surface required for the collector is recommended to supply 50% of the energy from the sun with the rest from the hybrid system. The results showed that 26 m² of a solar collector with an optimal slope of 45 degrees, and a tank volume of 440 L and a pump discharge of 1700 kg/h are required to provide 100% of energy. To receive the maximum amount of solar energy (maximum solar fraction (SF)), a collector surface equal to 30 m² is required. However, when the economic point of view is considered, the collector surface equivalent to 26 m² is recommended. To establish a balance, that is, 50% of the energy from the auxiliary system and the rest from the solar system, between the use of solar energy and the use of the auxiliary system, a collector area of 16 m² is needed. Based on this, 60 photovoltaic modules, which are 10 cells in series in 6 parallel circuits, is the most optimal mode. Full article

The goal of this investigation is the thorough analysis and optimization of a solar-assisted heat pump heating unit for covering the space heating demand for a building in Athens, Greece. The novelty of the studied system is the use of a high-temperature heat pump that can operate with radiative terminal units, leading to high thermal comfort standards. The examined system includes flat-plate solar thermal collectors, an insulated thermal storage tank, auxiliary electrical thermal resistance in the tank and a high-temperature heat pump. The economic optimization indicates that the optimal design includes 35 m² of solar thermal collectors connected with a storage tank of 2 m³ for facing the total heating demand of 6785 kWh. In this case, the life cycle cost was calculated at 22,694 EUR, the seasonal system coefficient of performance at 2.95 and the mean solar thermal efficiency at 31.60%. On the other hand, the multi-objective optimization indicates the optimum design is the selection of 50 m² of solar field connected to a thermal tank of 3 m³. In this scenario, the life cycle cost was calculated at 24,084 EUR, the seasonal system coefficient of performance at 4.07 and the mean solar thermal efficiency at 25.33%. Full article

Solar energy is the most available renewable resource and has great potential for various applications. Solar heat pumps are limited when operating alone due to weather and the unstable and intermittent nature of solar energy. The idea of combining a solar collector with an air-source heat pump (ASHP) is proposed to solve the problems. Taking solar energy and air energy as the heat source of the system can improve the heat collection efficiency and heating performance coefficient of the dual-supply heating system in realizing the efficient and stable operation of the whole unit. This study investigated the application of a solar–air-source heat pump (S/AS-HP) dual-supply heating system for a residential building in Lhasa and compared the winter work performance and economic benefits of three different heating forms: solar–air-source heat pump, air-source heat pump, and solar–electric auxiliary heating systems. A simulation model was established and analyzed using the measurement data. The results show that during the heating period, the temperature of the primary side water supply is stable at about 60 °C, and the total operating hours of the solar collector period accounted for 26.9% of the total hours, of which 23.16% were independent operating hours. The average COP_sys of the solar–air-source heat pump is 4.21, which greatly improves work performance compared with other systems, and the annual cost is the lowest among the three forms for the same service life at 41,824.6 CNY, saving 9.6% and 35.1% per year compared with the air-source heat pump system and the solar–electric auxiliary heating system. Considering conditions in alpine regions, S/AS-HP systems are the optimal heating solution for single buildings. Full article

In this work, an induced pre-saturation tower (IPST) for oil–water separation was built on a semi-industrial scale, based on experimental results obtained on a laboratory scale prototype. The main strategy for generating these criteria was to increase the efficiency of the bench scale prototype, which is limited by conditions of low levels of automation and control, with the use of a biosurfactant as an auxiliary collector. The validation of the developed criteria allowed the construction of an IPST with three stages, all fed with previously saturated effluents. The IPST was built in stainless steel, with multistage centrifugal pumps and adapted to generate microbubbles without the use of saturation tanks or compressors. The most relevant operational parameters were selected using a fractional factorial design, while a central composite rotatable design (CCRD) followed by the application of the desirability function allowed to optimize the conditions for partial and global variables, the latter with desirability of 95%. A nominal flow rate of approximately 1000 L·h⁻¹, a recycle flow rate of 450 L·h⁻¹, a scraper rotation speed of 80 rpm, an average pressure of the microbubble pumps of 11 bar, and an effluent temperature from IPST of about 38 °C ensured optimized operation for the proposed technological development. Full article

The properties of glass fiber composites were improved by strengthening the interlaminar regions using electrospun nanofibers mats. However, the chaotic nature of the electrospinning process at the collector restricts the controlled deposition and alignment of nanofibers and limits the use of electrospun nanofibers as secondary reinforcements. Hence, auxiliary vertical electrodes were used, which drastically reduced the diameter of the nanofibers from 450 nm to 150 nm and also improved the alignment of nanofibers. The aligned nanofibers were then used for doping the functionalized single-walled carbon nanotubes (f-SWCNTs) with nanofibers, which controlled the inherent issues associated with SWCNTs such as agglomeration, poor dispersion, and alignment. This process produced f-SWCNTs doped nanofiber mats. A series of tensile, three-point flexural, and Charpy impact tests showed that 30 vol% glass fiber composites reinforced with 0.5 wt% of randomly oriented nanofiber (RONFs) mats improved the properties of the hybrid composites compared to 0.1 wt%, 0.2 wt%, and 1 wt% RONFs mats reinforced glass fiber hybrid composites. The increase in properties for 0.5 wt% composites was attributed to the higher specific surface area and resistance to the relative slip within the interlaminar regions. The 0.5 wt% RONFs were then used to produce 0.5 wt% of continuous-aligned nanofiber (CANFs) mats, which showed improved mechanical properties compared to 0.5 wt% randomly oriented nanofiber (RONFs) mats reinforced hybrid composites. The CANFs mats with reduced diameter increased the tensile strength, flexural strength, and impact resistance by 4.71%, 17.19%, and 20.53%, respectively, as compared to the random nanofiber mats. The increase in properties could be attributed to the reduced diameter, controlled deposition, and alignment of the nanofibers. Further, the highest increase in mechanical properties was achieved by the addition of f-SWCNTs doped CANFs mats strengthened hybrid composites, and the increase was 30.34% for tensile strength, 30.18% for flexural strength, and 132.29% for impact resistance, respectively. This improvement in properties was made possible by orderly alignments of f-SWCNTs within the nanofibers. The SEM images further confirmed that auxiliary vertical electrodes (AVEs) reduced the diameter, improved the alignment and molecular orientation of the nanofibers, and thus helped to reinforce the f-SWCNTs within the nanomats, which improved the properties of the glass hybrid composites. Full article

In this study, a PVT-based solar-assisted ground source heat pump (SAGSHP) system with a small size borefield as the long-term heat storage component was energetically evaluated. The mathematical model of the system was formulated in TRNSYS and three cities with distinctive climates were chosen: Athens (Greece); Melbourne (Australia); and Ottawa (Canada). The parametric analyses were carried out for 10 years by varying the number of the PVT collectors and the size of the earth energy bank (EEB). The evaluation of the systems was made via two energy indicators, and the heat flow across the EEB was analyzed. The under-consideration system was found capable of establishing self-sufficiency as regards the energy consumption (renewable power fraction RPF > 1) for all locations. Namely, for Athens, any system with more than four PVT collectors, and for Melbourne, any system with more than eight PVTs was found with an RPF higher than 1, regardless of the EEB size. For Ottawa, self-sufficiency can be achieved with PVT arrays larger than 12 collectors for small EEBs, and with eight collectors for larger EEBs. The storage capacity was found to be an important parameter for the energy performance of the system. In particular, it was determined that, as the storage capacity enlarges the RPF and the seasonal performance factor (SPF) of the system improves, mainly due to the reduction of the electricity consumed by the heat pump and the auxiliary heating. Moreover, a larger storage capacity facilitates solar heat production by enlarging the available heat storage volume and by maintaining the EEB at relatively low temperatures. Full article