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The study intends to analyze the thermal performance of a novel solar air heater based on heat pipe vacuum tube solar collector and finned-tube heat exchanger. The solar collector has been introduced with a new header where heat transfer fluid (Therminol-55) gains heat directly in contact with the condenser section of the heat pipe. This eliminates thermal paste application between the condenser and manifold in the existing systems. The system's thermal performance has been experimentally evaluated using two different (four-row and eight-row) finned-tube heat exchangers at four varied air flow rates, viz. 100 kg h –1 , 400 kg h –1 , 700 kg h –1 and 1000 kg h –1 . The system with eight-row heat exchanger performed better than the four-row heat exchanger at each air flow rate. 100 kg h –1 resulted in a maximum rise in temperature of air (55.4 °C) and maximum outlet temperature of air (89.4 °C). Meanwhile, the maximum energy and exergy efficiency of 95.7% and 2.17% were observed at 1000 kg h –1 . The maximum effectiveness of the four and eight-row heat exchangers was found as 70.7% and 79.4%, respectively, at 100 kg h –1 . The monthly cost saving by utilization of the proposed system is 65.65 $, and the payback period is 12.4 months. The amount of CO 2 averted from releasing into the atmosphere is 787.7 kg per month. The results suggest the utility of the proposed solar air heater as an environment-friendly replacement for conventional air heaters for consistent operation in the daytime. The experimental study was performed at the campus of NIT Kurukshetra, India (29.9476°N, 76.8155°E).

Solar water heaters are one of the most popular applications of renewable energy. So, many modifications have been performed on them to boost their performance. The novelty of the current experimental work is to simultaneous employment of porous medium inside water reservoir and oil-based nanofluid as circulating fluid. Accordingly, TiO 2 nanoparticles with two concentrations of 0.2 and 0.4 mass% were dispersed in engine oil as-based fluid. As results, when concentration of 0.4 mass% TiO 2 in engine oil is integrated with porous medium, the temperature is increased by 6.4 °C. This temperature enhancement leads to boost the thermal efficiency more than 41%. Moreover, thermal efficiency increments of 5.4% and 19% are occurred, for the cases of employing porous media and simultaneous application of 0.4 mass% TiO 2 /oil with porous media, respectively. The exergy efficiency was assessed by means of the modified approach. Accordingly, utilization of only porous medium creates 19.6% improvement in the exergy efficiency of the system. Furthermore, the entropy generation in the system was calculated, too, and the base case showed 14.7% more entropy generation compared with TiO 2 /oil integrated with porous medium. Lastly, a comparative study has been done to show the superiority of this work in comparison with the others.

The scientific literature extensively mentions the use of a solar air heater (SAH) by utilizing solar energy for heating purposes. The poor heat-transfer rate of an SAH with a flat plate is caused by developing a laminar sub-layer near the heated base plate. The plate temperatures improve significantly, resulting in losses and a decrease in performance. The passive approach entails the placement of fins/turbulators/pouring material/ribs to the surface where the boundary layer forms to disrupt it. Artificially roughened SAH for gathering and efficiently using solar radiations for thermal purposes is extensively described in the literature. This paper includes a thorough literature overview of the history, basics, roughness evolution, forms of SAH, and recent breakthroughs in thermal performance improvement techniques for SAH compiled by several researchers. This paper uses a comparative evaluation of several roughness geometries and kinds of SAH to uncover thermohydraulic performance factors that may be considered in future research to pick the optimal configuration.

Integrating a solar water heater (SWH) with a phase change material (PCM)-based latent heat storage is an attractive method for transferring load from peak to off-peak hours. This transferring load varies as the physical parameters of the PCM change. Thus, the aim of this study is to perform a parametric analysis of the SWH on the basis of the PCM’s thermophysical properties. A mathematical model was established, and a computation code was developed to describe the physical phenomenon of heat storage/release in/from the SWH system. The thermal energy stored and the energy efficiency are used as key performance indicators of the new SWH–PCM system. The obtained numerical results demonstrate that the used key performance indicators were significantly impacted by the PCM thermo-physical properties (melting temperature, density, and latent heat). Using this model, various numerical simulations are performed, and the results indicate that, SWH with PCM, 20.2% of thermal energy on-peak periods load is shifted to the off-peak period. In addition, by increasing the PCM’s density and enthalpy, higher load shifting is observed. In addition, the PCM, which has a lower melting point, can help the SWH retain water temperature for a longer period of time. There are optimal PCM thermo-physical properties that give the best specific energy recovery and thermal efficiency of the SWH–PCM system. For the proposed SWH–PCM system, the optimal PCM thermo-physical properties, i.e., the melting temperature is 313 K, the density is 3200 kg/m3, and the latent heat is 520 kg/kg.

Evacuated tube solar water heaters are gaining more attention in the present market scenario as compared to conventional collectors. Such collectors are versatile because no solar tracking is required and the operating temperature range is also broad. Comparatively, it is cost-effective and may attain higher thermal efficiency. However, like other collectors, continuous energy supply is sometimes hampered by the intermittent nature of solar radiation. This problem can be partially resolved by using phase change materials (PCM) in the evacuated tube solar collector (ETC). PCMs can store the energy during the sunshine hours, which can be released when solar energy is not available. In the literature, several studies are available pertaining to the use of PCMs in ETC-based solar water heaters. The literature indicates that the integration of PCMs with ETCs has several merits. Nevertheless, systematic, and comprehensive review papers dedicated to such integrated energy storage systems with ETC solar water heaters are not available. Hence, the objective of this work is to compile the relevant experimental, numerical, and theoretical works reported in the literature. The present paper broadly reviews the recent design modifications, PCM integration with different kinds of ETC water heaters, and their life cycle assessment. Furthermore, studies in the literature pertaining to the application of nanoparticles in ETC systems are also discussed, and finally, a roadmap for this energy storage system is provided.

Solar water heaters represent a crucial component of sustainable energy systems, offering the potential to reduce energy costs and limit carbon emissions. This study focuses on the investigation of energy and exergy efficiency enhancement in evacuated tube solar water heaters deployed in the hot climate of Dezful, Iran. Specifically, the study evaluates the impact of engine-oil as a circulation fluid within copper U-tubes positioned inside evacuated tubes, with the addition of TiO 2 nanoparticles in two concentrations (0.2 mass% and 0.4 mass%). Additionally, the study assesses the effectiveness of a metallic twisted tape insert within the U-tubes to augment the heat transfer rate, with the aim of improving the overall efficiency and performance of the system. In the assessments, the thermal efficiency diagram was divided by three phases and the behavior of each one was elaborated. As results, employing metallic-insert leads to 1.5 °C more water temperature. Moreover, 5.6 °C difference between 0.4 mass% TiO 2  + insert and the base case was observed in the evening which results in 24.4% and 25.52% higher thermal efficiency and exergy efficiency, respectively.

The objective of this research article is to present a comprehensive review of the work carried out to improve the thermal as well exergetic performance of the conventional smooth absorber plate solar air heater (SAH) duct by the use of the various configurations and arrangements of extended surfaces (fins) for the forced convection. In the SAH duct, these extended surfaces are attached along the air-flow path on the top absorber, on the bottom plate, or on the both plate surfaces. It enhances the performance of the conventional SAH by increasing the surface area and makes flow turbulent by their presence. Several experimental, theoretical, and simulation works, which have been performed by the researchers by utilizing the extended surfaces to improve the thermal efficiency based on first law of thermodynamics, exergy, and entropy generation analysis on the basis of the second law of thermodynamics for SAH ducts, have been included in the present article. Subsequently, an effort has been made to calculate the Nusselt number and friction factor by using the correlations reported by the researchers for comparing the performance of different configurations of fin SAHs. This comprehensive review article will be useful for the investigators and researchers who are working in the area of extended surface SAHs.

A solar water heater has been developed to convert solar radiation into heat for use in residential and commercial settings. The collector makes up the bulk of a solar water heating system. The solar energy is captured by the collector and transferred to the tube that delivers the working fluid, water. In addition to the collector’s tube, which carries the working fluid, researchers have focused on the design of the collector’s tube. This paper examines the performance of a parabolic plate solar water heater that uses a copper dimpled tube with aluminum-coated tube channels. During the test, the flow rate of base fluid was in the range of 1.0 to 3.0 kg/min in steps of 0.5. The performance of the solar water heater was also evaluated and verified using CFD. The test data such as friction factor, Reynolds number, uncertainty analysis, Nusselt number, solar collector efficiency, coefficient of convective heat transfer, linear dimpled tube velocity analysis, achieving maximum energy efficiency and thermal efficiency have been used to generate parametric values for parabolic plate solar water heaters. The results suggest that the best outcomes can be achieved with a mass flow rate of 2.5 kg/min and the overall thermal efficiency was raised to 31.85%, which is 11% greater than that of the plain tube with base fluid. At mass flow rates of 2.5 kg/min, the pressure drop was found to be 6.24% higher than that of 3.0 kg/min. The experimental results were analyzed and compared with the CFD results, and the overall deviation was ± 3.24% which is in the acceptable range.

This paper focused on the performance monitoring and modeling of a 6.0 kW, 2000 L hybrid direct expansion solar assisted heat pump (DX-SAHP) water heater used for the production of hot water in a university students’ accommodation with 123 females. The data of total electrical energy consumed, volume of hot water consumed, ambient temperature, relative humidity, and solar irradiance were obtained from the data acquisition systems and analyzed in conjunction with the energy factor (EF) of the system. A multiple linear regression model was developed to predict the EF. The EF of the hybrid DX-SAHP water heater was determined from the summation of the coefficient of performance (COP) of the heat pump unit and the solar fraction (SF) of the solar collectors. The operations of the hybrid energy system were analyzed based on three phases (first phase from 00:00–08:00, second phase from 08:30–18:30, and third phase from 19:00–23:30) over 24 h for the entire monitoring period. The average EF of the hybrid energy system per day during the second phase of operation was 4.38, while the SF and COP were 0.697 and 3.683, respectively. The developed multiple linear regression model for the hybrid DX-SAHP water heater accurately predicted the determined EF.

Residential water heating represents one of the most energy-intensive household applications, particularly in South Africa, where immersed resistive element heating dominates. Solar photovoltaic systems provide a promising solution for augmenting grid-based electrical water heaters, offering energy cost savings and environmental benefits. This study evaluates a novel approach to integrate solar photovoltaic directly into electrical water heater systems without using inverters. Using a combination of field experiments and simulation, four heating strategies were assessed, namely: “grid only”, “solar medium”, “solar heavy”, and “solar timer”. Metrics such as solar augmentation ratio, solar utilization, and cold event frequency were analyzed for different seasons using real-world and simulated water usage profiles. Results demonstrate significant grid energy reductions through solar augmentation, particularly in warmer seasons. However, the effectiveness of the strategies varies, with increased solar utilization often correlated with a higher frequency of cold events. A hybrid seasonal strategy is proposed to optimize energy savings while maintaining user comfort. This work highlights the potential of direct DC solar photovoltaic integration as a cost-effective and sustainable enhancement for residential water heating.