Solar Water Heating Applications Research Articles

Numerical simulation of the melting and solidification processes of stearic acid/carbon fiber composite phase change material for solar water heating applications

Phase Change Materials (PCMs) are one of the most promising materials for storing thermal energy and supplying stored energy for Domestic Hot Water (DHW) applications. This paper presents a detailed numerical analysis to describe transient heat transfer in a phase-change composite thermal energy-storage system. The composite was composed of 92.5 % stearic acid, 7.5 % carbon fiber, and a heat transfer fluid (ethylene cellulose). Numerics were implemented using ‘The Integrated Computer Engineering and Manufacturing code for Computational Fluid Dynamics’. The results were validated using experimental data and demonstrated acceptable agreement and an accurate representation of this specific transient heat transfer problem. The difference between the simulation and experimental results was so small that we considered the simulation results reliable. When the phase change heat storage process is about 800 s, the heat is transferred to the entire phase change heat storage tank, and when the phase change heat storage process is about 10800s, the temperature of all composite phase change materials reaches the phase change temperature. When the phase change heat storage process is about 8 h, the temperature of the composite phase change material in the whole phase change heat storage tank reaches 90 ℃. The temperature tends to be stable after the phase transition heat release process for about 500 s, and there is no large fluctuation in temperature with the passage of time. When the phase change heat release process reaches 7200 s, the cold-water inlet temperature is 15 ℃, 20 ℃ and 25 ℃, and the outlet temperature is 25.8 ℃, 30.8 ℃ and 35.7 ℃, respectively, indicating that the application of composite phase change materials in phase change heat storage water tank has a good effect.

Experimental investigation of the solar latent heat thermal energy storage system integrated with salt hydrate phase-change materials

To achieve rational utilization of renewable energy sources, a solar latent heat thermal energy storage system for hot water application was developed in this study. The feasibility of the salt hydrates using in the solar heating was assessed and the comparative experimental investigation was conducted under various operating conditions. It shows that the higher flow rate and radiation accelerate the melting process of the phase-change material. The time taken for the storage medium to reach phase transition was reduced by approximately 48.9%; meanwhile, the collector efficiency was enhanced by approximately 10.2% as the flow rate increased from 10 g/s to 30 g/s. The accumulated charging energy increased by approximately 10.9% when the radiation increased from 850 W/m2 to 920 W/m2, resulting in a prolonged heat release process. The test results suggest the promising potential of the salt hydrates for the solar water heating applications.

A scalable phase change material-based system enhanced by multi-walled carbon nanotubes and fins for efficient solar water heating applications

Phase change material (PCM)-based harvesting and storage systems are promising solutions to solar energy's intermittence and non-uniformity issues. Previous efforts have focused on the absorption, conversion, and storage capability of PCMs. However, efficiently utilizing the stored thermal energy within PCMs remains challenging. Herein, we devise a facile and scalable PCM-based system with heat transfer and light absorption enhancement simultaneously by fins and multi-walled carbon nanotubes (MWCNTs) for solar water heating applications. Photothermal conversion experiments demonstrate that the water temperature of the PCM-based system with MWCNT and fins is up to 79.0 °C under the stationary condition, which is increased by 58.6 % and 55.2 % compared to the original composite and the MWCNT-doped one, respectively. Furthermore, numerical simulations indicate that fins act as a bridge between PCM and water, facilitating rapid heat transport and improving the thermal energy storage pattern, enabling efficient solar water heating. The water temperature can keep above 40.0 °C for 51 min at a flow rate of 11.34 l/h under ambient cooling conditions, and the maximum thermal efficiency is up to 89.2 %, which is higher than most flat plate and tubular solar collectors, demonstrating the superiority of the proposed system.

Preparation, stabilization, and thermal characterization of CuO/water nanofluids applicable to domestic solar water heater

In this contribution, an experimental investigation has been carried out to analyze the stability and light absorbance characteristics of CuO/water nanofluids applicable to domestic solar water heaters. Nanofluids are prepared at 0.01–0.05 wt% by dispersing dry CuO nanopowder in water in presence of Gum Acacia (GA) stabilizer via ultrasonic agitation. The stability of the nanofluids is examined through gravity sedimentation. The samples are exposed to natural sunlight as well as LED light to examine their light absorbance potential by virtue of temperature rise. The light absorbance potential of nanofluids as compared to water is expressed as Temperature Variation Ratio (TVR). The nanofluids remain stable for six months. The sedimentation is more in higher concentration relative to their dilute counterparts. The absorbance capacities of the nanofluids augment with the nanoparticle addition to base fluid. However, 0.01 and 0.05 wt% samples show relatively lower absorbance due to a higher sedimentation rate. Maximum absorbance is observed with 0.03 wt% which shows a maximum temperature rise up to 60 °C under sunlight and 56 °C under LED light. Whereas, water shows a maximum increase up to 52 °C under sunlight and 48 °C under LED. The TVR shows the highest values of 2.3 and 1.86 with 0.03 wt% sample when kept under sunlight and LED lights respectively. Hence, nanofluids are recommended as working fluids in solar water heating applications.

Optimization of collector area and storage volume in domestic solar water heating systems with on–off control—A thermal energy analysis based on a pre-specified system performance

Numerical simulations of solar water heating systems using on–off control were performed for four locations in the Portuguese territory, two collector types, and a wide range of parameters. Two main design parameters were considered: the collector area and the storage volume. An innovative technique was used to investigate the relationship between system performance and system parameters: a pre-specified annual solar fraction is selected and the optimal parameters needed to achieve this solar fraction are then computed. The optimum collector area is almost always higher for a double-glazed than for a single-glazed collector, suggesting that in Portugal, the single-glazed type is more effective for most solar water heating applications. This fact is more significant for lower solar fractions and warmer climates. A small increase in the optimum collector area leads to a very strong decrease in the optimum storage volume (an area increase of 1% leads to a volume decrease of 27%). Collector flow rate and storage volume increments result in lower collector areas. However, high flow rates lead to high pumping losses and lower collector efficiencies, and when the storage tank losses are significant, higher tank sizes may lead to higher collector areas. The solar fraction has a very strong impact on the collector area and storage volume (when the solar fraction increases from 0.5 to 0.99, the optimum collector area and storage volume increase about 17 and 56 times, respectively).

Electromechanical solar tracker system for a parabolic dish with CPU water heater

Abstract The parabolic dish reflected and concentrated the solar rays at the focus. But the limited actual working hours during the daytime is the most influential factor for not to be used widely among other solar water heating applications. Therefore, the current study aimed to develop a new dual solar tracking system for parabolic dish CPU water heater using a new Bi-axial tracking system based on the chronological Algorithms tracking system. Two models of solar parabolic dish water heaters have been investigated, the first one is a fixed solar parabolic dish (FFD), and the second one is a tracking solar parabolic dish (MFD). The experimental setup consists of a heating water system, Dual-axis solar tracking control system and a measuring system. Observed from this study that the water temperatures at outlet solar water heater for the two types was differed by about 20% (MFD larger than FFD by 20%), that’s mean that the dual tracking technology enhanced the water temperature of the CPU heat exchanger, and the highest water temperatures were at 1:00 pm for the two models (MFD and FFD), which are reached about 50.8 °C and 47.3 °C, respectively. In the MFD model, useful energy was produced throughout the daytime and recorded the largest value about 71.06 W at 1:00 pm, while in the FFD model, it recorded about. 56.4 W .

Investigation of the influence of adding MWCNTS to an alkyd-urethane coating on the thermal conductivity coefficient of the coating

In this study, the influence of adding MWCNTs to an alkyd-urethane coating has been studied on the thermal conductivity coefficient K of the coating, to determine its potential for use in solar water heating applications where the low value of the thermal conductivity coefficient of the polymeric coatings is an obstacle to their use as absorbent surfaces in solar collectors. A light source, a halogen lamp, was used as a heat source; the temperature measurement was done using an infrared thermometer. The results showed an enhancement in the thermal conductivity coefficient of 9.16% when it is added 4 % of the MWCNTs.

Thermal energy storage system operating with phase change materials for solar water heating applications: DOE modelling

Phase change materials have gathered wide acceptance globally due to its effective and economically efficient storage properties. It is emerging to find potential applications in both renewable and fossil energy systems. This paper analyzes the performance and models an experimental design for heat transfer enhancement of a thermal energy storage system by using honey and paraffin waxes. Experiments were conducted in a fabricated thermal energy storage cylindrical tank embedded with copper tubes that in turn filled with these waxes in a liquid state. This non-isothermal system was fabricated to improve the water heat transfer rate from the solar tank unit to waxes in the thermal chamber. The conservation of heat energy was achieved through implementation of this system, this offer a better solution to a conventional storage tank. Performance appraisal of results from experimentation during the processes of charging and discharging of phase change materials has been performed and examined. Good thermal energy storage characteristics of heat transfer, absorption and rejection were observed. The design of experiments modelling work- artificial neural network showed good agreement with experimental results. Mainly, it was found that the factor time has contributed more than 40% of the heat improvement in this storage system during charging and discharging process of paraffin and honey waxes. On the other side, the least number of residuals was observed for the honey wax heat absorption during charging process.

PERFORMANCE OF HORIZONTAL WATER-IN-GLASS EVACUATED TUBE SOLAR COLLECTORS

Water-in-glass evacuated tube solar collectors are widely used in two main configurations: (1) a single row of tilted tubes connected to a header tank, and (2) two rows of horizontal tubes on either side of a central manifold. Published studies on water-in-glass collectors have been focused almost entirely on the former, commonly used for domestic water heating applications. This study considers the latter type, which is well suited to larger solar water heating applications. Experimental data from outdoor testing demonstrates a good fit to the ISO 9459-2 expression for collector performance. This daily heat gain model is used in simulations to illustrate sizing and design applications.

Performance characteristics of a residential-type direct absorption solar collector using MWCNT nanofluid

In this study, the performance characteristics of a nanofluid-based direct absorption solar collector are investigated numerically and experimentally. The numerical model of nanofluid-based direct absorption solar collector was developed by solving radiative transfer equation combined with energy equation. The outlet temperature is analyzed by variation of internal emissivity of bottom wall, collector height, nanofluid volume fraction and flowrate. Then, a prototype of this new type of collector was built with applicability for domestic solar heating systems. As working fluid, different volume fractions of carboxyl functionalized multi wall carbon nanotubes in water and ethylene glycol mixture (70%:30% in volume) were prepared and their thermo-optical properties were presented. The procedure of EN 12975-2 standard was used for testing the thermal performance of the collector. The tests were performed in different flowrates from 54 to 90 l/h (0.015–0.025 kg/s) and two different internal surfaces (black and reflective) of bottom wall. By comparison of calculated and measured collector efficiencies for different volume fractions, it was shown that the numerical model was accurate within ±5% of the experimental results. The collector efficiency is increased by increasing nanofluid volume fraction and flowrates. The nanofluids improve the collector efficiency by 10–29% than the base fluid. The results of the study confirm that this new kind of collector can be best utilized in solar water heating applications.

Performance investigation of thermal energy storage system with Phase Change Material (PCM) for solar water heating application

In order to harvest solar energy, thermal energy storage (TES) system with Phase Change Material (PCM) has been receiving greater attention because of its large energy storage capacity and isothermal behavior during charging and discharging processes. In the present experimental study, shell and tube TES system using paraffin wax was used in a water heating system to analyze its performance for solar water heating application. Energy and exergy including their cost analyses for the TES system were performed. Accordingly, total life cycle cost was calculated for different flow rates of the Heat Transfer Fluid (HTF). With 0.033kg/min and 0.167kg/min flow rates of water as HTF, energy efficiencies experienced were 63.88% and 77.41%, respectively, but in exergy analysis, efficiencies were observed to be about 9.58% and 6.02%, respectively. Besides, the total life cycle cost was predicted to be $ 654.61 for 0.033kg/min flow rate, which could be reduced to $ 609.22 by increasing the flow rate to 0.167kg/min. Therefore it can be summarized that total life cycle cost decreases with the increase of flow rate.

Carbon conundrum, climate change, CO2 capture and consumptions

Carbon dioxide (CO2) emission and absorption components consist of biosphere, hydrosphere, atmosphere, lithosphere and fossil fuels. CO2 flow rates are governed by large scale fluid dynamic, thermodynamic and radio-active transfer processes. This results in dynamic flow of CO2 over land and oceans affecting regional climates. Convective uptake of CO2 from Asia flows at high altitude to America and then returns sweeping the local emissions back to Asia. In this process the bulk clouds of CO2 are absorbed in cold Pacific Ocean surface waters near America, causing regional cooling effect. Dynamic thermohaline circulations take away the dissolved carbon to warmer Asian waters maintaining the global carbon balance. Monsoon winds sweep Himalayan valley smoke and CO2 to Arabian Sea causing regional warming. Atmospheric CO2 and dissolved water carbon concentrations cause regional warming and cooling effects. Global carbon circuit may cause regional warming and cooling, irrespective of local emissions. In this study, nature's response to higher concentration of CO2 and its direct removal from atmosphere or sequestration at source is presented. This paper describes global carbon balance, regional climate changes and carbon fix alternatives by developing industrial use of CO2. ASHREA has envisioned 11 new future refrigerants for evacuated glass tube solar water heaters. Our simulation results show that supercritical CO2 is an optimum natural refrigerant in terms of thermodynamic and heat transfer properties in the range of −20 to 30 and 30–70°C. We demonstrated the utilization of captured CO2 as mediating fluid for refrigeration and solar water heating applications.

Enhancement of Thermal Storage System Using Phase Change Material

Solar energy, the inexhaustible source of energy is very intermittent in nature. So it is essential to develop efficient, economical solar thermal energy storage (TES) devices. Systems using PCM are more fashionable in latent heat storage today. The present work is about the savE® HS-58phase change material (PCM) filled in multiple spherical capsules for the improvement of the thermal storage system for domestic solar water heating application. Experimental investigation is carried out to understand the improvement of performance of thermal storage system using combination of water- PCM in comparison with only water. Experiments were conducted for same heat input during accelerated conditions in both for Water-PCM and also only water inside thermal storage system. It is experimentally proven that for the laboratory model of 10 liters per day capacity of system with 26% of volume occupied by PCM, improvement in thermal storage capacity is 22% which is comparably substantial improvement in thermal energy storage. Thus, the thermal storage system using PCM can be used with higher size solar collector or amount of storage can be reduced for the same size solar collector. This model has prospects for the development of better and economical storage system.

Evaluation of Solar Water Heating Systems in Botswana

This paper presents results of an assessment of several solar water units to determine causes of their malfunctioning. A survey of solar water heater (SWH) installations in the Gaborone area, Botswana was carried out to obtain performance characteristics of SWH in the local market. Extensive inspections were performed on both in-service and non-functioning units, problems were diagnosed and pragmatic solutions were proffered. The paper presents some of the discoveries made during the investigation, namely, several units did not last up to the payback period of say 10 to 15 years. The results obtained could provide guidance in selecting operating criteria and suitable system design for solar water heating applications.

Testing of a new solar coating for solar water heating applications

A novel and affordable solar selective coating exhibiting higher solar absorption efficiency compared to the commercial black paint coating used in most ordinary solar water heating systems (SWHSs) has been developed. The coating is fabricated by embedding a metallic particle composed of a nickel–aluminium (NiAl) alloy into the black paint. The optical behaviour of several percentages of the NiAl alloy in the coating is studied using UV–Vis and IR spectroscopies. The chemical composition of the coating was characterized using XRD and thermo-gravimetric analysis (TGA) for both the black and alloy-containing paint. The results allowed deducing that the optimum composition to consider for further testing was 6% NiAl alloy by mass. The applicability of the coating in a real thermosyphonic SWHS was evaluated throughout the year, spanning both hot and cold seasons. It is found that the new coating shows better performance compared to the untreated black paint by an average of 5 °C over a period of 1 year. The corrosion resistance of the coating was investigated using electrochemical polarization and weight-loss measurements in the corrosive medium of 3% NaCl in 0.50 M HCl. Higher inhibition efficiency of corrosion was found for the alloy-containing paint compared to the untreated paint by more than 12%. Finally, Scanning Electron Microscopy (SEM) was used to explore the morphology of the modified coating surface, and compared to the untreated surface.

Experiences With Using Solar Photovoltaics to Heat Domestic Water

The solar photovoltaic (PV) industry continues to make progress in increasing the efficiency while reducing the manufacturing costs of PV cells. Economies of scale are being realized as manufacturers expand their production capabilities. Products are commercially available that integrate photovoltaic cells within building fac¸ade, fenestration, and roofing components. Legislation and incentive programs by government and commercial entities are supporting both reduced first costs and greater rates of return. The combination of factors support improved cost-effectiveness. As this trend continues, more options for using PV become possible. One such application is a stand-alone, PV-direct, solar water heating application. Solar water heating can be effectively accomplished by directly using the DC power production from solar photovoltaic modules. A simple controller having multiple power relays connects the PV modules with different combinations of in-tank resistive elements. The controller actively changes the resistive combination so that the photovoltaic modules generate power at or near their maximum output. The technology, which has been patented, is applicable to configurations that use a single water heater and to two water heaters that are piped in series. Prototypes using both tank configurations were monitored at four field sites. This paper emphasizes the single-tank application and the field results from installations in Maryland and Florida.

Finite time thermal analysis of ground integrated‐collector‐storage solar water heater with transparent insulation cover

A transparent honeycomb insulated ground integrated-collector-storage system has been investigated for the engineering design and solar thermal performance. The system consists of a network of pipes embedded in a concrete slab whose surface is blackened and covered with transparent insulation materials (TIM) and the bottom is insulated by the ground. Heat may be retrieved by the flow of fluid through the pipe. A simulation model has been developed; it involves the solution of the two-dimensional transient heat conduction equation using an explicit finite-difference scheme. Computational results have been used to determine the effect of such governing parameters as depth as well as pitch of the pipe network and collector material on the thermal performance of the system. The pipe network depth of 10 cm and the TIM cover made of 5 cm compounded honeycomb seem suitable for the proposed system. Solar gain (solar collection efficiency of 30–50% corresponding to collection temperature of 40–60°C) and the diurnal heat storage characteristics of the system are found to be of the right order of magnitude for solar water heating applications. Copyright © 1999 John Wiley & Sons, Ltd.

Finite time thermal analysis of ground integrated-collector-storage solar water heater with transparent insulation cover

A transparent honeycomb insulated ground integrated-collector-storage system has been investigated for the engineering design and solar thermal performance. The system consists of a network of pipes embedded in a concrete slab whose surface is blackened and covered with transparent insulation materials (TIM) and the bottom is insulated by the ground. Heat may be retrieved by the flow of fluid through the pipe. A simulation model has been developed; it involves the solution of the two-dimensional transient heat conduction equation using an explicit finite-difference scheme. Computational results have been used to determine the effect of such governing parameters as depth as well as pitch of the pipe network and collector material on the thermal performance of the system. The pipe network depth of 10 cm and the TIM cover made of 5 cm compounded honeycomb seem suitable for the proposed system. Solar gain (solar collection efficiency of 30–50% corresponding to collection temperature of 40–60°C) and the diurnal heat storage characteristics of the system are found to be of the right order of magnitude for solar water heating applications. Copyright © 1999 John Wiley & Sons, Ltd.

Solar thermal analysis of transparent-honeycomb-insulated ground collector-storage system

Abstract This paper presents an analysis of heat transfer processes in a transparent-honeycomb-insulated solar collector made of such low-energy materials as soil/sand/concrete, which also acts as a heat store. The analysis assumes solar intensity and atmospheric temperature as well as the resultant temperature in the ground and concrete/sand region to be periodic. An explicit expression for the heat flux that can be extracted at constant mass flow rate and at constant heat extraction temperature is derived. Numerical computations corresponding to typical months of June, September and December at New Delhi are presented. The solar conversion efficiency of 30–60% corresponding to a collection temperature in the range of 40–70°C is reported. The solar gain and heat storage characteristics of the proposed system are found to be of the right order of magnitude for solar water-heating applications.

Storage tanks—A numerical experiment

A numerical study has been made of a two-dimensional model of the motion which takes place in storage tanks used for solar water heating applications. Up to two flow circuits have been allowed in the model and the geometric configurations have included horizontal and vertical entry into the tank. The effect of the entrance Reynolds number and the contribution of buoyancy in promoting stratification have been examined. A comparison has also been made with a simple one-dimensional approximation. The discrepancy between the two models has been shown to be small.