Solar Water Heating Collectors Research Articles

Heat Transfer Coefficient from the Sheet-Piped Light-Absorbing Panels of the Flat-Plate Solar Water-Heating Collectors to the Heat Transfer Fluid in Their Heat-Removing Channels

It has been proposed to introduce a new parameter into the practice of the heat calculation and testing of the flat-plate solar water-heating collectors (FSWHCs)—the coefficient of heat transfer from the light-absorbing panel (LAP) to the heat transfer fluid in its internal heat-exchange channels (HECs) reduced to the unit area of the frontal surface of their cases. The mechanism of the formation of this parameter is studied, the design expression is derived, and a practical example of the calculation to define its value is performed. The structures of the flowing LAPs of a sheet-piped thin parallelepiped form are selected as the objects of the investigation. The reliability of the results of the investigations is proved by comparing the values of the specific (relative to the area unit of the frontal surface of the case) heating efficiency of the collector obtained based on the various formulas.

EVALUATE THERMAL PERFORMANCE OF SOLAR AIR COLLECTORS

Solar energy has an important place in sustainable and clean energy sources. Solar collectors can play a vital role among applications of solar energy system. Solar collectors are divided into solar air heating collector (SAHC) and solar water heating collector (SWHC) according to the fluid used. Although its efficiency is low because of air’s worse thermodynamic properties in terms of heat exchange compared to liquid, SAHC is still widely used in the world for the advantages of simple structure, convenient installation and easy maintenance. The absorber surface material is the most important parameter in the design for solar air collectors. The present study aimed to evaluate the thermal performance of solar air collectors. The treatments under this study were three types of solar panels absorbent. Stainless steel, aluminum and iron) and three different air velocities of 1.7, 2.4 and 3.6 m/s represented. Stainless steel solar panels absorbent give the highest value of absorption efficiency, useful heat gain to storage and overall thermal efficiency and they were 86.4, 71.42 and 59.87 %, respectively at midday air flow inlet temperature (Tai =31.7 C°), air flow outlet temperature (Tao =49.9 C°) and Average plate temperature (Tpm =70 C°) at 2.4 m/s fan velocity.

Determination of the Convective Heat-Exchange Coefficient in Inner Channels of Light-Absorbing Heat-Exchange Panels of Flat-Plate Solar Water-Heating Collectors Based on the Results of Their Short-Term Thermal Testing in Full-Scale Conditions

The results of investigations to determine the convective heat-exchange coefficient in the inner heat-exchange channels (HECs) of the light-absorbing heat-exchange panels (LAHPs) of flat-plate solar water-heating collectors (FPSWHCs) are given based on the results of their short-term heat testing in fullscale quasi-stationary conditions. The research method is based on determining the value of the required parameter from the heat-balance equation formed for the inner surfaces of the LAHP HEC walls. The structures of the flow LAHPs with a sheet-piped and thin parallelepiped form are selected as the test objects. The thermal tests of the FPSWHC are carried out during the near-midday hours of the light day to ensure the quasi-stationary mode condition. The reliability of the proposed method and results of the investigations is proved by comparing the values of the thermal-efficiency coefficients of the FPSWHC LAHPs obtained using two independent approaches.

Experimental analysis of a flat plate solar collector with integrated latent heat thermal storage

In the present paper, an experimental analysis of a solar water heating collector with an integrated latent heat storage unit is presented. With the purpose to determine the performance of a device on a lab-scale, but with commercial features, a flat plate solar collector with phase change material (PCM) containers under the absorber plate was constructed and tested. PCM used was a commercial semi-refined light paraffin with a melting point of 60°C. Tests were carried out in outdoor conditions from October 2016 to March 2017 starting at 7:00 AM until the collector does not transfer heat to the water after sunset. Performance variables as water inlet temperature, outlet temperature, mass flow and solar radiation were measured in order to determine a useful heat and collector efficiency. Furthermore, operating temperatures of the glass cover, air gap, absorber plate, and PCM containers are presented. Other external variables as ambient temperature, humidity and wind speed were measured with a weather station located next to the collector. The developed prototype reached an average thermal efficiency of 24.11% and a maximum outlet temperature of 50°C. Results indicate that the absorber plate reached the PCM melting point in a few cases, this suggests that the use of a PCM with a lower melting point could be a potential strategy to increase thermal storage. Thermal analysis and conclusions of the device performance are discussed.

Performance evaluation of the senergy polycarbonate and asphalt carbon nanotube solar water heating collectors for building integration

Senergy building integrated solar thermal collectors aim to reduce costs of solar water heating systems by utilizing polymer materials and offsetting costs of conventional roofing construction components. Carbon nanotubes can be added to polymer materials to improve their thermal, optical and mechanical properties. Two working prototypes; one Polycarbonate Carbon Nano-Tube (PCNT) collector and one Asphalt Carbon Nano-Tube (ACNT) collector; have been tested using the solar simulator facility at Ulster University and their performances compared. The PCNT collector is single glazed and uses a twinwall sheet to act as both the solar absorptive surface and the heat transfer fluid channeling element. The ACNT collector is unglazed and has an asphalt based absorber with embedded serpentine copper tubing to channel the heat transfer fluid. Tests were conducted with 800 W m−2 illumination intensity and for water inlet temperatures between from 23 °C and 47 °C. The PCNT collector achieved 62% maximum collection efficiency compared to 45% for the ACNT collector. The heat loss coefficients were 6.0 and 8.1 W m−2 K−1 respectively. The performance of the PCNT collector was similar to benchmark values for single glazed collectors with selective absorber surfaces. The ACNT collector responded very slowly and performance was lower than a typical unglazed solar water heater with non-selective absorber due to the high thermal resistance between the absorber surface and the serpentine tubing.

Calculation of the temperature of the internal surface of the heat-removing channel wall of the ray-absorbing heat-exchange panels of flat-plate solar water-heating collectors

The results of numerical research on the determination of the temperature value of the internal surface of the heat-removing channel (HRC) walls of the light-absorbing heat-exchange panels (LAHPs) with the tubeon- sheet and thin-parallelepiped form of flat-plate solar water-heating collectors (FPSWHCs) are presented. The research method is based on compilation of the system of the balance equations for the light-absorbing plate (LAP) and HRCs of the LAHPs of the studied types and their designs with respect to the desired parameter. A practical example of calculation of the determination of the temperature value of the internal surface of the HRC wall of the tube-on-sheet LAHP, where the results of experimental research on the determination of the specific thermal efficiency of the mean-quality FPSWHC in full-scale terms, as well as laboratory and numerical research on determination of the optical and thermotechnical indicators of the copper tube-on-sheet LAHP.

The impact of the energy performance regulations’ updated on the construction technology, economics and energy aspects of new residential buildings: The case of Greece

This paper aims to analyse the changes that the new Hellenic Regulation on the Energy Performance of Buildings (REPB) has brought to the Hellenic residential buildings, which is in line with the European Directive 2010/31/EC. These changes refer to construction techniques, construction costs and energy performance. Our assessment is based on the numerical analysis of two typical residential buildings, a single and a multi-one. Both buildings were studied according to the requirements set before and after the application of the REPB for all (four in total) climate zones of Greece. The cost for implementing the two regulations was evaluated, as was also the energy consumption cost. Based on these costs we estimated the operating costs for heating, cooling and domestic hot water of the two buildings of this study.The implementation of the REPB significantly reduced the required heating loads for space heating in all climate zones by 37%–48% for both building types; this is mainly attributed to the improvement of the thermal properties of the building envelope and the improved energy performance of the electromechanical systems. The required cooling load was low and the implementation of the REPB did not change it significantly. Significant energy savings, in the range of 51%–58% were also achieved by installing flat plate solar collectors for Domestic Hot Water heating.

The Influence of Flow Tube Vibrations over the Efficiency of Solar Water Heating Collectors

The effect of vibrations over a flow tube from a solar water heating collector was studied in order to enhance the heat exchange. First, a hydrodynamic model for the internal flow of the tube was proposed, in order to obtain the pattern for the relative motion of the liquid. The results highlighted a strong exchange of liquid volumes between the upper and the lower part of the pipe over the transversal section of the tube for a vertical displacement of the flow. In order to validate the positive effect of the internal motion over the heat transfer between the pipe and the water flow, an experiment was accomplished. The flow tube filled with liquid was introduced in a water recipient and vibrated at several frequencies. The water temperatures inside and outside the tube were recorded. The values for water temperatures measured during the warming and cooling intervals confirm that by vibration, the time for heat exchange is decreasing if the vibrating frequencies near the resonance frequency are considered.

Experimental Study on a Line-Axis Concentrating Solar Energy Collector for Water Heating

This paper examines the experimental study on a line axis concentrating solar energy collector for water heating. The system considered consists of cylindrical solar radiation concentrator with a black coated tubular absorber positioned along its axis. A cold water tank is placed above the collector and a hot water tank positioned below it such that fluid flows in and out of the set up. Solar radiation absorber inlet header is connected to the cold water tank while its outlet header is connected to the hot water tank. These major components are supported by angle iron raised at a distance from the ground that depends on the location and function. Valves are used at strategic points on the connecting pipe lines to isolate the flow of water. When water is poured into the cold water chamber, and the control valve turned on, the water flows under gravity into the receiver/absorber tube. At the absorber section, heat is transferred from the steel tube to the circulating water and is consequently heated. The heated water, then flows into the returning tube against gravity, thereby restricting the heated water from flowing into the storage tank. At this stage, thermo-siphoning effect comes into play. As the temperature of the water increases, its density reduces while the mass remains constant in order to balance the effect of the reduction in density. Thus, there is a resultant increase in volume which consequently pushes the water level further along the returning pipe. Further increase in temperature reduces the water density and increases the volume of the water, thereby causing the heated water to flow into the insulated tank. Several experimental tests were carried out under meteorological condition at the Federal University of Technology Owerri, Nigeria at three different mass flow rates of 0.001kg/s, 0.002kg/s and 0.003kg/s. The solar water heater was tested while oriented in the East–West and North –South directions in order to determine the effects of orientation on the performance. Results obtained showed that a maximum temperature of 69.5°C, corresponding to 34.5°C increase in water temperature and a maximum instantaneous efficiency of 51.01% is possible. The aim of the study is to design a cheaper solar energy system capable of reducing energy bill within the developing countries of the world.

Simplified Method of Optimal Sizing of a Renewable Energy Hybrid System for Schools

Schools are a suitable public building for renewable energy systems. Renewable energy hybrid systems (REHSs) have recently been introduced in schools following a new national regulation that mandates renewable energy utilization. An REHS combines the common renewable-energy sources such as geothermal heat pumps, solar collectors for water heating, and photovoltaic systems with conventional energy systems (i.e., boilers and air-source heat pumps). Optimal design of an REHS by adequate sizing is not a trivial task because it usually requires intensive work including detailed simulation and demand/supply analysis. This type of simulation-based approach for optimization is difficult to implement in practice. To address this, this paper proposes simplified sizing equations for renewable-energy systems of REHSs. A conventional optimization process is used to calculate the optimal combinations of an REHS for cases of different numbers of classrooms and budgets. On the basis of the results, simplified sizing equations that use only the number of classrooms as the input are proposed by regression analysis. A verification test was carried out using an initial conventional optimization process. The results show that the simplified sizing equations predict similar sizing results to the initial process, consequently showing similar capital costs within a 2% error.

ENERGETIC PERFORMANCE ASSESSMENT OF A THERMO-SOLAR GREENHOUSE FISH (NILE TILAPIA) HATCHERY

Energetic performance of a thermo-solar greenhouse representing a fish hatchery system was suggested, developed and investigated. The developed system was mainly consisted of a double cover greenhouse coupled with solar collector and heat exchanger for water heating. The main aim was to control the water environment, namely temperature and dissolved oxygen, of a fish (Nile Tilapia) hatchery at the desired levels. The main experimental work was carried out during the period from December 2014 to February 2015. The suggested and investigated system based mainly on solar energy as the source of power. However, an auxiliary heating system, namely an electric heater was used upon request. The experimental system was constructed and investigated at the research farm, Faculty of Agriculture, Kafrelsheikh University (31.07oN and 30.57oE) Kafrelsheikh governorate, Egypt. Environmental parameters; namely temperature, solar radiation, relative humidity, wind speed and water quality in terms of dissolved oxygen were monitored. The results indicated an efficient control in water temperature and quality. The average temperature and dissolved oxygen concentration of fish pond water throughout the whole experimental period were 26.8 (SD = 0.15) °C and 7.62 (SD =0.68) ppm respectively. The average value of air temperature rise inside the greenhouse was 8.4 °C. The average value of total daily water energy gained via the heat exchanger system was 18.185 MJ/ day per m2of the fish pond water surface area at an average value of 13.433 MJ/ (m2.day) of the incident solar radiation on the horizontal plane. As a conclusion the weekly average percentage of energy contribution of both greenhouse action and heat exchanger operating times were 58.13 and 41.87% respectively as a percentage of the whole operating time.

The effect of time-of-use tariffs on the demand response flexibility of an all-electric smart-grid-ready dwelling

The paper is concerned with the development and evaluation of control algorithms for the implementation of demand response strategies in a smart-grid enabled all-electric residential building. The dwelling is equipped with a 12kW heat pump, a 0.8m3 water storage tank, a 6kW photovoltaic (PV) array, solar thermal collectors for domestic hot water heating and an electric vehicle. The building, located in Ireland, is fully instrumented. An EnergyPlus building simulation model of the dwelling was developed and calibrated using monitored data from the building. The developed model is used to assess the effectiveness of demand response strategies using different time-of-use electricity tariffs in conjunction with zone thermal control. A reduction in generation cost (−22.5%), electricity end-use expenditure (−4.9%) and carbon emission (−7.6%), were estimated when DR measures were implemented and compared with a baseline system. Furthermore, when the zone control features were enabled, the efficiency of the control improved significantly giving, an overall annual economic saving of 16.5% for the residential energy cost. The analysis also identified an annual reduction of consumer electricity consumption of up to 15.9%, lower carbon emissions of 27% and facilitated greater utilisation of electricity generated by grid-scale renewable resources, resulting in a reduction of generation costs for the utility of up to 45.3%.

THE THERMAL MODEL OF A FLAT-PLATE SOLAR WATER-HEATING COLLECTOR

The paper offers a thermal model to determine the specific heat productivity of flat-plate solar water-heating collector (FSWHC) depending of the pre-assigned temperature values of obtaining hot water. Unlike existing thermal models of FSWHC, for the first time in the proposed model the research results obtained by the authors are used to determine the average mass temperature of the heat-transfer (water) collectors, heat efficiency coefficient and the surface average working temperature of the light-absorbing heat-exchange panels (LAHP) by non-contact method, depending of the effective coefficient of LAHP heat losses. In order to determine the coefficient we have to take into account the partial absorption influence and conversion into heat of the total solar radiation passing through translucent cover of collector case and also the value of the LAHP surface average working and ambient temperature. It is provided a practical example of realization and proved authenticity of the model.

An experimental investigation on a small-sized parabolic trough solar collector for water heating in cold areas

When used in cold environment, the conventional flat plate solar collectors and all-glass evacuated tube solar collectors will cause various problems, such as large heat loss, low efficiency, freeze and tube-burst, which severely limit their applications. In this paper, a special small-sized parabolic trough solar collector (PTC), which could overcome the shortcomings of conventional solar collectors, was proposed for water heating in cold areas. An experimental platform was developed, and extensive tests were conducted to evaluate the characteristics of the proposed PTC. It was found that the thermal efficiency of the proposed PTC reached about 67% even under the condition of solar radiation of less than 310W/m2, indicating that the PTC could collect solar radiation efficiently. The results also showed that when the fluid temperature was under 100°C, the thermal efficiency was improved with increased fluid temperature, due to the increase of Reynolds number caused by the great variation of thermophysical parameters of the heat transfer fluid (HTF), which resulted from the increasing fluid temperature. Both the frosting on the reflector and the ambient wind velocity weakened the thermal efficiency greatly. The highest thermal efficiencies were respectively about 26% and 56% under condition of frosting and wind velocity of 5.0m/s. The comparison test showed the coated double glazing receiver had a longer temperature response delay to the deflected sunlight than that of the uncoated one. The tested PTC system operated normally in low fluid temperature condition, showing great anti-freezing property in cold environment.

Annual measured performance of building-integrated solar energy systems in demonstration low-energy solar house

This paper presents the details of the output and efficiency of the annual performance of building-integrated solar energy systems for a solar water heating system and solar photovoltaic (PV) modules of a demonstration near-zero-energy solar house that was constructed on the campus of the Korea Institute of Energy Research. The thermal systems installed in the house were a solar water heating system with building-integrated solar collectors for water heating and for part of the space heating, and a ground-coupled heat pump for space cooling and part of the space heating. Solar PV modules were installed on the roof of the house. The performance of these systems was monitored for more than 1 yr. The annual efficiencies of the building's integrated solar collectors and solar PV were 22.8% and 10.9%, respectively. The total annual solar fraction of the solar heating system was 69.7%, with an annual solar heat production of 248 kW h/m2. This paper also focuses on the efficiency of the house's solar storage, based upon intentionally varied drainage of hot water from the storage tank. It was found that the thermal loss from the solar storage tank has a strong functional relationship with the thermal demand of the solar storage tank per unit volume. For example, when the hot water consumption was reduced by half during September, the thermal loss increased to more than 70%, which would otherwise have been around 30%.

Ray Tracing of a Solar Collector Designed for Uniform Yearly Production

One of the problems with solar flat plate collectors for domestic water heating is that they produce more energy in the summer months, when the domestic hot water needs are lower than in winter months. This causes a significant difference between supply and demand and thus overheating during the summer. A method to avoid this problem is to design solar collector fields that offer a 100% of the water needs in the summer, but a small percentage during the winter, which is certainly not ideal.In this work, ray tracing is used to design a solar thermal collector that offers a more uniform production during the year. A novel geometry is chosen where the collector is split in two parts, a curved absorber and a mini parabolic concentrator. The concentrator is designed to concentrate the radiation during the midday hours of winter days and to not doing it in the midday hours of summer days. This increases the energy produced in winter and prevents the installation from overheating.In order to study the hours when this geometry will concentrate the solar radiation, ray tracing is used. As the solar collector has a design that allows the collector to be easily integrated into a facade, the simulations in the most useful architectural integration positions are simulated, those are horizontal positions, but vertical positions or any other position are suitable if the collector is installed on a roof.For each position, the amount of hours where the whole collector is working and the total radiation captured are calculated and compared with the solar radiation captured by an equivalent flat surface, which would corresponds to conventional flat plate collectors.Simulation results shows how for a concentrator designed to work properly in the 5 midday hours during the winter solstice it will not work during the 5 midday hours during the summer solstice, avoiding overheating.

Testing Solar Air-heating Collectors

For a sustainable market development, transparent and fair product information has to be available for the consumer. In the case of solar collectors, such information can be derived from testing according to a standardized test procedure. For the special situation of solar air-heating collectors the methodology has been revised and extended to align the technical background for product comparison and rating recently. For this kind of solar collector, technical aspects had to be taken into account, which are neglected for solar water-heating collectors in the actual testing standard. This is done because their influence seems to be insignificant. Comparability with water-heating collectors’ performance and functionality, as well as within different technical variations of solar air-heating collectors was prepared, by defining a set of parameters describing the collectors’ performance. The function tests described in this paper are the result of transferring as many test sequences of water-heating collectors as reasonable and define functional tests to prove the basic function of the collectors under typical operating conditions. As more and more rating procedures and certification issues are coming into focus of industry, these aspects were also taken into account. In the case of performance, rating is mostly dealt with a standardized power output calculation. Although many questions with regard to testing methodologies for solar air-heating collectors have been solved, some more remaining questions are named in the final chapter, to show further research needed.

Geographical View on Energetic Sources of Climate Northeastern Montenegro

This paper analyzes energy sources climate northeastern Montenegro, in the example municipalities Berane, Andrijevica and Plav in a geographical context its exploitation and use. Analyzed GeoScape from the standpoint of utilization of wind energy lose their its attractiveness due to high altitude mountain ranges that dominate in given area, it is the windy areas, often the located on slopes of the mountains, and most of them did not connected to the existing road network and infrastructure. The use of solar thermal energy is possible only with the help of passive solar architecture and active solar architecture (solar collectors for water heating and space heating in homes and tourist facilities). Program development and use of renewable energy in Montenegro, given the Energy Law of 2010 in which Montenegro has implemented parts of EU directive 2009/28/EC on the promotion of energy from renewable sources.

Geographical View on Energetic Sources of Climate Northeastern Montenegro

This paper analyzes energy sources climate northeastern Montenegro, in the example municipalities Berane, Andrijevica and Plav in a geographical context its exploitation and use. Analyzed GeoScape from the standpoint of utilization of wind energy lose their its attractiveness due to high altitude mountain ranges that dominate in given area, it is the windy areas, often the located on slopes of the mountains, and most of them did not connected to the existing road network and infrastructure. The use of solar thermal energy is possible only with the help of passive solar architecture and active solar architecture (solar collectors for water heating and space heating in homes and tourist facilities). Program development and use of renewable energy in Montenegro, given the Energy Law of 2010 in which Montenegro has implemented parts of EU directive 2009/28/EC on the promotion of energy from renewable sources.

Resource indexes of flat solar water-heating collectors in hot-water supply systems: 4. Specific collector thermal yield and efficiency

This study is a continuation of works [1–3]. The calculation results of daily variations in average hourly values of specific thermal yield and the efficiency of average-quality flat solar water-heating collectors (FSWHCs) in hot-water supply systems (HWSSs) are presented for typical days of the year; also, average monthly variations and annual values of these indexes for the considered collectors, which are based on the former calculations and depend on the temperature of the hot-water supplied to HWSS subscribers, are given.