Review on solar water heater collector and thermal energy performance of circulating pipe

The effect of thermal conductivity of the absorber plate of a solar collector on the performance of a thermo-siphon solar water heater is found by using the alternative simulation system. The system is assumed to be supplied of hot water at 50 °C and 80 °C whereas both are used in domestic and industrial purposes, respectively. According to the Rand distribution profile 50, 125 and 250 l of hot water are consumed daily. The condition shows that the annual solar fraction of the planning functions and the collector's configuration factors are strongly dependent on the thermal conductivity for its lower values. The less dependence is observed beyond a thermal conductivity of 50 W/m °C for the solar improper fraction and above 100 W/m °C for the configuration factors. In addition, the number of air ducts and total mass flow rate are taken to show that higher collector efficiency is obtained under the suitable designing and operating parameters. Different heat transfer mechanisms, adding natural convection, vapor boiling, cell nucleus boiling and film wise condensation is observed in the thermo-siphon solar water heater with various solar radiations. From this study, it is found that the solar water heater with a siphon system achieves system characteristic efficiency of 18% higher than that of the conventional system by reducing heat loss for the thermo-siphon solar water heater.     

Simulation studies of the position of the auxiliary heater in thermosyphon solar water heating systems

This paper investigates the effect of the physical location of the auxiliary source of energy in thermosyphon solar water heaters and shows that the performance of the system can be optimised with respect to the geometry of the system components. The investigation has been based on a domestic thermosyphon solar water heating system, which was simulated using the TRNSYS programme. The annual solar fraction of the system, at the weather and socioeconomic conditions of Cyprus, is, at best, approximately 77% with an in-tank auxiliary heater configuration and 86% with an external auxiliary heater. It is demonstrated that the arrangement with the external auxiliary unit has a higher collector efficiency and results in a higher annual solar fraction. In the case of in-tank auxiliary, the system performance increases with the height of the auxiliary position from the bottom of the storage tank; with the auxiliary at the bottom of the storage tank the annual solar fraction is approximately 59%, compared to 77% when the auxiliary is located at the top of the tank. The system performance also depends on the height of the collector return from the bottom of the tank.     

Design and performance of a large-size solar water heater

The paper reports the design details of a solar water heater suitable for the large, intermittent demands for hot water by hospitals and hostels. It employs a flat-plate collector consisting of a wire-tied aluminium fin of 28 gauge with galvanized iron pipes of 19 mm diam spaced at 10 cm centres. The unit is adjusted to give maximum efficiency per unit cost under Indian conditions. Various arrangements for connecting the collectors, such as cascade, series, series parallel, and true parallel, were experimentally studied. This revealed that for a solar water heating system having a large number of absorber banks, the true parallel arrangement yields maximum efficiency and economy.The system is fully-automatic and heats 600 l. of water up to 55°C in winter months at Roorkee. Heat losses at night may be compensated for, if required, by an auxiliary electric heater provided in the storage tank and controlled by a low-cost radiation-sensing device. A simple electric circuit controls the tank mean temperature of water in the storage tank.Required collector areas based on meteorological observations for various water capacities and water temperatures are given for several Indian cities.     

Technical note Best connection scheme of collector modules of thermosyphon solar water heater operated at high temperatures

Large scale thermosyphon solar water heater for high temperature applications is simulated by the use of the Transient Simulation Program (TRNSYS). A daily hot water load of 1500 l/day and 2500 l/day at 80°C was assumed. The hot water is consumed daily from 08·00–17·00 h. A back-up electric auxiliary heater was added to the system in two schemes: first, located inside the storage tank with a thermostat; second, outside the tank connected to the heating system between the tank and the facilities. The collector modules were connected in five different schemes: first, all collectors were connected in series in one line, or collectors were connected in two, three, four or five parallel lines each consisting of many collectors. The results showed that the best connection is when the 20 collectors, comprising the system, are connected in two parallel lines each consisting of 10 collectors. It was found that the monthly and yearly useful energy from the system was higher when the auxiliary water heater was added to the system outside the storage tank.     

Experimental studies of a new solar water heater system using a solar water pump

The research goal was to develop a new solar water heater system (SWHS) that used a solar water pump instead of an electric pump. The pump was powered by the steam produced from a flat plate collector. Therefore, heat could be transferred downward from the collector to a hot water storage tank. The designed system consisted of four panels of flat plate solar collectors, an overhead tank installed at an upper level and a large water storage tank with a heat exchanger at a lower level. Discharge heads of 1, 1.5 and 2 m were tested. The pump could operate at the collector temperature of about 70–90 °C and vapor gage pressure of 7–14 kPa. It was found that water circulation within the SWHS ranged between 12 and 59 l/d depending on the incident solar intensity and system discharge head. The average daily pump efficiency was about 0.0014–0.0019%. Moreover, the SWHS could have a daily thermal efficiency of about 7–13%, whereas a conventional system had 30–60% efficiency. The present system was economically comparable to a conventional one.     

The optimization of tank-volume-to-collector-area ratio for a thermosyphon solar water heater

Through the use of the TRNSYS simulation program, the performance of a domestic solar water heating system operating with natural circulation (thermosyphon) and a daily hot water load has been analysed. The effect of tank height on the annual solar fraction of the system has been investigated for different hot water load temperatures and storage tank volumes. Optimum values (values which maximize the annual solar fraction of the system) for storage tank height and volume are calculated for operating temperatures ranging from 50 to 80°C. The response of the system to the ratio of the storage tank volume to the collector area is investigated. The dependence of the solar fraction on tank height was observed to be more notable in the case of large tank volumes and high load temperatures. The results indicate the existence of an optimum value for the tank volume at a given tank height and a high load temperature. At lower temperatures, the solar fraction rises rapidly with tank volume to a nearly constant level. An optimum value of the storage-tank-volume-to-collector-area ratio was also observed at high load temperatures.     

Analysis of an integral compact solar water heater

The thermal performance of an integral compact solar water heater is analysed numerically and compared with experimental data. In the proposed system the collector and the water tank are built into one unit with water flow caused by thermosyphonic force. Two geometries of the proposed system are investigated. While the proposed system presents a new concept for solar water heater, the efficiency of such systems are shown to be larger than conventional ones. The numerical scheme used does not make any a priori assumption concerning temperature profiles.     

Performance of a non-metallic unglazed solar water heater with integrated storage system

The performance of a new design of non-metallic unglazed solar water heater integrated with a storage system has been studied. In this system, the collector and storage were installed in one unit. All parts of the system have been fabricated from fiberglass reinforced polyester (GFRP) using a special resin composition that provides good thermal conductivity and absorptivity. The storage tank has a capacity of 329 l. The design of the storage system was sandwich construction, with the core material made out of polyurethane foam, which combines stiffness and lightness of structure with very good thermal insulation. The width and length of the absorber plat were 1.4 and 1.8 m, respectively. The performance of the system has been investigated by two methods. In the first method, the storage tank was filled up with water the night before the test. The tank was then drained during the night, refilled and made ready for the next day’s test. The tests were repeated under varied environmental conditions for several days. The maximum water temperature in the storage tank of 63 °C has been achieved for a clear day operation at an average solar radiation level of 700 W m⁻² and ambient temperature of 30 °C. The decrease of water temperature with and without the thermal diode is 10 and 20 °C, respectively. In the second method, the testing was of the same way, but in this case without draw-off or draining of the hot water from the storage tank. All data readings were recorded from sunrise to sunset over the same period. The temperature was recorded for several days and ranges of 60–63 °C were obtained in the storage tank. A system efficiency of 45% was achieved at an average solar radiation level of 635 W m⁻² and ambient temperature of 31 °C.     

Simulation of a solar domestic water heating system using a time marching model

This paper presents the modelling and simulation of a solar water heating system using a time marching model. The results of simulations performed on an annual basis for a solar system, constructed and operated in Yugoslavia, which provides domestic hot water for a four-person family are presented. The solar water heater consists of a flat-plate solar collector, a water-storage tank, an electric heater, and a water-mixing device. The mathematical model is used to evaluate the annual variation of the solar fraction with respect to the volume of the storage tank, demand hot water temperature required, difference of this temperature and preset storage tank water temperature, and consumption profile of the domestic hot water demand. The results of this investigation may be used to design a solar collector system, and to operate already designed systems, effectively. The results for a number of designs with different storage tank volumes indicate that the systems with greater volume yield higher solar fraction values. The results additionally indicate that the solar fraction of the system increases with lower hot water demand temperature and higher differences between the mean storage water and the demand temperatures. However, when a larger storage tank volume is used, the solar fraction is less sensitive to a variation of these operation parameters.     

Performance analysis of solar water heater combined with heat pump using refrigerant mixture

In the research presented in this paper the thermal performance of a solar water heater combined with a heat pump is studied. A solar collector was modified from corrugated metal roofing with a copper tube attached beneath. The performance of the solar water heater was tested, and models for the collector efficiency and storage tank were developed and used for the evaluation of their performance when combined with a heat pump system.     

Analysis and performance of a low-cost solar heater

One of the alternatives to reduce the consumption of electricity for heating water is by popularizing the use of solar energy. This work contributes with studies on a Low-Cost Solar Heater (LCSH), a new concept of solar water heater made entirely of polymeric materials, which requires a relatively low investment and is user-assembled. The solar collector, which absorbs solar energy and transfers it to water in the form of heat, is composed of uncovered flat panels of rigid PVC. The storage tank that holds the water heated during the day is made of polyethylene coated with polystyrene. The results of the LCSH were compared with those of a conventional solar heater composed of a glass-covered copper collector and a stainless steel storage tank. The efficiency of the systems was evaluated by measuring the incident solar radiation and water temperature with the systems operating naturally (thermosiphon). The heat loss in the hot water storage tanks was measured to estimate the thermal performance of the solar heaters. Considering that the target temperature for the heated water is slightly above the ambient temperature, the results indicated that the LCSH showed a satisfactory global heat transfer coefficient for storage tanks and that it attained an excellent thermal performance, although it is not as efficient as the conventional heater.     

Economical and environmental assessment of an optimized solar cooling system for a medium-sized benchmark office building in Los Angeles,California

This paper presents a systematic energetic, economical, and environmental assessment on a solar cooling system for a medium-sized office building in Los Angeles, California by means of system modeling. The studied solar cooling system primarily consists of evacuated tube solar collectors, a hot water storage tank, a single-effect LiBr–H₂O absorption chiller, and a gas-fired auxiliary heater. System performance optimization and sensitivity analysis were conducted by varying two major parameters (i.e. storage tank volume and collector area). The results suggest that a trade-off exists between economic performance indicated by the equivalent uniform annual cost (EUAC) and the energetic/environmental performance indicated by the solar fraction and CO₂ reduction percentage, respectively. The cost of carbon footprint reduction was defined and served as an indicator for the overall system performance. Based on this indicator, the optimal system design could be found for a solar cooling system. The approach adapted in this study can be applied to other buildings located in different climate zones to reveal the cost and benefits of solar cooling technologies and facilitate decision-making.     

An experimental investigation into the performance of a domestic thermosyphon solar water heater under varying operating conditions

An experimental investigation has been carried out on a thermosyphon solar water heater. The system consisted of a flat-plate collector of 1.5 m² absorber area with 21 tubes/m width and storage tank of 125 litre capacity. Experiments were carried out for both cloudy and clear weather conditions in winter and summer. The hourly system performance was evaluated for all test conditions. The final mean tank temperature was measured daily which enabled the calculation of the possible contribution of solar energy for domestic hot water supply in Basrah, Iraq (latitude 30.76°N). The system was tested at both no-load and loading conditions. Intermittent and continuous load was imposed, and system performance was evaluated for each condition.     

Economic appraisal of small-scale solar organic Rankine cycle operating under different electric tariffs and geographical conditions

In the present paper, the economic feasibility of small-scale solar organic Rankine cycle power applications which are assisted with auxiliary gas heaters is investigated. The system is analyzed using three different capacities of ORC system with R-245fa (35, 65, and 110 kWe) in combination with solar water heating system (SWHS) using three models. Flat plate, compound parabolic and evacuated tube solar collectors were used to generate heat with overall heat transfer coefficient (F_RU_L) of 4.35, 1.57, and 2.23 W/m². K respectively. System Advisor Model (SAM) is used to simulate the solar water heater system and optimize the tilt angle, collector area, volume of storage tank and capacity of auxiliary heater under the climatic conditions of Abu Dhabi, New Delhi, Larnaca, Madrid and Munich. The simulation results revealed that the evacuated tube and the compound parabolic collectors performed better than the flat plate collectors. The economic analysis showed that Solar ORC Power Plant is economically and technically feasible with all types of the thermal collectors in Famagusta/Larnaca, Munich and Madrid where the electricity tariff is higher than other cities. Levelized cost of energy (LCOE) is calculated using mathematical model and it ranges between 0.07 and 0.2 USD/kWh based on the plant capacity and type of thermal collectors. Moreover, the profit increase as the plant capacity increase where SIR is 1.05, 1.71, and 2.10 for 35, 65, and 110 kW plant capacity SORC with CPC. A sensitivity analysis is also performed to investigate the effect of operating hours, electricity tariff, ORC unit cost and ORC unit type on the feasibility of the system. According to the results, the electricity tariff and operating hours are the most important parameters because they have a large effect and Play important role on the economic feasibility of the system.     

Similarity theory of solar water heater with natural circulation

The similarity theory of solar thermosyphon collector is developed in the present paper. Ten dimension-less groups or system characteristic parameters which uniquely determine the performance of the collector are derived. The solution shows that the mean efficiency generally increases with increasing incident solar radiation and relative height of the tank. For the frictional parameters N_e and N_f higher than 10⁵, the efficiency appears to be independent of the incident radiation and the relative height of the tank. Therefore, for parallel plate absorber, the tank may be designed to sit on the floor without sacrificing the efficiency since the values of N_e and N_f are usually larger than 10⁵ in most designs.     

Theoretical and experimental investigation on the application of solar water heater coupled with air humidifier for regeneration of liquid desiccant

Theoretical and experimental investigation on the application of flat plate solar water heater coupled with air humidifier for regeneration of liquid desiccant has been presented in this work. The heated water from the storage tank of the solar heating system is circulated in a finned tube air heater. Hot air from the air heater is blown through a packing of a honeycomb type for the purpose of regeneration of calcium chloride (CaCl₂) solution. An experimental system has been designed and installed for this purpose. The system comprises a solar water heater with a storage tank connected to an air/water heat exchanger. Hot air from the heat exchanger is blown to the air humidifier, which functions in this study as a regenerator. Calcium chloride solution is applied as the working desiccant in this study. Solution concentration is determined at the end of regeneration process and the mass of evaporated water is evaluated. It is observed that the heating temperature varies, at day time, in a range of about 5 °C. This limited variation in hot water temperature demonstrates the importance of the storage tank to attain a nearly steady state operation of the system. Experimental results show that solution with 30% concentration can be regenerated up to 50% using solar energy. In the theoretical part of this study, a multiple-layer artificial neural network (ANN) model has been applied to study the performance of a solar liquid-desiccant dehumidification/regeneration system when calcium chloride solution is applied as the working desiccant. The experimental results of the present study are used to construct and test the ANN model. Then the model has been utilized to describe and analyze the effect of the inlet conditions of air on the regeneration process. Good agreement between the outputs from the ANN model and the corresponding results from the experimental data has been found. The proposed model can work well as a predictive tool to complement the experiments.     

Thermal performance analysis of a direct-expansion solar-assisted heat pump water heater

A direct-expansion solar-assisted heat pump water heater (DX-SAHPWH) is described, which can supply hot water for domestic use during the whole year. The system mainly employs a bare flat-plate collector/evaporator with a surface area of 4.2 m², an electrical rotary-type hermetic compressor, a hot water tank with the volume of 150 L and a thermostatic expansion valve. R-22 is used as working fluid in the system. A simulation model based on lumped and distributed parameter approach is developed to predict the thermal performance of the system. Given the structure parameters, meteorological parameters, time step and final water temperature, the numerical model can output operational parameters, such as heat capacity, system COP and collector efficiency. Comparisons between the simulation results and the experimental measurements show that the model is able to give satisfactory predictions. The effect of various parameters, including solar radiation, ambient temperature, wind speed and compressor speed, has been analyzed on the thermal performance of the system.     

Transient investigation of a two phase closed thermosyphon flat plate solar water heater

This work presents an unsteady state theoretical and experimental investigation of natural circulation two phase closed thermosyphon flat plate solar water heaters. The governing equations of the heater storage tank and connecting pipes are presented and generalized in dimensionless form, while the governing equations of the different components of the collector were previously discussed by the author. Also, the author's earlier simulation program of the collector is modified to include the solution of the dimensionless governing equations of the present analysis. For verifying the modified simulation program, a two phase closed thermosyphon solar water heater is designed, constructed and tested at different meteorological conditions, initial storage tank temperatures and different hot water withdrawal load patterns. The comparison between the experimental results and their corresponding simulated ones shows considerable agreement.     

Experimental investigation on thermal performance of thermosyphon flat-plate solar water heater with a mantle heat exchanger

The thermal performance of thermosyphon flat-plate solar water heater with a mantle heat exchanger was investigated to show its applicability in China. The effect on the performance of the collector of using a heat exchanger between the collector and the tank was analyzed. A “heat exchanger penalty factor” for the system was determined and energy balance equation in the system was presented. Outdoor tests of thermal performance of the thermosyphon flat-plate solar water heater with a mantle heat exchanger were taken in Kunming, China. Experimental results show that mean daily efficiency of the thermosyphon flat plate solar water heater with a mantle heat exchanger with 10 mm gap can reach up to 50%, which is lower than that of a thermosyphon flat-plate solar water heater without heat exchanger, but higher than that of a all-glass evacuated tubular solar water heater.     

Performance calculations for closed-loop air-to-water solar hybrid heating systems with and without a rock bed in the solar air heater

A transient analysis has been carried out on a hybrid solar water heater which comprises a rock bed air heater with optimum design parameters in conjunction with an air-to-water transverse fin shell-and-tube heat exchanger (mixed air and unmixed water type) in which cold water from the storage tank receives heat from the hot air coming out of the air heater which flows in the shell at right angles to the water flowing in the tubes. The system's performance has been evaluated for typical winter weather conditions in Delhi for different combinations of flow rates of air and water for different volumes of the water storage tank. No hot water is assumed to be withdrawn from the tank to serve the load. A comparative analysis of the system's performance with and without a rock bed in the air heater reveals about 11°C higher temperature of storage tank in the former at 50 kg/h m² air flow rate. With both the air heater types, although the system performance was observed to increase with the rates of air and water flow, no significant improvement in system performance was achieved at .