Performance study of thermosyphonic circulation solar water heaters using packed bed collectors

In the present investigation the performance behaviour of thermosyphonic circulation solar water heaters using packed bed collectors has been analysed. Iron chips, gravels and stones have been used as packing materials. Average tank water temperature, collector as well as system efficiency and mony pay-back for these packed bed solar water heaters are compared with those for solar water heater using a plane collector. Experimental results reveal that the performance of solar water heater improves appreciably by packing its collector with packing material. Among the packed-bed solar water heaters tested the iron chips packed-bed solar water heater gives the overall best performance.     

Performance study of forced circulation solar water heaters using packed-bed collectors

A performance study of forced circulation solar water heaters using packed-bed solar collectors is presented. Iron chips, gravel and stones have been used as packing materials. Thermal energy stored in the tank, system overall efficiency and pay-back capital for these solar water heaters are compared with those for solar water heaters using a plane collector. It is observed that the performance of the solar water heater is improved appreciably by packing its collector with packing material. A solar water heater using an iron chip, packed-bed collector shows the best performance.     

Experimental and CFD investigation of an ICSSWH at various inclinations

The integrated collector storage (ICS) is the type of solar water heater that has retained its existance for well over a century. The flat absorber plate ICS collector type is a relatively recent addition. Being effective, low cost and simple to manufacture, their importance has been further enhanced by the recent upsurge in efforts to effectively tap renewable energy resources. Having different inclinations based on latitude, the design of flat plate heaters can benefit from extensive amount of research on the topic of natural convection in inclined cavities. More than half-century of exploration on inclined cavities has witnessed added activity particularly in the last three decades. Despite this consistent research, efforts to apply the outcomes to the flat plate collectors have been few and collectors reported in the literature appear to be deficient in embedding the knowledge into the design parameters. For an ICS type heater, natural convection studies gain even more weight as the apparatus is functionally an assembly of two natural convection cavities: an air cavity (space between the absorber and cover plates) and a water cavity (water storage tank). An extensive review of previous studies on inclined cavities relevant to flat plate collectors has been complied and discussed. Experimental tests of the ICS heater have been conducted for controlled heat flux up to 400 W. The thermal performance of the heater is recorded experimentally at angles 0–60° from horizontal, in 15° intervals. CFD analysis is also carried out for the same and is found to be in good agreement with previous studies. It was found that for any given constant value of heat flux, the performance of the heater is a strong function of the angle of inclination. The optimum configuration of the heater for Edinburgh conditions (latitude 55°55′N) is also evaluated. The present study also covers the convective behavior inside the water tank, which has been neglected in the past. A step-by-step build-up approach is adopted to resolve water tank behavior as its treatment as a simple natural convention cavity is invalid. This article would serve as a design guide for developing heaters tailored for a specific geographical location.     

Capital cost and economic viability of thermosyphonic solar water heaters manufactured from alternate materials in India

Many companies in India manufacture solar water heaters but these are not becoming popular in the domestic sector because of their high cost. The Ministry of Non-Conventional Energy Sources (MNES), New Delhi is recommending flat-plate collectors with copper (Cu) risers, headers and plate. Therefore, their cost is high. Long term studies have been carried out at the Central Arid Zone Research Institute, Jodhpur, to reduce the cost by replacing copper tubes with galvanised steel (G.S.) tube and copper plate with aluminium (Al) plate. The aluminium plate is wrapped over the G.S. tube by a special wire wound technique so that good contact of plate with risers and headers has been maintained. In this paper performance and testing of solar water heaters having G.S.–Al fin, Cu–Al fin and Cu–Cu fin in flat-plate collectors have been compared. It has been found that performance of all the three heaters is almost similar. The heater can provide 100 litres of hot water at an average temperature 62.0°C at 4 pm that can be retained to 50.4°C when average tap water temperature was 23.9°C. The efficiency of the heater is 51.9%. The cost of the heater with G.S.–Al collector is only Rs. 8,000.00 while it is Rs. 10,250.00 for solar water heaters with Cu–Cu collectors. The payback period of a solar water heater with G.S.–Al collector has been worked out by considering 10% compound annual interest, 5% maintenance cost, 5%, inflation in fuel prices and maintenance cost. The payback period varies between 2.92 years to 4.53 years depending upon which fuel it replaces. The payback periods are in increasing order with respect to fuels: electricity, firewood, LPG, charcoal, and kerosene.     

An optimum performance of flat-type solar air heater with porous absorber

This investigation is concerned with the design and performance of a flat-type solar air heater in which air flows perpendicularly from the transparent cover to a porous absorber plate. The design phase involved a stability analysis to determine the critical distance (maximum allowable distance) between the absober and transparent cover, for suppressing convection currents, at various environmental and operating conditions. These results are useful to designers of solar collectors of the proposed type. In addition, the thermal performance of this solar heater at its optimum design conditions was computed for a wide range of system parameters illustrating the contribution of conduction and radiative modes of heat transfer. The results indicate that the best operating efficiency can be obtained when running the collector with a mass flow rate of m > 40 kg/m².h. Furthermore, the collector thermal performance is superior than channel type solar air heaters operating under similar conditions and much simpler than honeycomb porous bed solar air heaters.     

Shape optimization for absorber plates of solar air collectors

Solar air heaters can be used for many applications at low and moderate temperatures. There are different factors affecting the solar air heater efficiency, e.g. collector length, collector depth, type of absorber plate, glass cover plate, wind speed, etc. The absorber shape factor is the most important parameter in the design for any type of solar air heater. Increasing the absorber shape area will increase the heat transfer to the flowing air, but on the other hand, will increase the pressure drop in the collector, this increases the required power consumption to pump the air flow crossing the collector. It was most important to find the optimizing angle of the triangular collector. The effect of the change of the absorber shape factor on the collector performance was studied. A theoretical model was constructed for the two types of collectors, taking into account the new parameter, called the absorber shape factor. The results can be used for all types of solar air heaters by changing the value of the absorber shape factor. The optimum angle of the triangular collector was deduced.     

Theoretical analysis of some configurations of double exposure solar air heaters

We present a theoretical analysis of three different configurations of double exposure solar air heaters. The heat-balance equations are written in each case and are solved explicitly. The periodic responses have been studied for different combinations of parameters. Measured values of solar radiation in the plane of the collector and the ambient temperature are used in the analysis. The effects of collector length, reflectance and flow rate have been studied.The outlet air temperature increases with an increase in plate length but the instantaneous and average efficiency decrease. The outlet air temperature is approximately the same, for a given model and combinations of parameters, when the ratio of the length of the air heater to the mass flow rate is constant. A double exposure solar air heater performs better than a single exposure air heater if the reflectance for solar radiation is greater than 10%.     

Investigation of twisted tape inserted solar water heaters—heat transfer, friction factor and thermal performance results

Heat transfer in a solar water heater could be enhanced by means of twisted tapes, inserted inside the fluid flow tubes, which induce swirl flow and act as turbulence promoters. Experimental investigations for a solar water heater with twisted tape inserts having twist pitch to tube diameter ratio ranging from 3–12 have been carried out for varying mass flow rates. The results on heat transfer and friction data have been found to compare well with available results. Within the range of investigated parameters, the heat transfer in the twisted tape insert collectors has been found to increase by 18–70%, whereas the pressure drop increased by 87–132%, as compared to plane collectors. An expression correlating the Nusselt numbers in twisted tape and plane collectors, the twist pitch ratio has been developed in the form of Nu_s/Nu=1.3+2.88/y, which predicts the heat transfer within the range of the present investigation. Results conclude that such collectors would be preferable for higher grade energy collection as it is also at higher rate.Solar water heaters having twisted tape inserts inside the flow tubes perform better than the plane ones. It has been observed that heat losses are reduced (due to the lower value of the plate temperature) consequently increasing the thermal performance by about 30% over the plane solar water heaters under the same operating conditions. The effect of twisted-tape geometry, flow Reynolds number and intensity of solar radiation on the thermal performance of the solar water heater has been presented. It has been found that the twisted-tape collectors perform remarkably better in the lower range of flow Reynolds number (Re≈12,000), beyond which the increase in thermal performance is monotonous. It has also been found that such collectors might perform even better at higher values of intensity of solar radiation.     

Performance of water-in-glass evacuated tube solar water heaters

The performance of water-in-glass evacuated tube solar water heaters is evaluated using experimental measurements of optical and heat loss characteristics and a simulation model of the thermosyphon circulation in single-ended tubes. The performance of water-in-glass evacuated tube solar collector systems are compared with flat plate solar collectors in a range of locations. The performance of a typical 30 tube evacuated tube array was found to be lower than a typical 2 panel flat plate array for domestic water heating in Sydney.     

Performance analysis of solar air heaters of conventional design

This article analyzes the technical performances of seven solar air heaters of conventional design. The study is generalized by means of two coefficients: air mass flow rate per unit collector area (G) and the collector geometric coefficient (K), which make collector performances invariant, under the same conditions of design, material choice and ambient values. By use of the zero-capacitance model, the air heater performances were computed for the most usual range of design and working conditions; the graphs presented can be used when dealing with planning problems of air collectors.     

Experimental investigation of effect of variation of mass flow rate on performance of parabolic dish water heater with non-coated receiver

Concentrated solar collectors have high efficiency. Therefore, when concentrating collectors are used for water heating application, the system yields higher efficiency. From a hot climate perspective, there is a huge potential available for low-cost solar water heating systems. With the system described in this paper, the needs of hot water in the domestic sector can be fulfilled instantly. Authors used the parabolic dish collector for instant water heating. This paper describes the effect of variation of mass flow rate on performance of the parabolic dish water heater prototype. Design of the solar parabolic dish collector consists of a novel truncated cone-shaped helical coiled receiver made up of copper at focal point. This prototype was evaluated for its performance during the month of April and May 2010.     

Experimental comparison of alternative convection suppression arrangements for concentrating integral collector storage solar water heaters

An experimental investigation of an inverted absorber integrated collector storage solar water heater mounted in the tertiary cavity of a compound parabolic concentrator with a secondary cylindrical reflector has been performed under simulated solar conditions. The solar water heaters performance was determined with the aperture parallel to the simulator for a range of transparent baffles positioned at different locations within the collector cavity. Results indicate that glass baffles located at the upper portion of the exit aperture of the CPC can reduce thermal losses through convection suppression without significantly increasing optical losses.     

On the effects of solar radiation variations on solar heating system performances

The effect of solar radiation availability on the performance of different solar heating systems has been studied. The systems include a solar water heater, passive solar houses and district solar heating systems with seasonal heat storage. Also, different collector orientations and collector types have been investigated. The hourly radiation data were generated by a simple computational simulation procedure. It was found that district solar heating systems with concentrating collectors and passive solar houses showed the largest variations for the given conditions.     

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.     

Experimentally derived efficiency and exergy analysis of a new solar air heater having different surface shapes

The aim of this study is to provide a remedy for the low thermo-physical properties of air which is used as different absorber surface of air heater. This paper presents an experimental investigation on the absorber surface of the collector whose shape and arrangement were made up to provide better heat transfer surfaces. In the study an experimental performance and exergy analysis of five types of air heating solar collectors: corrugated trapeze, reverse corrugated, reverse trapeze, and a base flat-plate collector are presented. The results of the experiments were evaluated at the same time of the days with the same radiation. The efficiencies were determined for the collectors and comparisons were made among them. The present data showed that heat transfer coefficient and pressure drop increase with shape of absorbers surface.     

Use of unglazed transpired solar collectors for desiccant cooling

The use of unglazed transpired solar collectors for desiccant regeneration in a solid desiccant cooling cycle was investigated because these collectors are less expensive than conventional glazed flat-plate collectors. Using computer models, we studied the performance of a desiccant cooling ventilation cycle integrated with either unglazed transpired collectors or conventional glazed flat-plate collectors. We found that the thermal coefficient of performance of the cooling system with unglazed collectors was lower than that of the cooling system with glazed collectors because the former system did not use the heat of adsorption released during the dehumidification process. Although the area required for the unglazed collector array was 70% more than that required for the glazed collector array in a 10.56 kW (3 ton) solar cooling system, the cost of the unglazed array was 45% less than the cost of the glazed array. The simple payback period of the unglazed collector was half of the payback period of the glazed collector when replacing an equivalent gas-fired air heater. Although the use of unglazed transpired collectors seems to make economic sense relative to use of glazed conventional collectors, some practical considerations may limit their use for desiccant regeneration.     

A critical review of photovoltaic–thermal solar collectors for air heating

Integrated photovoltaic–thermal solar collectors have become of great interest in the solar thermal and photovoltaic (PV) research communities. Solar thermal systems and solar PV systems have each advanced markedly, and combining the two technologies provides the opportunity for increased efficiency and expanded utilization of solar energy. In this article, the authors critically review photovoltaic–thermal solar collectors for air heating. Included is a review of photovoltaic thermal technology and recent advances, particularly as applied to air heaters. It is determined that the photovoltaic–thermal (PV/T) air heater is or may in the future be practicable for preheating air for many applications, including space heating and drying, and that integrated PV/T collectors deliver more useful energy per unit collector area than separate PV and thermal systems. Although PV/T collectors are promising, it is evident that further research is required to improve efficiency, reduce costs and resolve several technical design issues related to the collectors.     

The improvement of collector efficiency in solar air heaters by simultaneously air flow over and under the absorbing plate

The performance of double-flow type solar air heaters, in which air is flowing simultaneously over and under the absorbing plate, is more effective than that of the devices with only one flow channel over or under the absorbing plate because the heat-transfer area in double-flow systems is double. The effect of the fraction of mass flow rate in the upper or lower flow channel of a double-flow device on collector efficiencies, has also been investigated theoretically and experimentally. Considerable improvement in collector performance is obtained by employing a double-flow type solar air heater, instead of using a single-flow device, if the mass flow rates in both flow channels are kept the same.     

住宅太阳热水器的技术经济性分析

以福州地区典型气象年逐时气象数据为基础,对平板型太阳热水器的热性能进行逐时模拟。利用综合能源价格法,分析集热器面积对太阳热水器经济性的影响,并比较各类热水器的技术经济性。在当前能源价格体系下,集热器面积为8.5m~2时,系统的年平均太阳能保证率最大(为67.72%);集热器面积为4m~2时,综合能源价格现值最小(为0.283$/kWh),此时系统的年平均太阳能保证率为62.65%。     

Performance evaluation of solar photovoltaic/thermal systems

The major purpose of the present study is to understand the performance of an integrated photovoltaic and thermal solar system (IPVTS) as compared to a conventional solar water heater and to demonstrate the idea of an IPVTS design. A commercial polycrystalline PV module is used for making a PV/T collector. The PV/T collector is used to build an IPVTS. The test results show that the solar PV/T collector made from a corrugated polycarbonate panel can obtain a good thermal efficiency. The present study introduces the concept of primary-energy saving efficiency for the evaluation of a PV/T system. The primary-energy saving efficiency of the present IPVTS exceeds 0.60. This is higher than for a pure solar hot water heater or a pure PV system. The characteristic daily efficiency η_s* reaches 0.38 which is about 76% of the value for a conventional solar hot water heater using glazed collectors (η_s*=0.50). The performance of a PV/T collector can be improved if the heat-collecting plate, the PV cells and the glass cover are directly packed together to form a glazed collector. The manufacturing cost of the PV/T collector and the system cost of the IPVTS can also be reduced. The present study shows that the idea of IPVTS is economically feasible too.