应尽快开展太阳热水器产品质量认证工作

通过对国外太阳热水器产品质量认证现状的分析，对我国开展太阳热水器产品质量认证工作提出了若干意见：实施太阳热水器产品质量认证具有诸多好处；我国开展太阳热水器产品质量认证的条件已经基本具备；太阳热水器产品质量认证了工作可以由中国节能产品认证中心承担；太阳能热水器产品质量认证工作应当统筹规划，逐步进行。     

Year-round performance of an improved collector-cum-storage type solar water heater

Systematic studies have been carried out on collector-cum-storage type solar water heaters, and efforts were made to minimise heat losses so that this type of water heater can be used for getting hot water at 40°–45°C for taking baths in the early morning hours of the next day. This paper reports year round performace, the performance equation and economics of this new improved solar water heater. This heater can supply 100 litres of hot water at 60°–70°C in the afternoon, and 40°–45°C temperature can be retained till next day morning. Its efficiency is 70.1%.     

Studies on collector-cum-storage type solar water heaters under arid zone conditions of india

Conventional natural circulation type solar water heaters are very costly. Though manufactured in India, they are beyond the reach of the common man. To reduce the cost, a collector-cum-storage type solar water heater has been developed and its detailed study has been carried out and reported. The heater can provide 100 1 of hot water at a temperature of 55–60°C in the evening which can be retained at 40–45°C until the next morning. The efficiency of the heater varies from 57.4 to 66.0 per cent depending on design parameters.     

Energy conservation and payback periods of natural circulation type solar water heaters

Energy savings in relation to different fuels, namely firewood, coal, kerosene, LPG and electricity have been calculated for a pressurized natural circulation type solar water heater with blackboard paint and a selective surface on the absorber. The payback periods have been computed by considering 10% compound annual interest, 5% annual maintenance cost and 5% inflation per year in maintenance cost and fuel prices. The cash flow has also been worked out for both solar water heaters. The cash flow is more for a solar water heater with a selective surface. The payback periods are 2.08–8.67 years for a solar water heater with a selective surface and 2.13–8.96 years for a solar water heater with blackboard paint. The estimated life of a heater is about 15 years. This shows that use of a solar water heater for heating water is very economical.     

A review of the performance of double pass solar air heater

Improvement of the thermal performance of a solar air heater can be obtained by enhancing the rate of heat transfer. The thermal efficiency of double pass solar air heater is higher in comparison to single pass with the concept involved of doubling the heat transfer area without increase in the system cost. Numbers of studies have been carried out on the performance analysis of double pass solar air heater provided with heat transfer augmentation techniques viz. using extended surfaces, packed bed, corrugated absorber were reported in the literature and found more increase in the thermal efficiency in comparison to conventional double duct solar air heater. These studies includes the design of double pass solar air heater, heat transfer enhancement, flow phenomenon and pressure drop in duct. This paper presents an extensive study of the research carried out on double pass solar air heater. Based on the literature review, it is concluded that most of the studies carried out on double pass solar air heater integrated with porous media and extended surfaces. Few studies were carried out with corrugated absorber. Further no study has been reported so far on double pass solar air heater with absorber plate artificially roughened from both the sides. Mathematical models based on energy analysis of some configurations of solar air heater have been discussed.     

Year round performance of a cylindrical solar water heater

A cylindrical collector-cum-storage type solar water heater has been designed, developed and tested. Its year round performance has been carried out and reported in this paper. The heater can provide 50 litres of hot water at 50–60°C in the afternoon and a temperature of 35°C can be retained till the next day for early morning use. The heater receives approximately 30% more radiation as compared to a flat surface. The economics of the heater has been worked out and it has been found that the cost can be recovered within one year.     

Experimental observations on a continuous flow type domestic solar water heater

The operation of a continuous flow type domestic solar water heater is explained with the help of a schematic diagram. Steady state thermal analysis of such a water heater is carried out. A water heater of this type with a collector area of 1 m² is subjected to tests. The experimental results are compared with predicted results. The experimental results have also been compared with those obtained from a water heater operating on thermosiphon flow. The performance of the continuous flow type water heater is shown to be comparable to that of the thermosiphon flow type. It is concluded that, in the Indian context, the continuous flow type water heater has more advantages than the thermosiphon flow type water heater in view of its low capital cost and the ease of operation and maintenance.     

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 .     

Year round performance studies on a built-in storage type solar water heater at Jodhpur, India

An improved solar water heater (capacity 901) made up of a 112×80×10 cm rectangular tank which performs the dual function of absorbing heat and storing the heated water has been designed and a prototype tested in Jodhpur. The performance tests carried out at the Central Arid Zone Research Institute, Jodhpur, indicate an efficiency factor reaching as high as 70 per cent. The year-round performance tests show that this heater can supply 901 of water at a mean temperature of 50 to 60°C in winter and 60 to 75°C in summer (measured at 4:00 p.m.). The performance tests also indicate that sufficient hot water can be obtained in the early morning if the heater is covered with an insulation blanket overnight or if the hot water is stored in an insulated tank.A performance equation for this type of heater, where the inputs are the solar intensity, ambient air temperature and geometry and material specifications of the heater, has also been developed. With this performance equation the optimum gap depth, i.e. the distance between upper and lower plate of the heater, has been found to be 10·0 cm.     

Long-term performance of solar-assisted heat pump water heater

A long-term reliability test of an integral-type solar-assisted heat pump water heater (ISAHP) was carried out. The prototype has been running continuously for more than 13,000 h with total running time >20,000 h during the past 5 yr. The measured energy consumption is 0.019 kWh/l of hot water at 57 ^oC that is much less than the backup electric energy consumption of the conventional solar water heater.     

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.     

Performance evaluation of hybrid PV/thermal water/air heating system: A parametric study

In this paper, a thermal model of an integrated photovoltaic and thermal solar (IPVTS) water/air heating system has been developed. An analytical expression for the temperature of solar cell and water and an overall thermal efficiency of IPVTS system have been derived as a function of climatic and design parameters. Numerical computations have been carried out for composite climate of New Delhi for parametric studies. Four configurations, namely (a) unglazed with tedlar (UGT), (b) glazed with tedlar (GT), (c) unglazed without tedlar (UGWT) and (d) glazed without tedlar (GWT) have been considered. Comparison of the IPVTS system with water and air heater has also been carried out. It is found that the characteristic daily efficiency of IPVTS system with water is higher than with air for all configurations except GWT. It is also observed that an overall thermal efficiency of IPVTS system for summer and winter conditions is about 65% and 77%, respectively.     

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 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.     

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.     

Exergy analysis of integrated photovoltaic thermal solar water heater under constant flow rate and constant collection temperature modes

In this communication, an analytical expression for the water temperature of an integrated photovoltaic thermal solar (IPVTS) water heater under constant flow rate hot water withdrawal has been obtained. Analysis is based on basic energy balance for hybrid flat plate collector and storage tank, respectively, in the terms of design and climatic parameters. Further, an analysis has also been extended for hot water withdrawal at constant collection temperature. Numerical computations have been carried out for the design and climatic parameters of the system used by Huang et al. [Huang BJ, Lin TH, Hung WC, Sun FS. Performance evaluation of solar photovoltaic/thermal systems. Sol Energy 2001; 70(5): 443–8]. It is observed that the daily overall thermal efficiency of IPVTS system increases with increase constant flow rate and decrease with increase of constant collection temperature. The exergy analysis of IPVTS system has also been carried out. It is further to be noted that the overall exergy and thermal efficiency of an integrated photovoltaic thermal solar system (IPVTS) is maximum at the hot water withdrawal flow rate of 0.006 kg/s. The hourly net electrical power available from the system has also been evaluated.     

A review of: “World Energy Supply: Resource,Technologies” Perspectives MANFRED GRATHWOHL

A theoretical model for unsteady one-dimensional temperature field inside the hot-water storage tank of a thermosyphonic solar system is carried out. Hot water flows into a vertical storage tank via its top central line at low constant rates. The measured temperature profiles along the central axis inside the storage tank of a V-trough thermosyphonic solar heater are observed to be in line with the analytical predictions. The linearity of the temperature profiles as checked experimentally is distinctly observed for high inflow velocities of the hot water into the storage tank.     

Energy conservation and field performance of a natural circulation type solar water heater

A natural circulation type solar water heater has been fabricated and installed at the CAZRI Guest House. Its field performance has been evaluated. The heater provides 2001 of hot water at 50–60 °C at all times. This solar water heater is economical.     

Effect of artificial roughness on heat transfer and friction factor in a solar air heater

Convective heat transfer coefficient between absorber plate and air in a flat-plate solar air heater can be enhanced by providing the absorber plate with artificial roughness. An investigation of fully developed turbulent flow in a solar air heater duct with small diameter protrusion wires on the absorber plate has been carried out and expressions for prediction of average Stanton number and average friction factor have been developed. The results of these expressions have been compared with available data. The results have been found to compare with a mean deviation of 6.3% for friction factor and −10.7% for the Nusselt number. The effect of height and pitch of the roughness elements on the heat transfer rate and friction has also been investigated.     

分体式家用太阳热水器

指出了传统太阳热水器存在的一些问题,为克服太阳热水器在高层建筑应用中受到的限制,研制了 一种靠重力循环的分体式家用太阳热水器。在冬季,用集中供暖系统中的热水为辅助热源加热蓄热水箱中的 水,以解决仅利用太阳能加热供水温度太低的问题,与利用辅助电加热相比,可降低运行费用。