Effectiveness of solar water-heating systems

In order to protect the solar water heaters against freezing and corrosion, the antifreeze solutions are circulated in the collector loop and then in the second loop this fluid heats the water in a heat exchanger. For this two-loop system, the performance can be described in terms of effectiveness similar to that for conventional heat exchangers. In this note an attempt is made to combine the collector and heat exchanger effectivenesses into an overall effectiveness, which is useful to optimize and design the solar water heating systems. The study has also been extended to obtain an overall effectiveness for the three-loop system in which a heat exchanger is placed between the collector and store.     

Thermal performance of a water-phase change material solar collector

A new type of solar collector was developed and its short term thermal performance was investigated. The solar collector, which exhibited a net solar aperture area of 1.44 m², consisted of two adjoining sections one filled with water and the other with a phase change material with a melting and freezing range of about 45–50°C, i.e. paraffin wax in this study. The phase change material functioned both as an energy storage material for the stabilisation, theoretically, of the water temperature and as an insulation material due to its low thermal conductivity value. The results of the study indicated that the water temperature exceeded 55°C during a typical day of high solar radiation and it was kept over 30°C during the whole night. Covering the collector surface with an insulation blanket at a time when the water temperature was at its maximum improved the energy conservation of the water significantly. The instantaneous thermal efficiency values were between about 22% and 80%. The present solar collector was much advantageous over the traditional solar hot water collectors in Turkey in terms of total system weight and the cost in particular.     

Prospects for integrated storage collector systems in central Europe

The concept of an improved integrated storage collector is evaluated for Central European temperature and radiation conditions where integrated storage collector systems have so far not been used. The system studied works without a heat exchanger loop because care is being taken to prevent freezing. This is accomplished by a sufficiently large volume of water to provide inertia plus the use of high quality transparent insulation materials for the front cover. This extremely simple system is modelled using actual weather data for a year with exceedingly low temperatures. The conditions under which freezing is excluded are determined and the optimized system is evaluated for the entire year regarding solar fraction for a four person household and conversion efficiency. Also evaluated are different types of auxiliary heaters: Solar fraction ranges from 55.6 to 41.0% and efficiency from 35 to 26% for a 4 m² integrated storage collector. This is compared with other collector systems. It is found that the ISC is superior to active flat plate systems and thermosyphon systems. It is not as efficient as a very good system based on vacuum collectors.     

太阳集热器时间常数分析及测试讨论

时间常数作为集热器最重要的动态特性之一，表明了集热器对太阳辐照瞬变响应的快慢，时间常数的测试是集热器热性能测试的重要内容。本文在一阶系统基础上讨论了时间常数，提出了在集热器时间常数测量基础上，判定集热器与一阶系统的符合程度的方法。同时提出了当集热器很好的符合一阶系统时更准确得出时间常数的方法。     

整体式太阳热水器在寒冷气候条件下的冻结厚度与热损系数U值及水层深度的关系

利用一维焓法建立了第三类边界条件下有限厚度的水存在自然对流时的冻结过程的理论模型，并利用类似于反问题的方法。结合计算和实验的手段确定了热损系数U值，所建模型和计算结果通过不同的实验条件得到了验证。该模型可用来确定在寒冷气候条件下整体式（ICS）太阳热水器的冻结厚度与热损系数U值及水层深度的关系，并根据国内一些城市冬季的气象参数，给出了典型的计算结果，所得结果可对ICS太阳热水器的设计及对透明盖板材料和选择性涂层的选用提供参考。     

Experimental investigation and performance analysis on a solar adsorption cooling system with/without heat storage

A solar adsorption cooling system which can be switched between a system with heat storage and a system without heat storage was designed. In the system with heat storage, a heat storage water tank was employed as the link between the solar collector circulation and the hot water circulation for the adsorption chillers. However, the heat storage water tank was isolated in the system without heat storage, and the hot water was directly circulated between the solar collector arrays and the adsorption chillers. It was found that the inlet and outlet temperatures for the solar collector arrays and the adsorption chillers in the system without heat storage were more fluctuant than those of the system with heat storage. Also found was that the system with heat storage operated stably because of the regulating effect by the heat storage water tank. However, under otherwise similar conditions, the cooling effect of the system without heat storage was similar to that of the system with heat storage. Compared with the system with heat storage, the system without heat storage has the advantages of higher solar collecting efficiency as well as higher electrical COP.     

Thermodynamic design procedure for solid adsorption solar refrigerator

The thermodynamic design procedure for solid adsorption solar refrigeration is presented and applied to systems using activated carbon/methanol, activated carbon/ammonia and zeolite/water adsorbent/adsorbate pairs. The results obtained showed that zeolite/water is the best pair for air conditioning application while activated carbon/ammonia is preferred for ice making, deep freezing and food preservation. In all cases, the system depends strongly on adsorption and condensation temperatures and weakly on the evaporator temperature. The maximum possible net solar COP was found to be 0.3, 0.19 and 0.16 for zeolite/water, activated carbon/ammonia and activated carbon/methanol, respectively, when a conventional flat plate solar collector is used.     

Optimal design of orientation of PV/T collector with reflectors

Hybrid conversion of solar radiation implies simultaneous solar radiation conversion into thermal and electrical energy in the PV/Thermal collector. In order to get more thermal and electrical energy, flat solar radiation reflectors have been mounted on PV/T collector. To obtain higher solar radiation intensity on PV/T collector, position of reflectors has been changed and optimal position of reflectors has been determined by both experimental measurements and numerical calculation so as to obtain maximal concentration of solar radiation intensity. The calculated values have been found to be in good agreement with the measured ones, both yielding the optimal position of the flat reflector to be the lowest (5°) in December and the highest (38°) in June. In this paper, the thermal and electrical efficiency of PV/T collector without reflectors and with reflectors in optimal position have been calculated. Using these results, the total efficiency and energy-saving efficiency of PV/T collector have been determined. Energy-saving efficiency for PV/T collector without reflectors is 60.1%, which is above the conventional solar thermal collector, whereas the energy-saving efficiency for PV/T collector with reflectors in optimal position is 46.7%, which is almost equal to the values for conventional solar thermal collector. Though the energy-saving efficiency of PV/T collector decreases slightly with the solar radiation intensity concentration factor, i.e. the thermal and electrical efficiency of PV/T collector with reflectors are lower than those of PV/T collector without reflectors, the total thermal and electrical energy generated by PV/T collector with reflectors in optimal position are significantly higher than total thermal and electrical energy generated by PV/T collector without reflectors.     

Outdoor test method to determine the thermal behavior of solar domestic water heating systems

The dynamics of the market, the generation of new promotion programs, fiscal incentives and many other factors are to be considered for the massive application of solar domestic water heating systems (SDWHS) mainly of the compact thermosiphon type, makes it necessary to choose simple and inexpensive procedure tests that permit to know their characteristic thermal behaviors without an official standard being necessary. Moreover, it allows the comparison among systems and offers enough and reliable information to consumers and manufacturers.In most developing countries, an official national standard for SDWHS is not available, therefore it is necessary to adopt an international test procedure in which the cost and time of implementation is very important. In this work, a simple and inexpensive test method to determine the thermal behavior of SDWHS is proposed.Even though these procedure tests do not have an official standard structure they permit, by comparing different solar systems under identical solar, ambient, and initial conditions, the experimental determination of: (a) the maximum available volume of water for solar heating; (b) water temperature increment and available thermal energy at the end of the day; (c) temperature profiles (stratification) and the average temperature in the storage tank after it is homogenized; (d) the average global thermal efficiency; (e) water temperature decrement and energy lost overnight; and (f) the relationship between hot water volume and solar collector area as function of the average heating temperature. An additional proposed test permits to know the heat losses caused by the reverse flow in the collector loop. These tests will be carried out independently of the configuration between the solar collector and the storage tank, the way the fluid circulates and the type of thermal exchange. The results of this procedure test can be very useful, firstly, for the local solar manufacturers’ equipment in order to design and optimize its products comparing their systems against a reference system under identical test conditions and secondly, by the consumers in order to select the most suitable system. The resulting experimental data for a particular thermosiphon system is presented and discussed.     

Performance of Cylindrical Parabolic Collector with Automated Tracking System

Parabolic solar collector collects the radiant energy emitted from the sun and focuses it at a point. Parabolic trough collectors are the low cost implementation of concentrated solar power technology that focuses incident sun light on to a tube filled with a heat transfer fluid. However, the basic problem with the cylindrical parabolic collector without tracking was the solar collector does not move with the orientation of sun. Development of automatic tracking system for cylindrical parabolic collectors will increase solar collection as well as efficiency of devices. The main aim of this paper is to design, fabricate and analyze the performance of parabolic collector with automated tracking system. The automated tracking mechanism is used to receive the maximum possible energy of solar radiation as it tracks the path of sun. The performance of the parabolic trough collector is experimentally investigated with the water circulated as heat transfer fluid. The collector efficiency will be noted.