House walls as passive solar collectors: An assessment

The gross solar energy falling on a typical house during the heating season is greater than the space heating requirement. Conventional solar collectors produce hot water, which is then used to meet the domestic hot water and space heating requirements of the house. Such collectors, however, are expensive, and it is only possible to use them to collect a small proportion of the available solar energy. This paper looks at an alternative approach of using the entire wall surface as a passive solar collector, by using an external layer of translucent insulation. Measurements and calculations are reported which show that a wall with a double-glazed outer layer would be expected to show a zero net heat loss over the heating season. This is not considered to be sufficient advantage to overcome the cost and other problems associated with the system.     

Computational evaluation of solar heating systems using concrete solar collectors

This paper uses the F-chart technique to evaluate three types of solar heating systems, namely; space solar heating and domestic hot water system (SHDHW), domestic hot water system (DHW) and solar swimming pool heating system (SPHS), using three types of concrete solar collectors, models A, B, and C, and one conventional metallic solar collector.

The economical analysis of SHDHW system revealed that the concrete collectors provided about 49 and 63% of the annual load when the collecting area of the solar panel increased from 55 to 88 M² (25 to 40% of the building roof area). The corresponding solar contributions when conventional metallic collectors were used are 41 and 53%, respectively. This represents an improvement of the annual solar fraction of about 19% when concrete collectors are used instead of the metallic collectors.

It was found that solar heating systems with concrete solar collector models gave higher solar fractions and total life cycle savings than the conventional solar metallic collector.     

Thermal and exergy analysis of solar air collectors with passive augmentation techniques

One of the main disadvantages of solar air collectors in practical applications is their relatively low efficiency. In this experimental investigation, the shape and arrangement of absorber surfaces of the collectors were reorganised to provide better heat transfer surfaces suitable for the passive heat transfer augmentation techniques. The performance of such solar air collectors with staggered absorber sheets and attached fins on absorber surface were tested. The exergy relations are delivered for different solar air collectors. It is seen that the largest irreversibility is occurring at the conventional solar collector in which collector efficiency is smallest.     

Performance simulation of solar collectors made of concrete with embedded conduit lattice

A solar collector made of a lattice of fluid conduits embedded within a thin concrete slab is investigated. Such a configuration can be constructed to withstand some mechanical strain by reinforcing the concrete with glass fibers. This collector can be integrated within construction elements of buildings and therefore offers means for low-cost solar energy collection. The geometry of such a collector as well as its characteristic parameters are different from the conventional flat-plate thin-fin collector. Its performance cannot therefore be accurately predicted by assuming a thin-fin behavior. It requires a different and somewhat more involved thermal analysis. In the present analysis, a numerical solution of a two-dimensional cross-sectional slice is expanded in the longitudinal direction by superpositioning such slices in tandem. A parametric study of the relative influence of various operational, geometrical and material parameters is presented. The study provides the tools for a feasibility study of such collectors. Transient characteristics of the collector's dynamic response during a typical summer day with continuous or intermittent radiation are also presented.     

Testing of solar collectors

In order that tests on different solar collectors conducted at different times shall be comparable, it is necessary that the test define the governing equation of the collector. This involves measurements at different solar intensities, different operating temperatures and different flow rates.The paper describes the theory and the experimental procedure which involves connecting, say, four similar collectors in series and measuring the temperature rise across each collector. Since, at any instant of time, the flow rates and the solar intensity are identical for all the collectors, a number of points on the efficiency-temperature curve are obtained from which the characteristic equation of the collectors is readily established. Rules are established to limit the temperature rise permitted and a “standard” day is suggested to provide a quick comparison basis.     

Daily efficiency of solar collectors

It is shown that the daily efficiency of flat-plate solar collectors working at constant flow rate can be evaluated with a simple algorithm when their structural features are known. It is also shown that long-term performances can be calculated starting from monthly values of global radiation.     

Thermosyphon circulation in solar collectors

Theoretical predictions of flow rate in thermosyphon solar collectors are compared with experimental measurements obtained using a laser doppler anemometer. Modifications to the usual method of analysis are proposed to improve the accuracy of the predictions, and the results are compared with flow rate predictions and measurements in other investigations.     

Engineering of solar photocatalytic collectors

This paper briefly describes the different collectors used in solar photocatalysis for wastewater treatment and, based on prior experience, the main advantages and disadvantages of each. As the tubular-shape reactor configuration is the most appropriate for handling and pumping water, the compound parabolic collector (CPC) is proposed as an interesting combination of parabolic concentrators and flat static systems and constitutes a good option for solar photochemical applications. The design of compound parabolic concentrators for solar photocatalytic applications is described in detail and 25–50 mm is proposed as the optimum photoreactor diameter, based on the optical characteristics and optimum concentration of the two photocatalytic systems (TiO₂ and photo-Fenton) that can be used with sunlight for wastewater treatment. It has been demonstrated that since aluminium is the only metal that is highly reflective in the ultraviolet spectrum of solar radiation, aluminium-based mirrors are the best option. But, especially when exposed to outdoor conditions, aluminium must be protected and, therefore, at the present time, anodised and electropolished aluminium surfaces are considered the most suitable solutions. As the photochemical reactor contain the working fluid, including the catalyst, it must transmit UV sunlight efficiently and be able to work under enough pressure to handle the high volumes resulting from the large number of collectors in an industrial treatment plant, only low-iron glass is proposed as feasible for constructing the photoreactor (collector absorbers). Finally, ray-tracing algorithm simulations are presented as a design tool for the optical configuration of a particular reactor, drawing conclusions for its improvement and assisting in final engineering decision-making.     

CPC在太阳能集热器中的应用

CPC复合抛物聚光器是一种非成像低聚焦度的聚光器,它根据边缘光线原理设计,可将给定接收角范围内的入射光线按理想聚光比收集到接收器上。由于它有较大的接收角,故在运行时不需要连续跟踪太阳,只须根据接收角的大小和收集阳光的小时数,每年定期调整倾角若干次就可有效的工作。它可达到的聚光比在10以内,当聚光比在2以下时可做成固定式装置。它可接收直射太阳辐射和部分散射辐射,并能接收一般跟踪聚光器所不能接收的“太阳周围辐射”。此类集热器的结构比较简单,对聚光面型加工精度要求不严格,将其应用在太阳能集热器中,是一个值…     

Optimal operation of solar collectors

Optimal operation of a solar collector is investigated in terms of exergy delivery of the collector. Using the Bliss equation for the collector, an approximate exergy equation is derived and, through this equation, the optimal mass flow rate, and optimal inlet and outlet temperatures are obtained. The approximate equation is also compared with the non-linear exergy delivery equation of the collector.     

Testing solar collectors as an energy source for a heat pump

The article presents the experimental study of a heat pump possessing solar collectors as an energy source. A method to test the combined work of collectors delivering heat to the evaporator of a heat pump was devised. The layout of the test facility is shown and the system construction with the measurement equipment is described. The planning experiment to test the installation was chosen. The medium fluid condenser temperature , the fluid condenser mass flow rate and the medium fluid evaporator temperature were chosen as experiment factors to determine both objective functions—the coefficient of performance (COP) of the heat pump and the efficiency of the system η_s. The reverberation of both objective functions is shown.     

Optimum exergy efficiency of solar collectors

An optimum exergy efficiency is derived for flat-plate solar collectors as a ratio of exergy delivery of the collector to the maximum output exergy obtainable. It is a function of the optimum mass flow rate through the collector, which itself is obtained through an optimization of the exergy delivery of the collector.     

Mirror enclosures for double-exposure solar collectors

A conventional flat-plate collector panel can be employed in a double-exposure configuration when the panel is glazed on both sides and when mirrors are provided to reflect solar radiation onto the back side of the panel. In this paper, several flat-mirror configurations are evaluated and optimal configurations are determined for different solar energy applications at lat. 35, 40 and 45°. The various mirror configurations are evaluated theoretically by calculating direct-beam and diffuse solar radiation enhancement factors. The enhancement factors are defined as the ratio of the solar flux absorbed by both sides of a double-exposure panel to that absorbed by an identical single-exposure panel tilted at the latitude angle from the horizontal. The enhancement factors are calculated using the method of images and take account of the variation of glazing transmittance with incident angle. Optimal mirror configurations were determined for direct-beam solar radiation for both fixed-mirror configurations and adjustable-mirror configurations with semi-annual mirror rotations. Optimal fixed-mirror configurations were obtained for both winter space-heating and year-round applications. An adjustable-mirror configuration, however, was determined to be optimal for year-round solar collection and overall to be most adaptable to a variety of solar energy applications. The same adjustable-mirror configuration was determined to be optimal at all three latitudes and therefore a single design can be employed at diverse locations.     

Planar concentrators for flat-plate solar collectors

A systematic study has been made of the effectiveness of planar specular reflectors for solar energy collectors. Two daily averaged indices of performance were used. One, the area ratio, indicates the amount by which the reflector extends the effective receiver area. The other is the enhancement factor, which is used to compare the energy received by an augmented collector with that by a reference collector at optimum tilt.

A reflector can be mounted either above or below a flat-plate collector. Both combinations are evaluated fully, by varying separately the angular position and dimensions of the reflector and of the collector. The principal parameters are identified and the main characteristics summarised as a series of performance curves. These curves provide an easy method for determining optimum reflector geometries.

Use of the performance curves may be extended to obtain the configuration of the two reflectors in a trough concentrator. This also allows the single-reflector system to be compared directly with the trough concentrator. Evidence is presented which shows the advantages of an asymmetrical trough configuration over a symmetrical concentrator.     

Façade solar collectors

Rational use of energy in buildings leads to a concept of active energy façades such as transparently insulated massive walls, solar thermal or PV façades, advanced glazings for daylighting purposes or double ventilated façades. The paper is concerned with the façade-integrated solar thermal collectors concept for water heating in the existing building stock in the Czech Republic (panel and brick blocks of flats), which are ready for major renovations. Thermal behavior of façade collectors compared with standard roof-located collectors in solar DHW systems was investigated. Façade solar collectors should have an area increased by approximately 30% to achieve the usual 60% solar fraction compared with conventional roof solar collectors with a 45° slope. Further increases in the solar fraction above 70% lead to a required area comparable with roof collectors but with less stagnation periods compared with roof collectors. Application of façade solar collectors affects the indoor comfort in buildings in a reasonable range. Indoor temperatures increase by no more than 1 K in all investigated configurations. Building behavior is not strongly affected by façade collectors when sufficient insulation layers are present.     

赛恩斯公司推出新型太阳能集热器实现太阳能与建筑完美结合

赛恩斯公司位于江苏省扬州市邗江区工业园,集科研、生产、工程设计和施工于一体,是一家拥有自主知识产权的技术创新型企业,被国家建设部授予中国建设科技自主创新优势太阳能利用企业称号。最近公司推出最新专利的产品——内插金属流道换热式全玻璃真空管集热器(专利号:ZL200520076208)     

Experimental performance of three solar collectors

Simultaneous testing of solar collectors is important for the determination of accurate comparative performance data. Three flat-plate solar collectors were tested for over six months: a water trickle collector, a typical collector with double glazing, and a thermal trap collector. The first two collector types have been previously tested by other investigators, but the development of the thermal trap collector is unique to New Mexico State University, where in 1964 work was initiated on this type of collector. The thermal trap collector employs a transparent solid (methyl methacrylate) adjacent to the fluid cooled collector plate. It is found that by the use of this transparent solid, which has a high transmittance of short wavelengths combined with a low transmittance of long wavelengths and a small thermal conductivity, high temperatures can be achieved.

The comparative collector tests were performed for a variety of operational conditions. The collector efficiencies were experimentally determined, and analysis of the collector losses was accomplished. The thermal trap collector was found to have a higher operational efficiency than the other collector types and is capable of collecting solar energy for a longer period of time each day. At operating temperatures above 145°F, the thermal trap collector is more than twice as efficient as the water trickle collector.     

Stationary mirror systems for solar collectors

An angle in solar geometry termed the EWV altitude is defined, and its variation with time and season is shown. This variation indicates the necessary acceptance angle of a stationary mirror system for solar collectors. It is shown that a completely stationary mirror cannot give any useful concentration, but that if the tilt is varied with the seasons, an eastwest cylindrical parabolic mirror without diurnal movement can yield a concentration of approximately three. This may be increased to about four with the aid of a small auxiliary (fixed) mirror to provide a second stage of optical concentration.