Solar energy for the Australian food processing industry

Since the cost effectiveness of solar heat generating systems decreases as the temperature increases, the potential for large-scale use of solar energy for industrial processes is very dependent on the operating temperature of the process. Examination of a sample of the Australian food processing industry has shown that 70 per cent of the heat is used at temperatures below 100°C and there is no significant usage above 150°C. A feasibility study of a typical plant in Melbourne shows that it is technically practicable to phase solar energy heating systems into existing processes, and that using known techniques over 30 per cent of the annual heat requirements could be provided by solar collectors. The roof area is adequate for the mounting of collectors but space must be found for insulated hot water tanks to provide thermal storage. Since the gross return on investment in the solar installation is the value of the fuel saved, this directly related to fuel prices. In a situation where energy prices are changing rapidly, recommendations on cost effectiveness have no lasting significance. The paper describes simple methods of making accurate predictions for specific situations so that plant owners and operators can make their own judgements on cost effectiveness.     

Theoretical variations of the thermal performance of different solar collectors and solar combi systems as function of the varying yearly weather conditions in Denmark

The thermal performances of solar collectors and solar combi systems with different solar fractions are studied under the influence of the Danish design reference year, DRY data file, and measured weather data from a solar radiation measurement station situated at the Technical University of Denmark in Kgs. Lyngby. The data from DRY data file are used for any location in Denmark. The thermal performances of the solar heating systems are calculated by means of validated computer models. The measured yearly solar radiation varies by approximately 23% in the period from 1990 until 2002, and the investigations show that it is not possible to predict the yearly solar radiation on a tilted surface based on the yearly global radiation.The annual thermal performance of solar combi systems cannot with reasonable approximation be fitted to a linear function of the annual total radiation on the solar collector or the annual global radiation. Solar combi systems with high efficient solar collectors are more influenced by weather variations from one year to another than systems with low efficient solar collectors.The annual thermal performance of solar collectors cannot be predicted from the global radiation, but both the annual thermal performance and the annual utilized solar energy can with a reasonable approximation be fitted to a linear function of the yearly solar radiation on the collector for both flat plate and evacuated tubular solar collectors. Also evacuated tubular solar collectors utilize less sunny years with large parts of diffuse radiation relatively better than flat plate collectors.     

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.     

Status and prospects of local solar heating and cooling systems

In this paper, a state-of-the-art of solar heating and cooling systems is presented. Solar air heaters and different types of solar water collectors are discussed in detail. Storage systems including water, rocks, and heat-of-fusion salts are described as are space heating systems employing solar air heaters, in conjunction with rock or heat-of-fusion salt storage, and the use of water collectors plus hot water storage for space heating and domestic hot water. An indication of the commercialization of various space-heating systems and broad economic projections are presented. The three major solar cooling methods—absorption cooling, solar mechanical systems, and those involving humidification-dehumidification cycles—are also discussed in detail. Finally, an overview of solar heating and cooling activities in Kuwait is also given.     

Analysis and optimization of solar hot water systems

Use of a simplified method has been made to calculate the time-dependent thermal performance of various solar domestic hot water systems. to establish the value of solar hot water systems under given economic considerations a thermal analysis was carried out on three basic energy system designs, operating at several locations in the Federal Republic of Germany (F.R.G.) with various solar collectors. It is found that systems design can result in variations up to a factor of two in the per cent solar output. the location and year of operation in the F.R.G. result in variations up to 15 per cent in the solar output. A sensitivity study was also done with respect to all solar collector, systems and user parameters. From this it was found that the dominant effects on the systems performance were due to the collector-dependent parameters.     

Solar heat gains through train windows: a non-negligible contribution to the energy balance

The sector of transportation accounts for about one third of the total energy consumption in Switzerland. A monitoring campaign of the energy consumption of a regional train revealed the critical energy-consuming systems. Heating, cooling and ventilation were identified as major consumers. Windows are a source of non-controlled heat transfer. In summer, it may result in overheating leading to larger cooling loads while in winter, it is an important source of thermal losses. Selective double glazing and solar protection coatings can reduce these effects. Angular-dependent optical properties of a selective double glazing have been measured, and the solar heat gain coefficient (g value) was determined. An estimation of the solar gains received by a panoramic waggon was performed using the monitored solar irradiation and the measured properties of the glazing. These data were compared to the heating and cooling energy consumption monitored in this waggon. Solar gains were found to be in the same order of magnitude that the heating energy during some sunny days. They were also compared to the estimated thermal losses through the glazing and the entire envelope. These results show that the solar gains play a non-negligible role in the energy balance of the waggon. Furthermore, thermal simulations were performed to evaluate the solar gains in different conditions. It showed that 7 to 13% of energy can be saved using the glazing adapted to the climatic conditions. In addition, improving the thermal insulation of the train envelope or equipping the train with an efficient heat recovery system can lead to significant energy savings.     

Comparison of heating and natural ventilation in a solar house induced by two roof solar collectors

In this paper, two kinds of roof solar collectors (RSCs), namely, the single pass RSC, and the double pass RSC are analyzed and compared. The double pass roof solar collector, which is configured by integrating a double pass solar air collector with the building roof, can be operated more efficiently for space heating in winter, and for natural ventilation in other seasons. To evaluate the effects of two RSCs for both space heating and natural ventilation, a single traditional Chinese style house, on which the two RSCs will be mounted respectively, is developed. Through comparison, it is found that the instantaneous efficiency of solar heat collecting for the double pass RSC is higher than that of the single pass one by 10% on average, and natural ventilation air mass flow rate contributed by natural ventilation for the double pass RSC can be improved to a great extent for most cases, indicating that double pass RSC is superior to the single pass one from the points of view of both space heating and natural ventilation. The double pass RSC is therefore more potential for improving indoor thermal environment and energy saving of buildings.     

无盖板渗透型太阳能空气集热器热性能的实验研究

无盖板渗透型太阳能空气集热器是一种易于实现建筑一体化的高效新风预热及干燥装置。为了掌握无盖板渗透型集热器在实际工况下的热性能,建造了集热面积为2.2 m2的太阳能空气加热系统实验台,并在2009年2月至2009年4月对其热性能进行了户外瞬态实验研究。实验结果表明出口空气温度随辐射强度的增加而升高,太阳辐射强度是影响集热器出口空气温度的最重要因素,而室外空气温度的影响极小。空气温升随风量的增加而减小,集热器热效率随风量的增加而增大。在三个测试日中集热器的平均热效率分别为58%、63%和72%,高于普通平板太阳能空气集热器。     

Climatic predispositions of Yugoslavia for solar energy application

This paper is a summary report of an extended investigation of the practical usability of solar energy in Yugoslavia. The main tool for calculation was TRNSYS simulation program. Meteorological data and technical parameters of typical commercial solar devices were used as input data. Solar flux data on tilted planes were obtained by means of the Liu and Jordan method. For five locations, chosen to characterize all typical climatic regions in Yugoslavia, a detailed hour by hour simulation of the performance of the typical commercial domestic hot water solar heating system (DHW) was carried out. In summer the efficiency of such a device was similar for all locations, ranging from 40 to 45 per cent. In the winter months the efficiency varied from 30 per cent in sunny coastal regions to less than 10 per cent in poluted urban areas. The same type of calculations were worked out for a combined solar-traditional space-heating system, including the investigation of the influence of some important parameters on the efficiency of the solar part of the system. Calculations show that in every polluted urban areas only low-temperature load heat exchangers are to be recommended; in the coastal and southern parts of the country, however, higher working temperature (50°C) is allowed which results in the average efficiency of the system of more than 25 per cent even if the worst month and even if the ordinary black-paint, double glazed collectors are used.     

Solar cooling system using concentrating collectors for office buildings: A case study for Greece

On a European level there is intense research activity to broaden the applications of solar thermal systems beyond their established domains (hot water, space heating support) and to foster their participation in the energy maps of the EU-Member States. Concentrated Solar Thermal (CST) systems are expected to play a key role in this effort, especially for achieving the medium and high temperatures needed, for electricity generation, for industrial applications but also for hybridized solar heating/cooling and desalination applications.This paper presents a proposal for implementation of a CST system in the building sector, based on a research carried out in the Laboratory of Environmental and Energy Efficient Design of Buildings and Settlements at the University of Thrace. Specifically, an integrated solar cooling system using parabolic trough solar collectors and double-effect chiller is discussed, used to cover the cooling needs of typical office building in Greece.As it was shown, the use of concentrating solar collectors leads to significantly higher output temperatures that can enable the use of two stage absorption chillers with a higher COP. Alternatively, when low or medium temperature heat is required, the use of CST systems takes less space to cope with it than traditional flat plate collectors. The combination of these parameters can contribute to removing key barriers associated with the broader diffusion of solar cooling technology, enhancing the potential to become more competitive to the conventional air conditioning technologies.     

强制循环式太阳热水系统动态特性分析

基于集热器，水箱及换热器等部件热,地晴天无负荷条件下运行的强制循环式太阳能热水系统进行数值模拟，分析了贮热水箱内温度分层，水量，高径比和水流率等对瞬时集热效率和系统日效率的影响。特别探讨了带热交换器的复合回路系统在两种介质热容流率比值改变时，系统热性能变化规律。对设计和控制运行强制循环式太阳热水系统提出了一些建议。     

Perspectives for solar thermal applications in Taiwan

Taiwan has long depended on imported fossil energy. The government is thus actively promoting the use of renewable energy. Since 2000, domestic installations of solar water heaters have increased substantially because of the long-term subsidies provided for such systems. However, data on the annual installation area of solar collectors in recent years indicated that the solar thermal industry in Taiwan has reached a bottleneck. The long-term policy providing subsidies must thus be revised. It is proposed that future thermal applications in Taiwan should focus on building-integrated solar thermal, photovoltaic/thermal, and industrial heating processes. Regarding building-integrated solar thermal systems, the current subsidy model can be continued (according to area of solar collectors); nevertheless, the application of photovoltaic/thermal and industrial heating systems must be determined according to the thermal output of such systems.     

Mathematical modeling and thermal performance analysis of unglazed transpired solar collectors

Unglazed transpired collectors or UTC (also known as perforated collectors) are a relatively new development in solar collector technology, introduced in the early nineties for ventilation air heating. These collectors are used in several large buildings in Canada, USA and Europe, effecting considerable savings in energy and heating costs. Transpired collectors are a potential replacement for glazed flat plate collectors. This paper presents the details of a mathematical model for UTC using heat transfer expressions for the collector components, and empirical relations for estimating the various heat transfer coefficients. It predicts the thermal performance of unglazed transpired solar collectors over a wide range of design and operating conditions. Results of the model were analysed to predict the effects of key parameters on the performance of a UTC for a delivery air temperature of 45–55 °C for drying applications. The parametric studies were carried out by varying the porosity, airflow rate, solar radiation, and solar absorptivity/thermal emissivity, and finding their influence on collector efficiency, heat exchange effectiveness, air temperature rise and useful heat delivered. Results indicate promising thermal performance of UTC in this temperature band, offering itself as an attractive alternate to glazed solar collectors for drying of food products.The results of the model have been used to develop nomograms, which can be a valuable tool for a collector designer in optimising the design and thermal performance of UTC. It also enables the prediction of the absolute thermal performance of a UTC under a given set of conditions.     

A heating system using flat plate collectors to improve the inside greenhouse microclimate in Morocco

The use of solar flat plate collectors for heating agricultural greenhouses has proved to be interesting. Their efficiency depends at the same time upon the ambient climatic conditions and the thermal performances of solar collectors. In this study, we present the thermal results relative to the effect of the heater system on the microclimate greenhouse and the agronomic results of the greenhouse culture of melon. These results are of a big interest because, compared to a unheated greenhouse, a precocity of 14 days has been obtained, and a high homogeneity of melon grades has been observed. We also notice that, for the same density of plantation, a very good gain average in weight per plant has been recorded in the heated greenhouse.     

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 advantages for solar heating systems with a glass cover with antireflection surfaces

Investigations elucidate how a glass cover with antireflection surfaces can improve the efficiency of a solar collector and the thermal performance of solar heating systems. The transmittances for two glass covers for a flat-plate solar collector were measured for different incidence angles. The two glasses are identical, except for the fact that one of them is equipped with antireflection surfaces by the company SunArc A/S. The transmittance was increased by 5–9%-points due to the antireflection surfaces. The increase depends on the incidence angle. The efficiency at incidence angles of 0° and the incidence angle modifier were measured for a flat-plate solar collector with the two cover plates. The collector efficiency was increased by 4–6%-points due to the antireflection surfaces, depending on the incidence angle. The thermal advantage with using a glass cover with antireflection surfaces was determined for different solar heating systems. Three systems were investigated: solar domestic hot water systems, solar heating systems for combined space heating demand and domestic hot water supply, and large solar heating plants. The yearly thermal performance of the systems was calculated by detailed simulation models with collectors with a normal glass cover and with a glass cover with antireflection surfaces. The calculations were carried out for different solar fractions and temperature levels of the solar heating systems. These parameters influence greatly the thermal performance associated with the antireflection surfaces.     

Yearly average performance of the principal solar collector types

The results of hour-by-hour simulations for 26 meteorological stations are used to derive universal correlations for the yearly total energy that can be delivered by the principal solar collector types: flat plate, evacuated tubes, CPC, collectors that track about one axis, collectors that track about two axes, and central receiver.The correlations are polynomials of first and second order in yearly average insolation, latitute, and threshold (= ratio of heat loss and optical efficiency). With these correlations the yearly collectible energy can be found by reading a single graph and multiplying the coordinates by the collector parameters. This simple method reproduces the results of hour-by-hour computer calculations with an accuracy (rms error) of 2 per cent for flat plates and 2–4 per cent for concentrators.This method can be applied to any system where the collectors operate year-round in such a way that no collected energy is discarded. This includes photovoltaic systems; solar-augmented industrial process heat systems; and solar thermal power systems. In addition, the method is recommended for rating collectors of different types or different manufacturers on the basis of yearly average performance. The method is also useful for evaluating the effects of collector degradation, the benefits of collector cleaning, and the gains from collector improvements (due to enhanced optical efficiency or decreased heat loss per absorber surface). For most of these applications, the method is accurate enough to replace a system simulation.     

Design of a solar collector for year-round climatization

Solar heating systems in buildings have increasingly been studied in the past two decades. In several applications the primary energy demand is now for both heating and cooling, and modern solar collectors should be designed to provide climatization during the whole year. Solar systems are seldom applied in Europe, and large buildings, such as office buildings and schools, continue to be built with mechanical ventilation systems.The study presented in this paper is part of a European XVII Thermie project entitled “Pilot project for photovoltaic, energetic and biohousing retrieval in a school”, whose aim was to install a photovoltaic plant and solar air collectors coupled with a sun breaker structure at a scientific high school in Umbertide, in central Italy.This paper describes the research and development activities concerning a solar air collector suited for winter heating and summer ventilation, which was installed at the high school. The collector physical and numerical modelling of heat transfer and fluid flow in winter operation is presented. The system performance has been estimated as a function of different parameters in order to provide a tool for the design process. Furthermore, the climate in the area has been simulated through the available experimental data, and the system behavior under these conditions is presented.The collectors were installed at the scientific high school in Umbertide in spring 2001. Summer ventilation cooling is under testing and an experimental test period is foreseen next winter to validate the design of the collectors and their performance.     

A solar thermal cooling and heating system for a building: Experimental and model based performance analysis and design

A solar thermal cooling and heating system at Carnegie Mellon University was studied through its design, installation, modeling, and evaluation to deal with the question of how solar energy might most effectively be used in supplying energy for the operation of a building. This solar cooling and heating system incorporates 52 m² of linear parabolic trough solar collectors; a 16 kW double effect, water-lithium bromide (LiBr) absorption chiller, and a heat recovery heat exchanger with their circulation pumps and control valves. It generates chilled and heated water, dependent on the season, for space cooling and heating. This system is the smallest high temperature solar cooling system in the world. Till now, only this system of the kind has been successfully operated for more than one year. Performance of the system has been tested and the measured data were used to verify system performance models developed in the TRaNsient SYstem Simulation program (TRNSYS). On the basis of the installed solar system, base case performance models were programmed; and then they were modified and extended to investigate measures for improving system performance. The measures included changes in the area and orientation of the solar collectors, the inclusion of thermal storage in the system, changes in the pipe diameter and length, and various system operational control strategies. It was found that this solar thermal system could potentially supply 39% of cooling and 20% of heating energy for this building space in Pittsburgh, PA, if it included a properly sized storage tank and short, low diameter connecting pipes. Guidelines for the design and operation of an efficient and effective solar cooling and heating system for a given building space have been provided.