Showing papers by "Soteris A. Kalogirou published in 2012"

Modeling and simulation of passive and active solar thermal systems

Abstract: This chapter presents major passive solar technologies and systems, followed by in-depth sections on their modeling using both analytical and numerical models. Next, more recent developments are described with a focus on building-integrated photovoltaic/thermal systems and net-zero energy solar homes that combine passive and active systems to produce as much energy from sunlight as they consume in an average year. The proper sizing of the components of an active solar system is a complex problem that includes both predictable and unpredictable parameters. Predictable parameters are related to the performance characteristics of the collector and other components, and the unpredictable parameters mainly concern weather data (solar radiation, ambient temperature, wind speed, and direction). In the second part of this chapter, various design methods are presented as well as an overview of the simulation techniques and programs suitable for active solar heating and cooling systems. The design methods presented include the f-chart and utilizability methods. For more detailed results, modeling and simulation is used. The software programs described briefly in this chapter include F-chart, TRNSYS, and WATSUN.

Solar Selective Coatings

Abstract: Solar selective coatings are used on photothermal absorbers of solar systems. They enhance the efficiency of photothermal conversion, especially at elevated temperatures, by the reduction of thermal radiation losses. The spectral selectivity of the absorber is determined by its high ‘absorptance’ α in the short-wavelength region of the solar radiation of about 0.3–3 μm and low ‘emittance’ e at the far-infrared region of the spectrum corresponding to the blackbody thermal emittance at the operating temperature of the absorber. Typical values for these properties of selective surfaces are 0.90 for absorptance and 0.10 for the emittance. ‘Selectivity’ is defined as the ratio α/ e .

Solar Space Heating and Cooling Systems

Abstract: This chapter examines solar space heating and cooling systems. Initially, the basic system configurations are presented which include active solar systems in which direct circulation systems, indirect water-heating systems, and air water-heating systems are presented; space heating and service hot water systems which include air and water systems, issues concerning the location of auxiliary and heat pump systems; and solar cooling, which includes adsorption units, absorption units, lithium--water absorption systems, ammonia--water absorption systems, and solar cooling with absorption refrigeration. Subsequently, heat storage systems are examined which include air and liquid systems thermal storage. Finally, details of various aspects of system design are presented which include module and array design, heat exchangers, and differential temperature controllers.

Low Concentration Ratio Solar Collectors

Abstract: This chapter presents a review of low concentration ratio solar collectors. The concentration ratio ( C ) of the collectors belonging in this category is not more than about 10. Because of the low concentration ratio, these collectors usually collect both direct and diffuse solar radiation. According to their concentration ratio, these collectors can be steady ( C < 2) or tracking. When tracking is used and depending on the concentration ratio, this can be intermittent as high accuracy is usually not required. The frequency of tracking increases with the concentration ratio. Higher concentration ratio leads not only to higher collector operating temperature but also to higher tracking accuracy requirements. The types of collectors examined in this chapter are the flat-plate collectors with diffuse reflectors, the reverse flat-plate collector, the compound parabolic collector (CPC), and various designs applied to evacuated tube collectors (ETCs) with either external or internal reflectors. One type of cusp concentrator, which is used in integrated collector storage (ICS) systems, is also examined.

Solar thermal systems: Components and applications - introduction

Abstract: This chapter is the introduction of the volume on ‘Solar Thermal Systems: Components and Applications’. It initially examines energy-related environmental problems, which include acid rain, ozone layer depletion and global climate change, and how renewable energy technologies can be used to avoid these problems. Subsequently, the chapter examines the environmental characteristics of solar energy in terms of basic relations used to determine the position of the sun on the sky. Therefore, the chapter includes an analysis of the equation of time, longitude correction, solar angles, the incidence angle for fixed and moving surfaces, and finally presents easy ways to determine the basic sun angles using sun path diagrams. This is followed by an analysis of the solar radiation and, in particular, thermal radiation and transparent plates, which are two subjects that are of interest to the people dealing with the design of solar systems. Finally, the solar resource is examined. The operation of solar collectors and systems depends on the solar radiation input and the ambient air temperature and their sequences. These and other meteorological parameters are usually provided in terms of the typical meteorological year and the generation of such years from raw data is given.

Combination of taguchi method and artificial intelligence techniques for the optimal design of flat-plate collectors

Abstract: In this paper, artificial neural networks (ANNs) and genetic algorithms (GAs) are used for the design of solar flat-plate collectors. It is proved in this paper that by using the Taguchi method for selecting the data required for training the ANN is very effective in allowing the network to learn the behavior of the system satisfactorily. The parameters on which the flat-plate collector design depends are the collector tube material, the type of collector absorbing plate material, the number of collector riser tubes, the collector riser tube diameter, the type of absorber coating and the thickness of the bottom insulating material. By using the method of Taguchi experiments three levels of six variables were used together with three levels of available solar radiation intensity (Gt) and collector inlet minus ambient temperature difference to estimate the collector thermal efficiency. Thus a total of 162 patterns were collected from these combinations from which 130 were used for the training of the ANN and the rest 32, selected randomly, were used to validate the training accuracy. The input parameters are the factors on which the collector performance depends, listed above, and the output parameters are the collector optical efficiency and the loss coefficient. The trained ANN was then used with a genetic algorithm to find the optimum combination of the values of the input parameters, which maximizes the collector efficiency estimated from the optical efficiency and the loss coefficient. The results obtained are very similar to the results achieved by other researchers using much complicated optimization methods, whereas the present method not only is very accurate but it is also very quick.

Building integration of renewable energy systems towards zero or nearly zero energy buildings

Abstract: With buildings accounting for 40% of primary energy requirements in EU and the implementation of the Energy Performance of Buildings Directive (EPBD), developing effective energy alternatives for buildings is imperative. The increasing role for renewables implies that solar thermal systems (STS) and photovoltaics (PV) will have a main role as they contribute directly to the heating and cooling of buildings and the provision of electricity and domestic hot water. Meeting building electrical and thermal loads will be primarily achieved through an extensive use of renewables, following standard building energy saving measures, such as good insulation or advanced glazing systems. These systems are typically mounted on building roofs with no attempt to incorporate them into the building envelope creating aesthetic challenges, space availability issues and envelope integrity problems. This paper aims to give a survey of possible solutions of PV and STS integration on the building roofs and façades. The advantages of integration are quantified and suggestions are given to address the possible problems created.

Evaluation of a parabolic trough collector performance

Abstract: In this paper the collector erected at the Archimedes Solar Energy Laboratory is initially presented followed by the performance evaluation of the collector. The collector is made by Nep Solar from Australia. It has an aperture area of 14.4 m, a concentration ratio of 13.7 and can be operated up to 200°C. The collector aperture is 1208 mm and the receiver pipe is stainless steel 304 L with a diameter of 28mm, coated with selective coating having an absorptance of 0.93 and an emitance of 0.18. The collector is orientated with its axis in the East-West direction. The advantages of this tracking mode are that very little collector adjustment is required during the day and the full aperture always faces the sun at noon. A dedicated computer-operated tracking system is responsible for keeping the collector focused at all times. The collector is connected to a hot water storage tank which has a capacity of 300 liters. The collector fluid used in the tests is water, which is pressurized to avoid boiling in the receiver. The performance obtained is very satisfactory and agrees with the performance curve given by the manufacturer.