Economic evaluation and optimization of solar systems for space and domestic water heating

Solar energy will be utilized only if it proves to be economical. In this paper, we evaluate the economic feasibility of the use of solar energy for space and domestic water heating systems for a house in Benghazi, Libya. A comprehensive evaluation considerering 324 cases representing the proper ranges of economic and load factors and based on the annual equivalent cost approach is given. The optimum collector area for each case is determined. The results obtained and relationships developed permit generalizations that can be applicable in other locations.     

Analysis of natural circulation solar water heating systems

This paper presents an analysis of the performance of a solar water heating system with natural thermosyphon circulation between the collector and the storage tank. The analysis is based on the formulation by Ong except that provision for withdrawal of hot water from the tank (for domestic/ industrial use) has been made in the energy balance equation; further in contrast to the use of the finite difference method by Ong, explicit expressions have been obtained. The results of the present analysis (in the absence of withdrawal of hot water from the tank) are seen to be in better agreement with experiments than the corresponding results of Ong, obtained by use of the finite difference method.

Numerical results, corresponding to hot water retrieved from the storage tank, have been presented for two modes of hot water withdrawal viz. the constant flow rate and constant mean storage tank water temperature.     

Experimental and theoretical study on a solar assisted CO2 heat pump for space heating

In this paper, a solar combi-system which consists of solar collector and a CO₂ heat pump is investigated experimentally and theoretically. Two experiments are primarily conducted to show the performance of this solar combi-system under different operation conditions. A system model is developed and validated in TRNSYS to analyze the influence of main components parameters. Subsequently, a multi-parameter optimization is carried out in GENOPT to obtain a final optimal result. The simulated results show that the optimized system can save 14.2% electricity and improve the solar fraction by 8%. The solar fraction of the optimized system can reach 71.1%. Finally, the optimized system performance is studied with the weather and load characteristics in Shanghai. Compared with the CO₂ HP heating system alone, the solar assisted system can save 1790.8 kWh electricity on the basis of year round operation.     

A general chart for sizing the collectors of solar heating systems

A general chart is developed for calculating the collector area required to provide a prescribed value of the annual load fraction for solar heating systems. The relationship between collector area and annual load fraction can then be easily obtained for specified collector design parameters, load and location. The construction of the chart is based on correlating data generated by the f-chart method. Data of 13 locations in the U.S.A. are considered. The good agreement of the results obtained by the present simple method and the f-chart for both space and combined space/domestic water heating proves that the two methods are almost of the same accuracy. Since the present chart is not location dependent and allows direct comparison of different collectors, it is a very valuable design aid for sizing and selecting solar collectors.     

Transient analysis of parallel plate forced circulation solar water heating system

In this paper, a transient analysis of a forced circulation solar water heating system with and without heat exchangers in the collector loop and storage tank has been presented for a parallel flat plate collector. The effect of various water heating system parameters on its performance have been studied. Numerical calculations have been made for a typical cold day viz. 26 January 1980 in Delhi.     

Design and performance of large low-cost solar water heating systems

An analysis is presented for the monthly performance evaluation of a simple design low cost solar water heating systems. A sample of typical results is presented which confirms their suitability as solar heating systems for summer peacking or as solar preheaters for year around loads.     

Fuzzy model representation of thermosyphon solar water heating system

The aim of this paper is to focus on improvement in prediction accuracy of model for thermosyphon solar water heating (SWH) system. The work employs grey-box modeling approach based on fuzzy system to predict the outlet water temperature of the said system. The prediction performance results are compared with neural network technique, which has been suggested by various researchers in the last one decade. The outlet water temperature prediction by fuzzy modeling technique is analyzed by using 3 models, one with three inputs (inlet water temperature, ambient temperature, solar irradiance), next with two inputs (inlet water temperature, solar irradiance) and last one with single input (solar irradiance/inlet water temperature). An improved prediction performance is observed with three inputs fuzzy model.     

A simplified theory for a matrix solar collector

In this note we present a simple generalized analysis for a matrix collector and obtain closed form solutions for the equations. Numerical calculations were performed corresponding to the experimental data of Chau and Henderson.     

On the effects of solar radiation variations on solar heating system performances

The effect of solar radiation availability on the performance of different solar heating systems has been studied. The systems include a solar water heater, passive solar houses and district solar heating systems with seasonal heat storage. Also, different collector orientations and collector types have been investigated. The hourly radiation data were generated by a simple computational simulation procedure. It was found that district solar heating systems with concentrating collectors and passive solar houses showed the largest variations for the given conditions.     

Energy flow through the flat-plate solar water heating system

A simulation model of the flat-plate solar water heating system is used to trace the flow of energy through the system from the collector to storage and load for a system operating under idealised sunlight conditions.     

Optimum size and structure for solar energy collection systems

Procedures for sizing and optimizing the structure of solar collection systems are proposed. Four economical indices, including net present value and internal return rate, are given as examples of objective functions. Three solar energy applications were considered. A rather involved but still simple flat-plate solar collector model is used in calculations. The implementation was made for a specific geographical location with a detailed meteorological database available. In the case of solar collectors with uniformly distributed parameters, the procedure allows one to select the best devices from a given set of solar collectors. For every selected device the optimum range of the operation temperature is also determined. The best solution corresponds to systems with optimal non-uniformly distributed parameters. The general theorem proposed here shows how the modified optical efficiency and heat loss coefficient should be distributed for cost minimization. One finds that unglazed, single- and double-glazed collectors should be used on the same collection area in order to obtain the best performance. Also, the bottom insulation thickness should be changed accordingly.     

A demonstration site-built solar air collector using selective surface glazing, Boston, Massachusetts

A 450 ft ‘site-built’ air collector was completed in February 1981 in Boston, Massachusetss. The collector uses the Airco/Guardian ‘Passive Solar Glass’ with a selective surface coating on the inner lite of the collector's double glazing. This paper discusses the issues and theory that led to the building of the collector and estimates performance for the system. Preliminary data taken in late winter indicates that the system will perform seasonally as predicted.     

Performance analysis of new-design solar air collectors for drying applications

This paper presents a performance analysis of four types of air heating flat plate solar collectors: a finned collector with an angle of 75°, a finned collector with an angle of 70°, a collector with tubes, and a base collector. In this study, the first and second laws of efficiencies were determined for the collectors and comparisons were made among them. The results showed that the efficiency depends on the solar radiation and the construction of the solar air collectors. The temperature rise varied almost linearly with the incident radiation. The first law of efficiency changed between 26% and 80% for collector-I, between 26% and 42% for collector-II, between 70% and 60% for collector-III, and between 26% and 64% for collector-IV. The values of second law efficiency varied from 0.27 to 0.64 for all collectors? The highest collector efficiency and air temperature rise were achieved by the finned collector with angle of 75°, whereas the lowest values were obtained for the base collector. The effectiveness order of the collectors was determined as the finned collector with angle of 75°, the finned collector with angle of 70°, the collector with tubes, and the base collector.     

Comments on ‘a simplified theory for a matrix solar collector’

A critical analysis is given of Singh and Bansal's paper (1983) ‘A simplified theory for a matrix solar collector'. The following points are demonstrated:

• 1 Singh and Bansal use the equation of heat conduction to model an experimental system in which transfer of heat by conduction plays very little part. They make no attempt to show that the true radiative transfer equations can be approximated by a conduction equation.
• 2 The units and dimensions of the equations are internally self-inconsistent.
• 3 Correcting the equations to make them dimensionally consistent, and using the data given by Singh and Bansal, their calculations cannot be replicated. The values for outlet temperature are in the region 4°C rather than the 12°C claimed by Singh and Bansal.
• 4 Some of the data values quoted by Singh and Bansal are wrong (in terms of their stated objective of using values corresponding to the experimental system of Chau and Henderson) and others appear to have been assigned in an extremely arbitrary fashion. One crucial parameter (the absorptivity of the matrix material) is not even mentioned in Singh and Bansal's analysis.
• 5 Using the correct values for those parameters referring to the experimental system, and including the effect of absorptivity, the theory can be made to give results of the same order of magnitude as the experimental results. However, the variation of the outlet temperature as a function of the experimental parameters is very different to that obtained from Chau and Henderson's computer simulations. Indeed, Singh and Bansal appear not to have noticed that their solution possesses a singularity, so that for certain values of the parameters, an infinite outlet temperature can be obtained. This would appear to invalidate their model as a serious analysis of the matrix air heater.

     

串联式太阳能辅助地源热泵供暖系统的最优化研究

基于寒冷地区地源热泵运行的实验数据,建立了串联式太阳能辅助地源热泵供暖系统优化数学模型,并用约束变尺度法获得最优解。根据优化方法,以综合考虑系统运行性能和经济性为原则,对一实际工程进行了最优化研究。结果表明,采用优化设计后,系统总投资与采用传统设计时大致相当,但机组供暖运行性能有明显提高,COP提高了约16.7%,总功耗下降了17.2%,年均总成本降低了11.8%。     

Performance of flat plate solar collectors in off-south orientation in India

This paper presents the effect of off-south orientation on the performance of flat plate solar collectors. This study is done, taking into consideration the building's off-south orientation. The present work investigates collector performance and optimum tilt as functions of the off-south angle, collection temperature, latitude and wind velocity. The three latitudes considered are of New Delhi(L = 28.38°N), Bangalore (L = 12.97°N) and Madras (13.0°N). It has been found that, for the best average winter performance, the tilt is latitude angle +15°, whereas, for the best average summer performance, it is latitude angle ?15°. It has also been confirmed that, for year round operation, the maximum solar energy is collected when the tilt is 0.9 times the latitude angle. Further, it has been noticed that there is an optimum value of collector tilt for a given azimuthal angle at which yearly effectiveness is a maximum. The effect of increase in off-south angle is to decrease the yearly effectiveness.     

Smart switchable glazing for solar energy and daylight control

The exciting field of chromogenic materials for smart windows and other large-area applications is discussed. A selection of switchable glazing devices that change color electrically are detailed. The types of devices covered are the electrochromic which change color electrically, covering electrochromic, dispersed liquid crystal and dispersed particle glazing that switch under an applied electric field. Device structures and switching characteristics are compared. The status of prototype and commercial devices from commercial and university labs through out the world are covered. A discussion of the future of this technology is made including areas of necessary development for the realization of large area glazing in excess of 1m².     

Studies on gap spacing between absorber and cover glazing in flat plate solar collectors

The air gap between absorber and cover glazing in fiat plate collectors has been optimized experimentally by designing three identical collector-cum-storage type solar water heaters with 25, 50 and 150 mm air gaps. The heater with 50 mm air gap collects 11.64% and 7.72% more energy compared with heaters having 25 mm and 150 mm air gaps, respectively. The average overall efficiencies of the heaters are 52.5%, 57.8% and 54.1% having 25, 50 and 150 mm air gaps. A 50 mm air gap has, therefore, been found to be optimum.     

Thermal modelling of a few novel solar collector-cum-storage units for passive heating

Analytical models have been put forward to predict the thermal performance of passive heating systems, which have previously been suggested. The systems consist of a water vessel for heat storage and a structure positioned on its outside wall, which act as a solar collector and a thermal insulation for the storage, respectively. Four different variations of structures have been considered and numerical calculations performed corresponding to the physical parameters of an earlier reported experimental study. The analysis is able to predict the experimental results fairly satisfactorily.     

Performance of an inexpensive rural solar collector

In this paper we discuss an inexpensive solar collector in which the heat storage material is sand or sand mixed with iron filings. The heat is absorbed by the blackened portion of the heat storage material. The heat is withdrawn from the system by water flowing through a network of plastic pipes buried in the heat storage material at an appropriate depth. The large efficiency is obtained when the material is sand mixed with iron filings. It is shown that the efficiency of the system can be judged from the glass cover temperature. As the glass cover temperature decreases, the efficiency of the system increases.