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JESA Volume 13 (abstracts only)

JESA Volume 13 (abstracts only)

Vol. 13 No. 1: February  2002

The use of neural networks to baseline the energy use of a campus W.H. Kaiser and L.J. Grobler

This paper investigates the technique of modelling a baseline with the aid of Neural Networks (NN) for the tracking and evaluation of Demand Side Management (DSM). NN was used to develop the baseline purposes. The study was conducted at the main campus of Pretoria University. The NN model was trained with 12 months of actual measured data. The high accuracy of the results in the verification study with 9 months of test data indicate that NN can be used for a distribution area where there is wide diversity of energy use, with little information available of the underlying network and its energy use that has an influence on the energy use. This technique is simpler and faster with a timesaving of up to 90 % than traditional techniques used. The use of NN for modelling a baseline could be extended to model cities and even regions.

 

Energy analysis and environmental impact assessment of a cement plant  P.P.A.J. van Schijndel  and I.L. Greeff

Energy, exergy and cost-benefit analyses were conducted on a cement plant in South Africa in order to identify the best energy improvement options. It was found that an energy saving project is more likely to be attractive in Europe than in South Africa. This can be attributed to low fuel prices and high interest rates (long pay-back times) in South Africa. The utilisable exergetic efficiency was used to quantify the effect of proposed energy saving measures. The most promising option for saving energy and improving the exergetic efficiency proved to be insulation of the preheater system. A payback time of only 7.5 months was calculated for this option and the utilisable exergetic efficiency increased from 39% to 43%. The benefits obtained from increasing exergetic efficiency is not only financial, but can also be translated into a decrease in environmental impact in the case of cement production. This was shown using the Eco Indicator’95 method for quantifying environmental impact.

Vol. 13 No. 2: May  2002

Stakeholders interaction in developing policy around ESI restructuring in South Africa E.M. Tinto

 

The safety of paraffin and LPG appliances for domestic use  P.J.D. Lloyd

Households have an absolute need for thermal energy, particularly for cooking. Poorer households use coal, dung, fuelwood, LPG and paraffin. Unpressurised paraffin appliances are far from safe. The temperature in the fuel tank can easily exceed the flashpoint of the fuel, when the appliance becomes a time bomb waiting to “explode”. In contrast LPG appliances are safe, with annual incidents at least two orders of magnitude lower than those involving paraffin. The White Paper on energy required proper standards for paraffin appliances, but these are slow in evolving and do not address the hazards identified above.

 

A solar powered, back-to-back, liquid piston stirling engine for water pumping G B de Klerk and C J Rallis

A low temperature difference, back-to-back gamma type Stirling engine is presented with the emphasis on rural water pumping. A prototype engine was constructed and performance in terms of the characteristic pump curves measured. Two representative graphs of flow rate versus pumping head are given for two different configurations of the engine. Preceding a description of the construction of the engine, an overview of Stirling engine technology and the back-to-back concept is given. The engine consisted of two displacer cylinders connected to either side of a water-filled U-tube. Work was extracted by means of a diaphragm pump which makes use of an area difference to amplify the pressure attained in the water to be pumped and hence the pump head of the device. The prototype was heated by means of two 100W light bulbs that resulted in a temperature difference of approximately 35oC. With a collection area of 0.08m2, maximum power was achieved at a head of just over 1m and a flow rate of 54 litres per hour. Rural application of the engine will be solar powered with cooling achieved by routing the pumped water through a water jacket. The characteristics of the engine are such that stable operation is possible over a wide range of pumping loads.

 

Potential impacts of electricity industry restructuring on renewable energy and energy efficiency  H. Winkler and J. Mavhungu

The South African electricity industry is on the brink of considerable restructuring. The future of social and environmental public benefits provided in this context is uncertain. This paper focuses on environmental public benefits, such as renewable energy and energy efficiency, which face both opportunities and threats under restructuring. We conclude that, in the short term, policies and measures that could protect environmental benefits should focus on energy efficiency measures, an energy efficiency institution, power purchase agreements and non-discriminatory access to the grid for renewable independent power producers. In the longer term, the regulator should set a renewable electricity portfolio standard for electricity generation, and require distributors to invest a minimum percentage in energy efficiency. A systems benefit charge is one possible mechanism to finance such measures. These efforts need support from further public-interest research.

Vol. 13 No. 3: August  2002

24-Hour temperature prediction: a comparison of an AI-model with conventional algorithms/mathematical methods  L.J. Grobler, A.Z. Dalgleish, and W.L.R. den Heijer

Den Heijer developed a method in 2001, which expanded two monthly temperature values, one at 8:00 and the other at 14:00, into daily temperature profiles for that month. The disadvantage of that method was that the temperature profiles for each day of that month looked exactly the same. A new method was thus needed so that the daily temperature profiles would be more realistic. This paper investigates the application of artificial intelligence in predicting daily temperature profiles from known information. Cape Town and Pretoria are considered in this study. Data of the Council of Science and Industrial Research (CSIR) has been used to train the models. The models have been verified by using actual temperature data that was recorded by the South African Weather Bureau during 2000. The results from this model could be used in energy simulations where hourly temperatures are needed and in the calculation of degree-days. When the next day’s minimum and maximum temperatures are known, the developed models can also be used to forecast an hourly temperature profile for that day. The accuracy of the models was determined using three indices. To compare the results of this study with the work of Den Heijer, the same method was used that he used. The percentage-simulated data within 3°C of actual data was determined. Den Heijer obtained 88%. Using artificial intelligence, 94.5% of the simulated temperatures for Pretoria were within 3°C of the actual temperatures. For Cape Town, 93.9% of the simulated data were within 3°C of the actual temperatures. The Mean Absolute Error for the developed models was 1.09°C and 1.17°C for Pretoria and Cape Town respectively. The Mean Percent Difference for Pretoria and for Cape Town data were -1.38% and -1.17% respectively. An advantage of this method over the method of Den Heijer is that the temperature profiles are different for each day and thus more realistic. A disadvantage of this method compared to that of Den Heijer is that a model needs to be developed for each city.

 

Can carbon credits make solar home system projects more viable? R. Spalding-Fecher

This paper presents a financial analysis of using solar home systems as a Clean Development Mechanism (CDM) project under the Kyoto Protocol to the climate change convention. The main conclusion is that, while the carbon revenue can improve the internal rate of return for the local investors, this is highly sensitive to the ‘transaction costs’ – the costs of actually putting the CDM project together, especially the baseline and ongoing monitoring costs. This illustrates the need for standardised baselines for small-scale projects such as this one.

 

Prediction of the inside room temperature as well as temperature distribution in walls and roof of a building V.K. Bajpai, S. Kumar and K.S. Kasana

Flow of thermal energy inside buildings is evaluated by transient thermal analysis. The analysis takes into account composite layers of walls, roof, thermo-physical properties of building material, periodic variation of outside air temperature, intensity of solar radiation, convective heat transfer coefficients and absorptivity of surfaces. A mathematical model has been developed by using Finite Difference Method, followed by a computer program which can be used to predict room air temperature and temperatures at different nodes located in the structure of walls and roof at different times of the day. Due care has been taken to make the program flexible so that by minor changes the room temperature and temperature in the wall layers could be predicted for any type of building.

Vol. 13 No. 4: November  2002

An insight on a three-fluid absorption refrigeration machine based on experimental data G. Vicatos and A. Zulu

The technology of absorption refrigeration is gaining the interest of both the academic and manufacturing worlds due to its capability to operate at low-grade thermal energy. The domestic size fridge, however, has been inflicted by a bad reputation because the market has been “flooded” with units, which do not work according to the customers’ satisfaction. This is because many have been manufactured and serviced without the appropriate theoretical knowledge. Unlike its competitor, (the vapour compression fridge), the absorption system has a fine balance between its various components. Its proper design and construction therefore, is paramount if it is to regain its reputation in the market as a reliable fridge.

 

Energy savings in cryogenic plants S. C. Sarkar

Fertilizers, steel, petrochemicals, fuel, metallurgy, explosives, rocket and space research, food and biological material processing, and many other industries, need a substantial amount of air products such as oxygen, nitrogen, argon etc, either in liquid form or in gaseous form. This high demand has necessitated the installation of many cryogenic air separation plants of different capacities in India. The raw materials being air in these plants, which is abundantly available in the atmosphere, and the power input is considered to be a main factor on which the ultimate production cost will depend. As cryogenic plants are generally energy intensive, a small savings in power will reduce the production cost substantially. The article discusses the salient features of plants of lower capacities based on a reverse Stirling cycle as well as plants having higher capacities based on engine/turbine expansion and/or throttle expansion indicating various areas of improvement that could be incorporated for achieving energy savings, which in turn, will make use of cryogenic liquid viable for its various applications.

 

Development of a heat pipe (two-phase closed thermosyphon) heat recovery heat exchanger for a spray drier R.T. Dobson and S.A. Pakkies

A heat pipe or two-phase closed thermosyphon heat recovery heat exchanger may be used to reduce the overall operating energy requirement of a drier. The mathematical modelling of the process whereby heat is recovered from the hot exhaust stream and used to preheat the incoming process stream is presented. The functioning and thermal characterisation of a thermosyphon heat pipe and heat exchanger as well as the thermal and fluid dynamic characteristics are given for the case of a milk spray drier by way of a practical application. Empirically determined correlations for the heat transfer coefficients, maximum heat transfer rate, optimum evaporator to condenser length ratio, and the airside pressure drop of a R134a charged test thermosyphon are given. Correlating equations for the mass and heat transfer equations for typical operating conditions of the drier are also given. Using a heat exchanger with an effectiveness of 0.5, some 26.5 % of the total heat load can be recovered from the waste stream.

 

The potential for geothermal energy  M. K. Ghose

Ever increasing use of fossil fuels cannot be the basis for sustainable development. These have unexpected environmental consequences in a local and global scale. The need to increase energy supply in a developing country like India is unquestionable. Rapid growth of the energy sector has made environmental protection a highly complex and more difficult task. There is a pressing need for alternate sustainable supplies of energy. Geothermal power has the potential for a significant energy source and can be prescribed as a much cleaner source. This paper examines the potential for geothermal energy, focuses on the present scenario of geothermal energy utilization and some of the key environmental issues in these sectors. The Indian scenario of geothermal energy and the options available for the supply of energy have been discussed. There is a high potential for energy conservation in industry. This paper concludes by identifying geothermal energy as one of the potential sources of energy for maintaining a clean environment.

 

An optimal energy and greenhouse gas mitigation path for South Africa in the short to medium term M.I. Howells and M. Solomon

Following a description of the South African energy system, this paper discusses the results of the national Integrated Energy Planning (IEP) model and discusses why better management of existing energy resources provides and economic option for the country. Not only does this result in a more economic system and reduced energy demand, but it also has the effect of reducing carbon dioxide emissions. The paper goes on to reference local case studies, carried out by the Energy Research Institute (ERI), which clearly illustrate the potential benefits of energy management on a micro level.