ABSTRACT
A thermosyphon solar water heating system which captures and utilises the abundant solar energy to provide domestic hot water was designed, simulated, constructed and tested. The system was designed to supply a daily hot water capacity of 0.1m3 at a minimum temperature of 70oC for domestic use. The design approach was in three parts; firstly, since solar radiation and weather data which are driving function for solar systems design vary randomly with time, the monthly average daily solar radiation and weather data obtained from the typical meteorological year (TMY) solar data of Zaria were used to determine the design month as the month (August) with the least monthly average daily solar energy ratio. Solar radiation and weather data of the design month were used to design the system. Secondly, the design month solar radiations and weather data were used as input into the design equations coded using MATLAB programming language to determine the system characteristic and components sizes. A parametric study was also carried out to study the effects and sensitivity of varying some design parameters such as number of glass covers , collector tube centre to centre distance W, absorber plate thickness , collector tube internal diameter and collector tilt angle on the design objective function (the heat removal factor ). Thirdly, based on the values of the system characteristics and components sizes obtained from the design calculations and the parametric study, a model for the performance simulation of the system was formulated using the Transient System Simulation (TRNSYS) software. This model was used to predict the annual hourly performance of the system for recommended average day of the months using the TMY solar radiation and weather data of Zaria as input function. The system was then constructed based on the component sizes adopted for the simulation owing to the satisfactory performance of the system as revealed from the simulated results. To validate the simulated system performance, system performance tests
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were conducted for 3 days and the results were compared with the simulated results. The root mean square error (RMSE) and the Nash-Sutcliffe Coefficient of Efficiency (NSE) statistical tools were used to analyse the experimental and simulated results in order to validate the predictive power of the software. The results of this research led to the conclusion that a thermosyphon solar system with collector area of 2.24 m2 operated under the weather condition of Zaria, would be capable of supplying a daily domestic water of 0.1m3 at temperature ranging from 59oC for the worst month (August) to 81oC for the best month (April).The computed Nash-Sutcliffe Coefficient of Efficiency (NSE) values of 0.663, 0.956 and 0.885 and the low RMSE values of 8.09oC, 3.65oC and 5.31oC between the modeled tank inlet temperature and the observed tank inlet temperature for the three days tests conducted indicated that the model formulated using TRNSYS software was valid and closely agreed, capable of predicting the performance of the system with a 66.3 %, 95.6% and 88.5 % degree of accuracy for the 3 days that the experiments were conducted respectively.
TABLE OF CONTENTS
Title Page……………………………………………………………………………………..i
Declaration ………………………………………………………………………… ………..ii
Certification ……………………………………………………………………………….. ..iii
Dedication………………………………………………………………………………….. ..iv
Acknowledgements ……………………………………………………………………………………………….. ..v
Abstract …………………………………………………………………………………… ..vi
Table of Contents……………………………………………………………………………………………………. viii
List of Figures …………………………………………………………………………,…. xii
List of Tables ……………………………………………………………………………….xv
List of Appendices …………………………………………………………………………xvi
Nomenclature ……………………………………………………………………………..xvii
Abbreviation……………………………………………………………………………….xxii
1.0 INTRODUCTION ………………………………………………………………………1
1.1 Background of the Study …………………………………………………………….. ..1
1.2 Statement of the Problem. …………………………………………………….………..3
1.3 The Present Research …………………………………………………………………..4
1.4 Aim and Objectives …………………………………………………………… ………..5
1.5 Significance of Research ……………………………………………………………………………………5
2.0 LITERATURES REVIEW ……………………………………………………………6
2.1 Solar Potential and Resources of a Location ………………………………………….6
2.2 Solar Water Heating Systems ………………………………………………………. ..7
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2.2.1 Direct open-loop hot water system …………………………………………………….. ..7
2.2.2 Indirect hot water system ……………………………………………………………..9
2.3 Solar collector………………………………………………………………… ……….10
2.3.1 Selective surfaces …………………………………………………………… ……….12
2.3.2 Collector covers…………………………………………………………………….. 13
2.4 Thermosyphon System ……………………………………………………………… 14
2.5 Sizing a Solar Hot Water System…………………………………………. ………15
2.6 Collector Orientation ……………………………………………………………………16
2.7 Solar Water Heating System Applications …………………………………. ……… 17
2.7.1 Service hot water ……………………………………………………………………. 17
2.7.2 Swimming pools …………………………………………………………………….. 18
2.8 Solar Water Heating System Load …………………………………………………. 19
2.8.1 Average daily hot water consumption and load profile …………………………… 19
2.8. 2 Hot water load profile …………………………………………………………… 19
2.9 Review of Related Work………………………………………………………………. 20
2.10 Theoretical Background …………………………………………………………… 24
2.10.1 Angle of incidence of beam radiation …………………………………………… 24
2.10.2 Declination ………………………………………………………………………… 26
2.10.3 Solar hour angle ………………………………………………………………….. 27
2.10.4 The sunset hour angle ……………………………………………………………. 27
2.10.5 Extraterrestrial radiation and clearness index …………………………………… 27
2.10.6 Tilted irradiance: beam and diffuse Components………………………………. 28
2.11 Transmittance-Absorptance Product ……………………………………………. 30
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2.12 Monthly Average Absorbed Radiation ………………………………………….. 31
3.0 MATERIALS AND METHODS ………………………………………………….. 32
3.1 System Description ……………………………………………………………………32
3.2 Working Principle …………………………………………………………………….. 33
3.3 Materials Selection …………………………………………………………………… 34
3.3.1 Flat plate collector …………………………………………………………………… 34
3.3.2 Storage tank ……………………………………………………………………….. 36
3.4 Design Assumptions………………………………………………………………… 36
3.5 Design Considerations……………………………………………………………… 37
3.6 Design Theories ……………………………….…………………………………,…. 37
3.6.1 Solar resources and weather data………………………………………………,…. 37
3.6.2 Flat-plate collector…………………………………………………………………. 38
3.6.3 System load calculations…………………………………………………………… 46
3.6.4 System performance evaluation…………………………………………………… 47
3.7 System Design Approach and Calculations……………………………………….. 51
3.7.1 Determination of the design month………………………………………………. 52
3.7.2 Determination of design parameters………………………………………………. 53
3.7.3 Design parameters optimisation………………………………………………….. 53
3.7.4 System performance simulation…………………………………………………… 54
3.8 Construction of the System………………………………………………………… 55
3.8.1 Construction of the flat plate solar collector……………………..………………. 55
3.8.2 Construction of the storage tank…………………………………………… ……… 58
3.8.3 Construction of supporting frame…………………………………………… ……… 59
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3.9 System Cost Estimation…………………………………………………………….. 60
3.10 Validation of Simulation Model…………………………………………………… 61
3.10.1 Description of the experimental set-up………………………………………………63
3.10.2 Experimental procedure………………………………………………………….. .. 63
4.0 RESULTS AND DISCUSSION ……………………………………………………………………….. 65
4.1 System Design Calculation …………………………………………………………… 65
4.2 Collector Design Parameters Optimisation………………………………………… 68
4.2.1 Collector tilt angle ………………………………………………………………… 68
4.2.2 Collector tube diameter and centre to centre distance ……………………… ……… 69
4.2.3 Collector absorber plate thickness ………………………………………………… 70.
4.2.4 Collector number of glazing ………………………………………………………. 71
4.3 System Optimum Parameters and Simulation …………………………………….. 73
4.4 System Performance Evaluation………………….…………………………………. 83
4.5 Validation of Simulated Results …………………………………………………….. 84
4.4.1 Comparison of simulated results with experimental results ………………… ……… 84
4.4.2. Analysis of the predictive power of the simulation software …………………… 93
5.0 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS……………….…..98
5.1 Summary …………………………………………………………………… ………98
5.2 Conclusions ……………………………………………………………………………99
5.3 Recommendations …………………………………………………………………… 100
REFERENCES..………………………………………………………………………….. 101
APPENDICES ……………………………………………………………………………. 106
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CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Energy is considered a prime agent in the generation of wealth and a significant factor in
economic development. The importance of energy in economic development is recognized universally, and historical data verified that there is a strong relationship between the availability of energy and economic activity (Soteris, 2004). Although in the early seventies, after the oil crises, the concern was on the cost of energy, however during the past two decades, the risk and reality of environmental degradation have become more apparent. The growing evidence of environmental problems is due to a combination of several factors, since the environmental impact of human activities has grown dramatically (Soteris, 2004). This is due to the increase of the world population, energy consumption and industrial activities. Achieving solutions to the environmental problems that humanity faces today requires long term potential actions for sustainable development. Renewable energy resources appear to be one of the most efficient and effective solutions.
Of all the renewable sources of energy available, solar thermal energy is the most abundant one and is available in both direct as well as indirect forms. The Sun emits energy at a rate of 3.8 x 1023 kW, of which, approximately 1.8 x1014 kW is intercepted by the earth, which is located about 150 million km from the sun. About 60% of, this amount reaches the surface of the earth. The rest is reflected back into space and absorbed by the atmosphere. About 0.1% of this energy, when converted at an efficiency of 10% would generate four times the world‟s total generating capacity of about 3000 GW(Mirunalini, et al.,2010). It is also worth noting that the total annual solar radiation falling on the earth ismore than 7500 times the world‟s total annual primary energy consumption of 450 EJ (Mirunalini, et al., 2010). The annual solar radiation reaching the earth‟s surface, approximately 3,400,000 EJ,
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is an order of magnitude greater than all the estimated (discovered and undiscovered) non-renewable energy resources, including fossil fuels and nuclear energy ( Mirunalini et al. , 2010). However, 80% of the present worldwide energy utilisation is based on fossil fuels.
World demand for fossil fuels (starting with oil) is expected to exceed annual production, probably within the next two decades (Mirunalini et al., 2010). International economic and political crisis and conflicts can also be initiated by shortages of oil or gas. Moreover, burning fossil fuel releases harmful emissions such as carbon dioxide, nitrogen oxides, aerosols, etc. which affect the local, regional and global environment. By means of different mechanisms, solar radiation may be converted into other forms of energy, such as photovoltaic conversion into electrical energy, photochemical conversion into chemically bound energy, and photo thermal conversion into heat. The heat converted from solar radiation, is well suited to provide domestic hot water and space heating. In most parts of the world, the yearly solar radiation received by a single family house is several times greater than the energy needed for domestic hot water and space heating( Mirunalini et al., 2010).
For many years, solar domestic hot water (DHW) systems have gained great attention due to their considerable energy conservation, environmental protection and relatively good economy. The purpose of using a solar DHW system is to convert the solar radiation into thermal energy, and then to use it for domestic hot water heating, thus reducing the over dependence on and consumption of conventional energy. Recently, environmental issues have led to an even greater interest in solar DHW systems. There are several fundamental conditions that make solar DHW systems very different from conventional fossil-fuel systems. Firstly, the power density of solar radiation is relatively low and the collector has to cover a large area. Thus, the solar DHW systems cannot be as compact as conventional units. Secondly, the solar radiation varies considerably during the day, in the course of a
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year and between different locations. Therefore, the solar energy received by a collector is an irregular function of time and location, and the power output of the collector cannot be controlled in the same way as conventional heating systems. Consequently, heat storage and auxiliary energy are required to match the supply to the load.
1.2 Statement of the Problem.
There is a strong consensus among climate scientists that the environmental problems now observed is caused by human activities targeted to meeting our energy demand, especially the combustion of fossil fuels. When oil, gas, or coal are burned to generate electricity or provide heat, the products of the combustion which include carbon dioxide and nitrous oxide, lead to global warming and acid rain deposition, respectively . The expected impacts of global warming include sea-level rise flooding of coastal areas increased frequency and severity of floods, draughts, storms, and heat waves, reduced agricultural production, massive species extinction, and the spread of vector-borne diseases such as malaria and dengue fever (Christopher and Homola, 2006). Thus, the manners in which we produce and consume energy (conventional way) are to a large extent responsible for this impending environmental problem (Intergovernmental Panel on Climate Change (IPCC), 2001).
According to Christopher and Homola (2006), rising economic losses due to weather-related disasters are part of a trend being linked to climate change. The World Health Organization estimates that climate change is already responsible for 150,000 deaths annually (Christopher and Homola, 2006).
Domestic hot water use again represents a large proportion of domestic energy need. This energy need accounts for approximately one third of the total annual energy consumption for domestic purposes and therefore a greater portion of the family income is spent on domestic hot water (Retscreen International, 2004).
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1.3 The Present Research
This research involves the design, simulation, construction and performance tests of a solar domestic hot water heating thermosyphon system for Zaria, Nigeria, located on latitude 11.2o N and longitude 7.8oN. The design method employed is the simulation based method, where mathematical models for the determination of the system design parameters and characteristics were coded into a computer programme using the Matrix Laboratory (MATLAB) software in a manner that represents the conceptual design of the system.
The effects and sensitivity of the system design parameters on the collector heat removal factor were studied through programmes codes written in MATLAB in order to determine the size of the various components of the collector that will give better performance.
The system performance was simulated using the Transient Systems Simulation (TRNSYS) software for recommended average days of the months. The system was then constructed based on the adopted system configuration and components‟ sizes obtained from the studies. The performance of the system was then experimentally determined and the results obtained from the test were compared with the simulated results in order to validate the formulated model used for the performance simulation.
1.4 Aim and Objectives
The aim of this research is to design, simulate, construct and test the performance of a solar domestic hot water thermosyphon system for the city of Zaria, Nigeria.
The specific objectives are:
i. To carry out a parametric study on the effect and sensitivity of the tilt angle, , number of glasing , , absorber plate thickness, , collector tube diameter, and collector tube centre to centre distance, , on the objective function which is the
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percentage expression of the heat removal factor, , using Matrix Laboratory (MATLAB) programming language.
ii. To predict through simulation using TRNSYS, the annual performance of the system.
iii. To validate the predicted system performance through experiments.
iv. To estimate the cost of the system.
1.5 Significance of the Research.
Environmental concerns about global warming, local pollution and reduction of over dependence on conventional energy source for domestic hot water need in Zaria, is the primary impetus for this research. This research would provide alternative way to providing hot water for domestic use in various homes. It also has the potential of reducing family utility bills and thereby improving family savings.
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