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DESIGN, CONSTRUCTION AND PERFORMANCE EVALUATION OF A PASSIVE SOLAR WATER HEATER

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 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 NashSutcliffe 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.

CHAPTER ONE

INTRODUCTION

1.1  Background to the Study

Renewable energy resources of which the sun is a good example, are those resources which undergo a faster replenishment rate within a relatively short time than the rate at which they are utilized or depleted. The energy of the sun is generated from the nuclear fusion of its hydrogen into helium, with a resulting mass depletion rate of approximately 4.7 × 106 tons per second. The earth’s population currently needs 15 TW of power in total, but the solar radiation that reaches the earth on a continuous basis amounts to 120,000 TW; hence, just a fraction of the suns energy reaching the earth will cover the bulk of energy requirements (Bradke et al., 2011).

Solar energy being transmitted from the sun through space to earth by electromagnetic radiation must be converted to heat before it can be used in a practical heating or cooling system. Since solar energy is relatively dilute when it reaches the earth, the size of a system used to convert it to heat must be relatively large. Solar energy collectors, the devices used to convert the suns radiation to heat, usually consist of a surface that efficiently absorbs radiation and converts this incident flux to heat which raises the temperature of the absorbing material. A part of this energy is then removed from the absorbing surface by means of heat transfer fluid that may either be liquid or gaseous. One of the simple forms of solar energy collectors built is the flat-plate collector (Nosa et al., 2013).

Solar water heaters can operate in any climate. Performance varies depending on how much solar energy is available at the site, but also on how cold the water coming into the system is. The colder the water, the more efficiently the system operates. In almost all climates, you will need a conventional backup system. In fact, many building codes are required to have a conventional water heater as the backup. Even in our country Nigeria, people from several areas often put water outside, so that after getting warm, it could be used for things like bathing, drinking and other thermal comforts. Seeing the solar energy or solar water heater in particular today, it is clear that solar water heater have undergone several modifications for more efficiency.

1.2    Statement of Problem

Since the 1970’s, residential solar technology has emerged as a result of the increasing cost of energy consumption, which in most cases is used for heating and cooling, is typically the most significant operational cost in residential buildings. Many attempts have been made thereafter to save cost on heating and cooling energy. Although the features of each specific solar heating system vary, the basic components of a solar heating system are the same. It should at least include: a collector, where heat is collected from the solar energy; heat storage and a heat circulation system (Shurcliff, 1979). Thus, there is the need for adequate research to be carried out on the solar heating system so as to make recommendations on the right design to improve it performance and save energy costs.

1.3    Aim and Objectives

The main aim of this work is the development of a low cost solar water heater, constructed using a high percentage of locally available materials. The objectives of this work are:

(i)   To provide energy for heating water for domestic and industrial use.

(ii) To publicize the knowledge to potential users and for commercial purposes.

(iii) To make relevant recommendations based on the outcome of the research so as to improve the efficiency of the solar water heating system.