Design, Construction and Performance Evaluation of a Passive Solar Water Heater
CHAPTER ONE
Objectives Of Study
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:
- To provide energy for heating water for domestic and industrial
- To publicize the knowledge to potential users and for commercial
- To make relevant recommendations based on the outcome of the research so as to improve the efficiency of the solar water heating
CHAPTER TWO
LITERATURE REVIEW
Green House Effect
This is the principle generally used today in direct conversion of solar energy to thermal energy. As the name implies, the name comes from the green house where it was first use to grow an exotic plant in cold climate through a better utilization of the little available sunlight. Most of the energy we receive from the sun comes in the form of light, a short wave radiation out of which not all are visible. When this light strikes the solid or liquid, it absorbs the energy and transform it into heat such that the material becomes warm and it store the heat which will be conducted to the surroundings (air, water and other solid) or radiate to other materials with lower temperature. These radiated radiations are of long wavelength (Vaclav, 2013). Figure 2.1 below shows how earth surface temperature is affected through green house effect.
This visible sunlight is absorbed on the ground at lower temperature say 200C for example and emits infra-red at long wavelength of about 10µm, where the carbon dioxide in atmosphere absorbs this light and radiate part of it back to the earth. (Note that carbon dioxide does not absorb incoming sunlight of short wavelength).
Thus, green house effect brings about and explains the accumulation of energy on the ground. From the fact that any dark surface faces the sun is a heat collector, the reason for its darkness is that it used to absorb most of the light energy incident on it and stores it instead of reflecting it back.
Another important thing is anti-reflecting grazing (transparent cover) whose function is to ensure the retaining of heat on the collector surface. It can either be glass or plastic. Mainly, glasses are often used due their following characteristics:
- It has long life span in exposure to solar radiation
- It transmits only short wave radiation. that is, it allows solar radiation to pass through
- It is opaque to long wave radiation. That is, thermal radiation (infra-red radiation).
With these features of glasses, it allows the solar energy to pass through and be absorbed by the collector plate. However, the thermal radiation emitted by the plate is trapped and re-emitted by the grazing where part of this energy get back to the collector. Thus, increases the steady state temperature. This process is known the green house effect.
Glass materials has highly desirable property of transmitting as much as 90% of the incoming short radiation, while virtually none of the long wave radiation emitted by the absorber plate can escape outwards by transmission (Rhushi, et al 2010).
To be specific, glass cover for solar collector normally should be at least 0.33cm thick (Garg and Prakash., 2006).
Temperature from the Absorber Plate
As illustrated in the general principle of green house effect, the black painted plate absorbs the incoming sunlight through the fixed window glass. When the temperature of the black body increases, it emits that increment inform of heat (infa-red light), because the black body has not only the highest absorption rate, but also the highest emission coefficient for all wavelength of light (Nosa et al., 2013). Thus, emission increases following the Stephan-Boltzmann law which state that; the amount of electromagnetic radiation emitted by a body is directly related to its temperature. If the body is a perfect emitter (black body), the amount of radiation given off is proportional to the 4th power of its temperature as measured in degrees Kelvin. This natural phenomenon is described as Stephan- Boltzmann law.
CHAPTER THREE
MATERIALS AND METHOD
A careful study of already existing solar water systems was done; and a choice was made on the type of system to be designed with focus on simplicity, installation, and maintenance cost as well as durability. Use of locally available materials was made a matter of priority. A flat-plate collector was used as the absorber. It was integrated with underneath grids or coils of fluid carrying tubes and placed in an insulated casing with a glass or transparent cover and a storage tank placed above the insulated casing. The water gets heated up and flows into the storage tank through thermosyphon principle. The performance of the thermosyphon system depends upon the size and capacity of the storage tank, the thermal capacity of the collector, and the connecting pipes including fluid flow and on the pattern of hot water use (Abdollah et al., 2011).
Selection of Materials
In the selection of materials needed for construction stage of this system, two essential factors, namely, the economic consideration (cost) and properties of the materials were considered.
(a) The transparent cover
A transparent cover is needed in solar collector to help provide the “green house” effect necessary to heat up the water. A good cover material (transparent cover) should have high transmittance to ultraviolet radiation and low transmittance to infra-red radiation in order to trap the radiated heat from the absorber plate. Low-cost glass was preferred to plastic as the cover material in this work because it has high transmittance to visible light, low transmittance to infrared radiation, and stability. It suppresses the convective and relative losses from the top of the solar collector plate. However, the main disadvantage is that it has a low resistance to shatter.
Thickness of the glass-sheet must be at least 4 to 5 mm.
(b) Absorber plate (collector plate)
Some materials that could be used include copper, aluminum, mild steel, and galvanized iron. Copper is the best among these alternatives due to its high thermal conductivity, but it is very expensive., galvanized iron however, is used as absorber plate because it is relatively cheap compared to copper, and has good thermal conductivity. It is painted black, and on which the zigzag pipe containing the water is fixed. The black coating absorbs almost all the solar radiation that falls on it. The collected radiation is transformed into heat and simultaneously heats the water inside.
(c) Collector/tank insulation
Insulation is very important to reduce heat losses in the collector and hot water storage tank in order to improve the efficiency. An ideal insulation arrangement should be made to eliminate heat loss by conduction, convection, and radiation from bottom and edges of the collector. Insulation material includes glass wool, sawdust, wood shavings, and Styrofoam. Styrofoam, however, will be used because it is relatively cheap, is readily available, and has very low thermal conductivity.
CHAPTER FOUR
RESULTS AND DISCUSSION
Testing and Results
The solar water heating system was tested in the month of August, 2017 for three days with the purpose of estimating its performance. The device was placed outside the physics laboratory of Federal University Dutsin-ma, with the collector inclined at an angle of 120 facing the direction of the sun. A mercury-in-glass thermometer was used to take the readings at every one-hour interval for ambient temperature, inlet temperature, inlet temperature, outlet temperature, collector surface temperature, and tank temperature.
The results of the variation of temperature with time for the three-day testing period are shown in tables 4.2.1, 4.2.2 and 4.2.3 while figures 4.1, 4.2 and 4.3 shows the graphical representation of the measured temperature readings of the system against time. The average value for the three days experiment will be calculated and tabulated for all the parameters measured.
CHAPTER FIVE
SUMMARY, CONCLUSION AND RECOMMENDATIONS
Summary
We have seen that this flat plate collector performs satisfactory work under the average sunshine condition. Several readings were taken and their respective graphs were obtained. The whole experiment was carried out for three days in the month of august in year 2017.
Chapter one of this work introduced the work to us, the second chapter explained the principle behind it and review of other peoples work, chapter three describes the design, construction and experimental method and chapter four shows the collection of data.
It was observed that almost all parameters measured, e.g. ambient temperature, inlet temperature and outlet temperature attained their peak (highest value) around 1pm, 2pm and 3pm, after which they started falling till 6pm in the evening.
Some points are to be noted in the design of a solar water heater; points like collector’s tilt which is equal to the latitude of the area, the distance between the bottom of the tank and the head of the collector as the performance of a solar water heater will depend on them.
Conclusion
Experienced gained from this project work indicates that a flat plate collector together with an insulated storage tank can be successfully developed using locally available materials.
A solar powered water heater is a long term investment that can help us save money and energy for many years. Like other renewable energy systems, solar powered water heaters minimize the environmental effects of enjoying a comfortable, modern lifestyle at reduced cost because they do not have the hazards introduced by fossil fuels but are environmentally friendly and almost completely running cost free. The system designed in this work requires little or no maintenance because of the thermosyphon principle involved. It was made basically from locally available raw materials. It has no moving parts and almost the entire system works automatically.
Recommendations
Although the objectives of this work have been achieved, further research work can be conducted to improve the efficiency of the system.
- The insulation layer should be made up of styro-foam because it has greater ability to prevent heat lost and also reduced weight as compared to the use of
- An active solar water heater should be constructed instead of passive solar water because it has more
- In a case of producing larger volume of hot water, multiple galvanized pipes should be used in the collector
- Based on this research work, it is recommended that the department should provide a pyranometer for students and researchers who wish to build upon this research work for the comparison of the efficiency of various solar water heating
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