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The first step in determining sun angles is to obtain the local solar time.
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- CHAPTER Table of Contents
- INTRODUCTION.............................................................................................................
- 1.1 OBJECTIVES OF THE PROJECT
- 1.2 LAYOUT OF THE THESIS
- CHAPTER
- SOLAR RADIATION AND SOLAR GEOMETRY......................................................
- 2.1 SOLAR ENERGY
- 2.2 FUSION REACTIONS
- 2.3 LAYERS OF SUN
- 2.3.1 The Core......................................................................................................
- 2.3.2 Solar Envelope
- 2.3.3 Photosphere.................................................................................................
- 2.3.4 Chromosphere
- 2.3.5 Sunspots.......................................................................................................
- 2.3.6 Corona.........................................................................................................
- 2.4 SOLAR SPECTRUM
- 2.4.1 Stefan-Boltzmann Law
- 2.4.2 Wien s Displacement Law.........................................................................
- 2.5 THE SOLAR CONSTANT
- 2.6 SOLAR I NSOLATION
- 2.7 SOLAR GEOMETRY
- 2.7.1 Motion of the Earth About the Sun............................................................
- 2.7.2 Sun s Apparent Motion..............................................................................
- 2.7.3 Angle of Declination..................................................................................
- 2.7.4 Solar Time
- 2.7.4.1 Converting Clock Time to Local Solar Time....................................
- procedure:.............................................................................................................. Converting clock time to local solar time is accomplished by the following
- 2.7.5 Effect of Tilting the Reference Plane.........................................................
- 2.7.6 Apparent Trajectory of the Sun to an Observer on the Earth
- 2.7.7 Solar Angles and Their Determination
- 2.7.8 The Sun Angle Chart
- CHAPTER
- SOLAR WATER HEATING SYSTEMS
- 3.1 I NTRODUCTION
- 3.2 PASSIVE HEATING SYSTEMS
- 3.2.1 Batch Heaters............................................................................................
- 3.2.2 Thermosiphon Systems
- 3.2.3 Drawbacks of Passive Systems.................................................................. vii
- 3.3 ACTIVE SOLAR DOMESTIC WATER H EATING
- 3.3.1 Introduction...............................................................................................
- 3.3.1.1 Solar Collectors
- 3.3.1.2 Thermal Storage Tank...........................................................................
- 3.3.1.3 Heat Transfer Medium and the Mechanical Distribution System.........
- 3.3.1.4 Controls for Active Solar Systems
- 3.3.2 Types of Active Solar water Heaters
- 3.3.2.1 Direct or Open Loop Systems
- 3.3.2.1.1 Drain down systems
- 3.3.2.1.2 Recirculating systems......................................................................
- 3.3.2.1.3 Drawbacks.......................................................................................
- 3.3.2.2 Indirect or Closed Loop Systems
- 3.3.2.2.1 Drain back System
- 3.3.2.2.2 Double Walled Glycol Systems
- CHAPTER
- SOLAR HEATER COLLECTORS
- 4.1 EVACUATED -TUBE COLLECTORS
- 4.2 CONCENTRATING COLLECTORS
- 4.3 FLAT -PLATE COLLECTORS
- 4.3.1 Liquid Collectors.......................................................................................
- 4.3.2 Air Collectors
- 4.3.3 Components of the Flat Plate Collectors
- 4.3.3.1 The Absorber Plate................................................................................
- 4.3.3.2 Collector Glazing
- 4.3.3.3 Desiccants..............................................................................................
- 4.3.3.4 Collector front surface coating..............................................................
- 4.3.3.5 Insulation...............................................................................................
- 4.3.3.6 Piping System........................................................................................
- 4.3.3.7 Enclosure...............................................................................................
- CHAPTER
- DESIGNING OF A SOLAR WATER HEATER SYSTEM
- 5.1 DETERMINING THE DOMESTIC HOT -WATER LOAD
- 5.2 THE HOT -WATER STORAGE TANK SIZE .............................................................
- 5.3 EFFICIENCY OF THE COLLECTOR PLATE .............................................................
- 5.4 CALCULATIONS FOR THE AREA OF THE COLLECTOR PLATE
- 5.4.1 Insolation Data For Islamabad.................................................................
- 5.5 CALCULATIONS OF OVERALL HEAT LOSS COEFFICIENT (U L).............................
- 5.5.1 Heat Loss Through the Top.......................................................................
- 5.5.2 Heat Loss Through the Bottom
- 5.5.3 Heat Loss Through the Edges
- 5.5.4 Total Heat Loss Coefficient.......................................................................
- 5.6 CALCULATIONS FOR THE PUMP SELECTION
- 5.7 TEMPERATURE RISE OF THE FLUID
- 5.8 SPECIFICATIONS OF A DESIGNED SYSTEM viii
- CHAPTER
- DISCUSSION
- CONCLUSIONS:
- REFERENCES
- APPENDIX A
- Figure 2-1: The cross sectional view of different layers of the Sun [2]................ List of Figures
- by wavelength. Visible light has a spectrum that ranges from 0.40 to 0. Figure 2-2: Some of the various types of electromagnetic radiation as defined
- micrometers (μm) [12].
- Figure 2-3: The solar radiation spectrum [11].
- Figure 2-4: Sketch illustrating the components of total insolation. [3]..............
- Figure 2-5: Movement of the earth around the sun [3].
- (a) at about 40 0 N Lat and (b) at about 40 0 S Lat. [3]......................................... Figure 2-6: The apparent motion of the Sun, as seen by the observer on earth
- Figure 2-7: Solar Declinations [4].
- Figure 2-8: Solar Declination Vs the months of the year [3].
- Figure 2-9: Curve of the equation of time (ET) [3].
- Figure 2-10: Angles locating the Sun relative to a horizontal plane [4].
- Figure 2-11: Effect of tilting a surface towards south [4].
- Figure 2-12: The angles necessary for the solar system design [3].
- [3].......................................................................................................................... Figure 2-13: The Sun Angle Chart. Note that the times are in local solar time
- Figure 3-1: Batch Heater System [13]
- Figure 3-2: The thermosiphon Systems...............................................................
- Figure 3-3: The drain down solar water system.
- Figure 3-4: Indirect pumped system using antifreeze solution [6]....................
- Figure 3-5: Drain back hot water system [6].
- Figure 4-1: Evacuated-tube collectors are efficient at high temperatures [7].
- applications [7]..................................................................................................... Figure 4-2: Parabolic-trough collectors are generally used in commercial
- Figure 4-3: Glazed flat-plate collector [7]...........................................................
- Figure 4-4: The serpentine and parallel plate pattern [7].
- Figure 5-1: A graph plotted for the daily hot water consumption
- Figure 5-2: Solar Insolation For Islamabad [9].
- Figure 5-3: The flow chart for the designing a solar water heater
- Figure 5-4: Solar Water Heater System Design..................................................
- Figure A-1: Variation o the collector area with the number of occupants.
- Figure A-2: The variation of the pump power with the number of occupants
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Abstract
The renewable energy sources are very much needed nowadays when other sources are vanishing very quickly. Solar water heater is one of the uses of the renewable energy. The purpose of this project is to design a solar water heater for the location of Nilore, Islamabad. The source of energy for the solar water heater is sun so one needs to have maximum amount of energy from the sun. The optimum value for the maximum solar energy is +10 o^ to the latitude of the location where solar collector is to be placed in the winter season of the northern hemisphere. There are several solar water heating systems. They are classified into two classes i.e. passive and active heating systems. Different solar collectors have been studied but the preference is given to the flat-plate collectors with parallel flow piping system due to their low cost and simple designing. A complete solar water heating system is designed using a self-developed MATLAB code. This code helps in calculating different parameters such as hot water load, heat load, collector efficiency, the collector area and the pump power for the specific requirement of the user. Sample calculations have been done for 6 and 12 occupants of a typical household. The calculated values of the hot water load, heat load, collector plate efficiency, collector plate area and pump power for 6 occupants are 100gal/day, 3370 Btu/hr, 59%, 2.73m^2 and 0.0068hp respectively. Similarly, calculations for 12 occupants are 190 gal/day, 6417 Btu/hr, 59%, 5.1852 m^2 and 0.0131 hp respectively. The power of the pump lies in the range of the commercially used pumps for solar water heating which is 0.01-0.04 hp.
Chapter 1
Introduction
Solar radiation is a general term for the electromagnetic radiation emitted by the sun. This radiation can be captured and converted here on the Earth to useful forms of energy, such as heat and electricity, using a variety of technologies. The technical feasibility and economical operation of these technologies at any specific location is very dependent on the nature of the solar resource. The amount of solar energy shining on a building also affects the amount of energy required to heat and cool the interior of the building. Solar radiation has a spectral, or wavelength, distribution from short wavelength radiation (gamma and X-rays) to long wavelength radiation (long radio waves). The range of their wavelengths can describe the different regions of the solar spectrum [1]. The combined radiation in the wavelength region from 280 nanometers (nm; a nanometer is one billionth of one meter) to 4,000 nm is called the broadband, or total, solar radiation. About 99 percent of solar radiation is contained in the wavelength region from 300 nm to 3,000 nm. The region of the spectrum that is visible to humans (sunlight) extends from about 390 nm (ultraviolet) to 780 nm (near-infrared), and makes up only about 10 percent of the total solar spectrum. However, it is the most practically useful part of the spectrum for humans (and most other life on the planet). This is because the wavelengths of the solar spectrum also correspond to different energy levels. Short- wavelength radiation has a higher energy level than long-wavelength radiation [1]. The rate at which solar radiation strikes earth's upper atmosphere is expressed as the "solar constant." This is the average amount of energy received in a unit of time on a unit of area perpendicular to the sun's direction at the mean distance of the earth from the sun: 92,960,000 miles (149,604,970 kilometers). While the distance between the earth and the sun varies as the earth moves around the sun on its elliptical orbit, the variation in the distance does not have a significant effect on the amount of solar radiation reaching the earth. (The earth is closest to the sun in late December/early January, and farthest from the sun in late June/early July.) The average intensity of solar radiation reaching the
(kWh), or 12,969 Btu, per square meter (10.76 square feet) per day, while a vertical surface will receive 3.3 kWh (10,239 Btu) per square meter per day. In July, the horizontal surface will receive 6.6 kWh (22,526 Btu) per square meter per day and the vertical surface will receive 2.6 kWh (8,874 Btu), because the sun is higher in the sky in the summer and strikes the horizontal surface more directly. When the sun is lower in the sky in December, the horizontal surface will receive 1.9 kWh (6,485 Btu) per day, while the vertical surface will receive 3.4 kWh (11,604 Btu). For solar collectors where the angle is fixed (such as low-temperature, flat-plate water or space heaters) an optimum angle must be selected. The general rule of thumb is that for maximum solar reception during winter months, the optimum angle is the angle of latitude plus 10 degrees. For maximum solar reception in summer months, the optimum angle is the angle of latitude minus 10 degrees. Some types of solar energy conversion systems use a tracking device that positions a solar collector to face the sun. A tracking system is necessary for solar energy systems that concentrate sunlight onto an absorber. Concentrating solar collectors use primarily direct beam solar radiation. Flat- plate collectors (in fixed positions and on trackers) can use direct beam and diffuse radiation, and even radiation reflected off the ground or surrounding objects and fixed reflectors [1]. The use of the solar energy as a source of heat is very old but it was more useful when the principle of greenhouse effect was used in it. The principle of the greenhouse effect is that when the solar energy passes through some glass, it is trapped inside the glass enclosure and can be used as a source of heat energy. Solar water heaters also work on this principle. The solar collectors are used to collect the heat energy using the principle of greenhouse effect and then this heat energy is convected away with the help of some fluid (mostly water) and can be used as hot water for the household purpose. There are different methods of convecting the solar heat energy from the collector plate and these methods vary from system to system. There are basically two different categories of the solar water heater systems. These are:
- Passive Systems
- Active Systems
1.1 Objectives of The Project
The objective of this project is to design a solar water heater system for the residence of Islamabad. Also to develop a code in matlab for the designing of a complete solar water heater system.
1.2 Layout of The Thesis
Chapter 2 is related to the solar radiation and the solar geometry. It gives the brief introduction about the solar radiations and the solar geometry that are very necessary for the designing for a solar water heater.
In chapter 3, different kinds of solar water heating systems so far used in the world are discussed in details. This chapter also describes the advantages and disadvantages of each system.
Chapter 4 gives the complete information about the solar water-heating collectors. But the main emphasis in this chapter is given on the flat plate collectors.
In Chapter 5, different designing parameters and rules are defined and then, a complete specification of a system is given. In the end, a complete code is presented in the Appendix A, which is developed in MATLAB.
He He He H H
or
H H He e
H H H
H H H e
23 23 24 11 11
11 23 24 01
11 21 23
11 11 12 01
(2.1)
The energy released per reaction is about 25 MeV.
2.3 Layers of Sun
The Sun has different layers starting from the core to corona depending upon the variation in temperature and reactions taking place in these layers. These layers are discussed in details below.
2.3.1 The Core
The innermost layer of the sun is the core. It is shown in the black color in Figure (2.1). With a density of 160 g/cm 3 , 10 times that of lead, the core might be expected to be solid. However, the core's temperature of 15 million Kelvin (27 million degrees Fahrenheit) keeps it in a gaseous state. In the core, fusion reactions produce energy in the form of gamma rays and neutrinos. Gamma rays are photons with high energy and high frequency. The gamma rays are absorbed and re-emitted by many atoms on their journey from the envelope to the outside of the sun. When the gamma rays leave atoms, their average energy is reduced. However, the first law of thermodynamics (which states that energy can neither be created nor be destroyed) plays its role and the solar envelope will eventually become a large number of low-energy photons [2]. The neutrinos are extremely non reactive. To stop a typical neutrino, one would have to send it through a light-year of lead! Several experiments are being performed to measure the neutrino output from the sun. Chemicals containing elements with which neutrinos react are put in large pools in mines, and the neutrinos' passage through the pools can be measured by the rare changes they cause in the nuclei in the pools. For example, perchloroethane contains some isotopes of chlorine with 37 particles in the nucleus ( protons, 20 neutrons). These Cl-37 molecules can take in neutrinos and become radioactive Ar-37 (18 protons, 19 neutrons). From the amount of argon present, the number of neutrinos can be calculated [2].
Figure 2-1: The cross sectional view of different layers of the Sun [2].
2.3.2 Solar Envelope
Outside of the core is the radiative envelope, which is surrounded by the convective envelope. The temperature is 4 million Kelvin (7 million degrees F). The density of the solar envelope is much less than that of the core. The core contains 40 percent of the sun's mass in 10 percent of the volume, while the solar envelope has 60 percent of the mass in 90 percent of the volume. The solar envelope puts pressure on the core and maintains the core's temperature. The hotter a gas is, the more transparent it is. The solar envelope is cooler and more opaque than the core. It becomes less efficient for energy to move by radiation, and heat energy starts to build up at the outside of the radiative zone. The energy begins to move by convection, in huge cells of circulating gas several hundred kilometers in diameter. Convection cells nearer to the outside are smaller than the inner cells. The top of each cell is called a granule. Seen through a telescope, granules look like tiny specks of light. Variations in the velocity of particles in granules cause slight wavelength changes in the spectra emitted by the sun [2].
The corona is hotter than some of the inner layers. Its average temperature is 1 million 0 K (2 million 0 F) but in some places it can reach 3 million 0 K (5 million degrees F). Temperatures steadily decrease as we move farther away from the core, but after the photosphere they begin to rise again. There are several theories that explain this, but none have been proven [2].
2.4 Solar Spectrum
All objects above the temperature of absolute zero (-273.15 0 C) radiate energy to their surrounding environment. This energy, or radiation, is emitted as electromagnetic waves that travel at the speed of light. Many different types of radiation have been identified. Each of these types is defined by its wavelength. The wavelength of electromagnetic radiation can vary from being infinitely short to infinitely long (Figure 2.2).
Figure 2-2: Some of the various types of electromagnetic radiation as defined by wavelength. Visible light has a spectrum that ranges from 0.40 to 0.71 micrometers (μm) [12]. Visible light is a form of electromagnetic radiation that can be perceived by our eyes. Light has a wavelength of between 0.40 to 0.71 micrometers (μm). Figure (2-2) illustrates that various spectral color bands that make up light. The sun emits only a portion (44 %) of its radiation in zone. Solar radiation spans a spectrum from approximately 0.1 to 4.0 micrometers as shown in Figure (2.3).
Figure 2-3: The solar radiation spectrum [11]. The band from 0.1 to 0.4 micrometers is called ultraviolet radiation. About 7 % of the sun's emission is in this wavelength band. About 48 % of the sun's radiation falls in the region between 0.71 to 4.0 micrometers. This band is called the near (0.71 to 1. micrometers) and far infrared (1.5 to 4.0 micrometers) [3].
2.4.1 Stefan-Boltzmann Law
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 Kelvin units. The Stephan-Boltzmann Law describes this natural phenomenon. The following simple equation describes this law mathematically with =5.67 10 -8^ Wm-2^ K-4^ and T is the temperature in Kelvin
E T^4 (2.2) According to the Stephan-Boltzmann equation, a small increase in the temperature of a radiating body results in a large amount of additional radiation being emitted. In general, good emitters of radiation are also good absorbers of radiation at specific wavelength bands. This is especially true of gases and is responsible for the Earth's greenhouse effect. Likewise, weak emitters of radiation are also weak absorbers of radiation at specific wavelength bands. This fact is referred to as Kirchhoff's Law. Some
After many years of careful observations and measurements, lately with input from instruments carried by satellites and spacecraft, scientists have agreed on an average value for the solar constant as I 0 = 429 Btu/hr-ft 2 or 1.353kW/m 2. We speak of an average value for the solar constant because it does vary somewhat, partly because of the sunspot activity, which reduces solar radiation intensity. The elliptical orbit of the earth around the sun, however, causes the major variation. The sun and the earth are closest to each other in January and farthest apart in July. This distance variation causes the solar constant to be about 6 percent greater in January than it is in July. For solar heating, this is a fortuitous circumstance for the northern hemisphere, since solar power is at its maximum at the season of greatest need [3].
2.6 Solar Insolation
The usable solar power available at a location on the surface of the earth is referred to as insolation. (Note the spelling, and do not confuse this word with insulation, a substance that impedes heat transfer by conduction.) Insolation is accurately defined as the intensity of solar radiation that is incident normal (that is, perpendicular) on unit area of a plane surface. It is the rate at which solar energy is available per unit of surface area and is therefore a measure of solar power. Solar power, or solar radiation intensity, can be expressed in any of the units shown below in the Table 2.1.
Table 2-1 The units or solar insolation Parameter Units Btu/hr-ft 2 or Btu/day-ft 2 hp/ft 2 W/m 2 or kW/m 2 Ly/min or Ly/day KJ/hr-m^2
Solar Insolation
Kcal/sec-m^2 Insolation at the earth s surface consists of wavelengths in the general range from about 0.32 m to about 2.5 m, with nearly all of the usable energy in the visible and
near-infrared regions of the spectrum [3]. Total solar radiation intensity (insolation) received on a surface is denoted by the symbol I. It is made up of three components, defined as follows, and its value depends on
the angle between the incoming solar rays and the normal to the surface (Figure 2.4 ). I (^) DN is the intensity of direct-beam solar radiation on a surface perpendicular (normal) to the sun s rays. Direct-beam solar radiation follows a direct path from the sun to the receiving surface and forms an angle with the normal to that surface. The greatest amount of usable solar power is provided by this component [3]. I d is the component of total insolation contributed by diffuse radiation from the sky, caused by the scattering effects of air molecules, water vapor, or contaminants in the atmosphere. On clear days, diffuse radiation amounts to only about 15 percent of total insolation, while on days with complete cloud overcast, although total insolation will be small, I d could account for a large part of the insolation received. I (^) r is the component of total insolation contributed by reflection from bodies on the earth s surface buildings, paved surfaces, the surrounding ground, and bodies of water. is the angle between the incoming solar rays and the normal to the receiving surface. It is called the angle of incidence. In summary, then, the total insolation incident on a flat surface is I=I (^) DN cos + I (^) d + I (^) r (2.4) The term I (^) DN cos is the direct-beam radiation incident on a surface that is tilted in such a way that its normal forms an angle with the incoming solar radiation. Figure 2. illustrates the factors involved in Eq. (2-4).
Figure 2-4: Sketch illustrating the components of total insolation. [3]
