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PERFORMANCE STUDIES OF A

BUILT-IN-STORAGE TYPE SOLAR

WATER HEATER

AT DHAKA IN THE MONTH OF

JANUARY-MARCH

By

A. K. M. ABDUL HAMID

A Project Report Submitted to the Department of Mechanical Engineering in partial fulfillment of .the requirements for the

degree of'

MASTER OF ENGINEERING (MECHANICAL)

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RECOMMENDATIONOF THE BOARDOF EXAMINERS

The Board of Examiners hereby recommends to the Department of Mechanical Engineering, Bangladesh University of Engineering and Technology, Dhaka, the acceptance of the project report on "Performance Studies of a Built-in-Storage Type Solar Water Heater at Dhaka in the Month of January-March", submitted by A.K.M.Abdul Hamid, in partial fulfillment of the requirements for the degree of Master of Engineering in Mechanical Engineering.

Chairman

Dr. Md. Ab Professor,

Mechanical Engineering Department BUET, Dhaka.

•..

Member:

(Ex-Officio)

Member

Dr. Md. Wahhaj Uddin Professor

&

Head

Mechanical Engineering Department BUET, Dhaka.

Dr. Md. Abdul' Rashid Sarkar Associate Professor,

Mechanical Engineering Department BUET, Dhaka.

CERTIFICATE OF RESEARCH

This is to certify that the work presented in this project report is an outcome of the investigation carried out for the first time by the author under the supervision of Dr. Md. Abdur Razzaq Akhanda, Professor, Mechanical Engineering . Department, Bangladesh University of Engineering and Technology, Dhaka.

Prof. Dr. Md. Abdur Razzaq Akhanda Supervisor

Dated: July 15, 1993.

iii

ACKNOWLEDGEMENT

The author expresses his sincere gratitude and indebtness to Prof. Dr. Md. Abdul' Razzaq Akhanda for his guidance and supervision of this experimental investigations. His continuous encouragement, invaluable suggestions and patience, without which it was beyond the author's ability to finish this work, are gratefully acknowledged.

The author also expresses his sincere gratitude and indebtness with great pleasure to Dr. Md. Wahhaj Uddin, Professor and Head, Mechanical Engineering Department, Bangladesh University of Engineering and Technology (BUET), for going through the scripts. The author ever so gratefully acknowledges his invaluable suggestions and corrections of the final project report.

He is also grateful to Prof. Dr. Md. Qualllrul Islam for his encouragement and constructive suggestions from the beginning to the end of this research work.

The author would like to express his gratefulness to Md. Moniruzzalllan, Assistant Professor, for his guidance and cooperation without which this work would not have heen carried out properly.

He would also like to acknowledge the help and cooperation extended hy the office of the Department of Mechanical Engineering, Bangladesh University of Engineering and Technology (BUET), for allowing him to use the apparatus and the Instruments for this investigation. He expresses his thanks to MI'. Md.

Fakhrul Islam Hazra for the typing of the project repol't.

Lastly, he would like to thank his wife who persistently kept this at. ~ work and partly relieved him of family duties until this work was finished.

ABSTRACT

A Built-in-Storage Type Solar Water Heater (BSWH),115 litres in capacity, 1.25m² of collector surface area, and 92 mm in depth was studied at Dhaka during the months of January, February, and March, 1992. In four hours starting at 8 AM, the BSWHcan heat 115 litres of water to a temperature of 50°C absorbing 0.743 kW/m²in February and to 61°C absorbing 0.979 kW/m² in March. From February to March the energy is increased by 32 percent but the water temperature is increased by 22 percent. The monthly average heat energy absorbed by BSWHis 0.240 kW/m² with 59 percent efficiency in February and 0.270 kW/m² with 54 percent efficiency in March. From February to March, the average heat energy absorbed by water increased by 12.5 percent but efficiency reduced by 8.5 percent. This differences in heat energy absorption is because of the fact that loss of heat increases rapidly with the rise of water temperature in March. On

very dear bright sunny days, the maximum efficiency of 70 percent can be obtained with a mean water temperature of 56°C in February and 58 percent efficiency with a mean water temperature of 63°C in March.

I~C

Accui~lUl-a-te-d~V-aiue , .av Average Value

L:"~~__ . ._- --~

, ^Symbols A c

I M N Q

T AT

X Y 1)

Subscripts a

w p

m

NOMENCLATURES

Definitions Area

Cofficient of Specific Heat of Water Solar Insolation

Mass

Day Length of Bright Sun Shine Rate of Heat Energy

Temperature

Change in Temperature Solar Insolation

Heat Eneragy Efficiency

Ambient Water Pressure

Maximum

vi

Units

kJ/kg.K kW/m² kg

hr

W

°c

°c

cal/cm².day langley/min

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CONTENTS

Recommendation of the Board of Examiners Certificate of Research

Acknowledgement Abstract

Nomenclatures Contents

ii iii iv

v vi vii

CHAPTER- 1 Introduction

1.1 1.2

General

Solar Energy Collections

1 2

W

1.2.1 Natural Collections of Solar Energy

1.2.2 Technological Collections of Bolar Energy 1.3 Solar Collectors

1.3.1 Flat-Plate Collectors

1.3.2 Concentrating or Focusing Collectors

1.3.3 Intermittently Turned Concentrating Collectors

3 3 4 4 7 7

1.4

Prospect of Solar Energy Harnessing in Bangladesh 8

CHAPTER- 2 Literature Survey 10

2.1 2.2 2.3

Short Historical Review of Solar Energy Activities Built-in-Storage Type Solar Water Heater (BSWH) Scope of Work

vii

10 11

12

CHAPTER- 3 Experimental Apparatus and Test Procedure

13

3.1 3.2

3.3 3.4

General Description of the Apparatus

Fabrication of a Built-in-Storage Type Solar Water Heater

3.2.1

Built-in-Storage Solar Collector

3.2.2

Surface Covering

3.2.3

Insulation

3.2.4

Casing

3.2.5

Steel Stand and Structure Test Procedures and Measurements Reduction of. Data

13 13

14

14

15 15 15

15 16

CHAPTER- 4 CHAPTER- 5

Results and Discussions

Conclusions and Recommendations

17

21

REFERENCES

5.1

5.2

Conclusions Recommendations

21

23

25

APPENDICES Appendix Appendix

A B

Figures

Sample Calculations

viii

30

31

62

CHAPTER 1 INTRODUCTION

1.1 General

The rate of exploitation of any non-renewable sources of energy increases with time, reaches a maximum, and then ultimately reduces to zero. According to various estimates, world's production of fossil fuels and other exhaustible energy bases will last only for a limited time. For example, in Bangladesh, Oil will last for another 32 years, and Gas 58 years. From environmental point, to-day's use of conventional exhaustible energy sources is leading the world to its ultimate destruction. Hence it is a matter of concern, not only for better living .standard but also for very survival of the world, to device, develop, and deploy all possible techniques to extract energy from renewable energy sources .. It is essential to develop methods of diversification of energy sources, reduction of energy consumption and increasing the efficiency in the utilization of energy.

Otherwise, there will be world wide economic and political chaos.

Fortunately, the sun is an everlasting source of renewable energy. It is emitting energy at the rate of about 3.8 x 10²³ kW of which only a tiny fraction of L73 x lO^J4 kW is intercepted by the Earth. Ignoring all areas of seas, the amount of solar energy received by the rest of the land area of earth is 2.025 kW (or 162.2 x 10¹² kWh/day, assuming eight hours of sunshine a day, or approximately 60 x 1015 kWh/year) [Rai 1984].

Solar energy is clean and safe with no significant polluting effects. It exists in abundance all over the world. To utilize this energy for practical purposes it is essential to know how much of the energy is available and how much of this available energy can be collected and stored for use. Hence both theoretical and experimental data of solar radiation intensities at various locations of concern must be known.

The sources of informations on solar energy are wide spread. But for Bangladesh, year round practical data on solar radiation intercepted and converted into useful energy by various means are not available yet. Under these circumstances, it is necessary to record relevant data on solar radiation for scientists, engineers and for those who are interested in solar energy research and development work to enhance further studies.

Withrising fuel prices and increasing development of solar collectors, solar water heaters operating at temperature below 900Cmay conveniently be served by flat- plate collectors. The present research project is devoted to the development of a heater of this type for use in Bangladesh.

1.2. Solar Energy Collections

The continuous radiation of heat !;(enerated by the sun intercepted by the Earth is called Solar Energy. According to Solar Energy Panel of NSF/NASA,there are two collection systems of solar energy. These are

1. Natural Collections of solar energy such as wind, waves etc., and II. Technological Collections of solar energy such as photovoltaic,

thermal conversions etc.

2

1.2.1 Natural Collections of Solar Energy

Waves, Winds, Biological conservations are some examples of natural collections of ,

solar energy. About 71% of the world's surface is covered with oceans which provide tremendous store house of solar energy. The oceans holds the energy a"

sensible energy of water as well as wave energy. Utilization of wind power has been widespread since prehistoric days. The energy content of the wind increases as the third power of the wind velocity and hence wind power installations are economical where unidirectional winds of sufficient speed i"

available. In biological conversion the solar energy is present in the form of Vegetables, Plants, Animals, Organic Fuel><,Fossil Fuels etc.

1.2.2 Technological Collections of Solar Energy

There are two methods for technological collection". These methods are a. Photovoltaic Conversions Method, and

b. Thermal Conversions Method.

In Photovolt.aic Conversion Met.hod,the solar energy is converted directly into electricity by means of photo cells with efficiency ranging between from 15 to 20 percent. The technology involved is well developed but large scale application is absent due to high cost. of photo cells.

In Thermal Conversion methods, the solar radiation is collected as heat energy employing different techniques of collector technology like solar water beater, solar cooker, solar ponds, stills, etc. Thermal ,",onversiontechnology is discussed below in details under the heading of solar -tb,,=

3

1 collectors.

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1.3 Solar Collectors

Depending on the methods of collector technology, all solar collectors can be classified into three classes, namely,

I. Flat- Pate collectors,

II. Concentrating or Focusing collectors, and III. Intermittently turned concentrating collectors.

1.3.1 Flat-Plate Collectors

Flat- Plate collectors operate without concentration. It is simple, technically feasible and economicallyviable for obtaining temperature helow lOOoC.The basic technology involved is to place a dark surface in sunshine to absorb solar energy to heat up the plate and to transfer this energy into fluid in contact with it. To reduce the reflected and convected heat from the heat loss from the absorber plate, to the atmosphere, one or two sheets of glass or polythene are placed over the absorber. This type of collectors may further he subdivided into three classes. These are

I. The plain sheet collectors,

II. The plain sheet and tube collectors, and III. The corrugated sheet collectors.

The storage tank may he combined with the collector in a single unit.

Alternatively, the storage tank and the collector may be built separately as two different units.

4

/

I /

In the plain sheet and tube collectors, if the tube and sheet are not welded together or poorly welded, the thermal resistance between the tube and the sheet would increase leading to poor performance, [Whiller, 1964]. In plain sheet and corrugated sheet collectors, absorbed solar energy is transferred as fluid sensible heat through direct contact and hence, from the view point of heat transfer, the advantage is evident.

A typical liquid-heating flat-plate collector in its simplest form comprises the following five components

i. Collector plate and storage tank, ii. Surface covering,

iii. Fluid,

iv. Insulation, and v. Casing.

The.se collectors have been extensively studied by Garg et. a1.[1973, 68, 72, 67], Gupta [1967], Desa [1964], Morse [1961], Bliss [1959], and Hottel et. al. [1942].

Domestic solar water heater using natural circulation are gaining popularity in different countries like Australia [Morse, 1970], Israel [Yellet et. al., 1964], and USA[Hawkin,1947]. Large size solar water heaters, designed for community, have been developed by Garg 11973] and Morse [1970].

The materials used for collectors in decreasing order of coast and thermal conductivity are copper, aluminum, and steelo~Williereto al.91964] have found that steel pipes are as good as copper pipes. If the temperature difference between the collector and the ambient air exceeds 6.5°C, one layer of glass cover is justified. Two layers of glass covers are required when it exceeds 30°Cand three layers for temperature exceeding 75°C [Eggers et. al., 1979].

Glasswoolis most widely used in collectors as insulation materials because of its low thermal conductivity and moderate cost. Plastic foam may be used and can add structural strength when moulded integrally between the collector and the collector case [Eggers et. al., 1979].

Glassfibre reinforced plastics are used as cases instead of steel sheets, because they are strong, lighter, water proof, weather resistent and do not corrodes [Eggers et. al., 1979].

Prior to 1955, black paint was the coating that was usually employed for solar collectors. It is possible to produce highly efficient black coatings for solar collectors by electrolytic and chemical treatments like Nickel-Black, and Copper Oxide [Eggers eto al.,1979, (Tabor et.al.,1955)]. These coatings possesses high values of solar radiation absorptance and low value at logwave emittance.

Built-in-storage type solar water heater, proposed by Tanishita l196J.], is considered Lo be an improvement over conventional collectors because of its reduced overall size, cost, loss of heat, etc .. It is given in detail in Chapter-2.

1.3.2. Concentrating or Focusing Collectors

This type of collectors are designed to produce very high energy density and high temperature at the receiver (absorber) by means of accurate focusing devices and continuous tracking of the sun's motion.. In fact it is a special type of flat-plate collector modified by introducing a reflector or refracting surface between solar radiation and the absorber which increases the energy density by a factor of 1.5 to 10000or over. The absorber may be convex, flat or concave and may be covered or uncovered. French solar furnace at Odeillo, Trombe(1973), has achieved temperature over 3000oC.The operating and collector cost has restricted the utility of concentrating collectors. However, new materials and better engineering technology may make them of practical importance.

1.3.3 Intermittently Turned Concentrating Collectors

Between the above two extreme groups, with energy density increasing by a factor of 1.5 to 10, is the third group, called intermittently turned concentrating collectors. They are either fixed or occasionally turning to track the sun and

have no sharp focusing devices.

1.4 Prospect of Solar Energy Harnessing in Bangladesh

Bangladesh with an area of 150,000 km² and a population of about 110 million people is one of the most populous countries in the world. But its position is the lowest in terms of commercial fuel use.

Industrialization and mechanization of agriculture with increasing demand of electricity would continuously aggravate the energy scene creating serious problems in the energy sector and the future economic development of the nation.

With the rise of demand of energy, the research and development related with new energJ' sources is a primary requirement. Bangladesh is more vulnerable than any other country. Hence it is vital to explore alternative energy sources like solar energy.

Bangladesh, located between 24°26' and 26°20 latitude and 80°01' and 92°24' longitude, is endowed with an abundance of sunshine during most of the year and blessed with sufficient amount of indigenous non-depletable resources of solar energy. The average incident rate of solar energy in Bangladesh is about 3000 times its present consumption rate [Hossain, 1980J.

The mean monthly average daily total solar radiation in Dhaka is 0.376 kW/ml

and in Bangladesh 0.365 kW/m^2• The maximumand monthly average daily radiation in Bangladesh are found to be 0.473 kW/m²and 0.292 kW/m² during the month of April in Dhaka and January in .Jessore respectively [Helali, 1985J.

The yearly total diffuse in radiation in Dhaka is considerable. It is about 72 percent of the total radiation [Helali, 1985]. This aspect should be taken into corlsideration when one designs focusing collectors.

I

CHAPTER 2

LITERATURE SURVEY

2.1 Short Historical Review of Solar Energy

The first practical application of solar energy is not known. However, in prehistoric times, in Iraq, polished golden vessels were used to ignite fire by means of the sun. Around 1455 B.C., in Egypt, 'Sounding States' were found, the sound being caused by escaping air which had been heated by the rising sun falling on them. In China, the Han-dynasty (202 B.C.'>used concave mirrors to light torches for sacrifices.

Modern application of solar energy started probably in 1855, C Guntur, an Australian, invented a solar boiler using mirrors. The first major solar energy installation is probably the water distillation plant in Chile, built in 1872, covering an area of 4800m2 producing 2300 litres of distilled water a day.

Shuman et. a1., in 191.2-13,built the world's largest solar water pump of 37 to 40 kW to pump water from the Nile for irrigation. In October 1973, the Arab members of OPEC temporarily stopped the export of oil which lead to severe energy panic and subsequent realization of the importance of research and development of alternative energy sources without delay.

Industrialized countries, such as USA, USSR, Japan, France, Germany, and Canada are very advanced in solar energy technology and offer higher level teaching at their universities. Australia and Israel have contributed notably to solar science and technology with thousands of apartments enjoying solar water heaters. Brace Research Institution in Canada has done extensive research works covering almost all fields of solar energy.

Although, solar energy has been successfully utilized on space crafts, heating or cooling of buildings, solar water heaters, driers, cookers, pumps, refrigerators,.

furnaces, and photovoltaic conversions, the current developments in solar energy represents a milestone on the way to large-scale use of this inexhaustible source of energy in the future.

2.2 Built-in-Storage Type Solar Water Heaters (BSWH)

The Built-in-storage type solar water heater is the one in which the collector and storage tank are combined in one unit where water is heated and otored. The advantages of the built-in-storage type of solar water heater are absence of intricate mechanism to follow the sun and the ability to absorb both beam and diffuse components of solar radiation.

A comparative evaluation of the performances of three built-in-storage type water heaters of equal volume were carried out by Ecevit et. al. [1990J. They found that the triangular heater without baffle plate was most efficient (46 percent).

The rectangular and the triangular one with baffle plate heaters were 43 percent and 40 percent efficient, respectively. Ecevit et. al. [1989J studied three built-in- storage type solar water heaters with different volumes and found that the rate of heating rises as the heater becomes narrower, producing enhanced natural convection and Lhus resulting in better performance during heating period.

Vaxmanet. al. [1985J found the maximumbulk efficiency of triangular heater with baffle plate to be 53 percent from 9 to 1.1 AM and 15 percent at the end of 24 hour cycle due to no radiation. Sokolov et. al. [1983] also showed that the performance of Lhe rectangular and triangular one with baffle plates were same.

Garg [1982] carried out year round performance test on rectangular healer of capacity 90 ]itres and showed that it can supply 90 litres of water at a mean temperature of 50 to 60°Cin winter and 60 to 75°C in summer. Chinnappa et. al.

[1973] studied pressurized built-in-storage type heater and found that 30-50 gal of water could be supplied a day at 120°F (A8.89°G)and the efficiency was 46 percent. The pioneer work on this type of heater was done by many researchers like Chauhan [1976J, Tanishita [1970], Close et. al. [1967], Richards et. al. [1967J and Tanishita

r

1964J.

2.3. Scope of the Work

A variety of technologies are available for harnessing renewable energy sources as indicated in the preceding literature survey. Specially, a lot of research works have been carried out all over the world on Flat-plate collectors. Sufficient information and experimental data have been provided for analysing the performance characteristics. But the work on BSWH still is in its infancy.

Researchers of this country have carried out only limited work on solar collector and the experimental data available are quite inadequate for analysing the performance characteristics. Whereas, the geographical position of this country shows that this country is blessed with sufficient amount of solar energy throughout the year, as mentioned in Chapter-1.

It is expected that the major part of energy requirements in the future may be met from solar energy source. This suggests the scope to study and work on a BSWHat Dhaka. It was thus decided to study BSWHhere during months of February-March, to furnish adequate information and experimental data for its performance cbaracteristics. Accordingly, an extensive performance test of a built-in-storage type solar water heater was carried in the months of .Januaey, February, and March 1992. Both water temperature and ambient temperature Were recorded on hourly basis from 8 AMto 5 PM everyday. Solar insolations at Dhaka were taken from the work of Helali [1985]. Heat energy and efficiency of the collector were calculated. The results were compared with the available information in the literature.

'. f

CHAPTER 3

EXPERIMENTAL APPARATUS AND TEST PROCEDURES

3.1 General Description of the Apparatus

The experimental apparatus and measuring devices are shown diagramatically in Fig. 3.1. It consists of a Built-in-Storage Type Solar Water Heater (BSWH)and measuring equipments (Digital Voltmeter and Selection Switch), and Cold .Tonction (Ice Box). Solar energy in the form of heat is absorbed by the absorber plate of the collector and is transferred to the water of the built-in-storage tank of the collector. Five 36 SWGChromel-Alumelthermocouples installed in the storage tank at different depths are used to measure water temperature. These thermocouples are connected to the Digital Voltmeter (DVM)through the selector switch. The Digital Voltmeter (DVM)is used to measure water temperature in terms of e.m.f.

generated in the therinocouples.

3.2 Fabrication of a Built-in-Storage Type Solar Water Heater (BSWH)

The built-in-storage type solar water heater (BSWH)is illustrated diagramaU"ally in detail in Figs. 3.2-3.5 .The design details and of BSWH fabrication are explained as follows

3.2.1 Built-in-Storage Solar Collector

The storage tank and the solar collector were combined,and built as one unit. Its external dimensions are 137.16 cm x 91.44 cm x 9.21 cm with a capacity of 115 Htres. It consists of two 16 gauge G.I. sheets, one at the bottom and the other at the top. The top surface of the absorber plate was blackened with a dull paint in order to increase the absorptance of shortwave solar radiation. The wooden frame, made by 'Gorjon wood', supports the plate and, to avoid leakage of water, rubber gasket was used in between the frame and the G.I. sheet, securely tightened with nuts and bolts all around, as illustrated in Fig. 3.3a. For measurement of temperature of water at different depths, 5 Chromel-Alumel thermocouple probes were inserted inside the tank as illustrated in Figs. 3.3b and :3.4. Two G.I. pipes of diameter 19.05mmand length 45.72 cm were fitted one for cold water inlet at the front and the other one for hot water outlet at the back side of the collector unit.

3.2.2 Surface Covering

In order to admit as much solar radiation as possible as well as to reduce heat losses from the collector by re-radiation and convection to a minimumvalue, a glass cover of 142.24 cm x 101.60 cm x 5 mm, with optimum air gap of 25.4mm, iEggers, 1980], is used. This is due to high transmittance property of the glass, being highly transparent for short wave, high temperature solar radiation and practically opaque for longer wavelength infrared radiation emitted by the colledor plate below 1000. The glass rests on a wooden frame, made of 'gorjon'

of 142.24 cm x 101.60 cm x 24.61 cm and, is secured by wooden batten of 2.54 cm x 1.56.cm, screwed with the wooden box, as shown in Fig. 3.4(bl.

3.2.3 Insulation

The glass-wool because of its low thermal conductivity of 0.041 W/mK, and of moderate cost, was used as insulation having thickness of 2.86 cm at the bottom surface and 25.4mmat the sides.

3.2.4 Casing

The built-in-storage solar collector with insulation is contained in a wooden casing of 'Kerosine wood' having external dimensions of 147.32 cm x 106.68 cm x 29.21 em.

3.2.5 Steel Stand and Structure

The supplying steel stand structure consists of 152.40 em x 107.70 cm frame supported on a stand of 15.24 cm at the front and 152.40 em at the back. Another steel structure of dimensions 167.64 em x 108.92 cm, on which the BSWHis held rigidly, has the provision of setting the collector at. an y desired inclination

between 0⁰ and 40° manually, as shown in the Fig. 3.2.

3.3 Test Procedures and Measurements

Calibration of thermocouples was carried out in a hot water bath for temperatures

upto 100°C and in a muffle furnace upto a temperature of 200°C. The readings were compared with a precision thermometer. The indicated e.m.f. was compared with the tabulated values for Chromel-Alumel thermocouples of British Standard No. 4938, Part 4: 1973&. ASTME 230-72.

Before starting experiment, the. storage tank of the solar water heater was filled with fresh water through the gate valve attached to t.he collect.or's inlet pipe.

Care was taken so that no air bubbles were t.rapped in the tank.

The temperat.ure distribut.i.on along t.he depth of the tank was measured using 36 SWG Chromel-Alumel thermocouples. As mentioned earlier, a t.otal of 5 t.hermocouples (Figures S:::IR; 3.3b, ~ and 3.4) were used t.o obt.ain temperat.ure distribution. These temperatures and the ambient temperature were recorded every hour from 8 AM t.o 5 PM, everyday. The result.s obtained had a maximum error of :!: 2°C at. a maximumoperating t.emperature of 60°C.

3.4 Reduction of Data

The parameters which are pertinent to this investigation are ambient temperature

Ta, wat.er temperat.ure T^w' solar insolation I, heat energy q absorbed by the water in tank and efficiency 1) of the collector. The calculation of these parameters and plotting of graphs (Appendix: A) were carried out by a computer and the results were checked using desk calculator. The results are discussed in Chapt.er-4. The working formulas and sample calculations are provided in Appendix-A.

CHAPTER 4

RESULTS AND DISCUSSIONS

An experimental investigation was carried out for studying the performance characteristics of a Built-in-Storage Type Solar Water Heater IBSWH)in Dhaka during the months of January, February, and March, 1992. Everyday, the BSWH was filled with fresh water at 8 AMand, on hourly basis readings were taken until 5 PM. The results are presented graphically in Appendix-A.

~ The heat energy absorbed, the mean water temperature, and ambient temperature are shown in Figs. 4.1 to 4.38. It is observed from these figures that as the ambient temperature increases the mean water temperature also increases and reaches a maximum value at around noon. In the afternoon both water and ambient temperatures decrease at almost the same rate. The mean water temperature increases at a faster rate from 8 AM to 12 AM because the heat energy absorbed by water during tbis period is faster than that absorbed by water after 12 noon. From 8 AMto 5 PM, the average ambient temperature varies from 16 to Z9°C in February and 19 to 36°C in March. March is thus a relatively hotter month cbmpared to February. In four hours, starting from 8 AM,the heat energy absorbed by horizontally placed BSWHare considerably high varying from 0.572 to 1.067 kW/m²in February and 0.850 to 1.136 kW/m² in March. During this period the BSWHcan heat 115 litres of water upto a mean temperature of 50°C in February and 61°C in March. The heat energy absorbed on January 29, 1992 by the BSWHis presented in figure 4.1. The maximumheat energy absorbed by water and the maximum water temperature reached are 0.572 kW/m² and 41°C

17

••

respectively at noon. The average heat energy absorbed by water is 0.174kW/m^2•

The efficiency of BSWHis 51 percent compared with Helali [1985] and 35 percent compared with the value obtained by pyranometer on January 29, 1992.

The distribution of the daily maximumheat energy and the daily average heat energy absorbed by water are presented graphically in Figs. 4.39 & 4.40. The daily average heat energy absorbed by BSWHeveryday from 8 AM to 5 PM are quite low and these values varied from 0.183 to 0.292 kW/m² in February and 0.236 to 0.291kW/m² in March. The monthly average of maximum heat energy of 0.743 kW1m² measured at noon reduces to monthly average of daily average heat energy of 0.240 kW1m2 i.e. 68 percent less in February and the corresponding values in March are 0.979 kW/m2to 0.270 kW/m2i.e. 72 percent less. The maximum heat energy absorbed by water can be further increased and at the same time the losses in heat absorbed by the water can be reduced by placing the heater inclined at a certain angle in order to intercept maximumamount of direct beam of solar radiation during the first half of the day as well as by improving insulation technique.

In February, the maximumwater temperature reached varied from 42 to 60nCwith efficiency varying from 45 to 71 percent and in March from 56 to 65°C with efficiency varying from 47 to 58 percent, as shown graphically in Figs. 4.41 - 4.43.The monthly average maximumwater temperature and efficiency of the BSWH are 50°C and 59 percentinFebruary and 61°C with 54 percent respectively

in March. It is obserbed that, from February to March, the temperature attained by water increased by 22 percent but the efficiency reduced by 8 percent. So the efficiency of BSWHis greater at lower water temperature. Because, at higher

water temperature, the heat loss increases considerably and thus reduces the efficiency of the BSWH.On very clear bright sunny days, the maximumefficiency of 70 percent can be obtained with a mean water temperature of 56°C in February and 58 percent efficiency with a mean water temperature of 63°C in March.

In Fig. 4.44, the solar radiation measured by pyranometer on January 29, 1992 is presented along with mean water and ambient temperature. In the same figure the daily average hourly solar radiation for January recorded by Helali [1985] is also shown for comparison. It is found that the corresponding values of solar radiation measured by Helali are low.

The Fig. 4.45 represents the daily average hourly solar radiation recorded by Helali [1985] for the month of January, February, and March at Dhaka. The efficiencies are given on the basis of his data.

Results of February 11 and February 19 are compared with that of Chinnappa [1973] as shown in Figs. 4.46 - 4.49. Chinnappa studied combined collector and storage type solar water heater at Colombo.The heater consists of a square coil of 76.20mmdiameter pipe, 13.50m long, with two glass covers of 1.86 m2 in area and depth varying from 25.4 cm to 28 em. The heat energy absorbed by water is compared and the results are presented graphically i~ Figs. 4.47 and 4.48. The average heat energy at Dhaka and at Colomboare 0.243 kW/m² and 0.321 kW/m²

respectively. At Dhaka on February 11 and 19, the BSWHcan heat 115 litres of water in four hours from 8 AM to 45 to 56°C with efficiency of 59 percent compared with that of heating 490 litres of water to 64°C at Colombo with an efficiency of 46 percent. The heat energy absorbed by water at Dhaka is less

than that at Colombo.This is because of the fact that the corresponding values of the ambient temperature at Colombois much higher than that at Dhaka.

Also at Dhaka the ambient temperature is increasing upto 12 noon and then decreasing whereas at Colombo it is increasing from 8 AM to 5 PM as shown graphically in Figs. 4.47 and 4.49 on February 11 and 19 respectively.

The differences in results may be summarized as follows

a. Different types of heaters - one is flat plate collector with surface area 1.25m2 and single glass cover having a capacity of 115 litres (Dhaka) and the other one is square tubes welded to the collector with a surface area of 1.86 m² and two glass covers having a capacity of 490 litres.

b. Readings are taken at two different geographically located places and in different years (1992 in Dhaka and 1969 in Colombo).

c. The time of the year is same but the years as well as the weather conditions at two different locations are different.

CHAPTER 5

CONCLUSIONS AND RECOMMENDATIONS

5 • 1 CONCLUSIONS

From the investigations of the thermal performance of the Built-in-Storage Type Solar Water Heater under atmospheric conditions in January-March, the following conclusions can be drawn:

a. With the increase of ambient temperature the mean water temperature also increases but at a faster rate and reaches a maximumvalue at the maximum ambient temperature around noon. Both water and ambient temperatures then decrease at almost the same rate.

b. The heat energy absorbed by water from 8 AMto noon is faster than that absorbed' by water in the after noon. During this period the heat energy absorbed varies from 0.572 to 1.067 kW/m² in February and 0.850 to 1.136 kW/m² in March.

c. In four hours time from 8 AM the BSWHcan heat 115 litres of water upto a mean temperature of 50°C in February and 61°C in March.

d. The daily average heat energy absorbed by BSWHfrom 8 AM to 5 PM varies from 0.183 to 0.292 kW/m2 in February and 0.236 to 0.291 kW/m2

in March.

e. The monthly average of maximum heat energy of 0.743 kW/m² reduces to the monthly average of daily average heat energy of 0.240 kW/m2, that is 68 percent less in February and the corresponding values in March are 0.979 kW/m2 to 0.270 kW/m2 i.e. 72 percent less.

f. The maximum temperature attained by water varies from 42 to 60aC with efficiency varying from 45 to 71 percent in February, and in March, the maximumwater temperature attained varies from 56 to 65°C with efficiency varying from 47 to 58 percent. On the average, the maximum water temperature attained by water is 50°C with 59 percent efficiency in February and maximum water temperature of 6rC with 54 percent efficiency in March. The temperature attained by water is increased by 22 percent but the efficiency is reduced by 8 percent from February to March.

g. On very clear bright sunny days, the maximumefficiency of 70 percent can be obtained with a mean water temperature of 56°C in February and 58 percent efficiency with a mean water temperature of 63°C in March.

h. Considering the different types of solar collectors and also different modes of operation the results obtained by the BSWHat Dhaka are quite close to that obtained at Colombo.

5.2 RECOMMENDATIONS

The following recommendations concerning solar water heater are considered worth recording here for subsequent investigations.

a. The year round performance characteristics of the BSWHfor varying inclination should be studied.

b. According to Helali [1985], the yearly total diffuse radiation in Dhaka is about 72% of the total radiation. As the diffuse radiation corne from all directions, substantial amount of radiation can be captured by way of exposing all the sides of the heater unit like the top surface with glass cover. For designing the solar water heater to capture radiation from all directions, the storage tank may be built separately so that the water may be drawn off from the heater after achieving the desired water temperature and stored in a storage tank. This way maximumamount of water may be heated up leading to considerable increase of efficiency.

c. The built-in-storage type solar water heater should be strong enough to withstand severe winds, storms, hailstone, etc. They should be water tight yet should have vent holes located around the corner of the upheader to prevent condensation and at the same time the collector may set at a desired angle of inclination without spill over of water.

d. The performance of the heater at a predetermined constant water temperature should be investigated.

e. The performance of the BSWHfor different shapes of surface area of the collector with constant volume and varying inclination should be studied.

f. The effect on performance for various surface area with different depth of tank, keeping all other parameters fixed.

REFERENCES

Bliss R. W., 1959; "The Derivation of Several Plate Efficiency Factors useful in the Design of Flat-Plate Solar Collectors", Solar Energy 3, p. 55.

Chauhan R. S. and Kadambi V., 1976; "Performance of a Collector-Cum-Storage Type of Solar Water Heater", Solar Energy 18, p. 327.

Chinnappa J. C. V. and Gnanalingam K., 1973; "Performance at Colombo, Ceylon, of a Pressurized Solar Water Heater of the Combined Collector and Storage Type, Solar Energy" 15, p. 195.

Close D. J. and Lof G. O. F., 1967; "Solar Water Heaters in Low Temperature Engineering Application of Solar Energy", Ch. 6, p. 61478, ASHRAE.

DeSa, V.G. 1964; "Solar Energy Utilization at Dhaka", Solar Energy. Vol.8, No.3.

Duffie J.A. and Beckman W.A.,"Solar Engineering of Thermal Processes", A Wiley-Interscience Publication.

Ecevit A., Chaikh Wais M.A.M. and Al-Shariah A.M., 1990; "A Comparative Evaluation of The Performances of Three Built-in-Storage Type Solar Water Heaters", Solar Energy 44, 23.

Ecevit A., Al-Shariah A. M. and Apaydin E.D., 1989; "Triangular Built-in-Storage Solar Water Heater", Solar Energy 42, 253.

Eggers-Lura A., 1979;"Solar Energy in Developing Countries",VoJ.1,Pergamon Press.

Garg H. P. and Rani U., 1982; "Theoretical and experimental Studies on Collector/Storage Type solar Water Heater", Solar Energy 29, 467.

Garg H. P., 1975; "Year Round Performance Studies on a Built-in-Storage Type Solar Water Heater at .Jodhpur, India", Solar Energy 17, 167.

Garg H. P., 1973; "Design and Performance of a Large Size solar Water Heater", Solar Energy 14, 303.

Garg H. P. and Krishman A., 1973; "Development of a Low-Cost solar Water Heater at .Jodhpur", India and Easter Eng. 115, 339.

Garg H. P. , 1972; "Design and Performance Prediction of Low-Cost Solar Water Heater", Research and Industry 17, 125.

Garg H. P. and Gupta C. L., 1968; "System Design in Solar Water Heaters with Natural Circulation", Solar Energy 12, 163.

Gupta C. L. and Garg H. P. 1967; "Optimizing the Lilt of Flat-Plate Solar Collectors for India", J. Inst. of Engrs. (India), pt. GE, 21.

Hawkin H. M., 1947; "Domestic Solar Water Heating in Florida", Bulletin of the Florida Engineering Industrial Experimental Station, No. 18, 26.

Helali M., 1985; "Solar Radiation in Bangladesh", M. Sc. Thesis, BUET, Dhaka.

Hossain M. Anwar, 1980; "Possible Low Temperature Applications of Solar Energy in Bangladesh", Technical .Journal, BUET, Vol. ,pp.

Hottel H. C. and Woertz B. B., 1942 "The Performance of Flat-Plate Solar Heat Collectors", Trans. ASME64, 91..

Kreith F. and Kreider J.F.,"Principles of Solar Engineering"

Pub. McGraw-Hill Book Company.

Marshal E. and Adams G., 1978 "The Efficiency of Solar Flat-Plate Collectors", Solar Energy 30, 413.

Morse, R. N. 1970, "Solar Energy Research and Development and Industrial Applications in Australia", ISES Conf., Melbourne, Paper 1/84.

Morse R. N., 1961 "Water Heating by Solar Energy", UN. Conf. New Sources of Energy, Rome, Paper 5/38, 62-73.

Prakash J., Garg H. P. and Datta G., 1985, "A Solar Water Heater with a BuiJ.t-in- Latent Heat Storage", Energy Conversion. Mgnt 25, 51.

Proctor D., 1981 "A Generalized Method for Testing all Class of Solar Collector- I,II", Solar Energy 32, 377.

Rai G. D., 1984. "Solar Energy Utilization", 2nd ed.

Richards S. ,1. and Chinnery D. N. W., 1967, "A Solar Water Heater for Low Cost Housing", NBHI Bull. 41, CSIR Research report 237, South Africa.

Sokolov M. and Vaxman M., 1983 "Analysis of an Integral Compact solar Water Heater", Solar Energy 3D, 237.

Tanishita 1., 1970, "Present Situation of Commercial Solar Water Heaters in Japan", International Solar Energy Congress, Melbourne, Australia, Paper No. 2/73.

Tanishita I., 1964, "Recent Development of Solar Water Heaters in Japan, Proc.

U.N. Conf. on New Source of Energy", Rome 1961, 5, 102.

Vaxman B. and Sokolov M., 1985, "Experiments with an Integral Compact Solar Water Heater", Solar Energy 34, 447.

Whillier A., 1967, "Design Factors Influencing Solar Collector Performance", Low Temperature Engineering Application of Solar Energy (Editor R.C.• Tordan), ASHRAE.

Whiller A., 1964), "Thermal Resistance of the Tube Plate Band in Solar Heat Collector", Solar Energy Trans.

Yellot J. I. .and Sobatka R.,1964, "An Investigation of Solar Water Heater Performance", Trans. ASRAE70, 425.

APPENDICES

30 .

APPENDIX: A A.1. FIGURES

Built-in-Storage Type Solar Water Heater

I

I I I

J

I

Selection Switch

I I I

!

Digital Voltmeter

Fig. 3.1 The Schematic Diagram of Experimental Setup.

,.

ttire I Stand Struc . Stee ..

o

I • to set the BSWII at any The arrangement .

inclination manually.

e Water The Built-in-Storag

Heater.

I~.-_....

Fig. 3.2 The S.chematic Diagram of. .. . - BSWH and Steel Stan, d Structure.

32

li - - - -- - ---- --- ...•

~D CD CD CD CD ~D CD CD ~D

^T

8: ~~

I : ,-_.

, oj

I ~-... ...~.

.',0

: . -;:@:: ... -- -'".: €lr"

^.'C1

@, ._' ~~;:

: :8

,

'

-8'

^1- •••1...• __

"8

\W : \~..-'''~

A e: is VA

I '

8:

_h ^::@"':_,~-,'

^:'@': i8

I" .. ' I

::~;

:

~J

:8

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^L

PLAN

Fig. 3.3 (a)- The Plan View of BKt-IH.

.- WOODEN FRAME_

~ G.I_ SHEET_

~1. PIPE.

III

-STAINLESS STEEL PIPE.

.-//) JI~ THERMOCOUPLES -

---.--/ / / !

'1 2 3 45

SECTiON: AA

1

Fig.3.3(b) X-sectional View of BSWH Illustrating the Set-up of Thermocouples.

/

33

Storage Tunk .

--_.-

..

WATER INLET PIPE. (£i.-'05mm)

. I

, I

I

THERMOCOUPLE--J.J

I

STEEL PIP£C1.59mm.}- _ I STEEL PiPE

(12. 7mmJ-_1

I

I

.),

,

I

WOODEN BATTEN -

II ^GLASS SHEET (4mm)

I ^I r-- G.!. SHEET

(1. 59mm...-)-- _

/./ I, RUBBER GASKET

(U,7mm~)_

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! I

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'~

j

W A

J ¹

- - - - - -.1-.-

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,

,

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• ¹⁰⁰⁰

~

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f-

20 500

o

8 10 12 14 16

o

18 Time (hr.)

Fig. 4.1 The Heat Energy Absorbed and Mean Water and Ambient Temperature on January 29,1992.

18

o

14 16 10 12

o

8

100 3000

OJ

^,~

80

^{o TW ~}

""

0^•

₆₀ 2000 -

^E:8

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-

'5

_'"

_:;;

40

~

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f-

20

Time (hr.)

Fig. 4.2 The Heat Energy Absorbed and Mean Water and Ambient Temperature on February 01,1992.

100 ⁸⁰ OJ

^o

^{' T: r" 3000}

. ^""

-

^~8

0 E:

•

60 2000

^~

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-

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~

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f-

20

I

0

0

8 10 12 14 16 18

Time (hr.)

Fig. 4.3 The Heat Energy Absorbed and Mean Water and Ambient Temperature on Fabruary 02,1992.

18

o

16 12 14

o

10 8

100⁸⁰

_/ OJ

^{oo T,}

^T"

^{,(jJL 3000}

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/

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2000 -.;.~

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-

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I-

^0'

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Q; 40

Q.

E

'"

f- 1000

20

Fig. 4.4

Time (hr.)

The Heat Energy Absorbed and Mean Water and Ambient Temperature in February 03, 1992.

2000

1000

18

o

16

OJ

_{• q}

_o.e-

⁴⁰⁰⁰

o

T ,

o TW -

3000

a

- ^::::

12 14 100

80

~ ₆₀ ^/

/

'" I

-

':;

_'"

Q;

E

40

'"

f-

Time (hr,)

Fig. 4.5 The Heat Energy Absorbed and Mean Water and Ambient Temperature in February 04, 1992.

18

o

14 16 12

100 ⁸⁰ ClJ

^{aT.a T"}

^/

^/~

"'" ⁴⁰⁰⁰

^~

'"

,/

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~

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/

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. - ^:::

.,

/

I ;:]

3 ₂₀₀₀

<tl

Q;

40

g- .,

I-

20 1000

Time (hr)

Fig. 4.6 The Heat Energy absorbed and Mean Water and Ambient Temperature in February 05, 1992.

100

•

qu.-

4000

a T.

0

T"

_~.

3000 '"

~

- a :::

~~

2000

^0'

1000

18

o

Time (hr.)

Fig. 4.7 The Heat Energy Absorbed and Mean Water and Ambient Temperature in february 08, 1992.

100 3000

• q """

•

T

80 • T"

~

.' _'"

/ -8

9 ^/

2000 -.

60 / ^'-'-"

^;;::

Q)

/

^~~

-

:0;^al(;; ^C-

"'- 40 ,;

E

1000

Q)

/

I-

20

/

0 0

8 10 12

14

16 18

Time ( hr. )

Fig. 4.8 The Heat Energy Absorbed and Mean Water and Ambient Temperature in February 09,1992.

100

80 /

9

60 I

Q)

:0; I

//

-;;;

(;;

40

CLE

Q)

I-

20

I

0 /

8

10 12

14 16

4000

• q<l<k

• T

~.

I ^~

3000 '" -.

;;::₈

2000 "~

0'

1000

18

o

Time (hr.)

Fig. 4.9 The Heat Energy Absorbed and Mean Water and Ambient Temperature On February 10,1992.

100

3000

OJ

^{' T. /}

80 ^o T^{W /}

II

~

? ^{2000 ~}

""

60 a

" -

I

^:;::

':; ~~

-

^<rJ

" ⁴⁰

^C'

~

" ^.1000.

I-

20

o

8 10 12 14 16

o

18

Time (hr.)

Fig. 4.10 The Heat Energy Absorbed and Mean Water and Ambient Temperature on February 11, 1992.

100

80

60

40

20

3000

2000

1000

/

o /

8 10 12 14 16

o

18

Fig. 4.11 The Heat Energy Absorbed and Mean Water and Ambient Temperature on February 12. 1992.

100 3000

• _qoL-

,

T

80 ^/ ,

T"

// 2000

9

60 _/ '"

""^~_E

Q)

/ -

5 0::

:;; ~~

a; ₄₀

~ ^0'

Q)

1000

f-

20

o

8 10 12 14 16

o

18 Time (hr.)

Fig. 4.12 The Heat Energy Absorbed and Mean Water and Ambient Temperature on February 15, 1992.

100 3000

• _~

a T

80

^a

T"

/

./ 2000

/

^~

9 ""

60 -

^E

Q) 3=

5

:~

-

^as

!

a; ₄₀

~

1000

Q)

f-

20 /1

^{__ 9}

....•

o

8 10 12 14 16

o

18 Time (hr.)

Fig. 4.13 The Heat Energy Absorbed and Mean Water and Ambient Temperature on February 16,1992.

18

o

16 14

12

o

10 8

100 [JJ

^{•, Tq~ 2~O}

80

.I

^o T"

2000

/

_~

/

_""

9

⁶⁰ / ¹⁵⁰⁰ -

^:::E

~ ~~

'"

^.

- _{'" a;}

^0'

40 ." 1000

~

'"

I-

20 -- ^{..•. 500}

Time (hr.)

Fig. 4.14 The Heat Energy Absorbed and Mean Water and Ambient Temperature on February 17,1992.

18

o

16 14

12

100 4000

OJ

^{D T.}

80

o T"

3000

9

60 '--.

_""^~

a>

-

E

::;

2000

^:::

-

^roc

~f

" ⁴⁰

^{.0' .}

g-

a>

I-

20 1000

Time (hr)

Fig.4.15 The Heat Energy Absorbed and Mean Water and Ambient Temperature on February 18,1992.

18

o

16 12 14

o

10 8

100 ⁸⁰ _I

^loT"

~~j~1 ^{4000 3000}

^~

'"

~

⁶⁰ / -

^E

/ " ^e;~

0> ' ~

-2 I // ²⁰⁰⁰

0',

'"

" ⁴⁰

^.."

E-

O>

f-

20 1000

Time (hr.)

Fig. 4.16 The Heat Energy Absorbed and Mean Water and, Ambient Temperature on February 19,1992.

100 ⁸⁰ _/

^/'

[]

^{oo T.T"}

³⁰⁰⁰

~ ^/

~

^{'" 60} / ^{2000 '"} -

^~

~~.

^E

-2 '"

"

CL

40

0' .'

E

'"

f-

1000

20

o

8 10 12 14 16

o

18 Time (hr.)

Fig. 4.17 The Heat Energy Absorbed and Mean Water and Ambient Temperature on February 22,1992.

100 /---

OJ ⁴⁰⁰⁰

"

^cT.

80 /

^{c T*}

^'"

^~

9

⁶⁰ 3000 -

^a=8

'"

^~~

-

^<tl'5

²⁰⁰⁰

^0'

'" ⁴⁰

~

'"

f-

20 1000

10

12 14 16 18 0

Time ^(hr.)

Fig. 4.18 The Heat Energy Absorbed and Mean Water and Ambient Temperature

on February

_25,1992.

100

80

60

40

20

~ • q=

~ c T

/ ~L:.-T'

/

^{. ~}

4000

3000

2000

1000

o

8 10 12 14 16

o

18 Time (hr.)

Fig. 4.19 The Heat Energy Absorbed and Mean Water and Ambient Temperature on February 26,1992.

18

o '

14 16 12

o

10 8

':DJ/~ ₃₀₀₀ ⁴⁰⁰⁰

9 ' ~ ~

60 I .

_""

0>

~

E

;:;

-

-

;;;

_'" ²⁰⁰⁰

^3:

_~i

E- 40

^.<;l'

0>

I-

20 1000

Time (hr,)

Fig. 4. 20 The Heat Energy Absorbed and Mean Water and Ambient Temperature in March 02, 1992.

100 5000

[]

^{o T /}

80 d/~ ⁴⁰⁰⁰

9

60

~. ~

3000

~

0> ""

Z _'"

_;;;

-

^3:E.

40 2000

~~

E-

O> 0'

I-

20 1000

0 0

8

10 12 14 16 18

Time (hr.)

Fig. 4.21 The Heat Energy Absorbed and Mean Water and Ambient Temperature on March 03,1992.