Experimental evaluation of solar integrated water heater

Scientia Iranica B (2020) 27(4), 1878{1885

Sharif University of TechnologyScientia Iranica

Transactions B: Mechanical Engineeringhttp://scientiairanica.sharif.edu

Experimental evaluation of solar integrated waterheater

D.R. Mishraa;�, H. Jaina, N. Kumara, and M.S. Sodhab

a. Department of Mechanical Engineering, Jaypee University of Engineering and Technology, A.B. Road, Guna-473226, MadhyaPradesh, India.

b. Department of Education, University of Lucknow, Lucknow-226007 Uttar Pradesh, India.

Received 25 December 2017; received in revised form 5 December 2018; accepted 29 April 2019

KEYWORDSSolar water heater;Heat and masstransfer;Modi�ed conventionalbucket;Power saving;Cost analysis.

Abstract. Domestic immersion heaters used for heating cold water are characterized byan electrical resistance heating element, which is encased in a tube and directly placedin it. The most common method for heating cold water is the use of portable immersionrod water heater in an open bucket operating in operator control without a controllerunit (thermostat). This paper performs an experimental evaluation of portable modi�edconventional buckets of 10 l capacity. Out of ten portable modi�ed storages, the bestthree cases are discussed: non-insulated Open Plastic Bucket (OPB), non-insulated plasticbucket top surface covered with a transparent cover (CPB), and insulated plastic bucketclosed with a transparent cover (ICPB). Maximum temperatures arising after two hoursduring OPB, CPB, and ICPB are 29.82%, 47.36%, and 21.49%, respectively, comparedto the initial temperatures (22.8�C). At 14:45 hour, CPB temperature reaches 35.6�C,which is 17.88% and 23.61% higher than OPB and ICPB units. Due to the application ofsolar energy in CPB at 35{50�C, net saving increased by 12.34%, 25.76%, 40.73%, 57.93%,76.45%, and 97.18% from 2017 to 2022 as compared to the saving in 2016.© 2020 Sharif University of Technology. All rights reserved.

1. Introduction

The demand for domestic electrical power consumptionis increasing day by day due to the population growthin rural and urban areas of developing nations. Asigni�cant portion of domestic power is consumed forheating cold water in winter bathing. A detailed reviewof several solar water heaters was done by Raisul Islamet al. [1]. Several portable and �xed types of solarwater heaters are currently available in the market atdi�erent initial investment costs; however, their pricesare signi�cantly higher than immersion rods. Therole of nano- uid in the solar water heating system

*. Corresponding author.E-mail address: [email protected] (D.R. Mishra)

doi: 10.24200/sci.2019.50071.1510

was investigated by Natarajan and Sathish [2]. Aparametric study of domestic solar water heaters wasconducted by many researchers [3,4]. The utilizationof an electrical immersion rod in the bucket for theheating of the cold water in the winter session is themost common practice, especially within the rural andurban areas due to the low initial investment cost ofthe electric immersion rod. The techno-economic waterheating system in a bucket through the immersion rodwas evaluated by Sodha et al. [5]. They suggested threedi�erent methods for the system improvement: (i) in-sulating lateral and bottom surfaces, (ii) augmentationwith the oating cover over water surface, and (iii)augmentation with both. An experimental evaluationof heat ux and heat transfer coe�cient using inversemethod was done by Farahani et al. [6]. The water-heating system was designed and simulated by Zhanget al. [7]. Jahangiri Mamouri and B�enard [8] performed

D.R. Mishra et al./Scientia Iranica, Transactions B: Mechanical Engineering 27 (2020) 1878{1885 1879

a case study of a new design of an evacuated tubularwater heater performance in the climatic condition ofMichigan. The life cycle assessment of domestic waterhot water cycle was reported by Moore et al. [9]. Anevacuated tube collector water heater with a multi-layer absorber was investigated by Sobhansarbandi etal. [10]. The average economic performance of solarwater heater was studied by Ferrer [11].

As in most of the rural areas of di�erent countries,peoples are still using electric immersion rods for waterheating. In case of proper motivation for the partialor full application of solar energy using the proposedmethodology, the domestic power consumption can bereduced to a large extent.

2. Experimental setup

An real photograph and a schematic view of theportable water heater augmented with the incidentsolar radiations are shown in Figures 1(a) and 1(b),

Figure 1a. Actual photographs of OPB, CPB, and ICPB.

Figure 1b. Schematic representation of CPB along withthe immersion rod and oating transparent cover.

respectively. The black-colored surface has a bettercoe�cient of absorption than other color surfaces.Hence, the black-colored plastic bucket is characterizedby 10 l capacities. Three sets of the portable waterheater are made of the following: (1) non-insulated,Open Plastic Bucket (OPB), (2) non-insulated plasticbucket, top surface covered with a transparent cover(CPB), and (3) insulated plastic bucket closed with atransparent cover (ICPB). The schematic arrangementof the CPB along with the oating cover and theimmersion rod is that the oating cover gives credenceto the variation in volumetric mass water within thebucket. OPB, CPB, and ICPB are fed with 10 ltab water and have been kept exposed to the incidentsolar radiation for four hours. K-type thermocouplesand MDTI -027 temperature indicators are used formeasuring and recording the temperature rise. Thefollowing observations are recorded as follows:

� Water temperature rising within OPB, CPB, andICPB at a 15-min interval;

� Ambient temperature;� Potential di�erence (voltage) calculated using a

voltmeter;� Current owing through the immersion rod using an

ammeter.

3. Mathematical background

Three di�erent con�gurations of the water heating ina bucket by an electrical immersion rod are shown.

To perform a mathematical evaluation of the system,the following assumptions are considered:

a. Electric power supply at a constant rate;b. Cylindrical shape of the bucket;c. Constant mass of water;d. Uniform temperature of bucket water;e. Neglecting evaporative losses, covered bucket with

transparent material.

The energy balance mathematical relation for thebucket containing water is given as follows:

MwCwdTwdt

= ET �Qs; (1)

where:

ET = Ee + Es;

Qnet loss = Qc +Qe +Qr +Qs +QB :

Herein, ET is the total power supplied to the waterthrough solar radiation (Es) and electrical immersion

1880 D.R. Mishra et al./Scientia Iranica, Transactions B: Mechanical Engineering 27 (2020) 1878{1885

rod (Ee) in watts, whereas Qnet loss is the energy lossthrough the conduction, evaporation, and radiationthrough the top, lateral, and bottom surfaces [12].Various losses may be given below:

Qc = hcAT (Tw � Ta) ; (2)

Qe = 0:013hcAT (Pw � Pa) ; (3)

Qr = hrAT (Tw � Ta) ; (4)

Qs = hsAs (Tw � Ta) ; (5)

QB = hBAB (Tw � Ta) : (6)

Heat transfer coe�cients are given below [13]:

hc = 5:7 + 3:8v; (7)

hr ="eff�

h�Tw + 273

�4 � �T a + 273�4i

Tw � T a ; (8)

where ��= 5:67� 10�8W

�m2K2� is Stefan's constant,

and a bar represents the average (throughout theheating process) of the quantity over it, whereas thee�ective emissivity of the plate-glazing system can bewritten as follows:

1"eff

=�

1"w

+1"a� 1��1

; (9)

hs =

24 1hws

+Xj

2Kjrj

ln�rj+1

rj

�+

1h0

35�1

; (10)

hB =

"1hws

+Xk

LkKk

#�1

; (11)

where j and k denote the numbers of layers of side andbottom of the bucket, respectively.

It has become clear that the evaporative heattransfer coe�cient (he) has nonlinear dependency onthe temperature. The saturated vapor pressure in anarrow range of temperature variations can be repre-sented by linear temperature dependence.

P = R1T +R2; (12)

where R1 and R2 are the constants evaluated usingleast-squares curve �tting of saturation. The vaporpressure in a longer range of interest can be evaluatedthrough the following relation:

Pw = exp�

25:317� 5144Tw + 273

�; (13)

Qe = 0:013hc [R1 (Tw � Ta)�R2 (1� )] ; (14)

and:dTwdt

+ �Tw = �; (15)

where:� = [(H0AT + hsAs + hBAB)/MwCw]

� =�ET + (H1AT + hsAs + hBAB)Ta

�0:013hcATR2 (1� )�

1MwCw

;

H0 = (hc + hr + 0:013hcR1) ;

and:H1 = (hc + hr + 0:013hc R2) :

From Eq. (15), in the initial condition, Tw = Tw0 andt = 0, one can get the following:

Tw =��

+�Tw0 � �

�

�exp (��t) : (16)

In the cooling mode (E = 0) from Eq. (15), onecan get:dTwdt

= �� (Tw � Teff ) ; (17)

where:

Teff =�Ta � 0:013hcAT (1� ) (R1Ta +R2)

MwCW�

�:(18)

After solving Eq. (17), one can express water temper-ature:Tw = Teff + (Tw0 � Teff ) exp (��t) : (19)

It is analogous to Newton's law of cooling; it can beobserved that Teff reduces to Ta at zero heat loss. Thethermal performance of the system can be evaluatedusing the value of � (loss coe�cient) for the typicaldataset.

Other in uencing parameters can be evaluatedthrough the expressions written below:

i) Time taken to rise the temperature of water fromTw0 to Twf can be obtained.

TH = � 1�

ln�Twf � �/�Tw0 � �/�

�: (20)

ii) The e�ciency of utilizing solar and electrical energy� can be measured in the following.

� =MwCw (Twf � Tw0)th1R0Esdt+

thtRth1

Esdt: (21)


4. Cost analysis

The total annual cost of the system can be expressedin response to the corresponding initial investment asfollows [14]:

CTA = CBf1 + CHf2 + CE

1Y earZ0

ET dt; (22)

where f1 and f2 are the annuity factors that can beobtained as follows:

f1 =qLB (q � 1)qLB � 1

; (23)

f2 =qLH (q � 1)qLH � 1

; (24)

where q =�1 + Z

100

�.

Annual amount of useful energy (kWh) is obtainedbelow:

Qu =Z

Y ear

MwCw (Tw � Tw0) dt: (25)

The cost of 1 kWh of useful energy can be determinedas follows:

Cu =CTCu

: (26)

5. Result and discussion

All the experiments were carried out in January 2017at Jaypee University of Engineering and Technology,Guna (24.4348� N, 77.1606� E). Maximum and mini-mum incident solar radiations on the horizontal surfacewere recorded as 890 and 640 W/m2, respectively,during the experimentation. Variation in incident solarradiation was recorded, as shown in Figure 2. Atthe beginning of the experimentation, the incidentsolar radiation was recorded at 792 W/m2, whichincreased at 13:00 hour by 12.37%. After 13:00 hour, itstarted to decline by 28.09% at 14:45 hour during theexperimentation.

Figure 2. Variation of incident solar radiation withrespect to time.

At the beginning of the experimentation, OPC,CPB, and ICPB were �lled with the cold water (10l each) at a temperature of 22.8�C, and the resultsof the experimentation and theoretical evaluation andits variation due to the incident solar radiation as afunction of time are shown in Figure 3. Maximumtemperatures rising after a two-hour time intervalin OPB, CPB, and ICPB are 29.82%, 47.36%, and21.49%, respectively, as compared to the initial tem-peratures (22.8�C). Water temperature of OPB, CPB,and ICPB was determined at its highest value at 14:45hour during the experimentation, whereas the obtainedresults of the theoretical models slightly decreased after14:00 hour due to a reduction in the incident solarradiation.

Water temperature rise in CPB has maintainedits lead throughout the experimentation as comparedwith the OPB and ICPB, whereas ICPB lags behindas compared with OPB and CPB due to the lateralsurface insulation. Temperature rise in OPB is moremoderate than that in CPB and ICPB.

Temperature increase by water within OPB andCPB due to the Bajaj Vacco (Immersion Water HeaterRod) of 1000 W capacity.

The temperature rise in both cases was recordedat an interval of two minutes and is shown in Figure 4.Water within the CPB retains more heat as it iscovered from the top surface, which is the reason whythe temperature rise recorded in CPB maintains itslead as compared to the OPB throughout the heatingprocess. Due to the presence of the top cover duringwater heating by means of the immersion rod, the timerequired to rise unit degree temperature is shorter thanthat in the OPB and power consumption has reducedin CPB to a greater extent than that in OPB.

Eight sets (23{50�C, 24{50�C, 28{50�C, 30{50�C,34{50�C, 36{50�C, 38{50�C, and 40{50�C) of theexperiment are considered for analyzing the electricalpower consumption in OPB and CPB during waterheating through an electrical heater. The obtainedresults of the experimentation are shown in Figure 5.

Estimated cost saving on the basis of expected

Figure 3. Variation of bucket water temperature due toincident solar radiation with respect to time.


Figure 4. Variation of water temperature in OPB andCPB due to the immersion rod with respect to time.

Figure 5. Variation of power consumption with respectto the temperature range.

population growth by World Health Organization(WHO) is shown in Figure 6 due to recorded andexpected growth rates in the population of rural andurban areas.

Figure 7 shows the estimated saving from 2016to 2022 on the basis of the estimated population and10% price hike on electricity. Estimated populationgrowth has been recorded at rates of 2.13, 3.39, 5.74,7.86, 9.63, and 11.4%, which are higher than the ratesrecorded in 2017 to 2022, compared to the populationliving in 2016. However, net saving resulting from theutilization of solar energy in CPB in a temperaturerange of 35{50�C increased by 12.34, 25.76, 40.73,57.93, 76.45, and 97.18% from 2017 to 2022, comparedto saving in 2016.

6. Conclusions

Based on experimental theoretical investigations, thefollowing conclusions are drawn:

Figure 6. Variation of energy saving and estimated costas per the domestic rate of Madhya Pradesh (MP) Indiawith respect to saved energy.

Figure 7. Variation of estimated population growth ofurban area by World Health Organization (WHO) andcost saving with respect to the associated year.

� Open bucket water heating using immersion rod isan ine�cient process;

� Use of transparent plastic cover mater helps reducethe consumption of electrical power signi�cantly;

� The transparent oating cover can also be a cost-e�ective solution to cost reduction;

� For dry climatic conditions, the electrical heatingsystem operates more uneconomically;

� The application of solar energy for heating of waterreduces electric power consumption signi�cantly;

� To reduce heat loss, an immersion rod of higherpower rating can be used.

Nomenclature

AB Bottom surface area of the bucket, m2

AT Top surface area of water, m2

AS Area of sides, m2


CB Initial investments in bucket,insulation, and cover, INR

CE Electricity rate, INR/kWhCH Initial investment cost of an immersion

rod, INRCT Total system annual cost, INRCu Overall cost of useful energy, INR/kWhCw Speci�c heat of water, J/kg�CCTA Total annual cost of the system, INREe Electrical energy supplied through

immersion rod, WEs Solar energy received, WET Total energy supplied to the bucket

through the solar and electricalsources, W

hB Total heat transfer coe�cient fromthe water to the ground through thebottom, W/m2�C

hc Convective heat transfer coe�cientfrom top surface /water to ambient air,W/m2�C

hr Radiative heat transfer coe�cient fromcover surface /water to ambient air,W/m2�C

hs Total heat transfer coe�cient fromwater to the ambient air through sides,W/m2�C

Mw Mass of water, kgPa Partial pressure of saturated water

vapor at ambient temperature, N/m2

Pw Partial pressure of saturated watervapor at water temperature, N/m2

Tw Temperature of water, �CTa Ambient temperature, �CQc Convective heat loss from water/ top

surface to the surrounding, WQe Evaporative heat loss from water/ top

surface to the surrounding, WQr Radiative heat loss from water/ top

surface to the surrounding, WQnet loss Heat loss through lateral surface of

bucket, WQu Annual useful energy, kWhZ Percentage rate of interest"eff E�ective emissivity of cover/ water

surfacev Velocity of air, m/s� Stefan-Boltzmann coe�cient (=

5:67� 10�8 W/m2K4) Relative humidity

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Biographies

Dhananjay R. Mishra is an Assistant ProfessorSenior (SG) at the Department of Mechanical Engi-neering at Jaypee University of Engineering & Tech-nology, Guna. He received his PhD in MechanicalEngineering from National Institute of TechnologyRaipur, India in 2016. He has published more than50 research papers in reputable peer-reviewed nationaland international journals. He has supervised fourPhD students from Jaypee University of Engineering& Technology and National Institute of TechnologyRaipur. He is an Editor in `International Journal ofThermodynamics & Catalysis', an Associate Editor ofInternational `Journal of Applied Research', and aneditorial board member of nine other peer-reviewedinternational Journals. He has an a�liation with theSuprabha Industries Ltd., Lucknow, as an AssistantProduction Manager during 2002{2004 as a lecturerat the Mechanical Engineering Department, RungtaCollege of Engineering and Technology, Bhilai, C.G.During Sept. 2005 to March 2006, he was a Lec-turer at the Mechanical Engineering Department, ShriShankaracharya College of Engineering and Technol-ogy, Bhilai, C.G. (During March 2006 to July 2007) asan Assistant Professor at the Department of Mechan-ical Engineering at Disha Institute of Management &Technology. He has also been the incumbent AcademicAdministrator (July 2007 to July 2012). Since July2012, he has been an Assistant Professor (SG) atthe Mechanical Engineering Department, JUET, Guna(M.P.). He has established State Level Energy Parkat DIMAT funded by MNRE through Nodal agencyCREDA. He has also completed a research projecttitled \determination of the parameters a�ecting heattransfer between the ground and fully or partiallyunderground structures" sponsored by ChhattisgarhCouncil of Science and Technology at Disha Instituteof Management & Technology, Chhattisgarh.

Hrishi Jain is pursuing his MTech in Ocean Tech-nology from IIT Madras. He was born on September21, 1994 at the Tikamgarh district of M.P. Indiaand has completed his higher secondary school fromHope Academy Tikamgarh and secured 80%. Hecompleted his BTech in Mechanical Engineering atJaypee University of Engineering & Technology in2017 and worked as a Design Engineer for the ATV(All-Terrain Vehicle) in college team Ardent Clan andATV at Gautam Buddha University Noida in O�Road Challenge competition. He is currently pursuing

his MTech in Ocean Technology at IIT Madras andcompleted his thesis titled \development of thermallyrechargeable ARGO oat using ocean thermal gra-dient" with National Institute of Ocean Technology(NIOT) Chennai. He has an a�liation with the startupTerero Mobility mentored by Lockheed Martin at IITMadras a Finite Element Analysis (FEA) lead. He haspublished two international research articles in peer-reviewed international conferences/journals.

Nishant Kumar works with Shrota Enterprises Pvt.Ltd. as a Production Planning & Control (PPC)o�cer. He was born on November 11, 1993 in the Patnadistrict of Bihar India. He has completed his highersecondary school from R.K.S College, West Cham-paran and received his BTech degree in MechanicalEngineering from Jaypee University of Engineering &Technology in 2017. He has worked as a FabricationEngineer and Steering Incharge for the ATV (All-Terrain Vehicle) in college team Ardent Clan and racedour ATV at Gautam Buddha University Noida in O�Road Challenge competition and published two inter-national research articles in peer-reviewed internationalconferences/journals.

Mahendra Singh Sodha is a visiting Professor atthe Department of Education and Physics, Lucknow(UP). He was born in Ajmer district of Rajasthan onFebruary 8, 1932. He pursued his higher educationat the University of Allahabad. After receiving hisD Phil in \Theory of Spectroscopy Instruments" in1955, he joined Defense Science Laboratory in Delhifor a short period of time. From 1956 to 1964, heworked in Canada and the USA at di�erent capacities.He was appointed a Professor at the Department ofPhysics at the Indian Institute of Technology Delhi,New Delhi, 1964. Professor Sodha has made out-standing contributions in the areas of energy, plasma,solid state physics, optics, combustion, and ballistics.He has published more than 500 research papers inreputable national and international journals. He hasto his credit 13 books and 12 reviews. He has alsosupervised more than 65 PhD students from IIT Delhiand other Universities. Professor Sodha was awardedthe prestigious S.S. Bhatnagar award in 1974, HariOm Ashram Prerit Shri S.S. Bhatnagar award in 1978,and Padmashri award in 2003 for his outstandingcontributions in science and engineering. He is afellow in many professional bodies including IndianNational Science Academy and National Academy ofScience, India. He has been a member of the editorialboard of national and international journals. ProfessorSodha served IIT Delhi at many capacities includingHead of the Department of Physics (1966{1968); Headof the Centre for Energy Studies (1978{1982); Dean(Science, Students, PG Studies) (1970{76), and Deputy


Director (1982{1985). He has also served as the Vice-Chancellor of Lucknow University, Lucknow (1992{95)and Barkatullah University, Bhopal (1998{2000). Hehas played an active role in the promotion of highereducation in India. He has been instrumental in

setting up the Centre for Energy Studies at IIT Delhiand Faculty of Engineering Sciences at Indore. He iscurrently a Ramanna Fellow and a Visiting Professorat the Department of Education and Physics, Lucknow(UP).

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Experimental evaluation of solar integrated water heater