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Enrr,qv Vol. 9. No. 5. pp 461464. 984Printed nn Great Bntain.

OX&5442/84 53.00 + .I0c 1984 Pergamon Press Ltd.

NOTE

ENERGY CONSERVATION AND FIELD PERFORMANCEOF A NATURAL CIRCULATION TYPE SOLAR WATERHEATERN. M. NAHARCentral Arid Zone Research Institute, Jodhpur-342003, India

(Recei ued 27 Jul y 1983)Abstract-A natural circulation type solar water heater has been fabricated and installed at theCAZRI Guest House. Its field performance has been evaluated. The heater provides 200 1. of hotwater at 5&6OC at all times. This solar water heater is economical.

INTRODUCTIONFlat-plate collectors for water heating have been studied by Hottel and Woertz, Bliss,2and others. Natural circulation type solar water heaters have been extensively studied byYellot and Sobotka, Morse,4 Hawkin, Close,6 Gupta and Garg, and 0ng.8

Flat-plate collectors are either of the corrugated,9 bond duct, or tube in plate type,with different clamping arrangements. 2~3~12ariables include the glass cover, types andthickness of glazing,13 mirror coating on the inner glass,14anti-reflecting coating on the glasscover,5 type of coating on the collector plate,16 spacing between the collector and the innerglass, arrest of the convective movement between the collector plate and inner glass,18evacuated space between the collector and inner glass, type of insulation used,20 etc. Wehave considered an optimized flat-plate collector suitable for water heating.

DESIGNThe solar water heater consists of two optimized, flat-plate collectors, each with 1.4 m2

of absorber area. The storage tank is kept at an optimum height suitable for thermosyphonsystem. The absorber is made from galvanised iron pipes and aluminium sheet. It is encasedin a mild steel tray with 50 mm fiberglass insulation at the back. It is painted with dull blackboard paint and one glass cover is used over it. The flat plate collector is fixed at an optimumtilt to receive maximum radiation in winter. Both collectors are connected in parallel.The double-walled storage tank has 200 1. capacity. The inner drum is made of 20 SWGgalvanised iron sheet and the outer drum of mild steel. The height and diameter are chosenin such a way that their ratio is maintained at two for better maintenance of watertemperature. The spacing between the outer and inner drums is filled with resin-bondedfiberglass insulation. The line diagram of the solar water heater and its installation is shownin Fig. 1.

PERFORMANCE AND TESTINGThe performance of the heater has been evaluated. It provides 200 1. of hot water at anaverage temperature of 60-70C on winter afternoons, which can be retained at 50-6OCuntil the next morning when the tap-water temperature is as low as 15-20C. The per-formance on a typical clear winter day will now be described.Maximum and minimum air temperatures = 26.1 and 14.OC, respectively; dry bulbtemperatures at 7.35 and 14.35 hr = 14.6 and 25.3C, respectively; relative humidity at 7.35and 14.35 hr = 72 and 30/& respectively; average wind speed = 8.4 km/hr; total solar radi-ation in the collector plane between 8.00 and 16.00 hrs 6.56 kWhme2; tap watertemperature = 17C; average hot water temperature at 16.00 hr = 58.5C.461

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462 N. M. NAHAR

Cold water -

Hot water outletto bathroom

Fig. 1. Schematic of a natural circulation type solar water heater.

Table I. Cost estimate for a 200 I. capacity natural circulation type solar water heater.Material Quantity

Mild steal sheet, 24 gauge, 2.5 x 1.0 m2Galvenised iron sheet, 2.25 x 1.0 m2Mild steel angle, 31 x 31 x 3 mm3Alumlnium angle, 25 x 25 x 1.6 mm3Aluminium sheet, 28 gaugeGalvanised iron pipe, 25 mm dia

19 mm dia13 mm dia

Teak wood batten, 25 x 25 ran2Ordinary clear window glass 3 mm thidcAluminium strip. 25 mm widthFiberglass insulation, 50 mm thidcHard board, 3 mm thidcG.I. fittings. Union 25 mm

L-bow 25 mnTee 25 mmcap 25 mmSocket 25 mmsocket 13 mmUnion 13 mmL-bow 13 mmGate valve 13 mmTap 13 mmaampFloat valve

Black board paintEnamel paint blueletal primerzinc rich paint?olythene bags, 2.2 x 1.0 m2Silica jel?uttyNutt. bolts, screws, wires etc.Fabrication charges - 15% of thenaterial cost

4122 m12.8 m3.0 kg12 m28 m9m

16.8 m4.4 m24.0 m10.0 Ill21.3 n1234132!612:Y2 lit.1 lit.2 lit.100 ml4Y2 kgIt2 kg

400.00125.00150.0072.00

120.00200.00350.0090.00

. 30.00180.00

6.00300.0020.0040.0020.007.003.006.0020.005.00

18.0015.0015.005.00

15.00lJ.0040.0040.005.00

10.009.003.00

20.00350.00

ApprOx. US $ 270.00 2700.00

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464 N. M. NAHARThe efficiency of the heater is

s=j)Ud*,A j+!d, (1)where A = total absorber area, H = solar radiation at the collector plane, qU= rate of heatabsorption by water. From these data, the efficiency of the solar water heater is found to be52.4%.

ENERGY CONSERVATION AND ECONOMICSThe details of the materials required for fabrication and their costs are shown in Table1. The energy that can be saved by the heater in terms of various fuels is shown in Table 2.

The pay-back period of the heater for year-round performance is 2.6, 1.4, 2.4, and 1.6 yrwhen compared with firewood, charcoal, kerosine and electricity, respectively. It is3.6-6.5 yr when the heater is used in winter only, i.e., for four months. The durability of theheater is 12-l 5 yr.

CONCLUSIONThe natural circulation type solar water heater installed at the CAZRI Guest Houseshows satisfactory performance. The heater has replaced electric heaters in two rooms andsaves 3300 kWh of electricity per year. The pay-back period for the heater shows that itis economical.Acknowledgemenrs-The author is grateful to Dr. K. A. Shankamarayan, Director, CAZRI and Sri B. V.Ramana Rao, Head, Division of Wind Power and Solar Energy Utilization, for providing necessary facilities,useful suggestions and constant encouragements for the present study.

I.2.3.4.5.6.7.8.9.IO.II.

12.13.14.IS.16.17.18.19.

H: C. Hottel and B. B. Woertz, Trans. ASME 64, 91 (1942).R. W. Bliss, Solar Energy 3, 55 (1959).J. I. Yellot and R. Sobotka, Trans. ASHRAE 70, 425 (1964),R. N. Morse, Solar Energy Research and Development and Industrial Application in Australia, ISESCon/. Melbourne Paper l/84 (1970).H. M. Hawkin, Domestic Solar Water Heating in Florida, Bull. Florida Univ. Engng Ind. Exp. Station,Gainesville, No. 18 (1947).D. J. Close, Solar Energy 6, 33 (1962).C. L. Gupta and H. P. Garg, Solar Energy It, 163 (1968).K. S. Ong, Solar Energy 16, 137 (1974).K. N. Mathur, M. L. Khanna, T. N. Davey, and S. P. Smi, J. Sci. Ind. Res. 18A, 51 (1959).D. G. Patil. Solar Energy 17, Ill (1975).Annon., Solar Water Heaters, Division of Mechanical Engineering, CSIRO, Highett. Victoria, Australia,Circular No. 2 (1964).H. P. Garg and C. L. Gupta, J. Inst. Engng (India) Pt. CE-3 48, 461 (1968).A. Whillier, Solar Energy 7, 148 (1963).R. M. Winegamer, Heat Mirror-a Practical Alternative to the Selective Absorber, Proc. Con$ AmericanSection of ISES and SES of Canada, Sharing the Sun. 6, 337 (1976).C. K. Hsieh and R. W. Coldewey, Solar Energy 16, 63 (1974).N. M. Nahar and H. P. Garg, Renewable Energy Rev. J. 3, 37 (1981).N. M. Nahar and H. P. Garg, Applied Energy 7, 129 (1980).K. G. T. Hollands, Solar Energy 9, 159 (1965).B. F. Simon, Solar Collector Performance Evaluation with the NASA-Lewis Solar Simulator; Results foran All Glass Evacuated Tubular, Selectively Coated Collector with a Diffuse Reflector, Cleveland, Ohio,NASATMX 71695 (1975).20. A. Whillier and G. Saluja, Solar Energy 9, 21 (1965).

REFERENCES