N. M. Nahar

Central Arid Zone Research Institute, Jodhpur-342 003, India.

Email: nmnahar@gmail. com Fax: 91-291-2740706

Abstract

The cost of natural circulation type solar water heater has been reduced by combining both collector and storage tank in one unit and an integrated collector storage (ICS) solar water heater has been designed, developed and fabricated and its performance has also been compared with the natural circulation type solar water heater. The capacity of the heater is 100 litres of hot water per day. The average hot water temperature was 57.3o C and 62.0oC at 1600 hours same day that was retained to 43.0o C and 50.4o C till next day 0800 hours when tap water temperature was 17.0o C in ICS and natural circulation type solar water heater respectively. The efficiency of the heater has been found to be 61.3% as compared to 51.9 % of natural circulation type solar water heater. This suggest that performance of ICS solar water heater is as good as of natural circulation type solar water heater while cost of ICS solar water heater is Rs 8000.00 where as cost of natural circulation type solar water heater is Rs. 12000.00 ( 1.0 Euro = Rs 60.00). The cash flow of the heater with respect to different fuels has been carried out and it has been found that the cash flow is maximum with respect to fuel coal and minimum with respect to kerosene. The payback period is least, i. e. 1.42 yr, with respect to coal and maximum, i. e. 3.72 yr, with respect to kerosene (The cost of kerosene is highly subsidised). The payback periods are in increasing order with respect to fuel: coal, electricity, firewood, LPG, and kerosene. The estimated life of this solar water heater is more than 15 years. The shorter payback periods suggests that the use of ICS solar water heater is economical. The use of integrated collector storage solar water heater will conserve substantial amounts of commercial and non-commercial fuels, which are consumed for obtaining hot water.

Keywords: Solar energy, solar water heater, ICS solar water heater, energy conservation

1. Introduction

Hot water is an essential requirement in industries as well as in domestic sector. It is required for taking baths and for washing clothes, utensils and other domestic purposes both in urban as well as in rural areas. Hot water is required in large quantities in hostels, hotels, hospitals, industries such as textile, paper, food processing, dairy, edible oil etc. Water is generally heated by burning non­commercial fuels, namely firewood and cow dung cake in rural areas and by commercial fuels such as kerosene, liquid petroleum gas (LPG), coal, furnace oil and electricity in urban areas and in industries. Fortunately India is blessed with abundant solar radiation [1]. Solar radiation is available almost whole year through out India. The maximum daily average solar radiation 20.97 MJm-2 day-1 is received at Jodhpur which is known as Sun City of India while minimum 15.90 MJm-2 day-1 is received at Shillong. Solar water heaters, therefore, seem to be a viable alternative to conventional fuels for water heating.

The most commonly used solar water heater for domestic needs is natural circulation type. This type of solar water heater has been designed, developed and investigated in detail by Close [2], Yellot and Sobotaka [3], Gupta and Garg [4], Ong [5], Nahar [6], Morrison & Tran [7], Morrison and Braun [8], Vaxman and Sokolov [9], Nahar and Gupta [10], Norton etal [11], Nahar [12-17], Brinkworth [18].

Natural circulation type solar water heater has collector and storage tank in separate units, therefore, its cost is high and beyond the reach of common people. Considering this, the cost has been reduced by combining both collector and storage tank in one unit and collector-cum-storage type solar water heater has been designed, fabricated and tested. Such type of solar water heaters were studied by Tanishita [19], Richards and Chinnery [ 20], Garg [21], Nahar [22 ], and Nahar and Gupta [23-24], Fairman et al [25], Tripangnostopoulos et al [26], Smyth et al [27], Souliotis and Tripanagnostopoulos [28] and Madhlopa et al [29].These solar water heaters are simple in design, low cost, easy in operation and maintenance and easy to install. But life of this solar water heater was less than 8 years, therefore, it did not become popular in India. Considering this, integrated collector storage (ICS) solar water heater has been design, developed and fabricated.

The life of this solar water heater is more than 15 years.

2. Design

The ICS solar water heater consists of a rectangular tank 1000x1000x100 mm3, made from 3mm thick mild steel plate. The absorber area is 1.0 m2. The capacity of tank is 100 litres. The tank performs the dual function of absorbing solar radiation and storing heated water. It is encased in a galvanized steel (22 swg) tray having dimension 1240x1233x270 mm3 with about 100 mm glass wool insulation at the bottom as well as on the sides. Two glass covers have been provided over it. The front surface of the tank is painted with black board paint. Inner surface of the tank was painted with anti corrosive paint. An insulation cover is hinged over it so that the heater can be covered by it in the evening at 4 PM for getting hot water till next day morning. The heater works on push through systems. In urban areas, the inlet of the heater can be connected to water supply line through a gate valve. Hot water can be obtained by opening gate valve and collected through the outlet pipe. A funnel/bucket is provided for rural use where there is no water supply line. Hot water through outlet pipe can be obtained by putting cold water in the funnel/bucket. The heater is facing equator on a mild steel angle stand with к +15o tilt from horizontal for receiving maximum solar radiation during winter. Fig. 1 depicts actual installation of integrated collector storage solar water heater in the field.

3. Performance

The performance evaluation of the heater was carried out by filling it with cold water in the morning and recording hot water temperature at 4 PM and till next day morning when heater was covered in the evening by thermal insulating cover. The heater can provide 100 litres of hot water at an average temperature of 57.3o C that can be retained to 43.0o C till next day morning when cold water temperature was 17.0o C. The efficiencies of the solar water heaters have been obtained by the following relation:

0

Jo qu d0

П = _____________ (1)

0

A Jo Ht d0 Where,

A = Absorber area, m2 ,

HT = Solar radiation on collector plane, J m-2 hr-1,

qu = Useful heat collected by the solar water heater, j,

0 = Period of test, hr,

П = Efficiency of the solar cooker. The efficiency of the heater has been found to be 61.3%.