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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 9, September 2015)

1

Development of a Solar-Powered Mobile Refrigerator

A. O. Akinola

1

, T. S. Mogaji

2

, K. A. Adewole

3

Department of Mechanical Engineering, The Federal University of Technology, Akure, Nigeria.

Abstract - The dearth of energy supply in developing countries is worrisome, and this has made the preservation of perishable food items a common problem. This paper presents the development of a Solar-Powered Refrigerating System for the preservation and hawking of perishable foods such as fish, meat and vegetables; as well as water and other drinks.

A 12 volts DC battery-operated 700 W photovoltaic system and 220V/50Hz 400 Watt 12V Power Inverter was designed for a refrigeration load capacity of 0.747 kW and a cooling load of 0.3113 kW. The system when tested has a Coefficient of Performance of 4.73 at an average temperature of 9.46 oC, against an average room temperature of 25.6 oC. The inverter, at an average input voltage of 11.8 volts had an average output supply of 194.75 volts. The system had an overall refrigerating efficiency of 79.36%.

Keywords-- Power Inverter, photovoltaic system, Coefficient of Performance, refrigerating efficiency, Solar-powered.

I. INTRODUCTION

Energy; the ability to do work is essential to mankind as he make use of it in his daily life. It is one of the indispensable factors for continuous development and economic growth. The demand of energy is increasing rapidly in the developing countries due to automation, industrialization and urbanization, [1]. The growing population and technological developments have shown that the present sources of energy in use are not adequate. The world population has increased at an explosive rate from 1.65 billion to just over 6 billion people in the 20th century, and continues to increase. In the same century, mankind has consumed over 875 billion barrels of oil and it is very likely that even more oil will be consumed in the present century. Annual energy use in developing countries has risen from 55 to 212 kg oil equivalent over the last thirty years, while developed countries use as much as 650 kg oil equivalent per person, [2].

In the same vein, the prevalent hot weather throughout the year in the tropics, coupled with poor storage facilities has brought about a heavy demand for refrigeration and air conditioning. However, if kept below -300C, most food will deteriorate, often with change in texture, taste and smell. More important still, poisonous product may be produced. These changes can be due to micro-organisms such as bacteria, yeast. Food preservation is essentially based on methods that kill micro-organisms (such as bacteria) or at least inhibit the growth of such micro-organisms that make food unsuitable for human consumption.

Refrigeration is a method of lowering the temperature of substances below that of the surrounding in order to preserve or make them suitable for consumption in the nearest future [3, 4].

When these food items are stored inside a refrigerator at temperatures below the freezing point, the process of growth of micro-organisms is greatly impaired. The total breakdown of the cell and fibres in the food items is thereby inhibited. Also, the rate of oxidation and fluid loss through evaporation is retarded, [5].

Frozen foods have the advantage of resembling the fresh product more closely than the same food preserved by other techniques. According to ASHRAE, [6], the basic requirement is the lowering of the product’s temperature to between 0oC and 2oC. However, the storage temperature depends on the period for which the product would be stored and the availability of electricity to keep the refrigerator running.

As pointed out by Mogaji and Fapetu, [7], in developed countries, methods employed for extending shelf life and minimizing post-harvest losses of perishable produce include mechanical refrigeration, controlled atmospheres, hypobaric storage, and other sophisticated techniques. These techniques are highly capital intensive and for most developing countries, the required manpower is either lacking or inadequate. These cooling methods, except adiabatic cooling, are expensive for small scale peasant farmers, retailers and wholesalers, as they require electric power.

The non-availability or epileptic supply of electricity and the effect of its source on the environment is not making the use of refrigerators effective. The fossil fuel upon which we depend is getting depleted, and costs more to explore. This is making the product to cost more by the day. There is also the consideration for the environment. The climates are changing, the ozone layer is being depleted as a result of human activities, and the earth is getting warmer (global warming), [8]. Electricity where available is epileptic; and some villages had never enjoyed electricity supply for once, making the development of small economy difficult. Population growth is another crucial factor. Energy demand is increasing proportionately to population growth.

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 9, September 2015)

2

Desideri et al, [12] analyzed the technical and economic feasibility of solar absorption cooling systems, designed for two different application fields; industrial refrigeration and air conditioning. They described different technical installations for solar cooling, their way of operation, advantages and limits. Axaopoulos and Theodoridis, [13] experimentally investigated a solar photovoltaic powered ice-maker which operates without the use of batteries. It was reported that their study results have shown very good ice-making capability and reliable operation, as well as a great improvement in the startup characteristics of the compressors, which remain operational even during days with low solar irradiation and operate with improved utilization of the available photovoltaic power. Fan, et al. [14] published a paper on review of solar sorption refrigeration technologies: development and applications and pointed out that solar refrigeration technologies have the advantage of removing the majority of harmful effects of traditional refrigeration machines and that the peaks of requirements in cold coincide most of the time with the availability of the solar radiation. Ewert, et al, [11] experimentally investigated three different refrigeration technologies (thermoelectric, stirling, and vapor compression). They reported that proper sizing of solar-refrigerator components and system integration are essential for good design options. Also in Kaplanis and Papanatasiou [15], the design and development stages to convert a conventional refrigerator to a solar powered one were described.

Based on these views, in this study, a conventional hawking refrigerator system developed by Akinola et.al [16] was integrated to a solar powered one for cost effectiveness and user-friendliness in reducing, if not eliminate, the spoilage of food items, especially fish and meat, while they are being hawked in the market. This will equally prevent the contamination of the items. The results obtained from the study were presented and evaluated.

II. MATERIALS AND METHOD

A conventional hawking refrigerator was developed, [16]. It was designed for a 35 kg load using a 40-litres plastic cooler mounted on a welded mobile frame (Figure 1)

The solar system being incorporated was designed for the following components, and mounted unto the refrigeration system as shown in Figure 2;

(i) Photovoltaic (PV) module (ii) Charge regulator

[image:2.595.317.544.140.355.2]

(iii) Storage Battery (iv) DC to AC Inverter

Figure 1: Assembly Drawing of the Developed Mobile Refrigerator.

Source: Akinola, et al [16]

[image:2.595.326.536.393.723.2]
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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 9, September 2015)

3

Table 1:

[image:3.595.84.514.146.523.2]

Parts List of Developed Refrigerator.

Fig. 3: The Developed Refrigerator – (a) Front; (b) Side; and (c) Back Views

III. DESIGN

3.1 Determination of Cooling Load Capacity

The cooling load capacity of the system was determined by considering the various sources of heat into the refrigerated space. This was fully reported by Akinola, et al., [16].

The heat sources considered were: (i) Transmission Load (TL) (ii) Product Load (PL) (iii) Infilteration Load (IL) (iv) Cooling Load (CL)

The following equations were used in the design:

) , , (TL PL IL f

CL (1)

T AU

QR   (2)

ho hi

m

q   (3)

Q

T mcp

(4)

f p Te mc

Q  (5)

f mh

Q (6)

ff p T mc

Q  (7)

T Q

Q

(8)

)

(

)

(

Poultry

fresh

Q

Beef

fresh

Q

Q

TP

T

T (9)

QTLQTQIQP (10)

) (hev hcd

RE  (11)

E R

C E R m

. . .

 (12)

W E R P O

C. .  . (13) = 4.73

11 Switch 1 Plastic 10 Inverter 1 Standard 9 Battery 1 Standard 8 Solar Panel 1 Standard 7 Capillary Tube 1 Copper

6 Tyre (Wheel) 4 Rubber and Steel 5 Frame 1 Mild Steel 4 Condenser 1 Standard 3 Cooling Compartment 1 Plastic 2 Fan 1 Standard 1 Compressor 1 Standard

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 9, September 2015)

4

The ideal COP was calculated so as to be able to estimate the refrigerating efficiency of the system. This was done using the relation, [17];

1 2

1 T T

T

COPideal (14)

96 . 5

ideal COP

Therefore, Refrigerating Efficiency,

= 79.36 %

The load on the condenser and the heat transfer capacity of the of the evaporator were calculated using the relations, [18];

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(16)

3.2 Design of the PV System

The design of the PV system was done following the steps highlighted and the circuit system is shown in Fig. 4

3.2.1 Refrigerator Energy Requirement in Watt- hours (Wh)/day.

It is assumed that the refrigerator would run for 10 hours a day.

Therefore, for a 100 watts rated refrigerator, energy requirement

= 100 Watts x 10 hours/day = 1000 Wh/day.

3.2.2 Total Energy to be delivered by the PV panel per Day

Refrigerator load = 1000 Wh/day

Compensation for losses (20% of load) assumed = 200 Wh/day

Total energy needed = 1200 Wh/day

3.2.3 Sunlight Availability

The sunlight availability for Akure, Nigeria (Latitude 7o 15′ 00″ N, and Longitude 5o 11′ 24″ E was taken as 5.21 hours per day, [19].

3.2.4 Determination of PV Array Size Needed

This was determined using the relation;

(17)

= 230.33 Watts

3.2.5 Battery Bank Size

This is the Ampere- hours/day (Ah) to be delivered by the battery.

Total Refrigerator load = 1000 Wh/day Battery Voltage = 12V

Ah needed per day (1000/12) at 12V = 83.33 Ah/day A 12 V, 500 Ah deep cycle battery was selected. The battery has a Depth of Discharge (DOD) of 20%, which translates to 100 Ah.

3.2.6 Minimum Battery Capacity Needed.

Ampere-hours (Ah) needed per day = 100 Ah/day It is assumed that the battery would operate for 2 specified days of Autonomy

Battery size needed therefore = (100 x 2) = 200 Ah at 12V

[image:4.595.315.544.317.533.2]

This battery capacity can be achieved by using a 12V battery or by connecting two 6V batteries in series.

Fig. 4: The circuit Diagram

3.2.7 Charging Regulator

8-amps, low voltage cut-off solar charge controller was used to draw out or squeeze more charge out of the solar module, and protect the system from over or under voltage.

3.2.8 Inverter

12 Volt DC to 220 Volt 50Hz AC inverter, 400 watts continuous, 800 watts peak power, automatic inverter that converts DC current into conventional AC electricity was used. It has 85% efficiency

IV. CONSTRUCTION

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 9, September 2015)

5

The outer components and accessories were fitted using bolts and nuts; these are the condenser, compressor, evaporator, thermostat and electrical control board. The attachment of a movable system, which essentially is an iron frame, supported by four wheels make the developed refrigerator especially suitable for hawking.

It was constructed at a cost of six hundred and sixteen US Dollars ($616.00)

4.1 Installation of the PV System

The support structure for the PV module is mounted on top of the refrigerator frame and is tilted at an angle of 17° so that maximum Solar energy can be tapped, [20]. The module consists of a series connection of 36 square Solar cells, each 10 × 10 cm in size. The charge regulator, storage battery and inverter were arranged inside the frame structure. All the system components were connected with cables and connectors.

V. TESTS,RESULTS AND DISCUSSION 5.1 Tests and Results

The refrigerator was tested with perishable food items. Parameters taken were the room temperature, the cabinet temperature and the condenser temperature, using mercury-in-glass thermometer. The recorded temperatures were used to determine other parameters such as Refrigerating effect, Compression work, Coefficient of Performance, Mass Flow Rate, Power and Refrigerating Capacity. The results were presented in graphical forms and discussed by Akinola, et al, [16].

[image:5.595.60.539.371.542.2]

The same tests were repeated when the solar system was installed, and the input and output voltages of the inverter were recorded. The results are presented in Table 2

Table 2:

Recorded and Calculated Parameters from Tests

Evaporator Temperature

(oC)

Condenser Temperature

(oC)

Power (kW)

Compressor Work (kJ/kg)

Refrigerating Capacity

(kW)

Refrigerating Effect

(kW) COP

Voltage of Inverter (V)

In Out

3.0 75 0.32 24 0.046 74 3.08 12 200 4.0 73 0.29 22 0.047 76 3.45 12 198 7.0 70 0.25 20 0.047 80 4.00 11.8 198 10.0 67 0.22 19 0.048 84 4.42 11.6 196 11.2 64 0.20 18 0.048 90 5.00 11.8 188 12.5 60 0.17 17 0.048 94 5.53 11.8 192 13 57 0.16 16 0.049 98 6.13 11.6 190 15 55 0.15 15 0.054 118 7.87 11.8 196

9.46 65.13 0.22 18.88 0.048 89.25 4.73 11.8 194.75

From Table 2, the supply voltage from the DC battery and the output voltage from the inverter were not constant. This could be attributed to the fluctuation in the charging of the battery by the PV system, and the power demand of the refrigerator. However, an average voltage of 11.8 volts was supplied from the battery, and this was converted to AC at 194.75 volts by the inverter. This value is adequately enough to run the system. Also, power and compression work values decreases as evaporator temperature increases. This is due to the high torque required at start, which stabilizes as the system keeps running. Contrarily, the power and compression work increases with increase in condenser temperature, due to the high power required to compress the vapourized refrigerant after dissipating the high heat content at the condenser. The power and the compression work had average values of 0.22 kW and 18.88 kJ/kg at 9.46oC and 65.13oC evaporator and condenser temperatures respectively.

The organoleptic evaluation carried out on the products when the system was operated with a solar system exhibited good preservative characteristics such as appearance, colour, texture and consistency, smell and taste.

VI. CONCLUSIONS

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 5, Issue 9, September 2015)

6

The present analysis showed that the solar powered refrigerator results are comparable to the convectional refrigerating system from both quantitative and qualitative points of view as earlier reported, [16].

REFERENCES

[1] Hasanuzzaman, M., Saidur, R. and Masjuki, H. H. (2008). Moisture Transfer and Energy Losses of Household Refrigerator-Freezer during the Closed Door Operation. International Journal of Mechanical and Materials Engineering (IJMME), Vol. 3 (2008), No.1, 30-37.

[2] BP Statistical Review of World Energy. 2003. (mazamascience.com)

[3] Althouse A.D., Turnquist C.H. and Branco A.F. (1978): “Modern Refrigeration and Air Conditioning”. Good Heart Willox Co., London

[4] Fapetu O. P. (2002): “Principle and Practice of Refrigeration” Volume 1, Pin-Funky Press, Akure, Nigeria.

[5] Govindan, T. K. (1985): “Fish Processing Technology” Mohan Primlani for Oxford and IBH Publishing Co., New Delhi. [6] ASHRAE (1986): “Refrigeration Handbook” American Society

of Heating, Refrigerating and Air-Conditioning Engineers, New York.

[7] Mogaji, T. S. and Fapetu, O. P. (2011): Development of an evaporative cooling system for the preservation of fresh vegetables, African Journal of Food Science Vol. 5(4), pp. 255 – 266

[8] http://www.articlesbase.com/environment- articles/global-warming (Assessed on May 24, 2012)

[9] Kim, D. S. and Ferreira, I. C. A. (2008). Solar refrigeration options–a state-of-theart review. Int. J. Refrig., 31: 3-15. [10] Papadopoulos, A. M., Oxizidis, S. and Kyriakis, N. (2003).

Perspectives of solar cooling in view of the developments in the air-conditioning sector. Renewable Sustainable Energy Rev., 7: 419-438.

[11] Ewert, M. K., Agrella, M., Frahm, J., Bergeron, D. J., and Berchowitz, D. (1998). Experimental evaluation of a solar PV-refrigerator with Thermoelectric, Stirling and Vapor Compression Heat Pumps. Proceedings of Solar ’98, ASES http://solar.nmsu.edu/publications/pv_direct_refrig.pdf

[12] Desideri U., Proietti S. and Sdringola, P. (2009). Solar-powered cooling systems: Technical and Economic Analysis on Industrial Refrigeration and Air-Conditioning Applications. Appl. Energy, 86: 1376-1386.

[13] Axaopoulos, P.J. and Theodoridis, M. P. (2009). Design and Experimental Performance of a PV Ice-maker Without Battery. Solar Energy, 83:1360-1369.

[14] Fan,Y., Luo, L. and Souyri, B. (2007): Review of solar sorption refrigeration technologies: Development and applications, Renewable and Sustainable Energy Reviews. 11: 1758–1775 [15] Kaplanis, S. and Papanastasiou, N. (2006) The study and

performance of a modified conventional refrigerator to serve as a PV powered one. Renewable Energy, 31: 771-780

[16] Akinola, A. O., Akintayo, T. C. and Kuti, O. A. (2008) “Development of a Hawking Refrigerator”. FUTAJEET, Vol. 6, No 1: 88 – 96

[17] Stoecker, W. F and Jones, J. W. (1982) Refrigeration and Air Conditioning. Publisher McGraw – Hill Book Company International Edition.

[18] Khurmi, R. S. and Gupta, J. K. (2011): A Textbook of Refrigeration and Air Conditioning. Fifth Revised Edition. Eurasia Publishing House (P) Ltd. Ram Nagar, New Dehli – 110055.

[19] Melodi, A. O. and Famakin, S. R. (2011): “Assessment of Solar PV-Grid Parity in Akure, South-West Nigeria” Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 2 (3): 531 – 536

[20] Green, M.A., (2001). “Third Generation Photovoltaic: Ultra-high conversion Efficiency at Low Cost”, Progress in Photovoltaic: Research and Applications; Vol 19, pp 123 – 135

Nomenclatures

R

Q = the rate of heat transfer in watt (W)

A = the outside surface area of wall (m2)

U = the overall co-efficient of heat transmission (W/m2K)

∆T = the temperature differential cross the wall (K)

q = infilteration load (kW)

m= air infilteration rate into the refrigerated space (L/s)

o

h = enthalpy of outside air (kJ/kg)

i

h = enthalpy of inside air (kJ/kg)

Q= the quantity of heat (kJ/kg)

m = mass of product (kg)

p

c = specific heat of product (kJ/kg-K)

T

 = change in product temperature (K) T1 = Chosen Evaporator Temperature (K)

T2 = Chosen Condenser Temperature (K)  = Time taken (seconds)

ef T

 = change in product temperature (K) from entering to freezing.

= Temperature of medium to be cooled = Temperature inside the evaporator

f

h = the product latent heat of fusion (kJ/kg)

ff T

 = change in the product temperature (K) from freezing to final

Q = Summation of quantity of heat (kJ/kg)

TP Q

= Sum total of heat absorbed (kJ/kg)

QTL = Summation of all total heat loads (kW)

T

Q = Transmission load (kW)

QI = Infiltration load (kW) QP = Product load (kW)

Qc = Load on Condenser (kJ/kg)

Qev = Heat transfer capacity of the evaporator (J/s)

W = Work done by Compressor

(hevhcd) = the difference in enthalpy at evaporator and

condenser temperatures respectively.

m = mass flow rate (kg/s)

R.E.C. = Required Equipment Capacity (kW)

R.E. = Refrigerating Effect

Figure

Figure 1: Assembly Drawing of the Developed Mobile Refrigerator.
Fig. 3: The Developed Refrigerator – (a) Front; (b) Side; and (c) Back Views
Fig. 4: The circuit Diagram
Table 2:  Recorded and Calculated Parameters from Tests

References

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