Solar Domestic Refrigeration Equipment

A. Chikouche, B. Abbad, S. Elmetenani, M. Chikh, S. Bouadjab
Unit for development of solar equipments, Bou-Ismail, Wilaya de Tipaza

Abstract
In the last decade, the demand for perishable products has increased drastically, resulting in an increasing demand for domestic refrigerators and freezers. The use of solar energy for environmental control is receiving much attention as a result of the projected world energy shortage.

Solar refrigeration has the potential to improve the quality of life of people who live in areas with insufficient electricity The unit for development of solar equipments (U.D.E.S) is actually conducting different experiments on locally produced domestics refrigerators and freezers using solar electric energy on one part, and a new environmentally friendly refrigerant on the other part, and the results are very encouraging. The experimental system is the most widely used domestic refrigerator in our country which has an internal volume of 330 l, 1/5hp cooling capacity and works on R134A. The various achievements presented, show that UDES acts strongly in favour of the promotion of renewable energies, with less impact on the environment. The research projects undertaken are directed toward the development of refrigeration and air conditioning equipments and systems using solar energy and refrigerants with less global warming and ozone depletion potential.

INTRODUCTION
Solar photovoltaic (PV) systems, which convert sunlight directly into electricity, are extremely attractive as an energy technology. This is because photovoltaic modules produce no pollution, have a life of at least 20 years, and require little maintenance. Solar photovoltaic systems for lighting, water pumping, vaccine refrigeration and telecommunications are proven, commercially available and economically viable[1]. Solar photovoltaic power systems have the great advantages of low maintenance and long life under arduous environmental conditions. The cost reductions in photovoltaic arrays have once again stimulated interest in the possibilities offered by photovoltaic powered vapor compression unit [2]. These units are now becoming commercially available with either D.C. or A.C. power drive to the refrigeration compressor. Extensive field testing of solar photovoltaic refrigerators has been carried out[3].

Description of the system
The experimental system (fig.1) is the most widely used domestic refrigerator in our country with an internal volume of 330 l, 1/5hp power input and works on R134A. It has a single door hinged on the right, a top freezer compartment of about 40 l volume and uses a capillary expansion device. Its overall dimensions are 1650x590x700 mm. 25mm thick polyurethane foam insulation is provided all around. The inner liner of the refrigerator is PVC and the outer one is steel sheet with enamel paint finish. The thermostat of the refrigerator is fitted on the aluminum evaporator surface. 

The basic refrigeration unit is a conventional domestic refrigerator with an internal volume of 3301. It’s run on 50 Hz mains supply with an acceptable voltage range of 220-250 V. The normal rated power consumption of such a unit ranges from 120 to 140 W. The dimensioning of the photovoltaic installation answering the energy consumption of the refrigerator was carried out by using the PV3f software of RETSCREEN International. The system is composed of photovoltaic modules, batteries and an inverter. This calculation is based on: the solar resource (conditions weather of the site) loads of the system (in our case of the refrigerating unit) storage (standard and nature of the batteries, opened batteries, 100A.h-1, under 48V) the type and power of the photovoltaic modules (75W, of BP Solar) In our case, the calculated power of the PV field is based on the solar power potential of the south of the country (average solar daily global radiation of 5 to 6 kWh/m²/day) and a performance factor of : Pf = 0.6.

Algeria has a very good geographical situation for solar energy applications. The daily sunlight averages 10 hours /day, with a daily average global radiation of 5 to 7 kwh/m²/day in most parts of the country (see. Fig. 2), and solar energy heating and cooling equipments will undoubtedly have very good prospect in the future. Right now, a lot of research projects in research centers and state institutions are undertaken to develop equipments using renewable energies.

Figure 02: geographical repartition of solar energy in Algeria (July and December)

Description of the power station: A set of six PV panel has been used and a set of a six stationary batteries of 105 Ah/12 V each is used. The batteries are arranged to give a continuous output of 315 Ah /24 V, with three days autonomy (capability ?) and a lower discharge limit of 80 % on the batteries. Included in the PV system regulation are a charge regulator and an inverter. The power delivered by the PV system installed (900 VA) covers largely the electrical needs of the experimental setup.
Results
Fig.3 shows the variation of the compressor body temperature of 50 Hz sinusoidal AC. It can be seen that the compressor body temperature goes through cyclic changes in accordance with the on-off cycle of the refrigerator albeit. Compressor inlet and outlet pressure and temperature are normal for R134A.

Fig.3. compressor body temperature.

Legend: T1: upper freezer surface; T2: lower freezer surface; T3: lower cabinet; T4 upper cabinet; T5 middle cabine; T6: ambient temperature.
Fig. 4. Cool-down and warm-up characteristics of the refrigerator.

Conclusion
Calculations show that: for the system an energy input of 1.43KW/h; 6 panels of 75W occupying a surface of 3.9m ² will be necessary. Annually provided renewable energy is approximately 0.580 MWh with an output / m ² of 149.5KWh.m- ², an operating time ratio of about 14, 7% and a total output of approximately 6.1%.Better isolation (insulation ?) and better closing door frame will improve the energy effiency of the system. Another aspect of equal importance relates to the GES: the system offers the advantage to us of not emitting a quantity of GES of about 0.54 t CO2 per annum.

References
1. A. Derrick, Renewable Energy, Vol.5, Part I, pp. 229-236, 1994
2. THOMACHAN A. KATTAKAYAM and K. SRINIVASAN, Energy Convers. Mgmt Vol. 39, No. 1/2, pp. 21-26, 1998
3. A.Chikouche, S.Elmetnani and B. Abbad; ICR07, International Congress of Refrigeration 2007, Beijing,China