HYBRID SOLAR-CHILL RAFRIGERATION SYSTEM
Keywords: Solar Energy, Adsorption Refrigeration, Water Heater,
Refrigerator, Hybrid
INTRODUCTION
The SolarChill Project is developed and plans to make freely available a versatile refrigeration technology that is environmentally-sound, battery-free, technologically-reliable, affordable and multi-source powered. It has been developed with the objective to help deliver vaccines and refrigeration to regions of the world without electricity or with inadequate electrical supply. A combined cycle of heating and cooling adsorption operating working has been proposed working directly on solar panels, hence, bypassing the use of conventional lead batteries and kerosene refrigerators.
The unique feature is that energy is stored in ice instead of in batteries. Temperature control occurs through natural convection between ice – storage and food storage compartment.
An ice compartment keeps the cabinet at desired temperatures during the night. SolarChill is made from mass produced easily available standard components which needn’t be refueled, resulting in favourable cost compared with other battery operated refrigerators.
Moreover, this refrigerator incorporates environmentally-friendly
Green freeze technology which utilizes hydrocarbons for the refrigerant cycle, and thus bypasses the reliance on ozone layer depleting and potent global warming fluorocarbons, such as CFCs and HCFCs.
It has potentially high market demand for domestic and small commercial refrigeration applications in regions of developed and developing countries that are off the grid or have unreliable electrical services. Theoretical simulation has been done, which is

in good agreement with experimental results. The research shows that the hybrid solar water heating and ice-making is reasonable, and the combined cycle of heating and cooling is meaningful for real applications of adsorption systems.
BACKGROUND
The expanding population and the energy crisis have brought serious problems to the world environment and sustainable development.
The electric driven vapor compression refrigeration system has faced a challenge as CFCs and HCFCs are not suitable for sustainable development. The common substitutes of refrigerant are also facing the problem of Green-House effect.Li-Br water absorption systems for air-conditioning has a big market throughout. For energy saving (heat, gas, oil, electricity) absorption systems are now facing disadvantages as electric driven central air conditioning systems have reached a COP over
4.5, while absorption systems also facing the problem of green house effect.
The adsorption system is advantageous in small scale systems if compared with absorption systems, especially for the handling of the system and the cost. But its COP is usually smaller than absorption systems. For solar energy utilization, a solid adsorption system is possibly the best system for refrigeration purposes. The heating-desorption-condensation and cooling adsorption-evaporation processes are well suited for solar energy.
The solar radiation heat source varies with seasons, the hotter the climate, the stronger the solar radiation, which surely causes the need for more refrigeration. Adsorption refrigeration is a good way to utilize solar energy. This paper shows a combined cycle for solar heating and cooling, in which a hybrid system of solar water heater and an adsorption ice maker are incorporated.

BASIC METHODOLOGY:
A combined cycle capable of heating and adsorption refrigeration has been proposed, The system consists of a heater, a water bath, an activated carbon-methanol adsorption bed and an ice box. It has been found that with 55 MJ heating, the 120 kg water in the bath can be heated from 22°C to 92°C, of while 9 kg ice at 21.5°C is made in the ice box .The condensing temperature is controlled at about 30°C. The cooling capacity of the ice and the refrigerant in the evaporator will maintain the 100 liter cold box for about three days below 5°C. The calculated COPsystem is 0.0591 and
COPcycle is 0.41.The experiments show the potential of the application of the solar powered hybrid water heater and refrigerator. A combined cycle capable of heating and adsorption refrigeration has been proposed, The system consists of a heater, a water bath, an activated carbon-methanol adsorption bed and an ice box.
PROCESS SIMULATION
A stainless steel tube type adsorber filled with activated carbon is immersed in the water bath .The adsorber is designed as a group of tubes with a diameter of 50 mm, where each tube is embedded with activated carbon, and the center of the bed is incorporated with a 10 mm channel for mass transfer purpose. A total of 30 tubes with a length of 800 mm have been filled with 22 kg activated carbon.
The solar heat flux density is taken from the solar source. The total radiant energy to the collector is assumed to be 20 MJ/m2 per day, with a solar collector efficiency of 46 percent -depending on the product performance. A solar collector of vacuum tube heat pipe type is selected (2 m2 efficient area), and its performance parameters are based on the product performances.
The water thus, gets heated through heat conduction. Heating to the adsorber is well thermally insulated and the efficiency is high.

The desorbed refrigerant is condensed in the condenser and flows into the evaporator. When the adsorbent bed pressure is lower than the evaporation pressure, the refrigerant liquid in the evaporator will evaporate which causes the refrigeration effect. found that the refrigeration effect is strongly influenced by the condensing temperature; it would be suggested to put the condenser partly or fully in a water bath to decrease the condensing temperature, especially in summer time.
At 15 hours of operation, the beginning of adsorption may causes rapid temperature rise due to the strong adsorption heat release and the day – night cycle continues without any refueling of materials required.
During the night, if the hot water is drained out to another hot water reservoir or used directly, city water will then fill the water tank. The cold water will cool the adsorber very quickly, and the cooling adsorption-evaporation process can thereby be initialized.
During the cooling-adsorption-evaporation process, the sensible heat of the adsorber and the heat of adsorption will be transferred to water in the tank. After the adsorption process, the water temperature in the water tank will be higher than the filled water temperature.
This heat recovery process is important to save energy and thereby increase the total solar energy efficiency.
A hybrid system of a solar powered water heater and ice maker is constructed, which is simply a combination of a solar water heater and a solar adsorption ice maker. Hot water is expected to be higher than 80°C, which is needed for activated carbon–methanol adsorption refrigeration. Due to the use of a water tank and because the adsorber is immersed into water, the adsorbent temperature is usually less than 100°C, which makes methanol chemically stable.

RESULT
The experimental results have shown that for the case of 55 MJ and 50 MJ heat input, the lowest temperature of the evaporator surface is about -2°C, and the 9 kg of water in the evaporator is cooled by the methanol and iced completely. One such operation will yield a 100 liter cold box at 5°C for more than 55 hours.
However, 6–10°C temperature increase in the water bath will be generated by the sensible heat and adsorption heat in the adsorbent bed, which will spare the energy for solar heating.
Hence the problem of food and vaccine storage can be solved in remote areas and off the electric grid areas by usage of mass produced standard components. The refrigeration cycle can be made to run on its own life long without any refueling .Energy efficiency increases through efficient insulation.
Discussions and Conclusions
Based upon the proposed new idea of the combined cycle of heating and adsorption refrigeration, a hybrid solar powered water heater and refrigerator has been constructed and tested.
This work shows
1. In application: a solar collector for water heating and a solar collector for adsorption refrigeration can be unified as one solar collector for both water heating and adsorption refrigeration. One solar collector can be used for two purposes, which is reasonable for family use as both heating and refrigeration output is available.

2. In construction: a solar water heater and adsorption refrigerator are connected only with one tube for refrigerant flow, and the adsorber is immersed into the water tank. In this case, high efficiency solar collectors such as evacuated tube type and evacuated tube with heat pipe type can be used.****
The hybrid concept has solved the problem for good heating and good cooling to the adsorber.
3. In energy efficiency: the hybrid system has had good use of solar energy, the sensible heat and adsorption heat of the adsorption bed is obviously recovered, which is used again to heat the water bath in the water tank, and thereby saved solar energy.???
4. The Ice-storage Compartment can be partitioned into two separate chambers . Addition of varying amount of NaCl salt in the two chambers can help in maintaining one of them at a temperature of around 5 °C for normal cold storage purposes and the other chamber at around -2 °C for storage of items requiring freezing temperature. The temperature can be made to go as low as -30°C by increasing the concentration of the salt.
5. The basic concept can also be used to utilize the heat emitted by the engines of vehicles instead of using solar energy. With the usage of an air cooled condenser and a hybrid system with a combined cycle of heating and refrigeration, this model can help in providing air cooling inside the vehicles .
6. The usage of carbon fibres in place of activated charcoal can further increase the adsorption capacity and hence the efficiency of the process.
7.Cost analysis:

8.The proposed model has potentially high market demand for refrigeration applications in regions that are off the grid or have unreliable electrical services
FURTHER DEVELOPMENTS
The future developments in this project will include minimization of the module area for specific climatic regions. Optimization of the control strategy has to be done in order to minimize the needed
PV-power. Further simplification and cost reduction of the construction has to be carried out. Some future applications for this product could be milk chilling, vending booths for food and beverages, recreational purposes or as a grid independent household refrigerator.