solar air conditioning

Solar refrigeration: solar refrigeration and air conditioning by adsorption

Solar refrigeration adsorption

LESBAT: Catherine Hildbrand, Olivier Cherbuin Julien Mayor. Project leader: Philippe Dind

The purpose of this article is to introduce the principle of solar cooling adsorption which simply allows for the cold with solar radiation.

What is solar refrigeration?

The Solar Energy and Building Physics Laboratory1 (LESBAT) of the Haute Ecole d'Ingénieurs et de Gestion du Canton de Vaud (HEIG-VD) in Switzerland has been active in the field of renewable energies for more than two decades.

The development of solar adsorption refrigerator is one of the main axes applied research in recent years.

These systems were originally designed for cold production in non-electrified areas of the countries of the Sahel where refrigeration is sought for storage of medical and food products.

Based on work by various research teams in 80 years we have made 1999 a demonstration prototype, and various laboratory prototypes to achieve a solar sorption cooler whose construction is feasible in small series in the country in development.

We accompanied our development by technology transfer with the Ouagadougou Ecological Center.

In this article, we present the operating principle of solar refrigerators adsorption, examples of constructive developments and technology transfer to Burkina Faso.

Funding for this experimental development was mainly provided by the GEBERT RÜF FOUNDATION (Basel - Switzerland).

Why solar refrigeration?

An alternative and clean solution for developing countries to store medicines and foods.

Solar cooling is an alternative to the following:

    • absorption refrigeration (not adsorption) which also transforms in the cold hot but requires higher temperatures whose combustion,

 

    • the vector by a thermodynamic refrigeration refrigerant circuit including the pump is powered by a generator,

 

    • electro-solar refrigeration which poses a major problem of storage of electrical energy (batteries whose lifespan is very short, etc.)

None of these 3 solutions perfectly meet the needs of developing countries because they consume hydrocarbons (rare and expensive in Africa) and reject CO2 or indirectly pollute the technologies used (batteries, refrigeration fluids, etc.).

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Solar air conditioning by adsorption using the direct conversion of solar thermal energy into cold does not present such drawbacks.

How does adsorption solar refrigeration work?

Adsorption is the phenomenon that occurs when striking a balance between a gas and a solid.

The concentration of gas molecules is always greater near the surface of the solid than in the gas phase. Thus, in any solid, the surface atoms are subject to uncompensated attractive forces, perpendicular to the surface. The balance of these forces is partially restored by the adsorption of gas molecules.

It is frequently referred to as torque when referring to adsorption. The couple is composed of an adsorbent (solid) and an adsorbate (liquid acting as refrigerant).

The body used as adsorbents are generally body which have a very large exterior surface. We can cite activated aluminas, activated carbons, silica gels and zeolites. The choice of the adsorbent will depend on the desired temperature at the evaporator and temperature available at the hot source (collector).

The other part of the couple (the adsorbate) must meet two essential conditions: have a high latent heat of evaporation and be made up of small molecules, easily adsorbable. The fluids having these characteristics are in particular water, ammonia, methanol and carbon dioxide. In addition to these two ″ physical ″ ​​conditions, the nature of the fluid as well as its dangerousness (flammability, toxicity, etc.) must be taken into account.

Our applications have successively used the active coal-methanol couples, silica gel-water and water-zeolite. The use of these pairs requires an average vacuum level (10-3 mbar) to reduce to a minimum the presence of noncondensable gases which could obstruct the passage of the vapors of adsorbate. The cycle works intermittently, because the cold is produced only during the night.

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Refrigerators as designed in our developments include four main elements:

    • The sensor-adsorber: part containing the adsorbent which is heated by solar radiation, with the effect of
      desorption of the adsorbate.

 

    • The condenser: this element is used to condense the adsorbate vapors desorbed in the sensor-adsorber.

 

    • The refrigeration chamber: this element is the useful part of the refrigerator, consisting of the insulated chamber and the evaporator comprising the adsorbate in liquid and solid form.

 

    • Autonomous valve: Body to separate the high pressure part of the low pressure. This body developed LESBAT is automatic and has no electronic (patented).

Operating Cycle

The solar refrigerator operates on an adsorption heat cycle. The cycle
can be broken down into four distinct phases as explained below. We also give in this table the cycle represented in the Clausius-Clapeyron diagram (Ln (P) (pressure) as a function of (-1 / T) (temperature)).


Advantages / Disadvantages of air conditioning adsorption

disadvantages:

    • Times (at least) 12h production between hot and cold production (this could be quite easily solvable by buffer batteries)

 

    • Need to have a cold source (at night) to produce the “cold” adsorption cycle

 

    • COP widely (1 / 10 approximately) below the compressor refrigerating machines (but is it really important since the solar source is quasiement unlimited?)

Advantages:

    • No energy source other than the sun (or some other source of heat, such as heat loss) is needed.

 

    • No moving parts (except the shutter), maintenance is much easier.

 

    • Possibility of using refrigerating fluids as simple as water!

 

    • COP equivalent to see slightly higher than electro-solar air conditioning (photovoltaic panels supplying a mechanical refrigeration circuit), the disadvantages in less (wear and pollution of batteries, maintenance…)!

Economics

Regarding the cost of manufacturing an adsorption solar refrigerator constructed as described in this article, it is very difficult to articulate figures.

The cost of a prototype developed in Switzerland or in France has nothing to do with the cost price of a refrigerator built a few dozen copies per year in Burkina Faso with the country's skilled labor (goal referred to first). This price would fall all the more in the event of mass production of thousands of copies per year in an automated line here or in Africa.

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A market study carried out in Burkina Faso in 2002 by CEAS-BF showed that more than a hundred 300-liter adsorption solar refrigerators could be sold per year and this for three years with NGOs, hospitals, of hotels and Burkinabé agricultural cooperatives on condition that the selling price does not exceed 750 CFA francs (approximately 000 €).

The challenge is twofold: to meet the market demand after production start in a craft and pace to produce without exceeding the sales price mentioned above. Current market conditions and the price of labor Burkinabe make us think that the CEASBF is able to meet this challenge.

Conclusion

The experiments carried out in the field of adsorption solar refrigeration within LESBAT have made it possible to understand all the difficulties inherent in this technique.

In order for this to spread without suffering failures that could discredit it, it is essential to support the transmission of knowledge to developing countries by creating or strengthening effective skills on the spot, as we have endeavored to do as part of our collaboration with CEAS-BF.

Constructive changes in our solar refrigerator systems aimed constructive simplification while maintaining performance. This objective is achieved. The result of the project is to develop small coolers. This will define the optimum size of the room taking into account technological limitations of our system.

Adsorption solar refrigeration is one of the range of solutions to the environmental problems caused by our excess consumption of fossil fuels.

Furthermore, it should improve the quality of vied'un many people, especially the Sahel countries, giving them access to the conservation of medicines, vaccines and food.

More:
- LESBAT Site
- Download the LESBAT article in .pdf format
- General and operating principle
- Optimization of the solar collector
- presentation panel solar cooling: Operating
- presentation of the solar air panel: African collaboration

4 comments on “Solar refrigeration: solar refrigeration and air conditioning by adsorption”

  1. Hello I am a researcher and inventor, for environmental systems, the article on refrigeration I find the subjects interesting because I myself am looking for collaborators to exhibit and to make a prototype for my idea I could provide you with a complement, once you say goodbye to me

  2. Hi
    I am in energy license. we have been asked for the different applications of the adsorption refrigerating machine (preservation of perishable food and pharmaceuticals). I have made some research but unfortunately I do not find it.
    I would like to have links in which I can not consult to finally advance on my project
    cordially

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