Solar air conditioning

In the solar air conditioning a building, room, or seen abstract, a volume by solar energy cooled and dried. For this purpose, the drive power source of a chiller is operated by solar radiation, instead of electrical energy from the power grid.

• 2.1 air conditioning with solar power 2.1.1 principle
• 2.1.2 Pros and Cons

Building air conditioning

Problems of electrically powered air conditioning in buildings

The highest cooling demand coincides with the midday peak in the load profile of electricity consumption. It is thus responsible for the design of power plants and power grid. Peak load electricity is economically and ecologically costly.

Compression chillers work with refrigerants.

Compliance of solar radiation and air conditioning needs of buildings

Buildings must only then and there be air-conditioned, where they or their environment by solar radiation are heated. Solar energy is thus always available there, where air conditioning is to be operated.

On closer inspection, however, follows the need for air conditioning of the radiation with a delay, since the environment and the buildings are thermally inert by their heat capacity. In the daily course the highest exposure is at astronomical noon ( in Germany 13:15 clock summer -time), the highest temperature but in the afternoon around 15:00 clock. In transition is the most intense insolation on the northern hemisphere on June 21, the hottest day follow depending on the local climate in mid to late July. Nevertheless it can be considered in the dimensioning of a strong correlation between the radiation and heating.

Building air conditioning with solar power

Principle

An electric air conditioning is driven by locally generated solar electricity. Normally, such a system is also connected to the electricity grid in order to use the electricity generated outside of the summer months and be able to operate the air conditioning at no ongoing solar modules.

Pros and Cons

Advantage of such a system is that power generation and air conditioning independently of one another planned, built, and can be operated; a retrofit of existing air conditioning systems is possible. There are technically advanced equipment available. Solar panels and air conditioning can be separated spatially.

Drawback is the conversion of solar radiation into thermal thermodynamically valuable electricity in order again to operate a thermal application. Commercially available solar cells have efficiencies below 20%. It will continue refrigerant needed.

Building air conditioning with solar heat

In these methods, solar thermal energy is used to cool heat. Since solar thermal panels use the radiation up to 70%, a slightly less favorable ratio of heat removed to expended energy ( energy efficiency ratio, coefficient of performance, COP) can be taken as in electric chillers in purchasing. The solar system can also serve the hot water and heating.

Closed sorption

In closed method, the air over cold water distribution systems is cooled with an absorption chiller or adsorption chiller, this comes with the sorbent not in contact. Conventional fluid pairs in absorption are mixtures of ammonia and water or saline solutions, such as lithium bromide. When adsorption is carried out with solid sorbents such as silica gel or zeolite and the refrigerant water. A dehumidification of the supply air is possible as with compression chillers by cooling below the dew point and then reheating. Recent developments in this field are Sorptionskältemedien based on ionic liquids. In contrast to the lithium bromide -water mixture so far mostly used these have to water a significantly higher activity and can not crystallize also because they have very low melting points.

Open sorption

When open, the supply air is dried sorption by contact with water -attracting substance (for example, silica gel, zeolite A). Is then sprayed water on evaporation cools the air (cooling by drying and evaporation). The sorbent is then heat- dried ( regenerated).

To dry solids or liquids may be used. Example of methods with Feststoffsorbentien is the Rotationsentfeuchter. Suitable liquid sorbents solutions with calcium chloride, lithium chloride or lithium bromide are used so far. But sorbents based on ionic liquids are, increasingly interest.

Pros and Cons

One advantage of the sorption is that the thermodynamically unfavorable detour via the generation of electricity is avoided. Heat or water -attracting substances can be saved as opposed to power loss.

The disadvantage is proving that solar system and air conditioning must be designed and constructed together, subsequent changes are costly. So far there are only a few manufacturers that offer such systems. Another disadvantage is the very large volume of the cooling unit with respect to a compact electrical air conditioning systems. In addition, the secondary energy requirements for pumps and control is sometimes not negligible and must be included in the cost calculation.

Example of use

At the Bavarian Center for Applied Energy Research ( ZAE Bayern ) in Garching near Munich, an energy system for solar heating and cooling of the institute building is installed and in operation for several years. The core of the system consists of an absorption chiller that derives its heat from the drive installed on the roof of solar flat plate collectors. The peculiarity of this solar air conditioning system is the special concept of re-cooling of the chiller. The re-cooling is carried out through a conventional dry cooling tower, which is relieved at high outside temperatures by a latent heat storage ( PCM memory ) by waste heat from the chiller is daytime cached, which can then be efficiently delivered at night at lower outside temperatures to the ambient. Further information can be found here.

Cooling of mobile rooms and tanks

The featured at the building air conditioning method do not consider the weight and volume of the cooling unit. Come for building air conditioning cooling processes uneconomical here also used.

Air conditioning with solar power

Principle

The solar power generated by sunlight is used to drive compression chillers or Peltier elements for small volumes.

Pros and Cons

Advantage of such systems is that is air conditioned when demand for air conditioning is available. To compensate for the disadvantage of low efficiency and the cooling requirement slightly shifted with respect to the generation of heat by sunlight, here the isolation of the cooling volume is reinforced towards the environment. Examples are solar powered coolers (cooling with Peltier elements ), mobile homes with solar-powered air conditioners (cooling with compact compression chillers ), etc. Another advantage that is largely independent of the stationary power supply and that the weight of the cooling unit by eliminating electrical storage units ( second car battery, accumulator) decreased.

Disadvantage is the higher cost.

Air conditioning with solar heat

In these methods, solar thermal energy is used to cool heat. Both Ad and Absorption chillers and DEC devices use time-tested chillers. The use of commercially available flat-plate collectors is very limited, it has a preferential special medium temperature collectors come with reinforced insulation and double cover to use. For smaller systems and vacuum tubes can be used.

In addition to many more small projects in research and development again first commercial projects have emerged in recent years.

Passes some exotic methods using a mechanical intermediate step solar heat for cooling. These include:

• Rankine cycle compression →
• Vuilleumier process

These processes are present ( = 2005? ) Is used only for " exotic" cooling applications. For a commercial use are ongoing research projects that are motivated by the success of materials science.

Starting with 2003 different, increasingly larger projects to be built. Solar cooling for the Desert Outdoor Center near Phoenix, Arizona, USA, the Logistics Center Summer Olympic Games Beijing, China, the bank building of Caixa Geral de Depósitos in Lisbon, Portugal, and the United World College in Singapore. With collector of about 160-4000 m², start-ups from 2006 to 2011, four reference projects of SOLID, Graz, Austria.