SOLAR THERMAL ENERGY.
Introduction.
Solar cooling consists of the production of cold from solar radiation.
The main advantage of the use of solar energy for cooling is that the moments in which the demand for cold is greater coincide with those in which the solar radiation reaches its maximum values, thus obtaining very high yields.
It allows us to take advantage of solar energy installations throughout the year avoiding overtemperature during the summer, reducing the amortization period of equipment, energy consumption and greenhouse gas emissions.
Solar cooling also has a great facility to be combined with other types of applications, such as hydrogen, evaporation systems, trigeneration...
It is a technology in development that is not yet mature enough for its massive application, but due to the rise in energy prices, it has a great future.
The cycle of an absorption machine is based on two basic principles:
- The relationship between the boiling point and the pressure of liquids.
- The affinity of some substances for others.
The machine has four interconnected vessels, in which two are at low pressure (evaporator and absorber) and two others at high pressure (condenser and generator).
These pressure levels are conditioned by the condensation and vaporization temperatures of the refrigerant.
Below is the outline of a libr-water absorption machine with simple effect.
-Solar Cooling by Thermal Compression:
Solar thermal cooling equipment is based on the phenomena of absorption and adsorption. It takes advantage of the ability of some substances (sorbents) to attract others (sorbates).
In humid climates, the extraction of moisture contained in the air represents in proportion the largest cooling load, sorption desiccant systems are used to remove moisture from the air.
Most of the energy demand of these systems can be met with solar energy.
In absorption, the absorbent is a liquid and the sorbate, which serves as the system's refrigerant, is in a gaseous state when absorbed.
Adsorption is a phenomenon in which the molecules or losatoms of a substance are concentrated on the surface of another.
-Adsorption machines.
This equipment consists of one or more adsorbers (desorbers), a condenser and an evaporator connected to the different heat sources.
The adsorption cycle is analogous to the traditional compression cycle where mechanical compression is replaced by thermal compression.
Because the substrate is solid, there is no physical movement of the adsorbent, so its condition of adsorber or desorber, is imposed by the external connections and the point of the cycle in which it is located.
The chamber exchanges heat alternately with a hot focus at high temperature and a cold focus at intermediate temperature.
The condenser exchanges energy with the heat source at medium temperature and the coolant is transported between the adsorption chamber, reactor, condenser and evaporator.
-Desiccant systems:
These systems are based on adsorption, but unlike adsorption machines, they work in a continuous open cycle.
Unlike water chiller machines (whether conventional, absorption or adsorption) desiccant systems directly treat the air that is driven to the room to be air-conditioned.
To date, available desiccant refrigeration equipment has been considered very expensive compared to mechanical refrigeration equipment.
The drying capacity of the sorbent is related by the relationship between the water content in the desiccant equilibrium and the relative humidity of the air stream in contact with it.
Therefore, this type of systems are effective in areas where the relative humidity of the air is low, especially in summer, which is typical of areas far from the sea or large bodies of water, with high dry bulb temperatures, and low humid bulb temperatures.
ELECLIMA
