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    gas, have been introduced in markets all over the developed worlde in the US, Japan, France, Italy, Spain and more recently in
    Portugal. As to adsorption systems e in spite of several studies that
    demonstrate their technical feasibilities e, there exist only exper-
    imental units, though stand considerable chances of becoming
    economically viable, especiallywhere thermal comfort applications
    are concerned [11].
    This paper presents some of the adsorption fundamentals and
    also the energy equations for adsorbers. Then it puts forwards the
    characterization and the pre-dimensioning of a 20 kW air
    conditioning unit based on both the adsorption process and solar
    energy. Cold water is produced during night-time in an activated
    carbonemethanol adsorption chiller and then stored into a tank
    in order to supply cooling air during day-time. Solar energy is
    used for regenerating the adsorbent medium by means of highly
    efficient flat-plate collectors. Thermal energy is stored in a hot-
    water tank so as to feed the chiller at night. The central unit was
    created to provide thermal comfort to four adjoined laboratory
    rooms, whose total area is 110 m2
    .
    2. Adsorption fundamentals
    Adsorption constitutes a solid sorption process by which the
    binding forces between fluid molecules (adsorbate) and the solid
    medium (adsorbent) derive from an electrostatic origin or from
    dispersionerepulsion forces. It is an exothermic process as a result
    of the gaseliquid phase change. The energy liberated during
    adsorption is called isosteric heat, and it depends on the nature of
    the adsorbenteadsorbate pair.
    Anumber of state equationseknownas isostherms of adsorptione
    are proposed. These functions correlate the temperature T, the pres-
    sure P, and the concentration of the adsorbed phase a,sothat f(T, P,
    a) ¼ 0. The main isotherms of adsorption are: (a) Henry’s law, valid
    only for weak concentrations; (b) Langmuir’s approach, which takes
    up adsorption on monomolecular layers where there is a dynamic
    equilibriumbetween the phases; (c) Gibbs’ theory,which is based on
    the perfect gas equation, where the adsorbate is treated as a micro-
    scopic and bi-dimensional form; and (d) Eucken and Polany’stheory,
    the so-called potential adsorption theory, in which it is assumed that
    within the space around each solid, it is possible to find some iso-
    potential surfaces restricting the adsorbate that is adsorbed at pres-
    sures (or concentrations) lower than those corresponding to the
    potential value, being such isopotential surfaces specificforagiven
    solid surface [12].
    Dubinin and Radushkevich have proposed the micropore volume
    filling theory, which is related to Eucken-Polanyi potential theory.
    The DubinineRudushkevich isotherm describes adsorption as
    a single type of uniform pores that is similar to Langmuir-like local
    isotherms in adsorption on energetically heterogeneous solids. This
    theory was later expanded by Stoeckli, allowing it to describe
    adsorption on energetically heterogeneous solids with a contin-
    uous distribution of pore sizes. Leite [13] puts forward a detailed
    analysis of the thermodynamics of adsorption and its different
    isotherms.
    In general, all microporous materials are adsorbent and are
    characterized by their high porosity. Their structures have pores
    with diameters smaller than 20  A. The most common absorbents
    are silica gel, activated carbon, zeolite and alumines. Zeoliteewater
    and activated carbonemethanol are one of the most adsor-
    benteadsorbate pairs utilized in refrigeration systems. Methanol is
    easily desorbed from activated carbon when heated, whereas in
    zeolite, the water is sustained for much longer. Thus, the activated-
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