Thermodynamic treatment of air by solar radiation

Abstract Rise in temperature of matter by direct solar radiation is relatively small for conventional technical utilization, if solar furnaces or solar mirrors are not additionally employed. Additional solar machinery is expensive and reduces thermodynamic efficiency by additional heat losses as well as financial attractiveness by additional amortization costs. Exploitation of small differences in temperature for transforming solar radiation into air conditioning and into refrigeration at economic running costs has not yet been developed. The known thermodynamic reversible cycles are not economical, and other methods have to be evolved. A new reversible cyclic process for treating mixtures at atmospheric pressure with little rise in temperature has been set up, and its utilization for solar air conditioning and solar refrigeration is shown. It establishes procedures that are thermodynamically perfect and technically simple. Removal of drinking water from the air by solar pumping, solar refrigeration, and solar air conditioning are obtained without any intermediary machinery. The new reversible cycle completes for humid air the principle of reversibility for exchange of heat or of matter either by utilizing differences in temperature more perfectly than has been possible up to now, or by lowering the obtainable refrigeration temperature at the expense of the cooling effect. Exchange of heat and of matter are no longer different means to the same end. In joint action they can now be employed for solving opposite problems and thus complement each other. All changes of state in air conditioning and refrigeration within the considered range of temperature are performed in open atmosphere. In practice they are approximately reversible and do not demand mechanical or electrical work. The new reversible cycle extends exchanges of state and matter of humid air from the curve of saturation to the range of superheated steam. The cyclic procedure for solar refrigeration requires only water as a refrigerant and no other hygroscopic substance or pressure except atmospheric, and for drive small differences in temperature suffice.