Lecture 6B - Solar Thermal - Part 2

Lecture 6B - Solar Thermal - Part 2 - 2/17/11 ECE...

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2/17/11 1 ECE 4364/5374G-6B (c) Saifur Rahman 1 Professor Saifur Rahman Electrical & Computer Engineering Dept. Virginia Tech ECE 4364/5374G: Alternate Energy Systems Lecture 6B: Solar Thermal - 2 ECE 4364/5374G-6B (c) Saifur Rahman 2 Solar refrigeration can be achieved by the absorption refrigeration cycle. In this process, the pressure of the refrigerant vapor is raised by heating in the solar generator instead of by mechanical compression, thus eliminating the most energy intensive part of refrigeration. A simple solar-powered absorption cooling system is shown in figure 8.13. The vapor is condensed in a water cooled condenser, and the resulting liquid is passed through a reducing valve to the evaporator which is the cooling section of the unit. 8.5 Refrigera,on and Cooling
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2/17/11 2 ECE 4364/5374G-6B (c) Saifur Rahman 3 Figure 8.13. Solar Powered Absorp,on Cooling System ECE 4364/5374G-6B (c) Saifur Rahman 4 In the evaporator, the refrigerant chills the air/water as it evaporates. The resulting vapor (refrigerant) flows into the absorber where it is re- absorbed into a solution of the refrigerant. Then it is pumped back to the solar generator. The heat required to evaporate the refrigerant in the generator is supplied directly from solar energy. An overall steady-state energy balance on the absorption refrigeration cycle indicates that the energy received by the generator (Qg ) and the evaporator (Q e) must equal the energy delivered to the condenser (Qc) and absorber (Qa), and losses (Ql) (8.14) 1 Q a Q c Q e Q g Q + + = +
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2/17/11 3 ECE 4364/5374G-6B (c) Saifur Rahman 5 The other method of space cooling is evaporative cooling of the air with adiabatic vaporization of moisture into it. This process can, however, be used only when the air to be cooled has a comparatively low relative humidity. Direct evaporative cooling has been shown to be an economical way to cool homes in climates where the maximum wet-bulb temperature is usually below 25 o C. In a typical evaporative cooler air is drawn by a fan across wet wood-fiber pads that cool the air by humidification to a temperature a few degrees above the wet-bulb temperature. Evapora,ve Cooling
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Lecture 6B - Solar Thermal - Part 2 - 2/17/11 ECE...

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