Solar Cooling

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Solar Cooling In Chapter 5, we reviewed the principle of operation of a refrigerator (or an air conditioning system). Cooling occurs as a result of a refrigerant removing heat from the refrigerated (air conditioned) space and becoming vaporized (step 1). The vapor is then heated to a high temperature and pressure by a compressor (step 2); it then enters a condenser where it is condensed and becomes liquid (step 3). Finally the liquid is expanded 7 Hoagland, W., “Solar Energy,” Scientific American, V. 273, pp 170-173, September 1995. 8 Solar water heaters, sometimes called domestic hot water systems, can be either passive or active and open or closed loop. Passive systems rely on the principle that water in the collector becomes lighter and rises as it heats, while cooler water in the tank sinks, causing circulation by natural convection (thermosiphon). No pump is needed for water circulation through the collectors, making the system simpler and less expensive. For passive systems to work, the tank must be above the collector. Active systems use pumps to assist circulation. Open-loop systems are popular in mild climates where there is no danger of freezing. These systems require a circulation pump and are therefore inherently active. Closed-loop systems use a mixture of water-glycol antifreeze mixture and thus can be used in area where freezing is a possibility. 225 Chapter 10 - Solar Energy in an expansion valve, allowing the refrigerant to cool to the evaporator temperature (step 4). The refrigerant is now ready to remove additional heat and repeat the cycle. The point to remember is that some energy in the form of electricity or heat is needed to carry out step 2. The source of this energy can be natural gas, oil, or in this case, solar energy.

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