Document LJMDzLyZ6Nj4y9OOOmNB264Jw

708 i CHAPTER 39 1948 Guide Thermodynamically the effectiveness of a refrigerant-absorbent com bination increases directly with its negative deviation from Raoult's Law. Fig. 3 shows a typical absorption cycle flow,diagram.. Cooling water first goes through the absorber (where it extracts the heat of absorption which is liberated by the refrigerant vapor as it goes into solution), then through the condenser, and finally through the rectifier. Refrigerant from the evaporator enters the absorber where if goes into solution in the absorbent; the high concentration solution is then pumped to the gener ator where heat is supplied; the refrigerant (with some' absorbent vapor) leaves for the rectifier and the warm low concentration solution is re turned to the absorber. In the rectifier selective condensation occurs, the concentration of the absorbent in the condensate being much greater than its concentration in the entering vapor mixture; rectifier condensate is dripped back to the generator. The total energy requirements of an absorption cycle greatly exceed those of a compression system, but the energy required is of low avail ability (heat) in contrast with the high availability requirements (shaft work) of the mechanical compressor. Thus in localities where heat and cooling water are obtainable at low cost, it will be more economical to use a large quantity of inexpensive thermal energy in preference to a much smaller quantity of expensive shaft energy. For most absorption systems the heat required will be from one and one-half to five times as much as the heat extracted in the evaporator; cooling water requirements are proportionally high. Ice Systems Cold water systems using ice as the cooling agent have been installed in many theaters, restaurants, funeral homes, churches and other, places where short hours of operation and high peaks of cooling demand make this type of system desirable. A comparatively small quantity of ice in the water cooling tank of such a system can release refrigeration at a relatively rapid rate. For instance, neighborhood theaters having a peak demand of 1,200,000 Btu per hour (100 tons refrigeration) have found 8 ton capacity ice bunkers satisfactory. In operation, the water in the air conditioning system is circulated over ice placed in an insulated box and is cooled to the 38 or 40 F range or higher if desired. This cold1 water is pumped from the ice bunker to air cooling coils or spray type air washers. The blowers, coils, air washer or air handling sections are the same as those parts in any system employing cold water as a refrigerant. The ice water cooler or ice bunker is usually built at the installation in a location where it can easily be iced. It can be constructed of any desired material such as concrete, steel, or wood with an adequate amount of insulation to save the ice from one period of use to the next. The basic requirement is that the tank be durable and water tight. A typical bunker with connections to a coil type air conditioning system is shown in Fig. 4. About 60 cu ft of gross bunker volume are allowed per ton of ice capacity. The shape of the bunker usually conforms to the available space. The one illustrated has overhead sprays, but if head-room is lacking the ice is placed on the floor of the bunker with the water returned around the lower part of the blocks from a perforated distribution pipe run along one Refrigeration 709 side of the bunker. To secure good circulation the supply water is ..extracted from a similar perforated pipe on the opposite side of the bunker. The temperature of the water is controlled at a predetermined point by a thermostat in the supply line. If the temperature drops too low, a part of the return water is by-passed directly to the sump and is not cooled over the ice. In the larger systems it is customary to install an overflow control which, as the ice melts, discards the excess water through aneconomizer coil.. The surface of the economizer is large in relation to the flow so that the water is warmed to 60 F or more as it is discharged from the system. Storage Systems In an attempt to lower initial equipment cost and operating expense, or increase the refrigeration capacity of an existing air conditioning system, storage refrigeration has been utilized in a few applications. Some of the methods which have been.adopted, include the storage:.of refrigeration in :the form of. ehilled water, chilled brine, ice on evaporator coils * and the accumulation of thin sheets of ice on copper plates in a steel tank *. If the peak load factor is low as compared with a long period of operation, such as in a restaurant, .or if the hours of operation are short but the usage factor high as in a church, then it is possible to. con sider storage refrigeration. This method" of accumulating'refrigeration frequently makes'it possible to use low cost off-peak electric power. Power costs may also be reduced by installing a smaller refrigeration plant, augmented by a storage system, and by operating it for longer periods. ' The Reverse Cycle The reverse cycle--frequently referred to as a heal pump--is identical in theory with the ordinary refrigeration cycle and differs only in. the sense that the desired effect is a heat source rather than a heat sink. Since a condenser delivers more heat than is picked up by the evaporator (it discharges the heat equivalent of work supplied during compression) it follows that the effectiveness of a heat pump, its coefficient of perform-