Document ZqJBV6mB79pXkwx9jyM4M50d

HEATING VENTILATING AIR CONDITIONING GUIDE 1944 Capacity Tons 0 to 5 5 to 25 25 to 50 50 to 400 400 and Over Table 10. Basis of Equipment Selection Majority Used Some Used Few Used Unit systems in con Unit central systems Built up central sys ditioned space. using duct distribu tems. tion. Built up central sys tems using reciprocat ing compressors. Unit central systems using duct distribu tion. Unit systems in con ditioned space. Built up systems using absorption and adsorption systems. Built up central sys Built up central sys Central systems tems using reciprocat tems using centri using adsorption ing compressors. fugal compressors. systems. Built up central sys-. terns using reciprocat ing compressors. Built up central sys tems using steam jet and centrifugal com pressors. Built up central sys Built up central sys tems using centri tems using steam jet. fugal compressors. air handling sections are the same as those parts in any system employing cold water as a refrigerant. The ice water copier 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. 9. 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 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. Table 11. Typical Operating Conditions for Two Types of Load Tttb of Enclosure Load, Btu per Hour Sensible Latent Total Ratio Sensible TO Total Am Entering Con. Operating Balance Point Deg F Per Coit. RJL Evaporator Temp Deg F Condenser Pressure Lb per Sq In, Per Cent Sensible - Heat Restaurant Office 103,000 45,000 148,000 0.695 . 121,000 27,000 148,000 0.820 82 82. 45 45 34.4 42.2 123 100 69.9 82.1 488 CHAPTER 25. REFRICERATION 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 an economizer 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 chilled water, chilled brine, ice on evaporator coils2 and the accumulation of thin sheets of ice on copper plates in a steel tank3. 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. EQUIPMENT SELECTION The selection of proper refrigeration equipment for any air conditioning job is of utmost importance for satisfactory results. The most important factors in the selection of the equipment are: 1. Loads (as determined by the conditions of the space to be cooled)! 2. Economics (both initial and operating costs). 3. Codes (local safety codes must be adhered to and influence the type of system to be used). A broad division of equipment to be used for a particular installation or application may be made on the basis of the magnitude of the load. Current general practice is outlined in Table 10. ` Unit or packaged systems, consisting of a reciprocating compressor, condenser, evaporator and fans, are generally used in the smaller sized jobs where electric power is available, as they are manufactured complete, ready to install and are the most economical (see Chapter 23). The reciprocating compressor in the built-up central system (see Chapter 21) covers the widest range of application since it is applicable to either the direct expansion or indirect systems and can be driven by steam or gas engines, or by electric motors. The quantity of condensing The Application of Storage Refrigeration to Air Conditioning, by C.' F. Boester (A.S.H.V.E. Trans actions, Vol. 45. .1939. p. 675). Use of Cold Accumulators in the Air Conditioning Field, by R. W. Evans and C. J. Otterholm (A.S.H.V.E. Transactions, Vol. 48. 1942, p. 123). 489