CHAPTER III COMMERCIAL SYSTEMS OF REFRIGERATION (Part 4)

with the brine-circulation systems of similar capacities; but it must be remembered that both systems have the disadvantage of being inherently inefficient because of the necessity of operating under lower back pressures in order to pro- duce the correspondingly lower temperatures required to effect the double-heat transfer. At the lower pressures fewer pounds of the refrigerating medium are passed through the compressor per revolution and a greater niunber of pounds are necessary to pro- duce a given refrigerating effect, each of which conditions makes it necessary to speed up the compressor in order to produce the same amount of cooling duty. By the direct expansion of the refrigerant, cold is produced just where it is required and more nearly at the temperatures required. And incidentally, aside from the saving in power required to operate the compressor and to pump the brine, a saving is made in investment for a suitable room and for foundations of brine tanks and pmnps, as well as for the tanks and pumps themselves and the necessary piping and insulation, etc. Thermal losses due to radiation through the insulation of these members and through that due to the heating effect of pumping the brine are entirely eliminated. Small systems may be satisfactorily operated semi-automatic- ally at the expense of somewhat more attendance, and usually effect a considerable saving in cost of power by the substitution of some efficient type of combustion engine. The advisability of such a substitution at the present day of an unquestionably reliable combustion engine depends almost entirely on the relative local cost of attendance, and the cost of power developed by electricity, illuminating gas, gasolene, kerosene, fuel oil or producer gas. The type of system best adapted to a given set of requirements can be determined only after carefully considering the relative importance of such factors as cost of power, cost of attendance, allowable temperature variation, probable earning power of plant and availability of capital. Digitized by V^OOQIC