Short-time tests of refrigerating machines unfortunately furnish only incomplete information as to their relative merits. Such a test may disclose obvious defects and will readily show the power or gas and water consumption and the efficiency of the unit tested, when new. By operating the machine under extreme conditions, e.g., at high room temperature, it is possible to make an estimate of the margin of reserve in power, cooling capacity and strength of parts above ordinary requirements, but none of these tests gives information on the most important points, namely, the durability and reliability in service of the average machine under ordinary conditions.
Some of the factors to which the prospective purchaser of a machine should give attention are the following:
If the manufacturer does not remain in business the machine is likely to become obsolete in a very short time, since replacement of worn or defective parts may be difficult or impossible.
A machine in the experimental or development stage is a more speculative proposition than one which has stood the test of service.
Unless a machine runs quietly when new and continues to do so, it will be unsatisfactory to most of its users.
The aggregate cost of refrigeration depends to a considerable extent upon the length of life of the machine, and upon the cost of service and repairs. Very little information on this point is available, and the purchaser must depend upon the reputation of the product and such information as he can find in regard to durability.
There are considerable differences in the operating efficiencies of different machines, and figures on operating costs can sometimes be obtained. If a machine is not well made or is allowed to deteriorate, efficiency may be greatly reduced after a short period of use.
The refrigerator should be well insulated, preferably with not less than a two-inch thickness of some good insulating material. Refrigerators depending largely upon air spaces for insulation or those with thin walls and doors are likely to require considerable power or fuel and water to keep them cold.
If the machine is water cooled, the purchaser should determine that his water supply is suitable for the purpose, so that deposits from hard water will not be formed inside the machine, ultimately interfering with its functioning, and that the water supply is sufficient in quantity and not too expensive.
Preference should be given to a machine which could be easily and inexpensively serviced or repaired when necessary. A machine which could easily be removed entirely and replaced by another would be classed as easily serviced. If attention such as oiling or adjustments are required from time to time, the points requiring attention should be few in number, and should be readily accessible where the machine is to be installed, lest it suffer from neglect.
A machine obtained from a responsible dealer, who is prepared to attend to adjustments and repairs promptly when required, is to be preferred.
The purpose of this section is not to make an exhaustive comparison between machine refrigeration and ice refrigeration but merely to point out some of the more obvious facts, which, if kept in mind, may enable the prospective purchaser to avoid being puzzled or misled.
The owner of a refrigerating machine is free from whatever annoyance accompanies frequent or irregular delivery of ice. The machine can be set to maintain a lower temperature than is practicable with ice, so that left overs can be kept a somewhat longer time before being thrown away. Few subjects are more misunderstood by the public and by writers on refrigeration than that of temperatures required for proper refrigeration. Most writers draw a dead line at 500 F. and state, in effect, that useful refrigeration is not obtained above that temperature. The facts are, however, fairly simple and obvious. Time and temperature are equally essential factors in decay. Most foods will remain palatable and wholesome if kept as long as a day at a temperature as high as 6o° F. If they are to be kept for a week, 500 F. may not be low enough. If they are to be kept for a month, the temperature must be still lower. In any case, most users prefer to serve food while it is fresh; there are very few who purchase a refrigerator for the purpose of establishing a miniature cold storage plant to preserve foods for considerable periods, and the possibility of keeping foods for more than a limited time is of little practical importance. There is, of course, a wide difference in the keeping qualities of various kinds of foods. The user of a machine is usually less subject to loss from spoilage of food, and in some cases there may be a considerable saving in this respect.
Either an ice-cooled refrigerator or a machine-cooled refrigerator tends to maintain a dry atmosphere in the food compartments and thus to dry out moist materials stored in them. The water from the melted ice carries off material in solution thereby removing causes of odors.
The relative cost of refrigeration with ice and with a machine depends very largely upon the useful life of the machine and the costs of repairs, replacements and service. To make a comparison of costs, it is necessary to estimate the probable life of the machine and then to estimate operating costs, and costs of repairs, service, etc., over this period. To these add the initial cost (including interest charges if desired) and divide the total by the number of years to find the aggregate cost of refrigeration per year. A similar estimate may be made for a refrigerator using ice. Such computations indicate that a machine should have a useful life of at least ten years in order that the cost of refrigeration by machine should not be unduly high as compared with ice refrigeration. In many cases the operating costs of a machine are lower than the cost of ice for a refrigerator of comparable size, but this is rarely true of the aggregate cost of refrigeration, which means that the greater convenience and better service of machine refrigeration are obtained at somewhat higher cost.
In many cases the purchaser of a machine compares its operating costs for the first few months with those of his old refrigerator, which may have had but little insulation when new and is almost certainly no better after years of use. Such a comparison does not give a correct picture. It is true that the reluctance of makers of ice refrigerators, until recently, to use insulation, has been one of the important factors in popularizing the machines, which are usually installed in well insulated boxes. On the other hand, well-insulated refrigerators for ice are a comparatively recent development. As machines are usually set to maintain lower temperatures than are obtained in iced refrigerators, they require more insulation. The minimum requirement for any type of refrigerator is that the insulation shall be sufficient to prevent the deposition of moisture on the outside of the box, under all conditions in which it is to be used. Adequate insulation requires no secret formulas or knowledge not available to the public, but only the use of a sufficient thickness (not less than 2 inches) of a good insulating material, adequately protected from moisture. Recently, well-insulated refrigerators for ice have been obtainable, and when such are used, the public will have a better opportunity to compare refrigeration by ice, with refrigeration by machine, on their respective merits.
[Note. - A national safety code for all types of mechanical refrigerators has recently been approved by the American Standards Association. A technical committee representing over forty national organizations has been working on the code for years.]