( Originally Published Early 1900's )
Mechanical refrigeration is not considered a luxury or convenience, but rather a necessity in the majority of markets. There is no standard type of refrigerating equipment to suit the varying conditions as they exist in different meat markets. There-fore, a refrigerating plant should be designed and laid out to meet the particular conditions as they exist in each meat market.
While mechanical refrigeration is a profession in itself, an understanding of the simple principles of refrigeration is desirable for every user.
The Refrigerating Plant
A refrigerating plant is usually composed of certain standard equipment such as ammonia compresser, condenser and receiver, commonly called the "high side," and the coils or tanks which are usually called the "low side." The operation of practically all refrigerating plants is the same. By following the simple explanatory drawing in Illustration No. 137 the principles of the operation of a refrigerating plant are easily under-stood.
The refrigerant or the liquid which does the cooling, is stored in the container, No. 1. For the sake of simplicity, it is assumed that this system is operated by ammonia. No. 1 shows the ammonia receiver.
The ammonia in the receiver, No. 1, is in a liquid state. By opening up a valve leading from this ammonia receiver, the liquid ammonia forces its way by its own pressure through a very small opening in this valve. Here the ammonia expands from a liquid into a gas. Therefore, this valve is termed an "expansion valve."
After leaving this valve, the ammonia is a gas of very low temperature, and it travels through the refrigerator coils in the cooler, No. 2. As far as the cooling is concerned, the ammonia has now done its duty, and has accomplished its purpose, but ammonia being expensive, should be used over and over again.
For that reason the ammonia compressor now receives this cold gas.
The ammonia compresser, which is nothing but a pump, compresses this gas and heats it. This hot gas now leads into the condenser, whch is usually a double pipe affair. Water runs in one pipe and ammonia in another, each in opposite directions.
The hot gas comes into contact with the colder coils and transforms the ammonia into a liquid again, so that it can flow back to the receiver, No. 1. This explains the principle of a refrigerating plant, and the operation repeats itself while in operation.
Different Refrigerating Systems
There are three principal refrigerating systems most popular in the retail meat industry :
1. The straight direct expansion system.
2. The straight direct expansion system with hold-over brine tanks.
3. The brine circulating system.
The Straight Direct Expansion System
The straight direct expansion system consists of an entire refrigerating unit in itself, and has only direct expansion coils in the refrigerator. This system is used principally in large refrigerators where the machine is operated continuously or automatically. Unless the automatic refrigerating machine is used, this straight direct expansion system is rarely found in the aver-age market, as there are no provisions made for the holding over of the temperature when the meat market is closed.
The Straight Direct Expansion System with Hold-Over Brine Tanks
As the name indicates, this system is used primarily to hold over the temperature in the refrigerator when the refrigerating machine is not operated, such as for instance, during the night, over Sundays and holidays. In addition to the regular direct expansion coils in- the refrigerator, additional coils are placed in brine storage tanks.
Another direct expansion and brine storage system used quite extensively is the .brine tube system. Instead of having open brine tanks in the bunker, the direct expansion coils pass through a brine tube about 6 inches in diameter. This tube contains the brine and is sealed on both ends. This patented system has become very popular in certain sections of the country.
The Brine Circulating System
This system differs somewhat from the direct expansion system, principally in the fact that instead of the ammonia circulating in the coils, low temperature brine is used. This brine is cooled either by a brine cooler or a large brine storage tank, or a combination of both. From there, it is pumped through the cooler.
Comparing it to the direct expansion system, it may be called an indirect system. It is used principally where there is a considerable difference desired in the temperature of various refrigerators.
This system is also used extensively in meat markets where counter cases are refrigerated, and in many instances, it has been found to be more economical in operation than the direct expansion system. As an example, a market owner may have a refrigerator, size 10 by 12 by 10 feet. In addition, he may have 30 feet of refrigerator counter. While the refrigerator may be cooled very quickly, the market owner may want to use his refrigerator counter more than he wants to use the refrigerator. For that reason, he wants the maximum refrigeration for his counter.
Since the refrigerating machine is capable of handling more than is required for the counters, it will require that the large machine will operate for the counters only. By using a combination of the direct expansion system with brine hold-over tanks in the refrigerator, supplemented with a brine tank and a brine circulating system for the counters, it will usually result in more economical operation. The initial cost, however, will be slightly higher on account of the additional equipment required.
Factors to Consider When Buying a Refrigerating Machine
In view of the fact that there are so many different kinds of refrigerating machines on the market, and since a considerable investment is required for the installation of a machine, retailers are frequently puzzled as to what type of machine to install. There are, however, certain fundamental facts to be observed in the installation of a refrigerating plant.
Since mechanical refrigeration is a highly
technical subject, and the details are rarely understood by the aver-age meat retailer, the integrity and reputation of the firm or individual manufacturing or installing the unit is of the utmost importance. The buyer must have the utmost confidence in the engineering ability of the man estimating and selling the installation, and the financial responsibility of the firm with which he is dealing is, itself, of considerable importance. Many retailers have been led to install machines made or sold by firms or individuals with no financial responsibility behind them, and found out to their sorrow years after that the particular firm had gone out of business.
Plant Must Be Balanced
The cost of operating a refrigerating plant is influenced by the rate of power and water. For that reason, the entire plant must be well balanced. Where water is of high temperature, large condensers must be used. Water has a direct bearing upon the economical operation of the plant. For the simple reason that if the water does not ex-tract the heat on an economical basis additional power will be required on the part of the motor. This may make the operating cost of the plant very high.
Retailers who have bought refrigerating plants strictly on a price basis, without knowing the intricate details of the specifications, may have saved $100 or $200 on the original purchase price of the plant and later discovered that on account of their bargaining and forcing manufacturers to quote on the minimum equipment, it has cost them several hundred dollars more per year to operate their plant, than it would have cost if they had a good installation in the beginning.
The subject of window refrigeration is of great interest to the meat retailer. Investigations have actually proved that more meats are sold through attractive window displays than through any other form of advertising. For that reason, this subject will assume still greater importance in the future.
With very few exceptions, refrigerated show windows have not generally been successful. In analyzing the basic principles of show window refrigeration, one discovers the fact that meats are placed in the window only temporarily and rarely kept there over night. Therefore, the principal object is to keep meats cool temporarily.
Various arrangements have been worked out to cool meats temporarily. Show windows have been closed in with non-insulated walls and with regular partitions. Coils have been placed in the rear end of the show window, similar to the method used in refrigerated counters. But instead of using 4 coils, usually 6, 8 or 10 coils have been used in most of these arrangements. Another practice is to nest coils in the center of the show window, also on the sides and in the upper part of the window. Names of markets have been designed into display coils for show window cooling.
Analyzing the great majority of refrigerated show windows, it was evident that the effect of cooling has been more desired than the actual cooling itself. There is no question that the psychological effect of frosted coils impresses the window shopper.