CHAPTER V.REFRIGERATION REQUIREMENTS.

Refrigeration — Necessities — Ice Plants — Natural Ice — Chilling — Quantity Refrigeration to Provide — Space Per Ton Machine — Machinery Per Head — Ice Computation — Compressor Capacity — Summary Computations — Low Temperature Brine System.

—This word covers the “bugbear” and the “solace” of the packers. No other one thing is of so much importance. Since the abolishment of the use of chemicals, such as borax, boracic acid, etc., as a preventive or retardant in the propagation of bacilli during the curing process, the packer’s sole dependence is refrigeration. Consequently there has been considerable development and importance in its use.

From the moment the animal is killed until the parts are disposed of, refrigeration is a necessity. The proportion of freezing space to be provided or hired at a commercial storage house is growing daily. In many plants the total volume of freezer space approaches or exceeds, that given over for moderate temperature storage purposes.

—In the order of progress the first necessity for refrigeration is the use of ice for chilling water for fats and meats. Practically every packing house is now equipped with a small ice making plant both for its use, and with commercial possibilities of selling ice.

—Ice plants are of various kinds:

In the production of distilled water there are various methods which will not be treated upon here.

For the icing of cars and for ordinary cooling purposes ice made by process No. 1 is amply good except, perhaps, if the water from which the ice is made should not be clear, it may be necessary to use a portion of the bottom of the cake for car icing purposes only.

—The situation and climate has much to do with the determination as to whether the packer can afford to harvest natural ice for general use. For example, if the plant be situated in a northern climate alongside a suitable stream adjacent to the plant, the harvesting of ice and its storage can be afforded. However, if the ice is stored at a remote point and teaming or car shipment of ice is necessary, then the manufacturing plant will probably be the more economical.

—The chilling of the meat immediately after killing is perhaps the most important function in the whole refrigerating process and one that cannot have too much attention. In the matter of beef it is the practice of the best operators to see to it that immediately after the hide is removed the beef is placed in the coolers. At most it should not be allowed to stand out in the open air to exceed half an hour. Sheep and veal should be treated in the same manner. As for hogs in some climates, such as latitude equal to Chicago or north thereof, if space is available an open air hanging room is a valuable adjunct where the animal can be air dried, depending upon seasons, from one hour to over night. This feature also permits of increased slaughtering during the winter season. It is a custom that can be abused, however, by careless handling—resulting in sour meats.

—There are so many factors which enter into the question of packing house refrigeration, and so many details of construction and application of refrigerating apparatus, that it is almost impossible to cover this subject practically and intelligibly without devoting a volume to refrigeration alone.

To give a fixed rule for packing house refrigeration, applicable to all conditions, would be impossible, as much dependsupon conditions and surroundings, and the requirements would vary accordingly. For instance, atmospheric conditions, quantity of space to be cooled, temperature to be maintained, time for chilling, etc., these and many other factors affecting the general results must be taken into consideration and provided for, and as these vary, so will the refrigeration requirements vary. A few ideas will be set out to assist in the computation of the quantity of equipment to provide.

The capacity or size of the refrigerating equipment required for any given plant is variable but can be reasonably closely computed by assuming certain conditions.

—Practice has demonstrated that one ton of mechanical refrigerating effect duty, as rated by manufacturer used continuously during a period of twenty-four hours will maintain at a temperature of 33° to 38° F. from 7,000 to 12,000 cubic feet of storage space. Conditions of exposure, insulation and outside temperature affect this.

The minimum for beef storage coolers, the maximum for curing cellars. The area of room or quantity of space enters into each of these assumptions. If small rooms are used the unit to be assumed is smaller. Concrete buildings are easier to control due to the stored cold in the building mass of floors, columns and girders.

—It is customary to figure that in addition to that needed for cooling the space, one ton of refrigeration for twenty-four hours would be required for either one of the following items:

—For cold storage rooms, where meats which have already been chilled or cooled are stored and held for a greater or lesser period, the refrigeration requirements are not so great as in chill and cooling rooms. The animal heat has been removed and the meats cooled down to a low temperature, consequently but little more refrigeration is required than that necessary to take care of the heat leakagethrough the insulation, and possibly the recooling of the meat through a range of a few degrees, when the meats may have gained a little in temperature by exposure. Therefore it is estimated that one ton of refrigerating duty will handle 12,000 cubic feet of curing or storage space for temperature of 33° to 35° F.

—As will be explained in the chapter relating to refrigerating machine capacity, the capacity of a compressor very rapidly decreases when operating under conditions necessary to produce low freezer temperatures, and owing to the severe conditions imposed it seems necessary to compute that one ton of refrigerating duty will handle about 3,000 feet of freezer space.

—Before the application of mechanical refrigeration to packing house purposes, all artificial refrigeration was accomplished by means of ice melting alone, and at that time the packers computed ice melting requirements on a basis of cooling three pounds of meat from 80° F. to as low as it could be cooled by ice melting, for each pound of ice melted. While this rule undoubtedly was the result of practical experience with well constructed coolers, and was in no wise based upon theoretical or heat unit formulas, yet it is interesting to note how close this old rule compares with modern formulas of computing refrigeration. For example, the cooling of 100 head of hogs, averaging 250 pounds dressed, by the packer’s rule, would require—

100 × 2503= 8,333 pounds, or 4.16 tons ice melting.

And on a heat unit basis, cooling the same number and weight of hogs from 80° to 32° F. would require—

100 × 250 × (80 - 32)288,000= 4.166 tons refrigeration.

The above comparison shows that theory and practice approach very closely to a common line, although in the calculation the factor of specific heat of the meat is ignored, and in practice this may well be left out, as specific heat of meats at various temperatures has by no means been accurately established.

—The chilling of lard is a severe task on refrigerating equipment owing to the very heavy duty imposed in a short time. For example, with an eight-foot lard roll turning off 4,000 pounds per hour and changing the temperatures of the lard from 90° to 50° F. requires a very large compressor capacity per hour.

—Assuming the killing of 100 cattle and 250 hogs per day; making 10,000 pounds of lard, fifteen tons ice; maintaining a freezer of 100,000 cubic feet and the small work connected with the establishment:

For 100 cattle killed daily, and storage of 400 hanging, about 6,500 square feet area of cooler would be required; the height of this with the lofts would be about twenty-two feet or a capacity of 143,000 cubic feet.For 250 hogs daily or 750 total hanging, there would be required 3,000 square feet of floor area and a height of 18 feet or 54,000 cu. ft.The above number of hogs daily would also require a storage or cellar capacity based upon one hundred pounds meat sent to cellar for a turn over in sixty days equal to storing 1,500,000 pounds of product, or 15,000 to 20,000 square feet of floor area, requiring 200,000 cubic feet of building space.Ten thousand pounds lard daily in four hours running would require the extraction of about two tons of duty, but by reason of the heat transmission and the low temperature brine necessary would require twelve tons duty while applied.Fifteen tons daily ice making capacity requires about 30 tons refrigerating duty, allowing for radiation and other losses.A freezer capacity of 100,000 cubic feet which would store 1,500,000 pounds would not appear excessive. From known results this would require about one ton refrigerating duty for 3,000 cubic feet of space or thirty-five tons machine duty. We have then:

For 250 hogs daily or 750 total hanging, there would be required 3,000 square feet of floor area and a height of 18 feet or 54,000 cu. ft.

The above number of hogs daily would also require a storage or cellar capacity based upon one hundred pounds meat sent to cellar for a turn over in sixty days equal to storing 1,500,000 pounds of product, or 15,000 to 20,000 square feet of floor area, requiring 200,000 cubic feet of building space.

Ten thousand pounds lard daily in four hours running would require the extraction of about two tons of duty, but by reason of the heat transmission and the low temperature brine necessary would require twelve tons duty while applied.

Fifteen tons daily ice making capacity requires about 30 tons refrigerating duty, allowing for radiation and other losses.

A freezer capacity of 100,000 cubic feet which would store 1,500,000 pounds would not appear excessive. From known results this would require about one ton refrigerating duty for 3,000 cubic feet of space or thirty-five tons machine duty. We have then:

SUMMARY OF REFRIGERATION REQUIRED

—The use of low temperature brine, cooled by two stage compressors, a new development, is in the writer’s opinion preferable to direct expansion. (Seedescriptionof two stage compression in Chapter IV.) A lineal foot of pipe filled with a liquid like chilled brine seems to have greater heat absorbing power than the same pipe filled with a light gas and consequently less piping can be used.

—Occasion arose to compare for a new large installation the relative merits of direct expansion versus brine and the following items suggested themselves:

(1) The direct expansion plant would require 150,000 lbs. ammonia in excess of brine plant.

(2) There would be approximately 8,000 more joints to prevent leaking.

(3) Unavoidable ammonia leakage through rods, glands, valve stems, compressor rods and purging would amount to at least $20,000 per year based on experience with good practice.

(4) The installation by the same manufacturer estimated to cost 15% more than a brine system.

(5) There would be no stored energy in the ammonia pipes as in brine pipes should the refrigerating plant suspend operation temporarily.

(6) The compressor hazard from returning liquid and possible machine wrecking with line breaks, ammonia losses, and danger to life.

(7) In case of extension or modification of piping, the difficulty with ammonia pipes over brine is marked.

(8) In direct expansion plants the cooling effect is stopped immediately when the compressor is stopped. It is required to operate incessantly, or if speed be reduced the current is chiefly wasted in resistance grids if electrically driven. Whereas in a brine plant the compressors can be stopped several hours, the brine being circulated rises in temperature but not sufficiently to vary room temperatures. This is a great advantage, permitting keeping “off peaks” on commercial electric lines and consequently earning lower rates.

(9) With an electrically driven compressor, speed control is fixed within quite limited bounds and if direct expansionsystem is used more power is purchased than needed for reasons already mentioned.

(10) The total cost for operating pumps and calcium taken collectively will be far less than the uncontrollable ammonia leakage. The coil attendants can be less skilled.

(11) Brine temperature 25 degrees below zero, Fahr., can be carried, sufficiently low for all purposes. Rooms can not be controlled at as exact temperatures with direct expansion as with brine, owing to its sensitiveness.

(12) Lastly and very important, the complicated piping system to carry several back pressures to produce varying temperatures and the necessity of operating several compressor “ends” makes a complicated installation of small units as against a simple system carrying one temperature brine.

Plants of the character described usually operate on direct expansion, require three sets of temperatures, three sets of suction pressures and three sets of suction mains with various cross connections and intricate pump-out arrangements. This necessitates multiplicity of machines and connections to various cylinder ends.

Progressive authorities recognize the necessity of freezer storage in meat plants. In combination pork and beef or pork plants, newer installations will be made with far less curing space for sweet pickled meats and far greater space for storing meats frozen either before or after curing to the end of producing palatable meats, not salt soaked and of inferior quality. There are slaughtering plants for export where beef is shipped chilled or frozen, and mutton frozen. Some have exclusive freezer buildings, others parts set aside for freezers.

One temperature brine is circulated, the temperature in the rooms being governed by the quantity of pipe in service. In all instances, sharp freezers, storage rooms and curing rooms are equipped with pipes therein—and the chilling rooms for beef and pork closed coils or spray, optional.

Shell and tube coolers have proven so fitting that no hesitancy need be made about using them, and the possibility of freezing is negligible with reasonable prudence. Tanks with submerged coils can be used, but it prevents the saving made by using balanced brine pumping, on high buildings, a quite material one.

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