CHAPTER IVREFRIGERATION EQUIPMENT

Ammonia Machines — Ammonia — Compressor — Condenser — Receiver — Cooler — Condensing Water — Unit Basis — Computing From Unit Basis — How Rated — Freezer Requirements — Freezers in Small Plants — Cylinder Arrangement — Why Brine Circulation — Air Circulating — Force Draft — Coil Room Systems — Brine Chilling — Brine Methods — Types of Brine Coolers — Balanced Brine System — Direct Expansion — Two-Stage Compressors.

—This agent is of great consequence in the operation of packing houses, and, therefore, it is deemed essential to explain the principles briefly; as well as to describe the uses.

—The use of ammonia refrigeration equipment either absorption or compression has so generally displaced all others for stationary or land use, and particularly in meat plants and cold storage houses, that for the present purpose it is unnecessary to go into a discussion of others. The compression system being so predominant in its use, a description of same is given.

Thediagramindicates a compression system in elementary form consisting of:

(1) A pump or compressor which withdraws the gas from the cooler or expansion tank, prepares and passes it to the condenser.

(2) The condenser or liquifier which gives to the water flowing over it the heat carried to it by the gas from the cooler.

(3) The cooler or expansion tank in which the heat extracted from the carcasses, the building walls or elsewhere,is passed to the ammonia gas for conveyance to the condenser.

—Leaving for a moment the description of the apparatus to acquaint the reader with ammonia: In the form used in a compression refrigerating machine, it bears the name “liquid anhydrous ammonia” meaning in a “dry liquid” form differentiating from the common household ammonia which is a water solution containing ammonia gas in variable quantity. The distinction between these two is that “anhydrous ammonia” will evaporate to naught; from household ammonia the gas will evaporate but the water will remain.

FIG. 15.—DIAGRAM SHOWING AMMONIA COMPRESSION SYSTEM.

Ammonia is a chemical compound made up of one part nitrogen and three parts hydrogen and is expressed by the chemical symbol NH₃. It has some peculiar characteristics being analogous to water. It will assume a solid, liquid and gaseous form, at -115° F. and -28¹⁄₂° F. for solid and liquid respectively and will modify to a gaseous form at any temperature above -28¹⁄₂° F. under “atmospheric” or conditions of no pressure.

Water, as is known, changes from a liquid to a solid at32° F. and changes to a vaporous form at 212° F. but here the analogy ceases.

Ammonia has further peculiar advantages for use in refrigerating production that it becomes a liquid at variable pressures and temperatures; for example, when the temperature is reduced to 60° F. under a pressure of 92 pounds, when reduced to 80° under a pressure of 139 pounds and at 100°, under a pressure of 200 pounds; with variables above, between and below these conditions. Ammonia, as will be seen, has variable forms and capacities under the conditions imposed upon it. Substances passing from a liquid to a gaseous form require heat to make this change and consequently absorb it; the complement to the giving up of heat when the process is reversed and the substance changed from a gaseous to a liquid form. The adoption or harnessing of these principles is the nucleus upon which mechanical refrigerating effect is built. A pound of water passing to steam will absorb about one thousand degrees of heat, ammonia has the same characteristic to a different degree. They both return the heat when the process is reversed.

—Thediagramillustrates a single acting pump showing its piston, a liquifier or condenser where the ammonia is modified in form from a gas as received therein to a liquid; a receiver to which it flows and a cooler in which it is expanded and where the heat brought to it by the returning brine is picked up by the ammonia and carried to the condenser. The arrows indicate the direction of flow.

—The “Compressor” is a pump, a cylinder fitted with a piston which withdraws the ammonia from the tank in which it is expanded. The piston is tightly fitted and when it travels in one direction, the gas flows in, filling the space, like any ordinary pump whether it be a water or gas pump. Upon the return stroke, the gas is compressed in the cylinder until the pressure in the piston is sufficient to equal or overcome that exerted against it accumulated in the condenser, when it is discharged thereto. There are spring actuated valves interposed in the line of gas travel which close and retain in the condenser that gas which has been discharged, allowing the piston and compressor to repeat the just described performance many times per minute.

—The use of this element is to liquify the ammonia, really to extract the heat absorbed by the ammonia in the cooler and the heat generated in the compression. This condensing operation changes the form of the substance from gaseous to liquid. The most simple style of condenser is a series of pipes stacked together with ammonia on the inside of the several pipes, and water flowing over the outside. The gas on leaving the compressor is hot and at a high temperature, frequently as high as 250° F. or more, and the pressure from 140 to 220 lbs., depending upon the water supply, its temperature and quantity, and the area of the surface of the condenser.

The water flowing over the condenser absorbs the heat from within, the ammonia becoming cooled by contact with the comparatively cool walls of the pipe while flowing from one end to the other of the condensing coil, gradually changing from a gaseous to a liquid form.

—From the condenser the liquid ammonia is collected in the receiver so as to have a quantity stored for use and in reserve for the fluctuating requirements.

—A small but important item in the system is the expansion valve which is a valve with a controllable opening and comparatively small. This is interposed in the line between the liquid receiver and the cooler or expansion tank.

—The next element is the cooler in whatever form it may exist, whether it be ammonia coils submerged in brine tank, shell and tube cooler built like a boiler in which the ammonia surrounds the tube through which the brine solution is pumped, or ammonia “direct” expansion coils in the air within a room, it matters not. At this point the heat given off by the substance to be cooled is absorbed by the ammonia and taken up for discharge to the water flowing over the condenser.

No substance will change from a liquid to a gaseous form unless heat be supplied to perform the work of making this change. At the outset it was stated ammonia will boil or evaporate at 28¹⁄₂° below zero Fahr. when under no pressure or in the open air. Further, if ammonia be contained in a vesseland the pressure be reduced below atmosphere, the boiling point is lowered still further. For example at 10.6 vacuum gauge pressure the boiling point will be 40° below zero.

Imagine a brine cooler such as a tank with coil submerged and surrounded by a brine solution: This brine is circulated through the building and by common knowledge we know it absorbs heat and is returned warmer than it was sent out. It is supplying the heat for boiling the ammonia gas.

Reverting to the expansion valves: Assume there is a pressure of 180 pounds in the condenser and a liquid temperature of perhaps 85 to 90 degrees; the same conditions existing in the receiver; also assume a pressure of 15 pounds on the ammonia coils which will produce a temperature condition of zero. In the diagram, the coil in the tank is attached to the expansion valve while on the other end of the coil is made the connection to the pump or compressor. This by its action is withdrawing the ammonia gas as rapidly as it is generated, due to the tightness of the piston, which if it is properly fitted will pump a vacuum upwards of 22 to 25 inches upon the system attached to it, unless gas be supplied to fill the space. In operation, the expansion valve is opened slightly, the liquid is freed into a space where the pressure is lowered, a condition created for expanding the ammonia to a gas and the heat contributed by the surrounding brine is absorbed by the ammonia changing from a liquid to a gaseous form.

—The cycle, therefore, is a gas in the expansion tank at low pressure and temperature, admitted to the pump or compressor under this condition, compressed to a small volume and increased in pressure, discharged in this condition to the condenser where it becomes a liquid and in a condensed form at a lowered temperature and ready to return to the expansion tank to be used over again.

Ammonia gas is the heat carrier. If it be used in packing house service, either it absorbs the heat directly from the rooms in which the animals are suspended or the brine in the tank is circulated through the rooms to absorb the heat and carry it back to the cooler or expansion tank.

—In Chapter II reference was made to the condensing water for refrigerating system. This is importantbecause the lower its temperature, the less the pressure will be created which means the less the power must be exerted in the production of the mechanical refrigerating effect. The water flowing over the condenser carries the heat to the sewer. Thus the heat from the carcasses, the sun heat on the walls of the building, the actinic rays through the windows, the heat from the men employed within, that from the electric lights within, and that absorbed from the earth upon which the building stands must all be collected and eventually passed into the sewer.

—Absorption refrigeration equipment is used to some extent in packing house work, but its complexity makes unnecessary an attempt of its description in this work.

—The unit basis of refrigeration commonly used in expressing quantity is tons of refrigeration, meaning the tons of refrigerating duty that can be performed per day of twenty-four hours. The standard measurement per ton as adopted by the American Society of Refrigerating Engineers, is a cooling effect equal to 288,000 B.t.u., being equivalent to the extraction of this quantity of heat from any substance.

It has been established by the Bureau of Standards that in freezing one pound of water at 32° F., to ice at 32° F., 143.5 British thermal units of heat must be withdrawn from the water. For convenience in practice the fractional part is ignored, and 144 B.t.u. per pound of water is accepted as standard in calculations.

—If 144 B.t.u. are withdrawn from each pound of water at 32° F. to convert the water into ice at the same temperature, the melting of the pound of ice at the same temperature must re-absorb an equal heat in the process of freezing, consequently the melting of one ton (2,000 pounds) of ice to water at the same temperature would absorb 2,000 × 144 B.t.u., or 288,000 B.t.u., the accepted standard for computing the heat absorbed in the performance of one ton of refrigeration duty. In ice melting this absorption of heat islatent, not sensible to the thermometer, as no change is apparent by thermometer test in the temperature of the ice andthe water, nevertheless an appreciablecoolingof surrounding is measurable by thermometer wherever ice melting takes place; for example, in an air-tight room, or in contact with solid substances, or with liquids, having a higher temperature than 32° F.

—The rating of refrigerating compressors as usually stated by manufacturers is expressed in tons. This refers to the tons of duty that a machine will develop in a period of twenty-four hours continuous operation under assumed conditions of about fifteen pounds gauge, back or suction pressure, and 185 pounds head pressure. To perform this duty the compressor should be of sufficient size to displace or pump a volume of gas equal to 4¹⁄₄ cubic feet per minute. This rating of the machine is proper when you are producing temperatures of about 32° F. or over, and presupposes the plant to be properly balanced as to condensers, and to be properly provided with liquid receivers, oil extractors and other complementary equipment.

—The growing demand for freezer space in and about packing houses, however, is so important that special means and methods must be provided to meet the conditions. It is impossible to produce freezer temperatures and conditions under the same back pressure as described above; the back pressures must be lowered and in doing so the capacity of the compressor is reduced very rapidly. The same compressor producing one hundred tons refrigeration duty at fifteen pounds back pressure and 185 pounds head pressure will only perform half the work when operating under a back pressure of five pounds, the head pressure remaining the same.

The purchaser must never lose sight of the fact that in cooling freezer spaces the compressor capacity is reduced practically by half and that this is applicable to all portions of the system working under these conditions.

—No hard and fast rule can be adopted regarding the system of refrigeration to be adopted, whether by use of brine circulation or direct expansion. The case in hand and the nature of the business to be done seems to govern. For example, if the plant in which the business ismixed, wherein hogs, cattle and sheep are killed, curing performed, and lard made, with a limited amount of freezing, brine circulation for general use would seem the better. The excellent results obtained by the use of spray coolers, later described, seem to point to its use in chilling coolers, with brine circulated through ceiling or wall coils for cooling storage rooms.

—If the plant be quite moderate in size and only sufficient to justify the installation of one compressor the amount of space required for freezing purposes is thus limited, and if commercial freezer space is available it is a question as to whether the operator can afford to deplete his small equipment capacity by installing freezers.

FIG. 16.—SUCTION CONNECTION FOR DUO-PURPOSE COMPRESSOR.

—If the plant be sufficiently large so that the machine equipment can be afforded in two units then it would be proper to install freezers. Supposing then that the plant justifies this arrangement the compressors would be connected to the brine tank for chilling purposes, and to the closed cooler for circulating purposes. The gland end of the compressors would be arranged so that they could be operated independently upon the freezer space at will.

—The chief reason for using brine in the moderate sized plant is that with a reasonably large brine capacity there is a reserve cold (so to speak) stored in the brine which will permit of stopping the compressor, thebrine continuing in circulation by pumping, and there is less likelihood of changes in temperature. Direct expansion chilling requires an almost constant machine operation.

—The chilling of packing houses and methods involved are various, each with its advocates. In Europe and where English methods are followed the system is chiefly forced draft. This system has been used to some extent in the United States, but the majority of the coolers are handled with lofts, and circulation therefrom is of natural sequence. The cellars and freezers are handled by pipes hung in the rooms.

—The force draft or indirect cooling system consists of forcing chilled air, cooled by passing through batteries of expansion coils operated dry, or over which brine is passed, through a series of ducts, and withdrawing it; thence passing it through the coils and repeating. It is not favored among American packers owing to a belief that it increases shrinkage, and tends to darken beef; that large quantities of cold air are lost through open doors; because of the expense of operating fans, as well as the room taken up by ducts and the interference occasioned with meat rails.

—The overhead bunker system as described under “Construction” in this work details the application of the United States practice.

Accepting the use of the coil room system and of still storage the question arises as to the application. A visit of inspection to the various packing plants throughout America will impress one with the fact of the existence of a wide variation of opinion and practice with regard to the methods of applying refrigeration for packing house purposes. There are two principal applications—direct expansion, wherein the ammonia gas is circulated through the coils throughout the premises, and brine circulation, open or closed, where chilled brine is circulated throughout the works.

—The two types of brine chilling, open and closed, produce the same result, except as to the actual brine cooler, of which there are several, namely:

(1) Brine tank in which are submerged ammonia expansion coils.

(2) Double or triple pipe coolers in which brine and ammonia are circulated in annular spaces between pipes.

(3) Shell type coolers in which the brine is passed through tubes within a shell similar to an ordinary flue boiler.

For a close brine system, which is the term applied to a system where brine is circulated through pipes and not exposed to the atmosphere so as to absorb moisture, the shell type cooler is a convenient and economical means of chilling brine. It is so readily applicable to the use of a balanced system, thereby lessening the power requirement for pumping.

Double pipe coolers can be used in the same method, but are not quite so favorably considered owing to the aggregate quantity of joints.

Either the shell type cooler or the double pipe cooler can be safely used with an open system. The open type brine system is any system used wherein the cooling effect is produced by bringing the cold brine in direct contact with the air to be chilled, as in the spray system, the “Gardner” sheet system, or an open pan system.

—Where it would seem best for other reasons to use a brine system, and the plant would justify the expenditure, it would appear well to use a double brine system—open brine in the hog chill rooms, and a closed system on the freezers, beef chill rooms, storage rooms.

—Open tanks with submerged coils are used on some plants. The investment is greater, but the risk is slightly less than in the use of closed type brine coolers, commonly called shell and tube type. Unless the engineering force of the plant is fully qualified and alert, there is danger of diluted brine and freezing the solution in shell type coolers, which is likely to split the tubes, causing leaks and the possibility of brine finding its way to the ammonia compressors, rendering them liable to damage of a serious nature. Whereas, with the open type tank and submerged coils, weakened brine might cause ice to form on the expansion pipes and render them inert, but no comparable damage could arise. However, we advocate an alert engineering force and the closed system.

FIG. 17.—DIAGRAM SHOWING BALANCED BRINE SYSTEM.

—The balanced brine system as referred to in the preceding, is indicated bydiagramand has the advantage of keeping the pipes full at all times, also of reducing the power requirement to the actual friction through the pipes in the shell type cooler, and a slight increase for passing through the coils. In practice twenty to twenty-five pounds friction represents the total head to pump against in a building nine stories high. The two types of the balanced brine system are as follows:

—Beginning at shell and tube coolers the brine passes into supply pipes which decrease in size as they approach the ends. The return line tapers in opposite direction. The pressure carried is only sufficient to make a sufficiently rapid circulation.

A small pump is inserted in the line so that the pressure can be increased on that portion through the spray nozzles. This lessens the power over carrying the entire system at a high pressure.

The balance tank is located at such point as will best serve to collect the brine from closed coils and the return from the spray coolers. A vacuum valve is put on the closed line to prevent siphon.

A return connection to the main pumps is made, and also connections to the concentrator from balance tank so that a portion of the brine can be concentrated.

This system requires more concentration than the closed system. It has the advantage that coolers can be used as sharp freezers if insulation be proper.

—Beginning at shell and tube coolers the discharge mains and piping are the same as for the open system. Return mains as indicated. Balance tank is located elevated above upper coils.

A localized defrosting system is installed with individual pump circulating brine over coils, continuously as required. The collecting tank is located as near as convenient to lessen pumping head. The brine flowing over coils in the lofts is concentrated to a strength equal to circulating brine and introduce into circulation replenishing brine for defrosting from mains. Concentrator is located where suitable.

In using closed coils the arrangement is different for beef and hogs so as to assist in the circulation for hog cooler with a view to producing uniform temperatures.

FIG. 18.—CONCENTRATING ARRANGEMENT, BALANCE BRINE SYSTEM, CLOSED TYPE.

In any system using open brine, there is a quite appreciable gain in the quantity of brine in the system, and a weakening of its strength lowering the freezing point. This necessitates vigilance as if the brine weaken too much there is a possibility of it freezing solidly and insulating submerged coils in an open brine tank rendering them inert or splitting the pipes in a shell type cooler with disastrous results. It is consequently necessary to evaporate the brine which can be done with a concentrator as provided for inFigs. 17and18.

The concentrator apparatus consists of a balance or storage tank in elevated position according to whether the closed or open system is used; one or more stands of pipe coils; a catch pan for concentrated brine; a reservoir and a small pump for passing brine into system. The brine flows from storage tank, entering the bottom pipe of the coils and passes upward through seventeen pipes, from which point it is delivered to the trough at the top of the coil and allowed to flow down over the entire battery of pipes, steam being circulated through the top six pipes, thus heating the brine and concentrating it by evaporation. The hot concentrated brine is cooled as it passes over the lower seventeen pipes through which it originally entered as cold weak brine.

—Many plants are equipped completely with direct expansion systems. This is quite satisfactory provided means are arranged to dispose of the accumulating ice and snow on the coils. This is particularly applicable to coils in pipe lofts where moisture rapidly accumulates, and is accomplished by some arrangement of defrosting such as circulating a brine over coils by permitting it to drip over the coils, pumping over and over again.

—The revising editor brought into prominence the two-stage compression system by building a successfully operating plant which functioned with quite astounding results. The system consists of a large low temperature gas compressor and a smaller second stage compressor, arranged the reverse to a compound steam engine.

Ammonia gas which at the low temperatures resulting when low back-pressures are required, becomes highly attenuated (light), it is necessary to handle a very large volume perton of refrigeration developed. To provide for this, the low pressure cylinder is made about double the volume of the high pressure cylinder.

In the low pressure cylinder the gas is compressed to a pre-determined pressure and passed at a relatively high pressure, making for a very high efficiency. The gas is chilled by the introduction of expanded ammonia to take up the superheat.

The use of this compressor arrangement with its refinement makes an economical cold producing unit. A record of one year’s run follows:

Two-Stage Compression System.

—All of the above factors must be considered in the calculations for refrigerating requirements, and it is best to make allowances for a considerable factor of safety over and above the actual maximum, as well as for the economical operation of the plant. It never pays to crowd a plant to its limit or capacity. Guard against emergencies and possible abnormal demand for refrigeration by providing ample equipment. The plant should be constructed as far as possible in duplicate, not only as regards the machinery but also in the apparatus, as a safeguard against accidents and total cessation of refrigeration. With two machines and duplicate apparatus one-half the maximum refrigeration is always available, and the preservation of the product in storage is assured, even if it be found necessary to stop killing for a sufficient period to make the repairs on the broken machinery or apparatus, while with one machine only available, a breakdown might result in a very serious loss and considerable damage to the stored products.

With regard to insulation, it may be said that the best isthe most economical in the long run. There is no such thing as absolute insulation, some heat leakage must occur through the very best insulation, and the reduction of this heat leakage to the minimum should be the chief object or factor for consideration. First-class insulation costs more in original investment, but it creates a continuous saving and economy in refrigeration, resulting oftentimes in a less investment also in refrigerating, pumping and steam equipment.

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