UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA POWER REQUIREMENTS OF ELECTRICALLY DRIVEN DAIRY MANUFACTURING EQUIPMENT A. W. FARRALL BULLETIN 433 September, 1927 UNIVERSITY OF CALIFORNIA PRINTING OFFICE i BERKELEY, CALIFORNIA 1927 POWER REQUIREMENTS OF ELECTRICALLY DRIVEN DAIRY MANUFACTURING EQUIPMENT A. W. FAEEALLi INTRODUCTION That the use of electrical energy in dairy manufacturing has become general in California is evident from the fact that it is used in more than 900 plants of various sizes and types operated in the state. Data show that 92 per cent of the plants use electrical energy for power; that the total horsepower of electric motors installed in all plants exceeds 73,800; that the annual power bill amounts to approximately $2,486,000. There has been a considerable demand for information regarding the energy requirements and load characteristics of dairy manufac- turing equipment, and also regarding the energy requirements of various manufacturing processes in which electrical energy is used. This information is necessary as a basis for improving the design and the operating efficiency of the machinery, and also as a basis for determining costs in cost accounting. A study has been made by the Division of Dairy Industry in which numerous laboratory and field tests have been conducted and data have been secured covering these points, with special reference to California conditions. ENERGY REQUIREMENTS FOR DAIRY MANUFACTURING EQUIPMENT The energy used in the processing of dairy products is an import- ant item in the cost of manufacture. The dairy plant operator who keeps cost accounting records of this phase of his business has made a step toward greater efficiency. In order to obtain the maximum value, however, he must know the actual amount of energy consumed by each piece of his equipment and compare its performance with that of an established standard. One purpose of this publication is to offer a suitable basis for comparison. Data were secured covering the actual energy require- ments of the more important types of dairy manufacturing equip- 1 Junior Agricultural Engineer, Divisions of Agricultural Engineering and Dairy Industry Cooperating. 4 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION ment, when used under normal conditions such as would be found in the average dairy manufacturing plant. A summary of the data secured is shown in Table 1, which gives the name of the equipment used, the process carried on, the product treated, the rated capacity of the machine, the size of motor used, the unit of product taken as a basis for comparison, and the kilowatt hours of electrical energy used per unit of product handled. The results presented in this paper were obtained from a large number of individual trials with each machine, and for the most part from machines of average capacity. In making comparisons with equipment of sizes other than those given, one should remember that more efficient results will usually be obtained from larger equipment, and vice versa. The cost of energy used in carrying on a certain process may be calculated as illustrated in the following paragraph. Problem : Find the cost of electrical energy used in washing 1000 milk cans in a can washer of the type using motor-driven pumps, when electrical energy costs two cents per kilowatt hour. Solution : Referring to Table 1, line 10, it is found that the energy requirement for this type of washer is 3.5 kw-hr. per 100 ten- gallon cans washed. The cost of electrical energy for washing 1000 cans then, will be 10 X 3.5 X $0.02 = $0.70. Factors Affecting Energy Consumed. — The amount of energy used by a machine is affected by its mechanical condition and by the methods used in its operation. For most economical results, all valves and pistons must be kept tight and the stuffing boxes well packed, so that they neither bind nor leak. All bearings must be properly adjusted; the chains or belts used must have the proper tension and alignment, and all moving surfaces where there is friction must be kept properly lubricated. The machine should be operated at uniform speed and at as nearly its rated capacity as possible. Intermittent starting and stopping of a machine or process consumes energy needlessly. The operator should endeavor to turn off the power as soon as the process is completed, for motors operate very inefficiently at light load and disturb the elec- trical balance of the entire system. A large number of motors run- ning idle may cause such a low power factor 2 on the system, as to bring about undue heating of those fully loaded. 2 Low power factor increases the current flow for a given amount of energy transmitted. BUL. 433] ELECTRICALLY DRIVEN DAIRY MANUFACTURING EQUIPMENT 5 -5 w a o o *i o w ■d hj xi a o ompi 'omoj asteu asteu asteu ottlir hum reeze an wi an wi ottle ottle ream K » * * g g -i •essor renizer... rizer rizer rizer ig mach; P o rr 5' CD asher. asher. eparat 3" -D o 3 ? {gfggimi ifs- deration agenizat urizatio urizatio urizatio ing ning ing ice c ing cans ing cans ing bott ing bott ■ating cr hd o a » CO CO 3 5 55 P 3 3 ^ P 5" P c[££££op ) Sp ) p> rj o to Ogall Ogall bott] 00 po quar can can bott] Obot 00 po ° ° S-O c ;o2 5o2 : ^'-*- B^aBwrKB^lNp ft £- &r 3 ft » w ^ a p ft 5" 2. b 1 a a ^tJ^wCJrt-^Opili c cd <-► - s vi S e H 1 1^ 3 S-cT ous s elect ype* , elec gal t - CD -hori coil . ous... >11 << c+ [SI CD •o 9 3. p e § . fL CD » o O P- <" CD 3 II if* ■a i" < is 3 P- o 3 cr cd" P o c-t- B p o cr 5" CD •0 3 C 3 i < 3 5' 3 •a D co » i -a co ( oooooooooo So? i f > l Q^||p'a^'c , o 3 o 2 3 'O „ a ^3313:3330300 § g S 3_ Opp00 3p33 C 5 lliidii 3 5 3 B 3 3 2. ds of ere ds of ere t bottles ds of ere s of ice c ;allon cai ;allon cai t bottles t bottles, nds of m 3- P- TO ss. /) co en p ration of mi of mi S-13 CD -1 3 t? co co a> 8 p 3 P P C 7? H o 3 o cr -»o >- •o S < OOOOJOOOOOO cop— iooiooi>— ooo o o to OS 18. J OCSOiOOil^eOH-CO^ £ H< O CnajOOOt-OCn^I^-OicO 8o§ OOlQlOt^OOcO^IW et-tJ t- -1 CD O CD "1 <> p J < ft£ p CD 3 cj; 0.5.-^ b UNIVERSITY OF CALIFORNIA EXPERIMENT STATION The size of motor used should be equivalent to the power require- ment of the machine driven or, in order to care for overloads, it may be a trifle oversize. Most motors are made large enough to carry a momentary overload of 100 per cent. The efficiency of a motor is highest at or very near its rated capacity, and drops off markedly at loads below one-half or above one and one-fourth of its rated horse- power. In processes making use of electric heaters, it is very important to have all external heat radiating surfaces well insulated. It is often more economical to use large storage tanks for hot water, since a small amount of power used over a longer period of time lessens the cost of electrical energy on account of the lower power and energy rate. OPERATING CHARACTERISTICS OF DAIRY MANUFACTURING EQUIPMENT The information given on the following pages deals with the operating characteristics of certain types of dairy equipment. A study of these results shows the factors that affect the power con- sumption and general operating characteristics of each type of equip- ment. It is especially important to note how by varying such factors as head-pressure of a refrigeration machine or the type of ice cream freezer, the power consumption of the process is materially changed. It is also of importance to note how the uniformity of load varies with the different machines and with various methods of operation. Uni- formity of load is important from the standpoint of determining the proper size of motor to use and in assisting to balance the machine. An unbalanced condition, which usually causes a badly pulsating load, throws a severe strain upon all the operating mechanism, and there- fore should be avoided. POWER CONSUMPTION OF REFRIGERATION MACHINERY The variation in power consumption of a twelve-ton, double-acting, compression type of refrigeration machine, when operating under various head-pressures is shown in figure 1. From an observation of the curve, it will be seen that much more power is required to drive the compressor against a head-pressure 3 of 200 pounds per square inch, than against a pressure of 150 pounds, even though the back- pressure is the same under both conditions. - Head-pressure (sometimes called pressure on the high side) is the pressure in the condenser, against which the compressor must pump the refrigerating gas. BUL. 433] ELECTRICALLY DRIVEN DAIRY MANUFACTURING EQUIPMENT 22 a\ ao 19 18 17 150 160 I7D 180 190 230 220 \-\ead- pressure. Fbunds per squore inch. Fig. 1. — Belation of head-pressure to power requirements of refrigeration machines. The cost of energy per ton of refrigeration pressures, when electrical energy costs two cents in Table 2. A comparison of results upon this per ton to be 8.8 cents* greater when operating pressure than when operating at 150 pounds. From a number of actual observations under the conditions above, the power con- sumption has been found to increase 16.2 per cent, with a pressure rise of 50 pounds. This in- creased power con- sumption is due par- tially to increased friction losses in the equipment, but prin- cipally to the greater head which must be pumped against. at the various head- per kw-hr., is shown basis, shows the cost at 200 pounds head- TABLE 2 Cost of Energy fob Driving Refrigeration Machine as Affected by Variation of the Head-pressure Head-pressure, pounds per square inch 150 160 170 180 190 200 52.4 54.5 55.2 57.0 59.2 61 2 The yearly saving on the power bill of a 50-ton refrigeration machine operating at 150 pounds as compared to 200 pounds head- pressure and with electric energy at two cents per kw-hr. may be calculated as follows: Fifty-ton machine operating for 10 hours per day for 360 days 7,500 tons refrigeration Cost per ton at 200 pounds pressure 61.2 cents Cost per ton at 150 pounds pressure 52.4 cents Cost per year at 200 pounds pressure $4,590 Cost per year at 150 pounds 3,930 Saving per year by operating at 150 pounds head-pressure 8 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Factors Affecting the Head-pressure. — Several factors influence the head or condenser-pressure of a refrigeration machine. The most important of these are the temperature and the amount of cooling water supplied to the condenser. Other factors are the size and amount of cooling surface, the cleanliness of the condenser, and the presence of air or inert gases. It is recommended that at least two gallons of water at or below 70 degrees F. be supplied per minute, per ton of refrigerating capacity. In some sections of the country where there is a shortage of water or where it must be pumped a considerable distance, a cooling tower will be found economical. It will reduce the temperature of the water so that it may be used over and over again. The larger volume of water which is thus available for circulation, makes possible a better heat transfer from the condenser. The condenser should be large enough to allow plenty of surface for the cooling of the ammonia. The addition of more condenser capacity will often pay for itself in a short time, through the reduc- tion of head-pressure and the consequent saving of power. Since condenser tubes become scaled over, they should be cleaned occasion- ally. Instances are on record where a thorough cleaning with a rotary tube cleaner has caused a drop of 50 pounds per square inch head- pressure. # 1 ' Non-condensible ' H gases tend to accumulate in the condenser and fill space which should be occupied by the refrigerant, thus causing an increase in the head-pressure. Non-condensing gases are removed by frequent purging, 5 or by so-called " non-condensible gas removers." OPERATING CHARACTERISTICS OF CHURNS The power characteristics of a common single-roller type churn are illustrated by the typical curve shown in figure 2. The heavy curved line A represents the average power consumed at various intervals during the churning operation. It drops somewhat after the cream has been churned for a few minutes, but rises again as the churning nears completion. One of the principal features of figure 2 is shown by the shaded area. The extremes of this area represent the momentary variation in the pull on the motor, as measured by an indicating watt-meter. Twenty-four minutes after starting the pull varied from zero to 5% horsepower. At one instant the motor was drawing 5% horsepower from the line and at the next was drawing none. it is readily seen that such an unbalanced load not only 4 ''Non-condensible gases" are those such as air, nitrogen and hydrogen, which collect in a refrigeration plant and are not condensed at the usual" operating pressures and temperatures. 5 Purging is the operation of blowing off gases from the condenser. BUL. 433] ELECTRICALLY DRIVEN DAIRY MANUFACTURING EQUIPMENT 9 throws a severe strain upon the driving motor and gearing, but also upon the churn itself. To eliminate this unsatisfactory condition, designers of churns should produce a better balanced and smoother operating piece of equipment. The use of counterbalances would help to make the load more uniform. The average power consumption for the entire churning process is indicated by the heavy broken line marked "average" in figure 2. This is the value which should really determine the size of motor required, provided that the momentary load is never so large as to stall the motor or greatly reduce its speed. o 2 O r Average momentary load during churning Shaded area covers actual momentary power variation 12 £A - 36 Minutes 4S 60 Fig. 2. — Power consumption of a typical churn, showing variation during the churning process. OPERATING CHARACTERISTICS OF ICE CREAM FREEZERS Method of Freezing. — The power characteristics of ice cream freezers were found to vary considerably with the different types of machines, methods of freezing, and kinds of mixes. The data collected show that there can be no general recommendation of a definite size of motor for all freezers of a particular capacity. It shows also the necessity of the operator's keeping in close touch with the freezing process, and emphasizes the need for some method of indicating to the operator the exact state of the freezing process at all times. The simplest method of making ice cream is to freeze the mix to a given stiffness and then turn off the freezing medium and whip until 10 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION the desired amount of air is incorporated. Figure 3 shows the varia- tion in power consumed by a standard 40-quart freezer with the horizontal blade-type of dasher, so operated. With this method of freezing, it is apparent that the power consumption of the motor increases gradually, up to the point X where the freezing medium is turned off, after which there is a decrease down to the point Y, where 4 L O o_ 10 L. O I Jg) p 8 M mutes 12 16 Fig. 3. — Power consumption of a 40-quart freezer when the "freeze and whip" method of freezing is used. the ice cream is drawn from the freezer. The increase in the power consumed is caused for the most part by the increasing stiffness of the mix as it becomes colder and by the increase in friction of the driving mechanism. The two rates of decrease that are shown are both due to lessened resistance to the rotating blades of the dasher. The first or more rapid decrease, coming just after the freezing medium is turned off, results from the softening of the frozen film, which the dasher has been scraping from the sides of the freezer. The further or second BUL. 433] ELECTRICALLY DRIVEN DAIRY MANUFACTURING EQUIPMENT 11 one, is undoubtedly caused by the thinning of the mix and the incor- poration of air. Since there are a number of factors which affect the shape of the curve, no two freezers, even though they be similar, have been found to give identical curves. Some of the influencing factors are : change in composition of mix, brine temperature, and method of homogenization. One point worthy of special note is the effect of a leaky brine valve. This will ordinarily prevent the drop in power consumption after the freezing medium has apparently been turned off. A leaky brine valve may usually be recognized by the failure of L 8.2 in r ^X S^^z k_y O 5 10 20 Minuter Fig. 4. — Power consumption of a 40-quart freezer when the "freezing back" method of freezing is used. the pointer of an indicating ammeter or watt-meter, connected in the motor circuit, to drop back. An exception to this rule should be noted in the case of some freezers which employ the squirrel-cage type of beater and in which the power consumption does not materially decrease after the freezing medium is turned off. A second exception is in the case of a freezer operated in such a manner that the ice cream is "whipped" as it is frozen, the freezing medium not being turned off until the freezing operation is finished. The variation in power consumption of ice cream freezers when the "freeze-back" method was used, is shown in figure 4. The curve with this method, was similar to that obtained with the first method 12 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION described, until the point was reached where the cream would be drawn, if the first method of freezing were being followed. "With the second method however, the " whipping" was continued, and the power consumption decreased still farther down to point Y, at which time the mix had absorbed more air than was desired in the finished product. In order to drive this excess air from the mix, the freezing medium was again turned on at the point Y ; the frozen film was again built up on the inside of the freezer barrel and the cream became stiffer. There was an accompanying increase in the power consump- tion up to the point Z, at which time the mix was drawn from the L Q) la Du- ty <0 L O X /"® \ V<2) V-