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680 CHAPTER 49 1959 Guide good practice to rely entirely on blowing of air through the system. Drifting Snow It is quite likely that some drifting will occur on every system that is adjacent to a wall or vertical surface. The designer should try to anticipate this condition and add extra piping in these areas. If possible, coils should be added in the vertical surface. Another expedient is to carry the drainage to the area expected to be drifted. The drainage will tend to wash away some of the snow. Design Example Example t: Assume that there are three independent hy draulic systems to be used in the snow-melting application described in Example 1. One.system will be for the Class I area, another for the Class II, and the third for the emergency area, or Class HI area. Determine the hydraulic requirement for the Class II sys tem, nwnmiing an area of 100,000 sq ft. Solution: The beating requirement has been determined as 160 Btuh per sq ft. Since an area of this type has a large per imeter, assume the edge and back losses add about 40 percent or 64 Btu per sq ft. The total heat requirement, then, will be taken as 224 Btuh per sq ft or 22.4 X 10* Btuh tor the 100,000 sq ft area. The fluid temperature is determined by using Equation 7: Since U - 0.5 q. + t, q, 160 Btuh per sq ft, and tf * 33 F - t. - 0.6 X 160 + 33 - 113 F. If an oil antifreeze is used, the epecifio heat, a* , the kine matic viscosity rm , and the specific weight to. , at 113 F can be found by interpolation in Table 5 as Cm ~ 0.440 Btu per (lb) (F deg) -- 3.88 X 10"* sq ft per sec. An accurate determination of viscosity cannot be mads by interpolation in Table 5 and should therefore be made by use of ASTM Standard Viscosity Chart B. to. a 59.4 lb per cu ft Then from Equation 12 ,, _ _A*t10* X 225 160tA.c. 160 X 59.4 X 0.440 " 5380 811111 Equation 12 is based on a temperature drop of 20 F deg, therefore, the fluid must enter the slab at 123 F and leave at 103 F in order to have the desired mean temperature of 113 F. Assume that the coil with the longest equivalent length is 300 ft and has a flow of 12 gpm. Such an arrangement would suggest the use of a coil of 1 in. IPS- From Table 1, Chapter 31, thelD " 1.049 in. = 0.0875 ft which gives an internal crosssectional area of 0.00600 sq ft. For 12 gpm the flow is 0.0268 cu ft per sec and the velocity is 0.00600 1 and Reynolds number, Ns,, is N VD 4.47 X 0.0875 10,100 358 X 10"* From Fig. 4, Chapter 4, using a roughness factor e *=> 0.0001 whence e/D 0.00172, the friction factor / is found to be 0.0333. Substituting in Equation 10 yields L V* A/ 4.47*2 X 32.16 ** 35.8 ft of fluid -- 14.8 psia The friction loss could have been approximated two ways: (1) by using Fig. 2; and (2) by using Fig. 3 of this chapter in conjunction with Fig. 5 of Chapter 28. . In order to use Fig. 2, the viscosity of the oil must be known in SSU. As given above the kinematio viscosity of the oil at 113 F is 3.88 X 10"* sq ft per sec. From Table 6, 3.88 X 10"* sq ft per sec is equal to 37.9 SSU. Entering Fig. 2 at 37.9 SSU and reading friction less for 12 gpm gives 12.8 ft per 100 ft. For a 300-ft coil this is 38.4 ft of fluid. This compares fairly well with the more exact figure of 35.8 ft as found by using the Fan ning equation. If the friction loss were approximated by Fig. 3 and Fig. 5 of Chapter 28, the result would have been 40.5 ft which is determined as follows: From Fig. 5 of Chapter 28, the loss for water flowing at 12 gpm in a one-inch pipe is 1200 milinches per foot or 10 ft per 100 ft. In this case, then, the loss for water would be 30 ft. The correction factor for oil as compared to water is given in Fig. 3 as 1.35. The friction loss then would be 1.35 X 30 or 40.5 ft. Both of the approximation methods are conservative, but for large systems, this conservative approach may be costly. The pump must deliver 5380 gpm against a 145 psia bead. The heat exchanger must deliver 22.5 million Btun with an inlet temperature of 103 F and an outlet temperature of 123 F. Actually some allowance should be made for the temperature drop in the piping between the slab and the heat exchanger. Both the pump and heat exchanger manufacturers should be advised that the fluid is an oil and will operate over a wide temperature and viscosity range. If a low-limit thermostat is placed in the fluid line so that the minimum fluid temperature is --10 F, it can be seen from Tables 5 and 6 that the viscosity can reach about 300 SSU. From Table 7, it can be found that such a viscosity can reduce the pump head 5 percent and the capacity 3 percent. This means that the pump should be rated IX 8 RTfifi jig - 15-6 psia and jjjy - 5550 fpm. The expansion tank should be designed in accordance with the procedure outlined in Chapter 28, Hot Water Heating Systems. The amount of expansion should be based on the change in volume from the low temperature limit to the high temperature limit. Assuming the temperature range to be -- 10 F to +123 F, the expansion would be 62'7gg-j---* = 6.1 percent of the total volume in the system. REFERENCES 1 W. P. Chapman and S. Katuoich: Heat requirements of snow melting systems (ASHAE Transactions, Vol. 62, 1956, p. 359). 1 W. P. Chapman: Design of snow melting systems {Healing and Ventilating, April 1952, p. 95, and November 1952, p.'88). * W. P. Chapman: Calculating the heat requirements of a enow melting system {Air Conditioning, Heating and Ven. Mating, September 1956 through August 1957). *W. P. Chapman: Snow melting system hydraulics {Air Conditioning, Healing and Ventilating, November 1955). * P. B. Gordon: Antifreeze protection for snow melting sys tems (Heating, Piping and Air Conditioning Contractors Na tional Association Official Bulletin, February 1950, p. 21). * C. S. Cragoe: Properties of Ethylene Glycol and Its Aqueous Solution (National Bureau of Standards, Society of Auto motive Engineers, CKC report No. 9). 7 W. P. Chapman: Arc thermal stresses a problem in snow melting systems? (Heating, Piping and Air Conditioning, June 1955, p. 104, and August 1955, p, 92). CHAPTER 50 PROCESS AND PRODUCT AIR CONDITIONING General Requirement* for Manufacture, Processing, cod Preservation; Design Conditions and Application Data; Classification of Problems; Moisture Content and Regain; Conditioning and Orying; Chemical and Biochemical Reactions; Crystallization; Control for Machining, Pohshmg, and for Static Electricity Elimination; Laboratory Conditions; Calculations PROCESS and product air conditioning is concerned Air conditioning for industrial processes is so extensive with the design and application of equipment for ob and involved that a detailed treatment is beyond the scope taining proper conditions for the manufacturing, processing, of this chapter. In many industries the exact conditions and preserving of material, equipment, and commodities. (o be maintained are determined and knows only by the This chapter includes a general discuffiion of these condi manufacturer who specifies them. In other industries there tions and also a comprehensive list of specific requirements is a wide variance between manufacturers' requirements, for various types of products. depending on results desired, experience, and cost considera tions. .. GENERAL REQUIREMBnTTS FOR MANUFACTURE, PROCESSING, AND PRESERVATION CLASSIFICATION OF PROBLEMS In order to apply air conditioning to industrial processes, the air-conditioning engineer must have a thorough under standing of the processing problems involved. Since indi vidual processes and machines are changing rapidly, air con ditions must be revised constantly to meet new requirements. Table 1 lists the temperatures and relative humidities required for storage of certain commodities, and for man ufacturing and processing of others. In some cases the temperatures and relative humidities listed in Table 1 have no direct influence upon the product itself, but do affect the efficiency of employees and, in turn, the work--"" manship, uniformity, and cost of production. Sometimes, a compromise between the known optimum condition for processing and that required for worker comfort is unavoid able. In general, any industrial air-conditioning problem in processing may be classified under one or more of the fol lowing: 1. Control of regain. 2. Control of rate of chemical reactions. 3- Control of rate of biochemical reactions. 4. Control of rate of crystallization. 5. Control of temperature for close tolerance machining, and grinding. 6. Control of dew point for protection of highly polished surfaces. 7. Control of humidity for static-electricity elimination. . 8. Control of conditions for material-testing laboratories. (Text continued on p. 687) Table 1 .... Temperatures and Humidities Applicable to Industrial Air Conditioning* Procets Temp. F BAKERY Bread cooler (room or tunnel) 75-80 75-80 375-450 Cake mixing................................................ 75-80 70-75 95-110 *H.% 70-75 80-85 80-85 65 Shortening (depending on type), stor- 70 30-45 65-80 80 70-80 55-65 80-85 50-65 35 40-50 Methods of Mixer Cooling 1. 35-40 F water circulated through mixer jacket. 2. 15-25 F brine. 3. Direct expansion, refrigerant circulated through mixer jacket. 4. Cracked ice added to dough in mixer. 6. Cooled agitators are used in mixers. Mixer Load Calculations Refrigeration is required to remove: excess ingredient, if any; heat generated by the beating and mixing of dough; ex- and heat absorbed by mixer from atmosphere during mixing. Additional factors are the design and speed of mixer, con- . eistency, kind and mass of dough. Data Used in Calculations: 1 bbl. flour = 200 lb. Heat of hydration " 6.5 Btu per lb of flour. Specific heat of flour = 0.42 Btu per lb. Water is 65% of weight of flour. Flour is 65% of batch. Sponge is 60% of batch. Total motor output is converted to heat in the mixer. In fermenting rooms recentpractice is to use direct radiation for heating, atomizing sprays lor humidifying, and gravity con- * Integration in Table 1 ts drawn from man; sources. See bibliography at end of chapter. 681