Document Y9pKm6KL730KwvGedO4Q4QOqk

798 CHAPTER 73 inlet to tank most be arranged to minimize erosion of tank, turbulence, and aeration of water. 5. Return pumps should be sized to handle at least 120 percent ofsupply water quantity. 6. Return pump and supply water control valves or pumps should be interlocked to prevent flooding in event of return pump failure. 7. Proper air venting is extremely important because of the release ol large amounts of air dissolved in the water. BRINE PIPING Brines are used instead of water as the circulating heat transfer fluid whenever the fluid temperature in the system is below about 35 F. The entire design of low temperature sys tems, including brine piping, is a specialized field and becomes more critical and complex with decreasing operating tem peratures. (See Chapters 61 through 68.) The material pre sented herein is intended only as an introduction to the general principles involved. Recommendations and applica tion information concerning specific projects can be obtained from manufacturers of low temperature equipment or brines. A design engineer with proven experience and proficiency in this specialized field should be consulted on all such important or unusual applications. Further information on brines is contained in Chapter 20 of the 1961 Guide And Data Book. The selection of brine type is based upon consideration of the following factors: 1. Freezing point--suitable for lowest operating tempera tures 2. Process involved--open or closed piping system, Hung*? of product contamination by brine. 3. Cost and availability--quantity of make-up required. 4. Safety to operating personnel---toxic, poisonous, explosive, flammable, operating pressures. 5. Thermal performance--specific heat, density, viscosity, and film coefficient. 6. Chemical---stability and (corrosion) suitability for use with piping and system equipment material. 7. Acceptance by codes, ordinances, regulatory agencies, and insurer. Calcium chloride, sodium chloride, and ethylene glycol brines are commonly used in open systems.' Volatile brines such as methylene chloride (Refrigerant 30), methanol, trichloro-ethyleoe and trichloromonofluoromethane (Refrig erant 11) are usually applied with closed piping systems to prevent brine evaporation. The above brines are generally 1962 Guide And Data Boole suited to applications between --30 and +30 F. Volatile refrigerants such as Refrigerant 30 or Refrigerant 11 are used for temperatures below this range. All materials in the piping system, including flange gaskets, valve seats and packing, pump sods and other specialties must be compatible with the brine. Provision must be made for thermal expansion and contraction. Ordinary copper tubing and nickel steel pipe are suitable for operating tem peratures down to below--100 F. Standard steel pipe is suit able for general use above --20 F, and with special precau tion to code requirements may be used at lower temperature. Special attention should be given to providing adequate space around piping and equipment for the proper tioo of insulation. Extensions of valve bonnets, thermometer wells and other items are usually necessary to permit proper insulation. An adequate vapor seal is necessary, and special efforts should be made to obtain an adequate seal around valve bonnets, thermometer wells, and other items which pierce the vapor barrier. Piping for volatile refrigerant: brines should be installed similar to conventional refrigerant piping, kept as clean as possible, and dehydrated by evacuation before brine is charged into the system. A dosed expansion tank pressurized with dry nitrogen is usually provided to permit expansion of brine on system warm-up and maintain suitable operating pressures in the system at design temperature. Pumping head is obtained by calculating the total equival ient length of piping in the system and multiplying thi* by the friction rate for the brine type and temperature. The correct friction rate for a specific application can be obtained from brine or equipment manufacturers, or can be calculated through the use of Reynolds' number and the Darcy equa tion. Pipe friction, equipment pressure drop expressed in feet of brine, and hydrostatic lift, if applicable, are added to ob tain total system pumping head. The pump rating and motor horsepower should be based upon the particular brine being used and the actual operating temperature. REFERENCES 1 B. P. Morabito: How higher ennltng coil differentials effect system economies (ASHRAE Journal, August 1960, p. 60). * Chapter 1, Piping Design^--General (Part 3, System Design ManuaL, Comer Corp., 1961, pp. 4 and 6). * Chapter 2,-Water Piping (Part 3,.System Design Manual, Carrier Corp., 1961, p. 40). / CHAPTER 74 ODOR CONTROL Odor Removal by Ventilation, Absorption, and Adsorption; Reactivation; Activated Charcoal: Use, Quantity, Systems; Odor Most/ng: Appficcfron of Compounds, Control; Odor Modification: Air-Conditioned and Industrial Spaces, Application; Combustion: Use and life of Catalysts, Recovery of Heat DEVELOPMENT of methods to purify air has furthered will be seen, the already known standards of ventilation will the progress of air conditioning. Whether air is condi serve to determine the volume of recirculated air to be puri tioned in order to enhance comfort, raise production efficiency,fied. or extend food preservation, the quality of the air--its free Because many vaporous and gaseous impurities manifest dom from contamination--has come to be regarded as of themselves as odors or are recognized by the olfactory sense, equal importance with its temperature and relative humidity.1 the methods for their elimination have acquired the common Air polluting substances are divided into two kinds--those designation deodorization or odor control Before proceeding which are suspended, like dust, soot, and smoke; and those to the application of air purification, therefore, an under consisting of gases and vapors, which are in the form of in standing of both the properties of odors and our reaction to dividual molecules. Elimination of the former, or suspended, them b essential. The reader is referred to Chapter 10, Air substances is accomplished by filtration which is discussed Contaminants, in the 1961 Guide And Data Book for a dis in Chapter 48 of the 1961 Guide And Data Book. This chap cussion of the bftfiir properties and principles of odors. ter therefore, is devoted particularly to the mpjng and procedure for preventing or controlling the accumulation of ODOR REMOVAL BY VENTILATION air-entrained vaporous and gaseous impurities or odors within Ventilation is an effective mftana of removing the con an enclosure. taminated air in an enclosed space by dilution. In thia process The first important consideration in approaching a prob the vitiated air containing objectionable gaseous odors, ir lem of air purification is to determine whether the source of ritants, particulates that obscure vision, and toxic matter are air contamination lies within or outside the enclosure. If out replaced by outdoor air. As shown in Big. 5 of Chapter 10, ride the enclosure, as is frequently the case in congested or Air Contaminants, of the 1961 Guide And Data Book, an industrial areas, the usual solution is the removal of the con outdoor ventilation rate of only 4 cfm per person is sufficient taminants from tiie air entering the space. It will be obvious to meet the requirement for oxygen supply and carbon di that this cannot be accomplished unless the air supply is con oxide removal.1 It has been shown that the carbon monoxide trolled and purified at the point of entry. Also, the volume of concentration in smoking rooms is in general too nudl to have tir to be supplied and purified must, usually, be adequate at any known effect. It b usually less than 5 ppm at the breath least to maintain a positive inside pressure sufficient to ing zone as compared to a maximum allowable concentration counteract any uncontrolled infiltration of contaminated air. of carbon monotide of 100 ppm for exposures of 8 hours a day.1 When the source of contamination is confined to the inside, Air b required in excess of tins amount to provide for dilution as is more generally the case in occupied enclosures, two al of body, cigarette smoking, cooking, or other odors. If the ternative solutions are available. The objectionable accumula person b active, more air b required to remove generated tion of air-entrained impurities may be controlled by ventila body odors than if the person b sedentary. The amount of tion--i.e., by continuous dilution with outside air--or by air to remove such odors is a function of the cubic feet of continual elimination of the impurities generated within the space occupied per person. Ventilation requirements for ac enclosure. When the space is not air conditioned (heated or ceptable conditions will normally foil between curves C and IX, cooled), the first solution is ample and practicable, if the above mentioned Fig. 5. These curves present limitations outdoor air is of suitable purity. When, however, the enclosure based on research. They indicate a requirement range of 20 a air conditioned or heated, the cost of conditioning the out- to 28 cfm of air per person to reduce to an acceptable level door dilution air is often considerably greater than that of objectionable body and smoking odors for a population den eliminating the internally generated impurities. Elimination sity of 150 cubic feet per person. At 300 cu ft of space per be obtained by the same process that would be required person, the ventilation requirement ranges between 12 and 18 to purify contaminated outdoor intake air except that it is cfm per person. applied instead to indoor air in recirculation. Therefore, as These parameters present what may be considered the 799