Document 70Jq22p5K9yRkMM1VVwbQjV7a

'-1 Heating Ventilating Air Conditioning Guide 1939 ISrV Chapter 27. Fans Justification for liberal power provision exists also in the possib`1 of varying demand due to changes in ventilation requirements, inten'k? of occupation, and weather conditions. slv V * In selecting fans for quiet operation in public buildings: a. Should the outlet velocity of the fan be limited? b. Should the tip speed of the fan be limited? aTnhdeamrd__o__Ttivees_ tJp__Co__ow__d_e_e_r___of__of__rfaDnsisschaonudld be determined PronelW in ill Oat/-wbUirfAUSannCcCe wWiitth it. -gMT ' . BRUe^cuai.suseceo--aanllsllidcceoormmedmmeennrroocciiiisasayvll fIiaaiffnntssthheoeoppffeeaarrnnaattwiiwnnegegrreeaattttoopprrdeedississssccuuhhrraeearssrggesseuuddiiutiairiruebeiclceettllyyfoirinntItt.hoo..iSstthhceelasrrosoooommf,,waaonnrddk Standard Test--Co*--de1 tf.o..r,.1DiscA_a_n__d__P_r_oPpe. lleerr F^ ans, CCeennttrriiffuuggaall FFaannss aanjri 'IBB' k\"use the duct system omn tmhe fmanu discharge .is.. depe--n--d-ed up--on t-o---a--b--s--o-r-b---a---r-e--a-sonable Blowers, as adopted by the American Society of Heating and Ventni " ''.n"eScPa"T 0f..fan nois--e, it is adeTOs;irraaVbiIl<e. tno have a moderate run of duct work with some bends ^elbows included as sound deadeners. Where this duct is of necessity very short, the latino Engineers and the National Association of Fan Manufacturers vlet velocity must be kept down to the lower limits recommended in this chapter or Fans may be driven by electric motors, steam engines (either horizontal or vertical), gasoline or oil engines, and turbines, but as previously stated |Utl an efficient sound absorber must be used. The experience of the engineer must be 'Srguide in determining the allowable outlet velocity in each individual case. the drive commonly used is the electric motor. j- speed should not ordinarily be limited, because different types of fan blades have |(!t ntirely different allowable tip speeds for quiet operation. A fan having a backward blade at the tip can run at much higher tip speed than can a forward curved or a straight REFERENCES blade fan, with the same degree of quietness. Mine Ventilation, by J. J. Walsh (A.S.H.V.E. Transactions, Vol. 23, 1917, p, 659) Fan Blower Design, by H. F. Hagen (A.S.H.V.E. Transactions,Vol. 28,1922, p. 175} The Specific Characteristics of Fans, by M. C. Stuart and J. B. Lusk (A.S.H.V.E Journal Section, Heating, Piping and Air Conditioning, September, 1936, p. 507). ' Non-Dimensional Fan Characteristics, by H. Carlton Moore (A.S.H.V.E. Journal Section, Healing, Piping and Air Conditioning, September, 1937, p. 580). Section X, A.S.H.V.E. Code of Minimum Requirements for the Heating and Venti lation of Buildings (Edition of 1929). Coal Miners Pocket Book. Constructive Mechanism and the Centrifugal Fan, by George D. Beals. Fans, by Theodore Baumeister, Jr. Fan Engineering, Buffalo Forge Company. Heating, Ventilating and Air Conditioning, by Harding and Willard, Revised Edition 1932. Mechanical Engineers' Handbook, by Kent. Mechanical Engineers' Handbook, by Lionel S. Marks. The Centrifugal Fan, by Frank L. Busey. The Fan, by Charles H. Innes. The Theory and Performance of Axial-Flow Fans, by L. S. Marks and J. R. Weske. Theories and Practices of Centrifugal Ventilating Machines, by D. Murgue, trans lated by A. L. Stevenson. 3 Is a direct connected or a belted fan preferable in public building work? Where space is at a premium, direct connection is best. Next in space economy is the short V-belt drive. The flat belt drive fan requires the greatest floor space. In this dass of work, pressures are usually so low that even with the high speed fans the motor cost is greater for direct connected units than for belt drive fans. 4 a. What type fans are used in industrial work? b. What outlet velocity is suitable? a. All of the centrifugal types are suitable; the disc and propeller types are suitable for low pressure work, or they are often used as exhausters. i. The outlet velocities on fans for industrial work can be much higher than can those in public building work, where quietness is essential. Fans should be selected with outlet velocities as recommended in this chapter, using the upper limit of velocities. 5 Are direct connected or belted fans preferred in industrial work? In industrial applications, fans are often advantageously direct connected to motors. The pressures are usually high enough to use standard motor speeds. The high speed types of fans have limiting horsepower characteristics so that little margin in power must be provided in the driving motor. Belted fans may be used, but where high power is required a special arrangement is often necessary for shaft and bearings on account of the weight of the sheave and the belt pull. PROBLEMS, IN PRACTICE 1 What information must be supplied to the manufacturer when ordering a centrifugal fan? . Size of fan (catalog number). . Type of fan. c. Width of fan (single or double). d. Number of inlets (single or double). e. Fan performance and kind of application. /. Direction of rotation (clockwise or counter-clockwise). g. Direction of discharge (top horizontal, down blast, etc.). h. Drive arrangement (see Fig. 6). . Style of housing (full, three-quarters, etc.). 562 6 A forward curved multiblade fan which requires 5.4 bhp is delivering 22,800 cfm at 70 F against a resistance pressure of 1 in. of water at an outlet velocity ofl440fpm: a. What is the static efficiency? b. What is the total efficiency? 0. 66.3 per cent (see Equation 2). 1. 74.5 per cent (see Equation 3). 7 I If the above fan has a 54-in. diameter wheel and operates at 193 rpm, will It be suitable for a ventilating installation where a minimum of noise is desirable? yes. The tip speed will be 2720 fpm and this, together with the 1440 fpm outlet velocity, falls within the limits given in Table 1 for 1-in. resistance pressure. ? 4 What objectionable feature is inherent in the ordinary propeller fan when it is operating at high resistance pressures? It must operate at a high speed with consequent noise. 563