Document zQKyb4YZGMbmLb7pRgQwmdeX7

HEATING VENT/LAT/NC AIR CONDITIONING CUIDE 1943 CHAPTER 30. FANS is to set up a rather high static pressure against which the fan must operate. In such cases the sound level at the fan may be too high to be neglected and special sound treatment of the installation must be con sidered. When a fan is operating against higher pressures it should be located in a room either removed from the occupied areas, or in a room which has been acoustically treated to prevent sound being carried through the walls to adjoining spaces. The fan should be mounted on a resilient base along with its driving motor to absorb any noise or vibration which might be transmitted to the floor and thence to the building structure. All ducts should be connected to fans with unpainted canvas, or other flexible material, to prevent any vibrations being transmitted to the duct work. Ducts leading into the fan room or from the fan, should be acoustically treated on the interior and in special cases, should be pro vided with sound traps or filters. Many ventilating systems encounter noises which are connected with the fan in no way. Noises due to high duct velocities, abrupt turns, grilles, etc., may be present. Treatment of such.problems is covered in Chapter 33. FAN DESIGNATIONS Facing the driving side of the fan, blower, or blast wheel, if the proper direction of rotation is clockwise, the fan, blower, or blast wheel will be designated as clockwise. If the proper direction of rotation is counter-clockwise, the designation will be counter clockwise. (The driving side of a single inlet fan is considered to be the side opposite the inlet regardless of the actual location of the drive.)1 This method of designation will apply to all centrifugal fans, single or double width, and single or double inlet. Do not use the word hand but specify clockwise or counter clockwise. The discharge of a fan will be determined by the direction of the line of air discharge and its relation to the fan shaft, as follows: Bottom horizontal: If the line of air discharge is horizontal and below the shaft. Top horizontal: If the line of air discharge is horizontal and above the shaft. Up blast: If the line of air discharge is vertically up. Down blast: If the line of air discharge is vertically down. All intermediate discharges will be indicated as angular discharge as follows: Either top or bottom angular up discharge or top or bottom angular down discharge, the smallest angle made by the line of air discharge with the horizontal being specified: In order to prevent misunderstandings, which cause delays and losses, the arrangements of fan drives adopted by the National Association of Fan Manufacturers and indicated in Fig. 7 are suggested.. If double width, double inlet fans are selected, care must be taken that both inlets-have the same free area. If one inlet,of a fan is obstructed more than the other, the fan will not operate properly, as one half of the wheel will deliver more air than the other half. The backward curved and double curved types with backward tip operate satisfactorily in double or in parallel operation. FAN CONTROL In some heating and ventilating systems it is desirable to vary the volume of air handled by the fan, which may be accomplished by a number of methods. Where the change is made infrequently, the pulley or sheave `Recommendations adopted by the National Association of Fan Manufacturers. 587