Document QJYDwOa9dM00qEMaxjQq3jYNo

Heating Ventilating Air Conditioning Guide 1938 and thus provides a larger plenum chamber. Fig. 3 illustrates a complete residence fan furnace installation showing location of fan, furnace, filters, plenum chamber-and method of take-off of warm air pipe. FANS AND MOTORS Centrifugal type fans are most commonly used, and these may be equipped with either backward or forward curved blades. Low tip speed is desirable for the elimination of air noise, especially where forward curved blades are Used. Motors may be mounted on the fan shaft or outside of the fan with belt connection. Multi-speed motors or pulleys are desirable to provide a factor of safety and to allow for increased air circulation. For additional information on fans and motors, see Chapters 27 and 38. SOUND CONTROL Special attention should be given to the problem of noise elimination. The fan housing should not be directly connected with metal, either to the furnace casing-or to the return air piping. It is common practice to use canvas strips in making these connections'. Motors and their mountings must be carefully selected for quiet operation. Electrical conduit and water piping must not be fastened to, nor make contact with fan housing. The installation of a fan directly under a cold air grille is not recommended on account of the noise objection. See also Chapter 30. AIR WASHERS AND FILTERS Washers for residence systems may be provided in separate housings to be installed on the inlet or outlet side of the fan, or they may be . integral with the fan construction. They operate at water pressures of from 10 to 30 lb and use two or more spray nozzles for washing and humidification. The sprays should be adjusted to completely cover the air passages. Washers are usually controlled by solenoid valves wired in parallel with the fan motor. The water supply may, in turn, be controlled by a humidity-controlling device located in one of the living rooms, so that the washer will operate at all times when the fan is in operation, unless the relative humidity should rise beyond a desirable percentage. Washers used in connection with commercial or heavy duty plants should be a regulation type of commercial washer. / There are many satisfactory types of'filters on the market. These include dry filters, viscous filters, oil filters and other types, some of which must be cleaned, some of which must be cleaned and recharged with oil, and some of which are inexpensive and may be discarded when they become dirty, and replaced with new ones. The resistance of a filter must be considered in the design of the system since the resistance rises rapidly as the filter becomes dirty, thus im pairing the heating efficiency of the furnace, in fact, endangering the life of the furnace itself. Manufacturers' ratings of filters must be carefully regarded, and ample filter area must be provided. Filters must be replaced or cleaned when dirty. See also Chapter 26. 396 Chapter 20. Mechanical Warm Air Furnace Systems AIR DISTRIBUTION The conditions of comfort obtained in a room are greatly influenced by the type of register used and the locations of the supply registers and return grilles. In general it has been found that changes in the type, air velocity, and location of the supply register affect the room conditions much more than the changes in the location of the return grilles. Due to the economic considerations involved, it is common practice to locate the supply openings on the inside walls of a residence and the return openings nearest the greatest outside exposure. Many designers prefer, however, to locate the supply registers so that the warm air from the registers blankets a cold wall, and mikes with the cold air dropping off from the exposed walls. This may be accomplished either by the use of a supply register located on the exposed wall with warm air blowing into the room, or by the use of a supply register placed close to an outside wall in such a position that the warm air sweeps the cold wall surface. The ducts leading to supply registers which are located on the exposed walls should be adequately insulated to reduce the heat loss from the ducts. Register and Grille Openings Supply registers located in the floor are effective, but as they require frequent attention to keep them clean they should be avoided where another effective register location can be found. Tests conducted in the Warm Air Research Residence2 have indicated that excellent results are obtainable with the use of a deflecting-diffuser type-of baseboard register which throws the air downward toward the floor and diffuses the air at the same time. Unless registers located in the baseboard are well proportioned *Loc. Cit. Note 1.