Document gjpYQgxqdXJRgK9zxrRDXvOJ

400 . CHAPTER 22 1946 Guide Residence have indicated that comparable results are obtainable with either high side wall or baseboard registers, if proper registers and air velocities are selected. Baseboard registers should be of a deflectingdiffuser type which throw the air downward toward the floor and diffuse it at the same time. For baseboard registers air temperatures under 125 F and air velocities over 500 fpm should be avoided as they may cause drafts. High side wall registers must be of such type that the air is delivered horizontally or in a slightly downward direction, and must be so located as to avoid impingement of air on ceiling or wall. Directional flow diffusing type should be used to insure best results. Register air velocities Fig. 1. Recommended Type of Base- Fig. 2. Recommended Type of High BOARD AND Low SlDEWALL' REGISTERS3 SlDEWALL REGISTERS6 Vertical bars with adjustable deflection, or fixed vertical bars with deflections to right and left not exceeding about 22 deg. For low sidewall location; the deflection for horizontal, multiple'valve, registers should not exceed 22 deg. For baseboard locations, the deflection for horizontal,' multiple valve, registers should not exceed about 10 deg. ^Horizontal valves, in back or front, to give downward deflections not to exceed from 15 to 32 deg;~ should be such that the air stream carries to the opposite exposure. Velocities under 500 fpm are not recommended. Basic rules for the location and selection of registers are given in Section C of the Code and Manual (Textbook Section 7) of the National Warm Air Heating and Air Conditioning Association. Registers should be well proportioned and decorated to harmonize with, the trim. Air supply registers'should be equipped with dampers and all registers should be sealed against leakage around edges. The register types shown in Figs. 1 and 2 have been recommended as standard by the National Warm Air Heating and Air Conditioning Association. Velocities through registers may be reduced by the use of registers larger than the connecting ducts. Diffusers should be used to spread the air uniformly over the register face. Return air grilles may be located in hallways, near entrance doors, under windows, in exposed corners, or inside walls, depending on location of supply registers. Baseboard returns are preferable to floor grilles. Dampers Suitable dampers for air direction or volume control are essential to any trunk or individual duct system. Special care must be used in the design . Mechanical Warm Air Systems 401 of any system to avoid turbulence and to minimize resistance. Sharp elbows, angles, and offsets should be avoided. Three types of dampers are commonly used. Volume dampers are used to completely cut off or reduce the flow through pipes. Splitter dampers are used where a branch is taken off from a main trunk. Squeeze dampers are Used for adjusting the volume of air flow and resistance through a given duct. It is essential that a damper with positive locking device be provided for each main or duct branch. Labels placed on ducts should indicate the room being served. Damper positions should be marked for summer and winter operation, and to avoid tampering. Ducts The ducts may be either round or rectangular in cross section. The radii of elbows should preferably be not less than one and one-half times the pipe diameter for round pipes, or the equivalent round pipe size in the case of rectangular ducts. Warm air ducts'passing through cold spaces, or where located in exposed walls, should have to 2 in. of insulation. Special attention should be given to the problem of noise elimination. The metal duct connection to and from the furnace casing and fan housing should be broken by strips of canvas. Motors and mountings must be carefully selected for quiet operation. Electrical conduit and water piping must not be fastened to, nor make contact with fan housing. Installation of a fan directly under a cold air grille is usually not recommended. STANDARD COMBINATIONS OF PARTS The combinations of parts selected as a standard by the National Warm Air Heating and Air Conditioning Association are shown in Tables 1 and 2. A method for selecting these combinations is indicated in the section entitled Simplified Method of Designing Domestic Forced-Air Systems. AUTOMATIC CONTROLS Air stratification, high bonnet temperatures, excessive flue gas tem peratures, and. heat overrun or lag in a properly designed system can be largely eliminated through proper care in the planning and installation of the control system8. Controls which are considered desirable for this system are: 1. A thermostat located in a living room where maximum fluctuation in temperature can be expected, in order to secure frequent operation of fans, drafts, and burners. The thermostat location should not be on an outside wall, in a bed room, bath room or sun room, or in a location where it will be affected by direct radiant heat from the sun or from a fireplace, or by direct heat from any warm air duct, register or chimney. 2. A fan switch control located in the bonnet to start blower operations at tempera tures between 110 and 130 F, and to stop the blower at about 25 to 30 F below the cut-in point. The lower settings are used for high side wall register installations, and the higher settings for baseboard register installations. For most satisfactory results these settings should be as low as is feasible., 3. A protective high limit switch located in the bonnet to stop the system independently of the thermostat if the bonnet-temperature exceeds 175 F. 4. On oil and gas burner installations, a protective control should be included which will stop the system if the fire is extinguished or if there is a failure of the ignition system. 5. On automatic stoker installations, a control is usually included which will start the operation regardless of thermostat settings whenever the bonnet temperature indicates that the fire is dying, or a time interval contactor is used that will start the stoker to run a few minutes out of each hour. ... 6. A humidistal to regulate the moisture supplied to the rooms, located either in one of the rooms or in the main return duct near the furnace.