Supply Registers Diffusers and Return Grilles

^ Air for heating, cooling, and ventilation is supplied through registers and diffusers (Fig. 24-13). Grilles are rectangular openings with fixed vertical or horizontal vanes or louvers through which air passes. A register is a grille with a damper directly behind the louvered face to regulate the volume of airflow. The selection and placement of supply and return openings requires architectural and engineering coordination, and has a distinct effect on the interior design of the space. Registers, diffusers, and grilles are selected for airflow capacity and velocity, pressure drop, noise factor, and appearance.

The register or diffuser that introduces air into the space should create an air pattern that maintains the desired air temperature, humidity, and motion with only minor horizontal or vertical variations. Unwanted obstructions result in uneven, ineffective delivery. Thermostats should not be in the direct line of the supply air stream, or the result will be erratic operation of the system. Room air always moves toward the outlet as it is replaced by new air. This often results in smudge marks from dirt particles in heavily used or smoky spaces. If the ceiling surface is textured, the accumulation of dirt is even heavier. This is often a problem with existing ceilings in renovation projects.

Diffusers have slats set at angles for deflecting warm or conditioned air from the outlet in various directions. Ceiling diffusers spread low-velocity air out from the ceiling. They may be round, square, rectangular, or lin-

Square ceiling diffuser

Square ceiling diffuser

Linear diffuser

The slats in diffusers deflect air in various directions.

Linear diffuser

The slats in diffusers deflect air in various directions.

Grilles are gratings or perforated screens that cover and protect an opening.

Wall register with adjustable blades to control the flow of air

Floor register controls heat loss and condensation along exterior windows and walls.

Figure 24-13 Registers, diffusers, and grilles.

Floor register controls heat loss and condensation along exterior windows and walls.

Figure 24-13 Registers, diffusers, and grilles.

ear, or may be perforated ceiling tiles. In spaces where noise control is critical, like recording or telecasting studios, pinhole perforated diffusers can provide a large quantity of low-velocity air. Flat, linear slotted diffusers are used at the base of glass doors or windows. Careless placement of curtains, flowerpots, or other objects often obstruct floor diffusers.

Sidewall registers direct air above the space, paral lel to the ceiling. Floor registers control heat loss and condensation along exterior windows and walls, and are commonly located in the floor below areas of glass. Perforated metal faceplates can be placed over standard ceiling diffusers, creating a uniform perforated ceiling. It is generally best to use a mixture of register types to accommodate both heating and cooling.

Air supply units are designed to distribute air perpendicular to the surface. The throw distance and spread or diffusion pattern of the supply outlet, as well as obstructions to the air distribution path, are considered in their placement. The throw distance is the distance a projected air stream travels from the outlet to a point where its velocity is reduced to a specified value. The air velocity and the shape of the outlet determine the throw. The spread is the extent to which projected air stream diffuses at the end of the throw. The spacing of outlets is approximately equal to their spread.

Return grilles are commonly louvered, eggcrate, or perforated designs. They may be referred to as either grilles or registers. Return grilles are connected to a duct, lead to an undivided plenum above the ceiling, or transfer air directly from one area to another.

Return grilles can be located to minimize the amount of return air ductwork. High return grilles pick up warmer air that needs less reheating. Air may circulate continuously, being warmed or cooled as needed. The slotted type of return grille is usually used in walls, and the grid type in floors. Floor grilles tend to collect dirt.

Return air inlets for heating systems are usually located near the floor and across the space from supply outlets. Return inlets for cooling are located in ceilings or high on walls to avoid removing cooled air that has just been supplied to the room. Exhaust air inlets are usually located in ceilings or high on walls, and are almost always ducted. Supply registers can also sometimes be used as return grilles.

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