Dometic 39626.506, 39726.506 REGISTERS, DIFFUSERS, and Grille SELEC- Tion, Room AIR Distribution

INSTALLATION INSTRUCTIONS

4.Sudden contractions in air stream

5.Sudden expansions in air stream

2.1.7REGISTERS, DIFFUSERS, AND GRILLE SELEC- TION

One of the most important considerations in designing a conditioning system is the selection of the registers, diffus- ers and grills. Even though a system delivers the required amount of conditioned air to the room, discomfort results if the air is not satisfactorily distributed. Achieving good air distribution is as much an art as it is a science. Careful consideration must be given to the design of the air distribu- tion system. A forced air system is only as efficient as its air delivery components.

Whenever a jet of conditioned air is admitted into a room it affects all the air within that room. Movement of the supply air induces adjacent room air to move along with it. This process of the supply air dragging along the room air and setting it in motion is called “entrainment” of the room air. As the room air mixes with the supply air, the temperature difference between them is reduced. This effect is even more pro- nounced with a spreading jet than with a non—spreading jet because of the greater surface area.

2.1.8 ROOM AIR DISTRIBUTION

The final evaluation of air distribution in a space is determined by the occupants’ comfort level. In general, a person is thermally comfortable when their body heat loss just equals their heat production.

During cooling, currents carry warm air up the wall to ceiling level, and stratification forms from the ceiling down. The solution is to project cool air into this region near the ceiling.

Performance of any supply outlet is related to initial velocity and area. As it leaves the outlet, an air jet becomes a mixture of supply and room air, expanding due to the induction of room air.

The buoyant forces with non-isothermal jets cause the jet to rise during heating and drop during cooling. If the jet is projected parallel to and within a few inches of a surface, the jet performance will be affected by the surface, which limits the induction on the surface side of the jet. This creates a low pressure region between the jet and the surface, which draws the jet toward the surface. In fact, this effect will prevail if the angle of discharge between the jet and surface is less than 40°. The surface effect will draw the jet from a ceiling outlet to the ceiling. Surface effect increases the throw for all types of outlets and decreases the drop for horizontally projected air streams.

The air stream from the outlet tends to “hug” the surface. As a matter of fact, this characteristic is almost essential for good comfort air conditioning. Therefore, rather than trying to direct the air away from surfaces, the surfaces should be used intentionally. Note that where the surfaces are used

most effectively, the high velocity portions of the air stream have less tendency to enter the occupied zone of the space.

2.2HOW ROOM AIR MOTION IS RELATED TO OUTLET PERFORMANCE

The room air near the supply air stream is entrained by the air stream and, in turn, is replaced by other room air. The room air always moves toward the supply air. The only general statement that can be made regarding room air motion and the number of air changes is that 8 to 10 air changes per hour are required to prevent formation of stag- nant regions.

For most applications, a better approach is to supply air in such a way that the high velocity air stream from the outlet does not enter the occupied zone. It is practical to consider the region within 12 inches of the walls as outside the occupied zone as well as the region above the heads of the occupants.

Supply air should be spread in a thin layer over the surfaces, to surround the occupied zone with conditioned air. Air within the occupied zone will then move toward the total air stream, the mixture of primary and room air. The room air carries the load with it into the air stream and room conditions are maintained by constant mixing of room and supply air.

!WARNING

Improper installation may damage equipment, could endanger life, cause serious injury and/ or property damage.

2.3SPECIFICATIONS & REQUIREMENTS

Since it is necessary to install all or part of the duct work in the ceiling, sidewall or floor.

CAUTION

It is the responsibility of the R.V. manufac- turer to assure that structural integrity is main- tained throughout the coach.

The manufacturer should review each floor plan to determine proper duct design and register location.

The Dometic Product Engineering and Application depart- ments are available for recommendations and suggestions.

If the conditioned air is to be discharged from the ceiling area, the minimum roof cavity thickness for proper installation measured between the roof and ceiling structure is 4 inches. This does not include space required for insulation of the ductwork.

The air conditioner was designed to allow flexibility for layout of duct work and the types of registers employed. To ensure air conditioner maximum performance, certain parameters must be adhered to. Refer to Figures 3.4 for duct sizing and grill placement

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