Carrier 37HS Ð Consider Unit Combinations And Run, Ð Staggered Units, Ð Unit Spacing

STAGGER SPACING Ð A frequently used layout method is to stagger the units. This arrangement gives good cover- age, solves the problem of drafts when units blow at each other, and is low cost. It also gives good ¯exibility for future partition changes. (Fig. 17.)

Fig. 17 Ð Staggered Units

MAXIMUM UNIT SPACING Ð Interior zones use less air, as low as 0.4 to 0.6 cfm per sq ft. Using the large capacity 37HS4 unit at 250 to 350 cfm each may cause units to be too widely separated. This results in poor coverage and poor air distribution.

A good solution is to use a larger number of lower ca- pacity 37HS2 units at 150 to 190 cfm each.

The maximum distance between units parallel to each other (blowing at each other) can and should be fairly great, 25 to 45 ft. (See Tables 4 and 5.) But the maximum distance be- tween the ends of the units in the same row must be more limited for good coverage.

The unit will effectively cover a strip whose width is 3 to

4 times the unit's length. A 4-ft unit would therefore cover an area whose width is 12 to 16 ft (maximum). See Fig. 18.

The high induction ratio of the Moduline diffuser keeps total room air motion up to acceptable levels when the cfm per sq ft is low.

Step 3 Ð Consider Unit Combinations And Run-

Out Duct Ð When the preliminary office layout is com- plete, the trunk or main duct can be laid on the ¯oor plan. We are now ready for positioning the units in the space ac- cording to the load calculations and the design of the run-out ducts.

The zone load calculation provides the cfm requirements for each space. Using those requirements and the ceiling lay- out, the unit location and run-out can be determined. Figure 19 shows a single Moduline unit located on the grid line in the approximate center of the space. Figure 20 shows mul- tiple units in an air series located in similar fashion.

RECOMMENDED UNIT COMBINATIONS Ð Tables 6-8 list the recommended combinations of Moduline terminals. Each model (size) of Moduline terminal is shown in com- binations of 2, 3, 4 and 5 plenum sizes. To illustrate the use of the tables, consider the 37HS2 for a space requiring 550 cfm. Three units in air series will provide the capacity. (Note that 550 cfm is below the max cfm limit of 660 shown in Table 7.) Six combinations of 37HS2 units are available; all will produce a good installation. However, some factors in- ¯uence the choice:

If it is desirable to have common plenum sizes throughout the space, the choice will be three 9 x 9-in. plenums.

The lowest inlet velocities will result in the least variance of discharge cfm among the 3 units on one control. If this is a consideration, the choice would be three 11 x 11- in. plenums.

The lowest cost choice would be 9- x 9-in., 9- x 9-in., and 7- x 7-inches.

If the requirement of the space is for maximum cfm from the unit combination, one of the larger plenum combinations would be favored.

Conversely, a conservative design with small cfm per unit can use the smaller plenum sizes.

The selection of plenum sizes will not affect the sound level of the space; there is no measurable difference in the recommended plenum combinations.

NOTE: The listing of recommended air series combinations does not indicate that one controller will always handle the combination; in some cases, a second controller may be re- quired. Refer to Determine Controller Location section, page 37.

Table 9 provides an overall limitation on cfm in the inlet collar of units in air series.

Fig. 18 Ð Unit Spacing

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