Handbook of air conditioning and refrigeration / Shan K

varies from 0.5 to 1.75 in. (13 to 45 mm). Slots are usually available in lengths of 2, 2.5, 3, 4, and
5 ft (600, 750, 900, 1200, and 1500 mm).
The capacity of return slots is also expressed in cfm/ft (L/s� m) of slot length. If a return
slot has the same configuration, slot width, and slot intensity as the supply slot diffuser, then its total
pressure loss, in in. WC (Pa), is nearly the same as the vertical projection total pressure loss of
the supply slot diffuser. Return slots are usually inner-lined with sound absorption material. This
material prevents sound transmission between two rooms via the return slots and the ceiling
plenum.
Exhaust inlets are similar to the return inlets but they often have a simpler design.
In return and exhaust inlets, air velocity decreases very sharply as the distance from the surface
of the inlet increases. This phenomenon is the major difference in airflow characteristics between a
return or an exhaust inlet and a supply outlet.
Light Troffer Diffuser and Troffer-Diffuser Slot
FIGURE 18.13 Return slots: (a) single-slot; (b) double-slot.
AIR SYSTEMS: SPACE AIR DIFFUSION 18.19
Light troffer diffuser combines a fluorescent light troffer and slot diffuser, sometimes in saddle
type, as shown in Fig. 18.14a. The slot can be used as a supply outlet or return inlet. A troffer-diffuser
slot is a combination of light troffer, slot diffuser, and return slot, as shown in Fig. 18.14b.
Light troffer diffusers and troffer-diffuser slots serve two main purposes:
1. To maintain a lower air temperature in the light troffer, which increases the luminous efficiency
of fluorescent lamps
2. To form an integrated layout of light troffer, diffuser, and return slots on suspended ceilings
In addition to these benefits, a combination of a light troffer and return slot also reduces the space
cooling load because return air absorbs part of the heat released by the fluorescent lights.
In a light troffer diffuser, surface slots are often used. Air can be discharged horizontally or vertically.
Troffers and slots are available in 2-, 3-, and 4-ft ( 600-, 900-, and 1200-mm) lengths.
To prevent the deposit of dust particles on the surface of the fluorescent tube, the light troffer
should be designed so that return air does not come in direct contact with the fluorescent tube. The
result is a high ventilation efficiency and a neat appearance.