Handbook of air conditioning and refrigeration / Shan K

18.36 CHAPTER EIGHTEEN
FIGURE 18.22 Layout of slot diffusers for a large open office in Example 18.1. All dimensions in feet.
Supply temperature differential 15°F (8.3°C)
Sound level NC 40
Cooling load density in perimeter zone 50 Btu/h� ft 2 (158 W/m 2 )
Linear density of heating load 300 Btu/h� ft (288 W/m)
Design a space air diffusion system for this office for year-round operation using a VAV system.
Its minimum supply volume flow rate is 50 percent of the design volume flow at part-load operation.
The ceiling plenum is used as a return plenum.
Solution
1. For a large, open office using a VAV system, a space air diffusion system of mixing airflow
pattern using ceiling slot diffusers is a suitable choice because of its good surface effect and wider
T 100/L (T 0.5/L) range.
2. For the perimeter zone, the overhead two-way two-slot diffuser should be located on the suspended
ceiling parallel to the external wall and window glass. One of the slots should discharge
downward toward the window glass. The space between the slot diffusers and the window glass is
1 ft (0.3 m). Another slot discharges horizontally inward from the window glass.
3. In Table 18.3 the range of T 100/L for slot diffusers having ADPI � 80 percent at a load density
of 50 Btu/h� ft 2 is between 0.3 and 0.95. Considering the reduction of supply volume flow rate
at 50 percent load, select a T 100/L ratio around 0.7. Because the characteristic length L in the
perimeter zone is L � 15 � 1 � 14 ft, the required throw for the slot diffuser in the perimeter zone