1. Objectives - Air Distribution Systems -Diffuser selection -Duct design Reading Assignment: Chapter 18

2. Near Human Body flow Diffuser flow https://www.youtube.com/watch?v=LFgJn75LhGc https://www.youtube.com/watch?v=5e3gixnmNzM https://www.youtube.com/watch?v=550fA39PpbQ

3. Computational Fluid Dynamics

4. Contaminant concentration in a kitchen CFD in Air Distribution Design

5. Buoyancy driven flow: Example of airflow in a stairway Heater (radiator)

6. Forced driven air flow Diffusers Linear diffusers Grill (side wall) diffusers Horizontal one side Vertical

7. Diffusers types swirl diffusers wall or ceiling floor Valve diffuser ceiling diffuser

8. Low mixing Diffusers Displacement ventilation

11. 18.7

12. Diffuser Selection Procedure Select and locate diffusers, divide airflow amongst diffusers V = maximum volumetric flow rate (m 3 /s, ft 3 /min) Q tot = total design load (W, BTU/hr) Q sen = sensible design load (W, BTU/hr ) ρ = air density (kg/m 3, lbm/ft 3 ) Δt = temperature difference between supply and return air (°C, °F) Δh = enthalpy difference between supply and return air (J/kg, BTU/lbm)

13. Find Characteristic Length (L)

14. Indicator of Air Distribution Quality ADPI = air distribution performance index Fraction of locations that meet criteria: -3 °F < EDT < 2 °F or -1.5 °C < EDT < 1 °C Where, EDT = effective draft temperature Function of V and Δt (Eqn 18.1) EDT=(t local -t average )-M(V local -V average ), M=7 °C/(m/s) ADPI considers ONLY thermal comfort (not IAQ)

15. Ideal and Reasonable Throws

16. Select Register Pick throw, volumetric flow from register catalog Check noise, pressure drop

17. Summary of Diffuser Design Procedure 1)Find Q sensible total for the space 2)Select type and number of diffusers 3)Find V for each diffuser 4)Find characteristic length 5)Select the diffuser from the manufacturer data

18. Example 18.3 Q tot = 38.4 kBTU/hr Δh = 9.5 BTU/lbm a

19. Pressures Static pressure Velocity pressure Total pressure – sum of the two above

20. Relationship Between Static and Total Pressure

21. Total and static pressure drops are proportional to square of velocity Plot of pressure drop vs. volumetric flow rate (or velocity) is called system characteristic Duct Design

22. Frictional Losses

23. System Characteristic