1. Objectives Air Distribution Systems -Diffuser selection -Duct design

2. Air Distribution System Design Describe room distribution basics Select diffusers Supply and return duct sizing

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

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

5. Coanda effect on ceiling and walls https:// www.youtube.com/watch?v=AvLwqRCbGKY Coanda effect

6. Diffusers http://www.titus-hvac.com/techzone/ http://www.halton.com/halton/cms.nsf/www/diffusers Perforated ceiling diffuserJet nozzle diffuser Square conical ceiling diffuser Round conical ceiling diffuser Wall diffuser unitSwirl diffuser Floor diffuser Auditorium diffuser DV diffuser External louvre Smoke damper Linear slot diffuser

7. Low mixing Diffusers Displacement ventilation

10. 18.7

11. 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)

12. Find Characteristic Length (L)

13. 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)

14. Ideal and Reasonable Throws

15. Select Register Pick throw, volumetric flow from register catalog Check noise, pressure drop http://www.titus-hvac.com/utility/getfile2.aspx?fileid=8967

16. 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

17. Example 18.3 Q tot = 38.4 kBTU/hr Δh = 9.5 BTU/lbm a omission in text

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

19. Relationship Between Static and Total Pressure

20. 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

21. System Characteristic

22. Electrical Resistance Analogy

23. Frictional Losses

24. Non-circular Ducts Parallel concept to wetted perimeter

25. Dynamic losses Losses associated with Changes in velocity Obstructions Bends Fittings and transitions Two methods Equivalent length and loss coefficients

26. Loss Coefficients ΔP t = C o P v,0

28. Example 18.7 Determine total pressure drop from 0 to 4

29. Conversion Between Methods

30. Reading asignement Chapter 18 18.1-18.4 (including 18.4)