1. Presented by Dan Int-Hout, Chief Engineer ASHRAE Fellow Life Member
Basics of Room Air
Distribution and ADPI
Presented by Dan Int-Hout, Chief Engineer
ASHRAE Fellow Life Member

2. Agenda Diffuser performance terminology.
Thermal comfort and ASHRAE Air Diffusion Performance Index (ADPI).
LEED V3 & 4 air distribution prerequisites.
Selecting air distribution components and system parameters for effective air mixing.
ASHRAE Standard Thermal Comfort and determining optimum occupant comfort strategies.
Predicting end use acoustic environments.
Ventilation requirements of ASHRAE Standard and air distribution component selection.
Objectives 2

3. Terminology

4. Understanding the Terminology
Primary Air Jets - Air jets from free round openings, grilles, perforated panels, ceiling diffusers and other outlets can be defined by three variables.
Throw
Drop
Spread
As air leaves a grille, it drops, spreads and entrains room air. We define this phenomena using several terms. 4

5. Understanding the Terminology
DROP
THROW

6. Understanding the Terminology
Spread - is defined as the divergence of the airstream in a horizontal or vertical plane after it leaves the outlet.
50 fpm
22.5
Typical 100 fpm
22.5
150 fpm

7. Understanding the Terminology
Coanda Effect - a negative or low pressure area is created between the moving air mass and the ceiling at or near the supply air outlet. This low pressure area causes the moving air mass to cling to and flow close to the ceiling surface and increases the throw.
Coanda Effect

8. Understanding the Terminology
Understanding primary air jet variables enables:
Accurate prediction of room air flow.
Improvement of thermal comfort.
Proper selection of grilles, registers and diffusers.
Adherence with ASHRAE Ventilation Standard as a LEED PREREQUISITE. 8

9. Understanding the Terminology
The Basis of Catalog Performance Data
Throw – The horizontal or vertical axial distance an airstream travels after leaving an air outlet, usually assumes a surface adjacent to the air outlet.
Pressure – Can be total pressure or static pressure.
Sound – Can be either NC or Octave Band data. 9

10. Throw
Throws are cataloged for 150, 100 and 50 fpm terminal velocities.
Throws should be selected so that jets do not collide, but have sufficient projection for the area to be served.
150fpm
100fpm
50fpm
150 short throw
50 long throw
7 – 8 – 12 10

11. Pressure
Pressure – Air outlet pressure data is required to properly size the air delivery system within a building.
Static Pressure – The outward force of air within a duct, measured in inches of water column.
Velocity Pressure – The forward moving force of air within a duct, measured in inches of water column.
Total Pressure – The sum of the velocity and static pressures, expressed in inches of water column and can be obtained by use of a pitot tube.
PT = PV + PS 11

12. Sound
Sound levels reported for diffusers are conducted in accordance with ASHRAE Standard 70.
Catalog sound data assumes 10 diameters of straight duct.
Room absorption is assumed to be 10 dB in all bands.
In practice however, room sound levels are probably 5 NC higher than reported. 12

13. Non-Inductive Air Distribution Laminar & Radial Flow Outlets
Laminar Flow
Radial Flow
Hospital Operating Suites
Hi-Tech Electronics and Other Industrial Applications
Clean Rooms
Laboratories

14. Well Mixed, High Induction Diffusers
Commercial Office Spaces
High Velocity Jets
Long Throw
Designed to Mix in Zone
PLQ-R
1400
Prism

15. Air Distribution, Poor Pattern
IMPROPERLY ADJUSTED/SELECTED DIFFUSER
T-STAT

16. Air Distribution, Poor Pattern
Question: Who is responsible for adjusting the pattern controllers in a linear slot diffuser?
Answer: Apparently, no one.
My observation: Almost all linear slot diffusers are either set, or ignored, to blow down!
Who should adjust slots?
The installing contractor – It is the specifying engineer’s responsibility to state who is to adjust the air outlets they specify.

17. Air Distribution, Good Pattern
PROPERLY ADJUSTED/SELECTED DIFFUSER
T-STAT

18. Thermal Comfort ASHRAE Standard 55 mandates a maximum 5.4°F
vertical temperature stratification in Occupied Zone
Velocities within the occupied zone shall be ≤ 50 FPM 3’ 3’
Floor to Occupants’ Head Level
(3.5 ft. for seated, 6 ft. for standing occupants)
ASHRAE Standard defines the occupied zone in regards to thermal comfort. 18

19. Understanding ADPI

20. ADPI
ADPI is the percentage of points within the occupied zone having a range of effective draft temperatures of -3° to +2° of average room temperature at a coincident air velocity less than 70 FPM.
ADPI is essentially a measure of the degree of mixing in zones served by overhead cooling systems.
When air distribution is designed with a minimum ADPI of 80%, the probability of vertical temperature stratification or horizontal temperature non-uniformity is low and conformance with ASHRAE Standard 55 (Thermal Comfort) requirements is high.  
ADPI does not apply to heating situations or ventilation-related mixing.

21. ASHRAE Fundamentals Chapter 20
ADPI selection using T50 / L was developed in the ‘60s where L is the distance to the nearest wall or halfway to the nearest air outlet. See Fundamentals Chapter 20 table 2 for more details on definition of L.
A relationship was found between 50 FPM/min isothermal throw and cooling throw, and was built into the selection charts included in ASHRAE Fundamentals, Chapter 20, table 3.
Using this table engineers can assure clients that diffuser selections will provide acceptable mixing and air change effectiveness.

22. Perforated 24X24, 10” inlet, 4 way, 20° Delta-T
Spacing for 80% ADPI 16 14
CFM
NC=35 12
420 10
350
300
1/2 Unit Separation Distance 8
250
160
This is a standard perforated diffuser’s envelope. Note that operation below 0.5 CFM/sq. ft. is probably not a good idea with this diffuser, but it will handle very high loadings if required.
Range 6 4 2
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
CFM/Sq.Ft. 22

23. Prism, 24”x24”, 10” inlet, 20°ΔT
Spacing for 80% ADPI 23

24. Measuring ADPI – ASHRAE 113
ASHRAE Standard 113 describes how to measure room air speeds and temperatures. The Standard was developed at Krueger in the early 1980’s, along with omni- directional anemometers and radiant shielded temperature probes.
The data can be presented in text form, or color graphics.

25. ADPI Calculation Program

26. Room Air Speed – Issues & Factors
Standard 55 says thermal comfort can be achieved with 0 fpm air motion.
Uniform air temperatures indicate good mixing when loads are present.
With conventional (well-mixed) systems, room air speed is driven primarily by room loads when air supply is below 0.9 CFM/sq. ft. and air diffusion is adequate, per ASHRAE sponsored research.
Partitions can provide excellent comfort with ceiling diffusers when cooling.
ASHRAE RP 1515 recently proved acceptable comfort at cfm/sf in a million sq ft office complex.
Air motion is not required for comfort if the temperature is low enough. Of course, some air motion is required to maintain uniform temperatures. These are often driven by the loads themselves.
Recent ASHRAE-sponsored research has shown that when the air supply rate is below 0.9 CFM/sq. ft., and the air diffusion is adequate, air speed is primarily driven by loads, not the diffuser system.
ASHRAE-reported research has also shown that properly selected air distribution systems are fully compatible with office partition systems. 26

27. ADPI, LEED, & Thermal Comfort
One can get a LEED point for meeting ASHRAE Standard 55 (Comfort).
The LEED comfort point now has a checklist requiring input of design clothing, metabolic rates and vertical temperature stratification calculations.
Currently, the only way to prove compliance to Standard 55’s vertical temperature stratification limitation, at the design stage, is to show an ADPI > 80%.
The new Standard 55 Users’ Manual describes how to use ADPI to prove compliance.
LEED requires that the ASHRAE Standard 55 (Comfort) be met as a prerequisite. ADPI is also covered in DOA (Designing for Occupant Acceptance). 27

28. ADPI, LEED, & Thermal Comfort
Establishing a 73°F (22.7°C) setpoint satisfies most Standard 55 input conditions.
In most cases, Radiant effects are negligible.
PMV and SET Analysis

29. Proper Overhead Heating Design

30. Common Overhead Heating Design
COLD
OUTSIDE
WINDOW
T-STAT

31. Perimeter Considerations
Maximum temperature difference between supply air and room temperature for effective mixing when heating, per ASHRAE handbook = 15°F (90°F discharge), continuous operation.
150 FPM must reach 4.5 feet from the floor or less.
ASHRAE 62.1 requires that ventilation be increased by 25% when heating, if the above rules are not followed.
ASHRAE Handbook says that one should use linear diffusers, with throw toward and away from glass, to get acceptable performance in both heating and cooling.
Put a return slot above the window to carry away solar heat gain.
Know the rules. ASHRAE may well mandate them. 31

32. Proper Perimeter Example4’
< 90oF SUPPLY AIR, T150 > 8’
COLD
OUTSIDE
WINDOW
T-STAT

33. Perimeter Considerations
March 2007
ASHRAE Journal
Know the rules. ASHRAE may well mandate them. 33

34. Non-typical Throw Analysis

35. Special Applications High Bay Application - Ceilings Over 12’ High
Heating is a challenge due to buoyancy.
Take advantage of vertical stratification where possible.
Required Heating airflow rate may exceed cooling airflow rate.
Keep heating supply air temperature to room temperature ΔT to a minimum.
If supplying air distribution from the ceiling, consider using round diffusers, drum louvers, or diffusers with some vertical projection.
One cannot use ADPI to predict heating performance.
Consider Displacement Ventilation
Every job requires 35

36. Diffuser Selection & Buoyancy
ADPI isn’t always the best way to analyze, select and place diffusers, especially with heating and high bay applications.
One can estimate Throw as a function of ΔT and buoyancy.
Simple rule: Distance to 75 ft/min is affected by % / degree(F) ΔT.
Example:
1. 20°ΔT Cooling, Vertical Down = +20% projection
2. 20°ΔT Heating, Vertical Down = -20% projection
3. 20°ΔT Heating, Along Ceiling = +20% projection
Goal: Keep 75ft/min away from occupants
When not using ADPI, the goal is to keep drafts away from people. Often it is necessary to account for buoyancy. 36

37. Side Wall Register Selection & Buoyancy
Horizontal Free Jet:
Vertical 75 ft/min is affected by 1% of 75 fpm throw/F0 ΔT.
Example: 15oF Delta T heating
15% T75
Goal: Keep 75ft/min away from occupants
When not using ADPI, the goal is to keep drafts away from people. Often it is necessary to account for buoyancy.
T75
Note: T150 is not affected by Delta-t 37

38. Entrained vs. Free Jets
Most catalog throw data assumes jet is along a surface.
Exceptions include drum louvers, duct mounted grilles and vertical linear diffusers.
A free jet will be shorter than an entrained jet because it has more surface area to induce surrounding air, which shortens throw.
In our catalog, we have taken that in to account 38

39. Special Applications Continuous Duct Application Suggestions:
Use multiple drum louvers, duct mounted grilles and continuous linear applications (longer than 10’).
Size duct as large as possible (Duct inlet velocity < 1000 fpm).
If inlet velocities are less than 1000 fpm, maintain constant duct size through entire length of run and balancing will be minimal.
Fabric duct uses constant diameter. 39

40. Returns Typically, returns are located in the ceiling in offices.
Returns have an almost immeasurable effect on room air flows below 1.5 cfm/sf.
Suspended ceilings typically leak 1cfm/sf at 0.1” differential pressure.
Spaces with high airflow rates can benefit from low returns.

41. Summary
LEED 2009, and V4 (October 2013) requires meeting Standard 62.1 for project approval No Compliance = No LEED project designation!
Documented use of ADPI is the ONLY way to assure compliance to ASHRAE Standard 55 in the design phase for cooling.
Reheat needs to be carefully considered in terms of discharge temperatures and velocities. High heating supply temperatures will void meeting Standard 55 (and lose a potential LEED point).
Software is available to assist in selecting the best mix of products.

42. Dan Int-Hout dint-hout@krueger-hvac.com www.krueger-hvac.com Contacts:42