1. Room Air Distribution
Presented by Randy Zimmerman

2. Introduction TC 5.03 update Mixed air systems vs. stratified systems
Thermal comfort
Ventilation effectiveness
Diffuser performance
Overhead heating
Product selection
Questions and answers

3. TC 5.03 Room Air Distribution
TC 5.03 Officers
Jerry Sipes – Chair
Randy Zimmerman – Vice Chair/Research Chair
Kevin Gebke – Secretary
Fred Lorch - Membership
Curtis Peters – Handbook
Andrey Livchak - Programs

4. TC 5.03 Room Air Distribution
TC 5.03 Activities
RP-1546 – ADPI Update (due 2014)
RP-1629 – Energy Performance of Active Beam Systems (just started)
SPC 200 – MOT Active Chilled Beams (public review)
SPC 130 – MOT Terminal Units (public review)
SPC 70 – MOT Air Inlets and Outlets (just formed)

5. TC 5.03 Room Air Distribution
Join TC 5.03 – a large and active committee
Chapters in (3) ASHRAE Handbooks
Fundamentals
Applications
Systems and Equipment
Subcommittees
Room Fan Coils
Chilled Beams
Underfloor Air Distribution
Air Curtains

6. So Many Choices
There’s a Good, Better and Best System for Every Building
Old and New Technology
Overhead Air Distribution
Underfloor Air Distribution
Active Chilled Beams
Displacement Ventilation
Let me assure you that the purpose of this webcast is not to sell displacement ventilation as the best system for every building. We’ll discuss the reasons why certain applications are recommended while others are not, but it’s important to consider displacement ventilation as one more possible solution. I like to think of displacement as one more tool in my toolbox of air distribution systems.

7. GRD’s Grille Register Diffuser They are all outlets!
Outlet similar in size to duct size
Register
Grille with an integral dampering device
Diffuser
Outlet that is often larger than duct size
Designed to create an air pattern
They are all outlets!

8. The Occupied Zone Occupied Zone 6.0 ft above floor
3.3 ft from outside wall
1.0 ft from interior wall
3.3’
6.0’
1.0’

9. Conventional Mixed-Air System

10. Fully-Stratified System

11. Mixed-Air System Concepts
Supply air 38-55oF
Cold air supplied outside the occupied zone, thoroughly mixes with room air
Creates an air pattern on the ceiling and/or walls
Picks up heat and pollutants at the ceiling level
Creates low velocity room air motion
Ideally creates uniform temperature throughout the space and minimizes stratification
Displacement systems typically supply 63-68°F air through specially-designed diffusers that are located on low side walls. This cool air discharges at less than 80 fpm from the face of the diffuser and quickly cascades down to the floor. The air continues to move slowly across the room in a layer about 4” deep until it locates a source of heat or an obstruction. In office applications the heat sources in the occupied zone are usually people and equipment. When this slow moving pool of air encounters a heat load, it quickly rises and carries the heat and pollutants towards the ceiling. Internal heat loads and contaminants are then carried away by the return air. We refer to this as a thermal plume.

12. Fully-Stratified Concepts
Supply air oF
Cool air supply displaces warm room air at low velocities
Uses the natural buoyancy of warm air to provide improved ventilation and comfort
Cold air moves slowly across the floor until it reaches a heat source, then rises
Improved IAQ
Displacement systems typically supply 63-68°F air through specially-designed diffusers that are located on low side walls. This cool air discharges at less than 80 fpm from the face of the diffuser and quickly cascades down to the floor. The air continues to move slowly across the room in a layer about 4” deep until it locates a source of heat or an obstruction. In office applications the heat sources in the occupied zone are usually people and equipment. When this slow moving pool of air encounters a heat load, it quickly rises and carries the heat and pollutants towards the ceiling. Internal heat loads and contaminants are then carried away by the return air. We refer to this as a thermal plume.

13. Improved Contaminant Removal
Stratification creates a single pass
Unlike mixed-air, contaminants are not redistributed throughout the room
Displacement ventilation can be thought of a single pass system. Unlike a mixed-air system that tends to distribute contaminants more or less evenly throughout the entire room, displacement uses natural buoyancy to collect pollutants at the ceiling where they can exit the room. This action results in lower concentrations in the occupied zone.
Displacement Ventilation
Overhead System

14. Improved Ventilation
ASHRAE Standard Ventilation for Acceptable Indoor Air Quality
Zone Air Distribution Effectiveness, Ez
Best Overhead System (Ez = 1.0)
Displacement Ventilation (Ez = 1.2)
UFAD also qualifies if T50 is 4.5 ft or less
16.7% Less Fresh Air Required
Displacement ventilation is known to be a way to increase comfort through improved ventilation. The goal of any air distribution system should be to efficiently deliver ventilation air to the breathing zone. For this reason, ASHRAE Standard 62.1 rates various types of systems with regard air change effectiveness. These ratings take into account the supply and return locations as well as the discharge pattern and temperature. According to this standard, the very best overhead systems qualify for a rating of 1.0 and other lesser systems could be as low as 0.5. On the other hand, displacement qualifies for the highest possible rating of 1.2. This means that displacement ventilation is 20% more effective than the best overhead system and the minimum fresh air requirement can therefore be reduced by nearly 17%.

15. Thermal Comfort
ASHRAE Standard 55 – Thermal Environmental Conditions for Human Occupancy
Maximum recommended ∆Thf = 5.4°F
ASHRAE Standard 55 is often referred to as the thermal comfort standard. It recommends that for good thermal comfort the temperature difference between the head and foot level of a standing person should not exceed 5.4 °F. If we assume a constant floor-to-ceiling stratification gradient of no more than 1°F per foot, any design that provides comfort for a standing occupant should also work for a seated occupant because a seated occupant would experience no more than a 3.6°F differential. In addition, we need to pay attention to the difference between the supply and exhaust temperatures. As a rule-of-thumb, exhaust temperatures should not be more than 36°F higher than supply temperatures to avoid a sensation of draftiness.

16. What About Heating?
Fully-stratified systems typically use a secondary system for heating
Low velocity warm air would short circuit to the ceiling
Fin tube perimeter heat is often used

17. Dual Plenum Diffusers Dual plenum diffusers provide
Displacement outlet for cooling
Grille for low sidewall heating
Internal diverting damper
Allows a single system to cool and heat in mild climates

18. Outlet Performance Tested per ASHRAE 70 SP and TP Area factor, Ak
Sound level
Throw, drop and spread

19. Outlet Performance Pressure drop (in wg) Area factor, Ak (ft2)
SP measured
TP = SP + VP
Area factor, Ak (ft2)
cfm = Ak x fpm
Sound level (dB ref w)
NC assumes 10 dB room effect

20. Outlet Performance Throw Drop Spread Terminal velocities
T150, T100, T50
Measured from centerline
Isothermal (unless specified)
Drop
Distance below ceiling to center of discharge jet
Spread
Unbounded jets spread at 11°angle (on each side)

21. Area Factor vs. Free Area
Free area does not govern outlet performance
Performance is related to geometry
Hole size/shape/number
Material depth
Curved/angled surfaces
Free area may or may not be easy to determine, but it’s not really useful information

22. ADPI Air Diffusion Performance Index (ADPI)
Statistically relates local temperatures and velocities to occupant comfort
Ratio of diffuser T50 to characteristic length of the room being served
ADPI > 80 is acceptable
Currently only applies to cooling applications
Soon may be expanded to include more diffuser types and add heating applications

23. ADPI ASHRAE RP-1546 Conducted at University of Texas at Austin
Verify original research
Expand the types of outlets
Run heating tests
Testing will be completed by August, 2014

24. ADPI Example ADPI Example Results for 24x24 diffusers with 8” necks
200 cfm
20° ∆T
400 ft2
Results for 24x24 diffusers with 8” necks
Plaque Face = 93.0
Multi-Cone = 93.0
Perforated = 84.8
It often makes sense to look at typical rather than 100% design conditions…

25. Overhead Heating Discharge temperature affects minimum ventilation
In overhead heating applications, discharge temperatures should never be more than 15°F higher than the desired room temperature and T150 must be within 4.5 ft from the floor (Ez = 1.0)
If ΔT > 15°F, then Ez = 0.8 and cfm increases by 25%

26. Split Pattern Linear
50/50 throw pattern is the best compromise for both heating and cooling
Works best when splitting the diffuser length, rather than splitting slots
In the cooling mode, 50% of the supply air is directed down the exterior walls – which also wastes energy and causes drafts near the floor… 26

27. Air Patterns
Cross flow
Ceiling
Longer throw

28. Air Patterns
Round
Ceiling
Shorter throw

29. Air Patterns Swirl (floor) Displacement (sidewall) Linear (ceiling)
Linear (air curtain)
Laminar (OR, clean rooms)
Hemispherical (lab, industrial)

30. Return Grilles
Contrary to popular belief – return grille locations generally do not affect room air motion
Return grilles merely provide an exit

31. Surface Effects Discharge jets attach themselves to surfaces
Ceilings
Walls
Glass
Obstructions with an angle of incidence greater than 15° can kick the air pattern off the ceiling

32. Open Ceilings Unless otherwise specified assume
Ceiling diffusers were tested with a ceiling
Side wall grilles were tested near a ceiling
Internal vs. external Coanda pocket
Most diffusers need a ceiling for horizontal air pattern
Sometimes a small lip can be added to create a ceiling effect
Free jets result in a 30% throw reduction due to increased expansion

33. Temperature Effects T150 is temperature independent – velocity driven
Horizontal ceiling throw
Cooling decreases throw by 1% per °F
Heating inceases throw by 1% per °F
Example – Catalog (isothermal) 4-7-9
Cooling 4-6-7
Heating

34. Active Length
Linear diffusers should not have active sections longer than 10 ft
Overly long active sections cause problems
Extended and unpredictable throw
Undulating air patterns
Solutions
Provide 1-2 ft inactive breaks between sections
Alternate throw direction

35. Acoustics Select diffusers such that they will not be heard
Noisy diffusers create a poor communication
NC set by in octave bands 4-6 (500, 1000, 2000 Hz) – speech interference bands
10 NC points lower than desired room level, and rarely higher than NC25 unless it’s an industrial application

36. What Type To Select? The choice can depend on many things Air pattern
Performance
Appearance
Cost
Space limitations
Installation/ceiling type

37. Summary
Many types of systems and outlets are available, but there’s always a best choice
Selecting the right air pattern is critical
Be aware of surfaces and ceilings
Keep overhead heating temperatures low
Select diffusers to be inaudible

38. Questions and Answers
Questions?
Thank-you!