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Room Air Distribution Presented by Randy Zimmerman.

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Presentation on theme: "Room Air Distribution Presented by Randy Zimmerman."— Presentation transcript:

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 2

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 3

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) 4

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 5

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

7 GRD’s  Grille –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  Supply air o F  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 Mixed-Air System Concepts

12  Supply air o F  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 Fully-Stratified Concepts

13 Improved Contaminant Removal  Stratification creates a single pass  Unlike mixed-air, contaminants are not redistributed throughout the room Displacement Ventilation Overhead System

14  ASHRAE Standard Ventilation for Acceptable Indoor Air Quality  Zone Air Distribution Effectiveness, E z  Best Overhead System (E z = 1.0)  Displacement Ventilation (E z = 1.2) –UFAD also qualifies if T 50 is 4.5 ft or less –16.7% Less Fresh Air Required Improved Ventilation

15 Thermal Comfort  ASHRAE Standard 55 – Thermal Environmental Conditions for Human Occupancy  Maximum recommended ∆T hf = 5.4°F

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, A k –Sound level –Throw, drop and spread

19 Outlet Performance  Pressure drop (in wg) –SP measured –TP = SP + VP  Area factor, A k (ft 2 ) –cfm = A k x fpm  Sound level (dB ref w) –NC assumes 10 dB room effect

20 Outlet Performance  Throw –Terminal velocities –T 150, T 100, T 50 –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 T 50 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 –200 cfm –20° ∆T –400 ft 2  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 T 150 must be within 4.5 ft from the floor (E z = 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

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  T 150 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) –Cooling –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!


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