Transcript Template Samples - Central Pennsylvania Chapter of ASHRAE

Room Air Distribution
Presented by Randy Zimmerman
Introduction
TC 5.03 update
Mixed air systems vs. stratified systems
Thermal comfort
Ventilation effectiveness
Diffuser performance
Overhead heating
Product selection
Questions and answers
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TC 5.03 Room Air Distribution
TC 5.03 Officers
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Jerry Sipes – Chair
Randy Zimmerman – Vice Chair/Research Chair
Kevin Gebke – Secretary
Fred Lorch - Membership
Curtis Peters – Handbook
Andrey Livchak - Programs
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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)
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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
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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
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!
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’
Conventional Mixed-Air System
Fully-Stratified System
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
Fully-Stratified Concepts
 Supply air 63 - 68oF
 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
Improved Contaminant Removal
 Stratification creates a single pass
 Unlike mixed-air, contaminants are not redistributed
throughout the room
Displacement Ventilation
Overhead System
Improved Ventilation
 ASHRAE Standard 62.1 - 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
Thermal Comfort
 ASHRAE Standard 55 – Thermal Environmental Conditions for
Human Occupancy
 Maximum recommended ∆Thf = 5.4°F
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
Dual Plenum Diffusers
Dual plenum diffusers
provide
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Displacement outlet for cooling
Grille for low sidewall heating
Internal diverting damper
Allows a single system to cool
and heat in mild climates
Outlet Performance
Tested per ASHRAE 70
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SP and TP
Area factor, Ak
Sound level
Throw, drop and spread
Outlet Performance
Pressure drop (in wg)
– SP measured
– TP = SP + VP
Area factor, Ak (ft2)
– cfm = Ak x fpm
Sound level (dB ref 10-12 w)
– NC assumes 10 dB room
effect
Outlet Performance
Throw
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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)
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
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
ADPI
ASHRAE RP-1546
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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
ADPI Example
ADPI Example
– 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…
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%
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
Air Patterns
Cross flow
– Ceiling
– Longer throw
Air Patterns
Round
– Ceiling
– Shorter throw
Air Patterns
Swirl (floor)
Displacement (sidewall)
Linear (ceiling)
Linear (air curtain)
Laminar (OR, clean rooms)
Hemispherical (lab,
industrial)
Return Grilles
Contrary to popular belief – return grille
locations generally do not affect room air
motion
Return grilles merely provide an exit
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
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
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 4-8-11
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
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
What Type To Select?
The choice can depend on many things
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Air pattern
Performance
Appearance
Cost
Space limitations
Installation/ceiling type
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
Questions and Answers
Questions?
Thank-you!