Transcript Ductwork Systems

Ductwork Design
Arch 432
Attendance
The Empire movie
theater in
Montgomery,
Alabama holds the
distinction of having
the first temperature
controlled cooling
system in the United
States. When was
this feat
accomplished?
A.
B.
C.
D.
E.
1918
1925
1931
1938
1946
What You Need To Know
Become familiar with the materials and
methods of ductwork systems
Identify the different systems of
transporting air
What You Need To Be Able To Do
Recognize advantages and
disadvantages of ductwork systems
Calculate duct dimensions as a variable
of ceiling height
Make the right distribution selection for
the Albrook
Terms
Aspect ratio
Flexible ductwork
Overhead system
Underfloor air
distribution (UFAD)
system
Displacement
system
Dumping
Diffuser
Grille
Register
Slot diffuser
Shift Zone
Plenum
Materials
Sheet metal (by gauge)
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Galvanized
Iron
Aluminum
Stainless steel
Flexible
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Insulated
Tube (socks)
Other
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PVC
Fiberglass
Ductwork Considerations
Shape
Size
Aspect ratio
Velocity
Static Pressure
of the system
Space conflicts
Congested Corridors
Shape and Size
Rectangular
Round
Oval
Rectangular
W
Lower aspect ratios
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D
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1 to 1
Aspect ratio = W / D
More energy efficient
Use less ductwork
Velocity and Area have
an inverse relationship
to the CFM (CFM = V x
A)
Velocity and Pressure
Drop have a direct
relationship
So Why Is This A Problem?
Conventions
Air Distribution Systems
Three Types
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Above Ceiling
Displacement
Underfloor
Services
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Supply air
Return air
Ventilation air
Relief air
Exhaust air
Above Ceiling Distribution
System
horizontal
heat pump
return
duct
return air
grille
diffuser
American Standard © 1999
supply
duct
How Do You Dilute the Air?
OA
200 CFM
SA
1600 CFM
RA
1400 CFM
MA
1600 CFM
+ pressure
Intake Distances
Outside Air (OA) v. “Fresh Air”
Source of outside air
must be carefully
considered.
May have to prefilter or condition
Other Design Considerations
Thermal mass
Prevailing winds
Natural light
Solar shading
Control strategies
Life safety issues
Infiltration
Bioterrorism
Mixed Air (MA)
conditions
Energy in the air
Comfort level of the
air
The amount of
water in the air
Diffusers/Grilles/Registers
Above Ceiling
Advantages/Disadvantages
Advantages
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Inexpensive
Very common (thus well
understood)
Disadvantages
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Takes ceiling height
Uses high velocity
 Heating
 Air conditioning
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Uses mixing
ventilation to achieve
set point
Mixes contaminants
Aesthetics
What are the
issues?
Air Distribution, Poor
Pattern Example
POORLY ADJUSTED / SELECTED DIFFUSER
THERMOSTAT
LEED EQ Credit 2
Increase ventilation
effectiveness

Increase breathing
zone outdoor air
ventilation rates to all
spaces 30% above
the minimum rates of
ASHRAE 62.1-2004
Strategies
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Avoid supply and
return in the ceilings
Displacement
ventilation
Underfloor ventilation
Natural ventilation
LEED EQ Credit 2
Increase ventilation
effectiveness
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Ventilation
effectiveness refers
to the movement of
the supply air
through the occupied
zone
Prevent “short
circuiting” of airflow
delivery
Strategies
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Avoid supply and
return in the ceilings
Displacement
ventilation
Underfloor
ventilation
Natural ventilation
Short Circuiting
DISPLACEMENT VENTILATION
•Thermal Displacement Ventilation
is based upon natural air movement
•Specially designed displacement
diffusers are strategically placed
within the “occupied” zone.
•Depending on application, supply
air is delivered at between 55° F and
65° F.
•Generally, the closer occupants are
to the diffuser, the higher the
discharge temperature
DISPLACEMENT PRINCIPLES
•Conditioned air moves upward
past the persons breathing
zone.
•This invisible plume continues
an upward movement toward
the ceiling.
•A person will breathe lower
contaminant levels vs. a mixing
design.
DISPLACEMENT DIFFUSERS RECESSED IN WALL
FORM FOLLOWS FUNCTION WITH
DISPLACEMENT DIFFUSERS.
•Supply air cascades from the
diffusers.
•This forms a continually
replenished pool of clean
conditioned air at the floor
•Since velocity is very low air
movement is not perceptible to
the occupants within the zone.
DISPLACEMENT PRINCIPLES
•Exhaust is provided at
strategically located
grilles installed at the
high point of the ceiling.
•Return grilles can be
positioned within the
shift zone to allow
lower return air
temperatures.
Thermal Displacement Ventilation
Temperature Stratification
UNOCCUPED ZONE
SHIFT ZONE
H
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G
H
T
OCCUPIED ZONE:
TEMPERATURE
GRADIANT
By only cooling the occupied zone, tonnage
requirements may be reduced
DISPLACEMENT:
Delivering fresh air where it is needed
•Better IAQ, lower
particulate
concentrations than
mixing systems.
•Increase use of
outdoor air without
energy penalty.
•Quiet diffusers,
draftless conditions for
the occupants.
Displacement
Advantages/Disadvantages
Advantages
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Moderate supply air
temperature
Low velocity
Air delivered to the
comfort zone without
mixing
Aesthetics
Better IAQ
Can accommodate more
outside air for same
energy cost
Very quiet
Disadvantages
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Higher initial cost
Less well understood
Aesthetics
Too quiet
Advancements in Building Systems
Potential Benefits: Access Flooring
For cable-management & UF-HVAC
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Improved flexibility for
building services
Improved ventilation efficiency
and indoor air quality
Improved occupant comfort,
productivity and health
Reduced energy use
Reduced life-cycle building costs
Reduced floor-to-floor height in
new construction
Tate Building Technology Platform®
Design Principle: UF-HVAC Systems
 Air supply at 63-65º F
 Bottom to top air movement; single pass
 Stratified temperature distribution
Video
Underfloor System
Reduces floor to
floor height
Tate Building Technology Platform®
Design Principle: UFAD Systems
UNOCCUPED ZONE
78 to
80o
SHIFT ZONE
76o
OCCUPIED ZONE
TEMPERATURE
GRADIANT
72o
65o
63o
Tate Building Technology Platform®
What is an Access Floor?
An elevated or “raised” floor upon another floor,
typically a concrete slab
Occupied space
Interstitial space
Access floor panels
Concrete slab
Adjustable understructure
support pedestals
Underfloor Systems
Tate Building Technology Platform®
Air Delivery: UF-HVAC Diffuser Types
 Passive swirl diffusers; pressurized
plenum; displacement theory
 Occupant may control airflow
volume; 3’ clear zone around
diffuser
LEED EQ Credit 6
Credit 6 – Controllability
of Systems
 6.1 – Provide at least
one window and one
lighting control zone
per 200 square feet
for all regularly
occupied areas
within 15 feet of the
perimeter wall
Credit 6 – Controllability
of Systems
 6.2 – Provide controls
for each individual
for airflow,
temperature and
lighting for at least
50% of the
occupants in nonperimeter, regularly
occupied areas.
Tate Building Technology Platform®
Packaged (DX) Rooftop HVAC Solution
Return air riser
Roof top HVAC unit
Supply air riser
Supply air loop
VAV or
CV MIT terminals
Stub duct
Supply air outlet
Tate Building Technology Platform®
Rooftop Chiller HVAC Solution
Equipment room
(chiller, pumps, controls)
Cooling tower
Chilled water supply
& return
Indoor air handler
Supply air outlet
Stub duct
Supply air loop
VAV MIT
terminals
Advancements in Building Systems
Access Floors…
Advancements in Building Systems
...they’re not just for Computer Rooms anymore!!
Underfloor (UFAD)
Advantages/Disadvantages
Advantages
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Eliminates overhead
ductwork
Higher energy efficiency
Uses moderate air
temperatures
Low velocity
Greater flexibility
Provides better IAQ
Provides greater personal
comfort
Very Quiet
Shorter buildings
Can use more outside air for
same energy cost
Disadvantages
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Higher initial cost
Too quiet
Take-Aways (The Ah Hahs)
Eliminate the contaminant is always
the first step
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Capture it if you can’t eliminate it
Healthy buildings are well ventilated
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Watch your outside air sources!
Operating cost and usually first cost go
up as your ventilation goes up