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.1918 B.1925 C.1931 D.1938 E.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) Galvanized Iron Aluminum Stainless steel Flexible Insulated Tube (socks) Other PVC Fiberglass

Ductwork Considerations Shape Size Aspect ratio Velocity Static Pressure of the system Space conflicts

Congested Corridors

Shape and Size Round Oval Rectangular

Lower aspect ratios 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 W D Aspect ratio = W / D 1 to 1

So Why Is This A Problem?

Conventions

Air Distribution Systems Three Types Above Ceiling Displacement Underfloor Services Supply air Return air Ventilation air Relief air Exhaust air

Above Ceiling Distribution System horizontal heat pump supplyduct returnduct diffuser return air grille American Standard © 1999

How Do You Dilute the Air? + pressure 1600 CFM 200 CFM 1400 CFM OA SA RA MA 1600 CFM

Intake Distances

Outside Air (OA) v. “Fresh Air” Source of outside air must be carefully considered. May have to pre- filter 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 Inexpensive Very common (thus well understood) Disadvantages Takes ceiling height Uses high velocity  Heating  Air conditioning Uses mixing ventilation to achieve set point Mixes contaminants Aesthetics

Air Distribution, Poor Pattern Example THERMOSTAT POORLY ADJUSTED / SELECTED DIFFUSER What are the issues?

LEED EQ Credit 2 Increase ventilation effectiveness Increase breathing zone outdoor air ventilation rates to all spaces 30% above the minimum rates of ASHRAE Strategies Avoid supply and return in the ceilings Displacement ventilation Underfloor ventilation Natural ventilation

LEED EQ Credit 2 Increase ventilation effectiveness Ventilation effectiveness refers to the movement of the supply air through the occupied zone Prevent “short circuiting” of airflow delivery Strategies 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.

UNOCCUPED ZONE SHIFT ZONE OCCUPIED ZONE: TEMPERATURE GRADIANT HE IGHTHE IGHT Thermal Displacement Ventilation Temperature Stratification 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 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 Higher initial cost Less well understood Aesthetics Too quiet

For cable-management & UF-HVAC  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 Advancements in Building Systems Potential Benefits: Access Flooring

 Air supply at 63-65º F  Bottom to top air movement; single pass  Stratified temperature distribution Design Principle: UF-HVAC Systems Tate Building Technology Platform ® Video

Underfloor System Reduces floor to floor height

Design Principle: UFAD Systems Tate Building Technology Platform ® TEMPERATURE GRADIANT OCCUPIED ZONE SHIFT ZONE UNOCCUPED ZONE 65 o 72 o 76 o 78 to 80 o 63 o

Adjustable understructure support pedestals Concrete slab Occupied space Access floor panels What is an Access Floor? An elevated or “raised” floor upon another floor, typically a concrete slab Interstitial space Tate Building Technology Platform ®

Underfloor Systems

 Passive swirl diffusers; pressurized plenum; displacement theory  Occupant may control airflow volume; 3’ clear zone around diffuser Air Delivery: UF-HVAC Diffuser Types Tate Building Technology Platform ®

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 non- perimeter, regularly occupied areas.

Packaged (DX) Rooftop HVAC Solution Return air riser Supply air riser Roof top HVAC unit Supply air loop Stub duct Supply air outlet VAV or CV MIT terminals Tate Building Technology Platform ®

Rooftop Chiller HVAC Solution Equipment room (chiller, pumps, controls) Chilled water supply & return Cooling tower Supply air outlet Stub duct Indoor air handler VAV MIT terminals Supply air loop Tate Building Technology Platform ®

Access Floors… Advancements in Building Systems

...they’re not just for Computer Rooms anymore!! Advancements in Building Systems

Underfloor (UFAD) Advantages/Disadvantages Advantages 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 Higher initial cost Too quiet

Take-Aways (The Ah Hahs) Eliminate the contaminant is always the first step Capture it if you can’t eliminate it Healthy buildings are well ventilated Watch your outside air sources! Operating cost and usually first cost go up as your ventilation goes up