Volume dampers shall be provided in all supply air branch ducts and at all supply air outlets. Volume dampers shall not be placed upstream of VAV terminal units. Supply air duct systems shall be designed with care and considerations to minimize the overall system pressure drop.
Low Pressure Supply Return or General Exhaust
Maximum pressure drop: 0.10 inches w.c. per 100 ft.
Supply Diffuser run out: 500 fpm.
Return or exhaust grille run out: 600 fpm.
Branch duct above ceiling: 1750 fpm.
Mains in mechanical rooms or shafts: 2,000 fpm.
Exposed mains: 1,450 fpm.
Medium Pressure Supply
Maximum pressure drop: 0.35 inches w.c. per 100 ft.
Branch to terminal unit: 2,200 fpm.
Round branch above ceiling: 3,000 fpm.
Rectangular branch above ceiling: 1,750 fpm.
Round main in mechanical rooms or shafts (above 35,000 CFM): 3500 fpm.
Rectangular main in mechanical rooms or shafts: 2,500 fpm.
Exposed round mains: 2,600 fpm.
Exposed rectangular mains: 1,450 fpm.
Ductwork and exhaust systems (serving Type I or Type II kitchen hoods) shall be designed and constructed per NFPA requirements.
Ductwork serving a Type I hood will be constructed from stainless steel, pitched back to the hood with condensate drains, fire sprinklers, access doors at changes in direction, and separate from any other exhaust systems.
Dishwasher exhaust will be constructed from aluminum or stainless steel.
Hood exhaust fans shall be approved specifically for this application and shall meet the requirements of the local authorities having jurisdiction and NFPA.
Locate supply and exhaust grills away from exhaust hoods to prevent air being discharged from affecting hood performance.
Provide makeup air systems, per State Energy Code.
Minimum velocity for duct design: 1,500 fpm.
Maximum velocity for duct design: 2,500 fpm.
Lab Exhaust Duct Design
Ductwork for lab exhaust systems will be 316 stainless steel.
Ductwork for fume hood exhaust systems shall be welded 316 stainless steel duct, pitched back to the hood.
VAV lab exhaust systems are preferred for new construction where there are multiple exhaust hoods in a building. See Variable Air Volume (VAV) Systems in this standard.
Locate supply and exhaust grilles away from fume hoods to prevent air being discharged from affecting hood performance.
Hood stacks will terminate a minimum of sixteen (16) feet above the standing surface at the point where service personnel will stand to work on the equipment or perform other tasks.
Stacks located on sections of buildings within fifty feet of taller section of the building will be constructed as if they were on the taller section (i.e., sixteen feet above the standing surface of the taller section).
Other physical arrangements may be suitable with equipment that is designed for outside dilution air, high discharge velocities, and higher effective stack height. Such systems will be reviewed and approved on a case-by-case basis by EH&S. In no case will physical stacks terminate LESS than seven (7) feet above the standing surface.
Maximum pressure drop: 0.35 inches w.c. per 100 ft.
Recirculation of any laboratory exhaust is prohibited.
Heat recovery systems in lab exhaust air will NOT utilize filter media. Another design must be used.
Mains- maximum 2500 fpm
Branches – maximum 1500 fpm
Minimum stack exit velocity 3,000 fpm
Do not locate rotating equipment above hard ceilings
Seal all low and medium pressure metal supply exhaust and return ductwork, per SMACNA Class A standards using either adhesive, gaskets, or tape systems.
DUCT PRESSURE TESTING
Test all ductwork slated to operate at ≥ 4 inches water gauge.
Randomly test three sections of medium and three sections of low pressure ductwork slated to operate at ≤ 4 inches water gauge.
Utilize spiral round duct wherever possible for low velocity.
Utilize rectangular where round duct will not fit.
For medium velocity, mains and branches utilize flat oval ducts where round ducts will not fit.
Utilize rectangular ductwork where flat oval sizes are not available for supply ducts.
For return and exhaust ducts utilize round where possible and rectangular otherwise.
Provide exterior zones around the perimeter of the building and interior zones for the remainder of the area.
Perimeter zones to be a maximum of 15 foot deep.
Corner rooms having two different exposures shall be made a separate zone if practical.
Meeting and conference rooms shall be made separate zones.
Other specific zoning requirements will be provided by the PM.
Terminal Unit Area of Coverage:
Maximum exterior zone size: 1,000 sq.ft.
Maximum interior zone size: 1,800 sq.ft.
Indicate the desired layout on the Construction Drawings using double lines to delineate ducts to scale; use standard symbols.
Show items such as dampers, lining, turning vanes, extractors, splitters, air flow measuring stations, and other features required for good control of air.
Indicate round ductwork where possible.
If rectangular ductwork is used, specify radius turns where possible.
Keep the duct aspect ratio at 3 to 1 or less where possible, but not over 5 to 1 unless approved by the OSU Project Manager. Arrange the layout to avoid items that pass through ductwork unless absolutely necessary. When penetrations occur, specify an airfoil section around them.
Coordinate the location of ducts with other building features such as columns, ceilings, conduit, piping and lighting fixtures. Position ductwork to allow for the removal of, or access to, filters, terminal box coils or controls, lighting fixtures, fire dampers and other similar items.
Ductwork design: To design the system, consider noise, pressure drop, the type of system, the type of duct material, vibration, drumming, fire and smoke control, and any other factors that may affect sizing.
Hangers and supports
The type and size of hangers and support shall follow ASHRAE and/or SMACNA recommendations. Seismic restraints where applicable shall be designed, specified and detailed as recommended in SMACNA's "Guidelines for Seismic Restraints in Mechanical Systems". Spring or other resilient supports shall be used in hangers where sensitivity to vibration is a problem. Coordinate with the other design disciplines when specifying or designing the duct support and hanger locations.
Manual and automatic opposed blade volume control dampers, back draft dampers, inlet vanes, and fire and smoke dampers shall be shown in duct layouts where required. Provide adequate room around shafts for fire/smoke damper sleeves.
Where possible, select 100 percent free area fire and smoke dampers that have their entire assemblies approved by the Underwriters' Laboratories and any governmental agencies having jurisdiction.
After completion of the duct layout, review the design for proper arrangement and for adequacy of the volume dampers to ensure ease of initial balancing and of rebalancing to accommodate future modifications.
Knife or gate dampers shall be provided at each constant volume fume hood for balancing purposes.
Specify that duct systems are to be wiped down, vacuumed, or blown clean with compressed air before installation, and that all ductwork is sealed with plastic after cleaning and during assembly to keep ducts clean. All ductwork shall be shipped sealed to the job site and kept sealed until construction is complete. Store ductwork out of the weather at all times.
The return duct system shall be kept sealed at all times during construction to keep it clean. If heat is required in the building prior to finish of construction 100% outside air shall be used.
Require the contractor to provide and install a new, complete set of clean filters shortly before final acceptance.
Fans shall be operated with construction filters installed, at full air volume for 24 to 48 hours after installation.
Supply and return ductwork
Use galvanized sheet metal spiral round, rectangular, and flat oval ductwork, in that order, unless special conditions dictate use of other materials. Use pressure and/or velocity criteria to select gauge thickness according to the ASHRAE Guide or SMACNA.
Ducts must convey ambient temperature or heating exhaust, smoke and grease from kitchen hoods, moisture, abrasives, and other exhaust air streams that are not acids or caustics. Use the following materials for these exhausts:
Specify the gauge for galvanized sheet metal as recommended in the ASHRAE Guide or SMACNA. Ductwork for kitchen exhausts and abrasives shall have material thickness as recommended in the references.
Kitchen Cooking Hoods: Welded steel (conform to NFPA).
Dish Washing Exhaust: Use 304 stainless steel material for moisture latent air streams. Pitch ductwork to dish washing hood or to duct mounted drains.
See Section 11 53 13 for Laboratory Fume Hood ductwork requirements
All accessible ductwork shall be color coded and identified with wording and arrows every 20 feet on straight runs, at each riser, at each junction, at each access door, adjacent to all valves and, flanges, on both sides of floor and wall penetrations and where required to easily identify the medium transported.
Smoke dampers shall be permanently identified on the exterior by a label with letters ½ inch in height reading: Fire Damper, Smoke Damper, or Fire/Smoke Damper, as appropriate. The label will be constructed from same material as equipment nameplates.
Terminal Units: Mark all terminal units with a permanent marking system so that the markings can be easily read from the most likely viewing position (i.e., catwalk, through the ceiling below, etc.).
VARIABLE AIR VOLUME (VAV) SYSTEMS
VAV systems shall be used for general office and circulation areas including lobbies, cafeterias, and meeting rooms, unless otherwise approved by the Project Review team and directed by the PM.
VAV air handling systems must be capable of stable operation over a wide air quantity range. The selection and arrangement of terminal units shall minimize modification required to accommodate changing tenant configurations.
Terminal units shall also be capable of stable operation over a wide control range.
VAV terminal units serving perimeter zones shall be provided with hot water heating coils.
Supply and return fans serving VAV systems shall be provided with a variable frequency drive to varying the air volume in response to system pressure.
VAV terminal units may be allowed to go to shut-off where applicable or go to a minimum setting. Zone controls shall be designed to maintain required minimum ventilation rates.
VAV re-heat terminal units shall close to 40% or greater as required for ventilation prior to re-heat.
Recirculation of any laboratory exhaust is prohibited when using a VAV system for lab hood exhaust.
Recirculated air systems equipped with an economizer cycle shall be capable of supplying 0-100% outside air.
Air economizer systems shall be used whenever practical. Provide both dry bulb and enthalpy controlled economizers.
For conditions under which economizer systems are not required and shall not be used, reference ASHRAE/IES Standards 90.1-1989.
Constant volume systems shall be used for areas requiring constant air flow and areas with constant exhaust requirements.