Terms
The horizontal or vertical distance an airstream travels after leaving an air outlet.
What is Throw? How is throw measured and cataloged?
Cataloged sound data assumes this many diameters of straight duct.
What is 3 Diameters? Why do we assume this distance of straight duct?
The percentage of throw reduction when throwing air into a free space rather than across a wall or ceiling.
What is 30 percent?
The area that is located 2-3 feet from a perimeter wall and up to 6' above the floor.
What is the Occupied Zone?
A return slot should be located here to carry away solar heat gain.
What is Above a Window. Why is this a good idea?
The divergence of the airstream in a horizontal or vertical plane after it leaves the outlet.
What is Spread? What is the average spread of a mass of air entering a space?
Sound performance tests for diffusers are conducted in accordance with this Standard.
What is ASHRAE Standard 70?
This published information includes three different values for the same performance term.
What is Catalog Throw Data? Why are there 3 different numbers?
The velocity at which the air must be travelling inside the occupied zone (6 feet standing or 3.5 feet for sitting occupant).
What is 50 feet per minute (FPM)? Why is this velocity important?
Which diffusers carry a higher overall system cost (labor, install, etc), perforated diffusers or plaque diffusers?
What are perforated diffusers. Why might this be?
This effect causes the moving air mass to cling to and flow close to a surface.
What is Coanda Effect? Why do we want to utilize Coanda?
This standard is used to estimate room sound pressure from known sound power.
What is AHRI Standard 885.
This Standard mandates a 5-deg F vertical temperature stratification in the Occupied Zone.
What is ASHRAE Standard 55?
This is the best way to present a sound requirement on a specification or a schedule.
What is octave band sound power. Why octave band and not NC?
The ASHRAE Handbook suggests that this diffuser should be used, with throw toward and away from glass, to get acceptable performance in both heating and cooling.
What are Linear Diffusers? Why should we throw across a window?
The mass of air which enters a room through free round openings, grilles, perforated panels, ceiling diffusers and other outlets is called?
What is a Primary Air Jet? What is a design consideration to take into account with primary air jets?
The 10 dB reduction allowed by Standard 885 during grille testing.
What is room absorption.
Which diffuser performs better in a VAV system, a perforated diffuser or a plaque diffuser?
What is a Plaque Diffuser. Why is this the case?
The two requirements of ASHRAE 55 when heating from the ceiling.
What are 15 degree dT and a 150 FPM velocity that reaches 4.5' above the floor. In the Un-Occupied zone.
These two types of Air Distribution devices are beneficial in Hi-Bay designs (over 12') due to the need to heat/cool the occupied area only.
What is Displacement Ventilation and Underfloor Air Distribution (UFAD)? Why are these two good ideas for high-ceiling applications?
The primary jet which enters a space without traveling along a ceiling or wall.
What is a free jet of air. What is the opposite of free jet?
This is what sound measuring instruments detect, in decibels, to give you sound measurement in the space.
What is Sound Pressure?
This is the ideal Delta-t for a displacement (DV) or underfloor air distribution (UFAD) application.
What is 65 degrees.
The Required amount of Ventilation air that must be added (per ASHRAE 62.1) if you do not meet the 15 deg. delta T and the 150 fpm rules and the 5 deg. temperature stratification (from Standard 55).
What is 25 %? Why might this be?
This device utilizes chilled/heated water, primary air supply and induced room air to treat the space. (not a Terminal Unit)
What are Chilled Beams. What is the typical induction ratio for overhead CB's?