ASHRAE grd selection
-
Upload
tesengineering -
Category
Business
-
view
195 -
download
2
Transcript of ASHRAE grd selection
© 2005. All rights reserved
Overview
Throw OverviewThrow ConsiderationsThrow During Heating
Hints and TipsADPITerminal Unit Overview
Terminal Unit Selection
© 2005. All rights reserved
How to Measure Throw
To determine the throw, one needs to measure the velocity in the air stream at various distances from the air supply device
The velocity measurements are taken at three or four distances from the ceiling to obtain the maximum velocityCataloged at 150, 100, and 50 fpm
© 2005. All rights reserved
Typical Louvered Diffuser
Cross flow patternExternal Coanda effect
Ceiling Dependent
Smudging
-Sp
© 2005. All rights reserved
Typical Cone Diffuser
Circular patternInternal Coanda effect
Ceiling Independent
No Smudging
-Sp
© 2005. All rights reserved
Open Ceiling Designs
What happens when you have an open ceiling design?
Internal Coanda Pocket
© 2005. All rights reserved
Surface Effects
How do different ceilings and obstructions affect the jet?
The angle between the kicker and the obstruction should be less than 15o or the jet will drop excessively
© 2005. All rights reserved
Colliding Air Streams
What happens when airstreams collide?
Airstreams should not collide at greater than 100fpm isothermal or 50fpm in cooling (20oF ∆).
© 2005. All rights reserved
Hints and Tips
Ceiling dependent diffusers do not work as well with obstacles in the jetThe angle from the obstacle to the kicker will determine whether the obstacle will make the air drop
150 fpm = 150 fpm Cooling or Heating100 fpm = 50 fpm Cooling - Free Jet100 fpm = 100 fpm Cooling with Walls
© 2005. All rights reserved
ADPI
Air Diffusion Performance IndexStatistically related the space conditions of local or transversed temperature and velocities to occupants’ thermal comfortADPI >= 80 is considered acceptableEffective draft temperature
Θ = (tx-tc) – 0.07(Vx-30)
Percentage of points where -3<= Θ <= +2 equals room ADPI
© 2005. All rights reserved
ADPI
The grey area represents -3<= Θ <= +2
You can vary temperature or velocity to maintain comfort