ashrae grd selection

GRD and VAV selectionJenny Abney

Regional Manager - Titus

© 2005. All rights reserved

Overview

Throw OverviewThrow ConsiderationsThrow During Heating

Hints and TipsADPITerminal Unit Overview

Terminal Unit Selection


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


Throw Considerations

Surface EffectsSmudging


Typical Louvered Diffuser

Cross flow patternExternal Coanda effect

Ceiling Dependent

Smudging

-Sp


Typical Cone Diffuser

Circular patternInternal Coanda effect

Ceiling Independent

No Smudging

-Sp


Linear Diffusers

-Sp

-Sp


Open Ceiling Designs

What happens when you have an open ceiling design?

Internal Coanda Pocket


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


Colliding Air Streams

What happens when airstreams collide?

Airstreams should not collide at greater than 100fpm isothermal or 50fpm in cooling (20oF ∆).


Throw During Heating


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


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


ADPI

The grey area represents -3<= Θ <= +2

You can vary temperature or velocity to maintain comfort


Throw vs. Characteristic length

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