Thursday, October 18, 2012

Q&A: How Do I Determine Vertical Throw For a Grille When Catalogs Only Show Horizontal Throw?

Vertical throw for supply grilles is not usually required since grilles mounted in a ceiling are not a normal application. But it sometimes happens and diffusers can be set to throw vertically.

The method of obtaining throw data is as follows.

1. Determine the flow rate in CFM and the jet velocity from the published horizontal throw data pages.

2. Refer to the engineering section of the Titus catalog; page B24. Find the sections entitled Estimating Downward Vertical Projection.

3. Using the table below, find the vertical line representing your flow ate in CFM.

4. Follow the vertical line to the jet velocity curve that corresponds to core velocity listed in the published data.

5. Project a horizontal line from where the vertical flow rate line intersects the velocity curve to the column on the right hand side of the figure.

6. Select the appropriate temperature differential (delta T) column and read that vertical distance.

Example: Using the published data from the data page above, determine a vertical projection of a 36 x 18 grille supplied with 2500 cfm at a delta T of 20 degrees.The core velocity at the top of the data page for that grille size and volume is 600fpm.

Using the procedure described above and Figure 24, we can estimate vertical projection for a grille supplied with 2500cfm and a core velocity of 600 fpm to be nearly 12 feet with a 20 degree delta T.

Additionally, the table is also useful for comparing isothermal throw to differential throw when only the isothermal data is available, by simply reading across the vertical projection columns on the right.

For example, when an isothermal vertical throw of 25 feet is known, simply read across the column to determine a vertical throw of 15 feet for vertical throw when the delta T is 20 degrees.

Mark Costello - GRD Product Manager

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