Designing Ventilation Grilles For Electronic Equipment

The following article originally appeared in the August 9, 1990 issue of Machine Design and is reprinted with the permission of Penton Publishing. All portions of the article are copyright © 1990 Penton Publishing. Questions and comments should be directed to Machine Design. The article provides a detailed analysis of different grille designs and their effects on cooling air flow and radiated EMI. Safety issues are also touched upon.

Synopsis of the article

The type and surface area of ventilation grilles has an important effect on the efficiency on either convection or forced air cooling. In convection cooling the required outlet area (A_o) is greater than the inlet area (A_i) because the air in the equipment is heated and thus expands. The article provides formulae to estimate the required ventilation areas, though the designer is urged to test prototypes to verify actual temperatures. Guidelines to calculating the open area of various hole patterns are also given.

When using forced air one must also consider the fan performance curve. That is, a fan produces the rated CFM only in an open area. In an enclosure restricted by limited grille area a fan will produce less than the rated CFM. One can plot the fan performance curve on a graph along with the enclosure airflow resistance curve to find the actual fan CFM in that particular enclosure. There are two ways to improve cooling performance:

1. Increase outlet open area.
2. Use a fan with higher CFM at the real operating point of the enclosure. (Note that in some cases a fan may have a higher rated CFM than another but may perform poorly with resistance to airflow.)

Depending on the specific grille design, more or less EMI will be radiated out the enclosure at various frequencies. The pattern and size of the individual holes has an important effect on EMI. Methods for estimating the radiated EMI for various designs are given.

The various safety agency standards include requirements for ventilation grilles, for example to prevent a conductive object from being inserted into the cabinet. These issues are touched upon but not covered in detail.

Synopsis Copyright © 2000 Evox Rifa Written by Andy Bellavia, 17 October 1997.

Because the source material is a printed magazine it is offered here only in Adobe Acrobat format. Click here to download the article (244K).

Last modified: april 10, 2008

Go to top

Catalogs and tech notes viewable with Adobe Acrobat. Get the latest version for proper viewing.

Technical questions, printed materials, price & delivery: Contact us
Do you have comments about this web site? Write the webmaster  
Copyright © 2007 Evox Rifa