GRD: Frequently Asked Questions

Titus encourages questions, as they lead to knowledge and a refinement of processes. It is understood that customers have varying requirements to meet job needs. This holds especially true for our largest offering, GRD products. With that said, we thought it would be worthwhile to explore common GRD inquiries and provide relevant application examples: 

How do we estimate Oversized Grille Performance? 

Grilles ordered with neck sizes larger than 48” are supplied in multiple smaller grille sectionals, and referred to as "oversized construction." Oversized grilles can be ordered to fill very large hole openings, up to the max size of 144” x 96”. To determine the performance of an oversized grille, we have to analyze the performance exhibited by each grille sectional. Please refer to page H48 of the current Titus catalog for illustrations showing the breakdown of grille sectionals.  

Example: We want to know the performance of a 96” x 96” oversized grille handling 2,000 cfm. We know the oversized construction will consist of four 48” x 48” sectionals based on the 96” x 96” neck size. Dividing the 2,000 cfm by 4 sectionals results in a cfm load of 500 cfm per 48” x 48” sectional. Finally, use the performance tables in the Titus catalog to determine what NC level and/or throw value the 48” x 48” grille will exhibit. The performance of the grille section is indicative of the performance for the entire oversized construction.

How can Supply Diffusers be used for Exhaust/Return Air Applications? 

Supply air diffusers can also be used for return air applications. When using a supply diffuser for return air, you have to make a slight adjustment to account for the increased pressure. Return air is now entering the smaller face area, instead of the larger neck area, which results in increased negative static pressure. Since pressure is increasing, so will the noise emitted by the diffuser. A safe rule of thumb is to convert the NC level of a supply diffuser to a return air application is to add 3-4 extra NC to the published NC value. 

Example: A 24” x 24” module OMNI with a 10” round neck can supply 436 cfm at 20 NC. In a return air application, the same OMNI will be able to exhaust 436 cfm at 23-24 NC. 

How are Grilles Sized based on the Free Area Requirement? 

Free area is the sum of the areas of all the space between the bars or blades of a grille, and is often expressed in square inches (in²) or square feet (ft²). FA is commonly used for supply and return grilles, but not ceiling diffusers. To determine the free area for the Titus grille in question, you must first locate the free area percentage for that product. The free area percentages for all Titus grilles and registers are listed in the Air Balancing Guide, located on the Titus website.

Air Balancing Guide - https://www.titus-hvac.com/file/11072/AirBalancing_AG_2016.pdf

Once you have located the appropriate FA% for the model in question, you must then lookup the core area based on the nominal grille neck size. The Titus performance data lists the core area for all supply and return grilles. Multiply the core area by the FA% and the result is free area for that neck size in ft².

Example: A 22” x 22” neck size 350 grille has a core area of 3.14 ft². Looking at the Air Balancing Guide, the FA% for a 350 grille is 58%. Our resulting free area for a 22” x 22” 350 grille is 3.14 ft² x .58 = 1.82 ft².

Please direct questions toward Titus Communications (communications@titus-hvac.com) and/or Neal Holden, Titus' GRD Application Engineering Manager (nholden@titus-hvac.com).