Zone air distribution ventilation effectiveness

Maria Kutelova

LEEDuser Basic Member

46 thumbs up

December 13, 2011

I need help with determining proper case for the Air Distribution Configuration per table per Table 6-2. The forth entry required a velocity of 150 cfm to be reached within 4.5 ft of floor levels. Does it mean that this velocity should be achieved at this height or this is the requirements for the velocity measured at grid level. Our mechanical engineer is claiming that this is velocity is too high for that height, and wants to make the case for 150 cfm to be measured at grid levels. Please advise!

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Roger Chang

Principal, Energy and Engineering Leader

DLR Group | Westlake Reed Leskosky

LEEDuser Expert

267 thumbs up

Wed, 04/18/2012 - 13:43

Maria, a terminal velocity of 150 fpm does need to be achieved at 4.5 ft above finished floor level. Ensure the supply air temperature is no greater than 15 degrees above the room setpoint, to limit the potential for stratification in heating mode. It's a good idea to use an Ez of 0.8 for heating design, regardless.

Andrew Mitchell, P.E.

Principal

Mitchell Gulledge Engineering, Inc.

LEEDuser Expert

97 thumbs up

Wed, 04/18/2012 - 13:40

Roger, you are correct in saying that the velocity must be 150 fpm at 4.5 ft AFF. However, simply having a SAT of less than 15 degF higher than room setpoint is not an alternative that will allow you to use an Ez of 1.0. To use Ez 1.0 you must comply with both the temperature and the air jet requirement. In my experience it is almost impossible (because of the velocity requirement) to use an Ez of 1.0 with a ceiling supply and ceiling return system for both heating and cooling.

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