[Bldg-rate] ASHRAE 62.1 Compliance with Underfloor-Air Distribution

Dan Russell danr at engineeringinc.com
Tue Nov 4 08:07:06 PST 2008

Hello All,

I am struggling with determining how the common UFAD systems today are meeting ASHRAE 62.1.  The systems which I have seen utilize floor grilles with either a motorized damper controlled via wall-mounted t-stat or a manual damper.  When the space is satisfied the dampers close and all of a sudden there is no supply air entering the space.  This is also the case during all heating modes I have observed in UFAD systems.  During heating mode for these systems the primary supply air is completely shut-off and the space is heated using 100% re-circulated air from the space.

I recently attended a seminar by a UFAD manufacturer where one of the speakers was a chief engineer for the company.  After the seminar I posed this question to him, only to have him respond by saying that it's a tough issue to tackle and he's not sure how compliance would be met.  I've also been told that since heating only takes place on the perimeter that ventilation is drawn from interior zones.  I've also been told, "Well we generally only see corridors on the perimeter of buildings with UFAD."  To my knowledge ASHRAE 62.1 doesn't allow ventilation from interior zones to compensate for perimeter zones that have little or no primary air flow.  Also, ASHRAE 62.1 requires ventilation in corridors anyways so this argument seems to be just as weaselly.  ASHRAE 62.1 requires zones to be adequately ventilated during all load conditions, which includes no load or heating load

UFAD seems to be touted as the Messiah of multi-story office HVAC, but the lack of ventilation air appears to be a glaring omission.  Am I missing something about these systems?

Does anyone know how to design a UFAD system that complies with ASHRAE 62.1?  Surely there have been several successful LEED certifications for projects utilizing UFAD technology;  does anyone know if the USGBC has given guidelines for this issue?


 Dan Russell, EIT

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