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

John E. Beeson jbeeson at quinnevans.com
Wed Nov 5 06:14:10 PST 2008

I passed your note over to some experienced UFAD mechanical engineers
(they have done many projects with UFAD that met LEED and ASHRAE 62.1).
The response is below.  I hope this helps some!

 Sent: Tuesday, November 04, 2008 4:15 PM
Subject: RE: ASHRAE 62.1 Compliance with Underfloor-Air Distribution

A combination of factors and options must be considered. Most UFAD
systems include large open office areas, for which C02 monitoring can be
applied, and there is a non-trivial amount of general leakage of supply
air through the floor and the diffusers, even in minimum settings.
Depending on the UF plenum pressure and the floor and carpet systems
used, this may be 0.25 CFM per SF, beyond what the diffusers provide at
their minimum. Some UFAD diffusers have definable minimum stops, and
some (e.g. the Titus TAF-LV system) can be designed and controlled to
provide a minimum aperture area, which, in conjunction with known
underfloor plenum pressures, can provide defined amounts of supply air.




From: bldg-rate-bounces at lists.onebuilding.org
[mailto:bldg-rate-bounces at lists.onebuilding.org] On Behalf Of Dan
Sent: Tuesday, November 04, 2008 11:07 AM
To: bldg-rate at lists.onebuilding.org
Subject: [Bldg-rate] ASHRAE 62.1 Compliance with Underfloor-Air

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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