[Bldg-rate] ASHRAE 62.1 Compliance with Underfloor-AirDistribution

John E. Beeson jbeeson at quinnevans.com
Thu Nov 6 06:17:35 PST 2008

The simplified response from the engineer (he's pretty busy right now,
so I don't want to press much) is:
"Talk to floor manufacturers. Model all energy and air flow paths.
Expect improvements in energy programs. Monitor CO2." 
Some comments from past discussions with him about UFAD and the GSA that
may be of some use to you:
Starting with this article:
GSA Moving Towards Ban on Underfloor Air Distribution 

"Thanks for referring this. The past several releases of the GSA P-100
standard have incrementally retreated from an earlier strong UFAD


We need to inform the GSA and those refining the energy modeling of our
recent use of insulated ceramic coatings on the top of the floor slab
and exterior plenum edges, which offers multiple benefits: 

*	It helps seal the supply air plenum against air leakage, 
*	it increases the R value (by 3 or more, depending on coating
thickness) between the supply air plenum and the return air plenum
typically located beneath it, 
*	it insulates the supply air plenum from the exterior wall's
typical strong conductive path to the floor slab/structure, thus
directing a greater portion of the absorbed solar/conductive heat gain
into the return air plenum and into thermal storage instead of into the
supply air plenum, 
*	it helps speed the morning cool-down process by reducing the
thermal link to the mass of the slab, and 
*	it provides a clean, known surface in the supply air plenum
(addresses construction dust in all projects and adhesive/VAT/other
residues in renovation projects). 

<snipped..> The article's mention of GSA possibly delaying judgment
until definitive load calculation procedures are available is on point.
That also would allow the benefits of top-of-slab ceramic insulation
coatings to be quantified and assessed for cost-effective thicknesses/R


The Center for the Built Environment at the University of California,
Berkley, has done some notable UFAD modeling, including some runs with
insulation below the floor slab, but not on top (they weren't aware of
the possibility). I had discussed the advantages of the latter approach
[i.e. as above] with them, and they were intrigued with the
possibilities, though their research docket was heavily loaded."


John E. Beeson, LEED AP 
d 734 926 0425 



From: Dan Russell [mailto:danr at engineeringinc.com] 
Sent: Wednesday, November 05, 2008 10:51 AM
To: John E. Beeson; bldg-rate at lists.onebuilding.org
Subject: RE: [Bldg-rate] ASHRAE 62.1 Compliance with



Thanks for the response.  I suppose when designing a UFAD project one
needs to utilize controllable diffusers with adjustable minimum settings
or determine acceptable leakage rates through access-floors and
diffusers.  The latter, I'm sure, will take a greater degree of
coordination with the architectural team, and would likely need to be
documentable to satisfy the USGBC.  Do your colleagues have any common
resources for determining the expected leakage through access-floor
assemblies?  The diffuser leakage should be attainable, I would imagine,
from the diffuser manufacturer.  


This whole idea of using leakage to meet ventilation requirements is
sort of funny when I think of at least one premier LEED Platinum
building that was constructed in the downtown area here in Boise, ID.
When the air balance was being performed for the air handlers they
determined that they were losing a significant amount of air thru the
floor system.  So, the construction/design (I'm not sure which) decided
this was a problem that needed to be solved because leakage was
unacceptable in their minds.  The story goes that they proceeded to hire
a bunch of high-school kids to come in and tape every access-floor joint
in the building...floor-by-floor, wing-by-wing until it was completely
"sealed up."


I have no idea what the actual leakage rate was before or after this
process, but I would think for it to be a good design one would need
some documentation or accepted calculation methodology for accurately
determining the real leakage rate thru the floor system.  Also, this
leakage rate, though small, should probably be considered in a space
heating load calculation.  Furthermore, leakage if present should be
accounted for in energy simulations either as re-heat load, or reduction
in cooling load - which I don't recall reading in the UFAD modeling
resources I have used.


Lastly, with leakage at 0.25 CFM/SF that will rarely be sufficient to
meet minimum ventilation requirements unless the OA% at the air handler
is near 100%.  With that in mind, it seems almost imperative to have
controllable minimum setpoints on the UFAD diffusers so that compliance
with ASHRAE 62.1 can be calculated, documented, and realized.


Quick recap of questions I posed above:


1.       Are there any commonly accepted calculation methodologies for
determining the expected leakage through access-floor assemblies?

2.       Should UFAD designers consider leakage as increased space
heating load or reduced space cooling load?

3.       How are energy simulations accounting for expected leakage?


Thanks again for your response,


 Dan Russell, EIT 


cid:image001.jpg at 01C840A4.E711B250


From: bldg-rate-bounces at lists.onebuilding.org
[mailto:bldg-rate-bounces at lists.onebuilding.org] On Behalf Of John E.
Sent: Wednesday, November 05, 2008 7:14 AM
To: bldg-rate at lists.onebuilding.org
Subject: Re: [Bldg-rate] ASHRAE 62.1 Compliance with Underfloor-Air




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 


cid:image001.jpg at 01C840A4.E711B250


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