[Bldg-sim] eQuest: Slab on Grade Ueff Calculation (Underground Wall)

[Kruis, Neal]

Brett,

 

My understanding is that the PERIM-CONDUCT and PERIM-EXPOSED keywords
are not yet implemented in the DOE-2.2 engine (used by eQuest). The
U-EFFECTIVE keyword, taken from the DOE-2.1E engine, is no longer used
in DOE-2.2 (but for some reason the program doesn't complain when you
try to use it - instead it just ignores any input for this keyword).
This doesn't seem to leave much for us to work with. *Does anybody know
if eQuest does something other than specifying the U-EFFECTIVE keyword
when it asks for a U-eff input for underground surfaces? 

 

The concept for all of these keywords comes from a paper released by
Fred Winkelmann in Building Simulation User News Vol. 23, No. 6
(http://gundog.lbl.gov/dirun/23n_d_1.pdf). The article suggests creating
a fictitious resistance layer in the wall to create the correct overall
U-value for the foundation configuration. Using the U-EFFECTIVE keyword
in addition to specifying this fictitious layer seems redundant, and you
should be able to get the same results without specifying it.

 

My suggestion would be to specify the fictitious layer in detailed edit
mode. That is of course if eQuest isn't already doing something behind
the scenes to calculate this layer.

 

 

Neal Kruis

Center for Buildings and Thermal Systems

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, CO 80401

(303) 384-7591

________________________________

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Brett Fero
Sent: Tuesday, March 25, 2008 9:24 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] eQuest: Slab on Grade Ueff Calculation (Underground
Wall)

 

I am modeling a slab-on-grade floor using the methods described under
the help for the U-EFF.  This is the described in the Volume 3: Topics/
Envelope Components / Underground Wall eQuest 3.61e help files.  A
sample calculation is presented for the 100 ft x 50 ft slab-on-grade
floor.  The sample input is given as follows;

LAY-SLAB-1 = LAYERS
     MATERIAL           = ("Soil 12in","Conc HW 140lb 4in (CC03)")
     INSIDE-FILM-RES    = 0.77 ..

CON-SLAB-1 = CONSTRUCTION
     TYPE               = LAYERS
     LAYERS             = LAY-SLAB-1 ..

SLAB-1 = UNDERGROUND-FLOOR
     HEIGHT             = 50
     WIDTH              = 100
     TILT               = 180
     PERIM-EXPOSED      = 300
     PERIM-CONDCUT      = 0.50
     CONSTRUCTION       = CON-SLAB-1 ..

eQuest 3.61e does not appear to accept the PERIM-CONDUCT and
PERIM-EXPOSED keywords as input.  Instead it uses the keyword U-EFF.

In Vol 23, No.6 of the Building Energy Simulation User News for DOE2.1E,
slab-on-grade calculations were presented using the following;

Reff = A/(F2 x Pexp) where Reff = Reffective, A = area of slab (ft), F2
= perimeter conduction factor, and Pexp = exposed perimeter length (ft).

So, is U-EFF required in eQuest 3.61e calculated as U-EFF = 1/Reff = (F2
x Pexp)/Area using F2 factors from Table 9?

Or, is there a way that I should be entering PERIM-EXPOSED and
PERIM-CONDUCT for each floor?

Thanks in advance for any help clearing this up for me.

 

Brett Fero, P.E., LEED AP

RobsonWoese, Inc.

5824 Widewaters Parkway

East Syracuse, NY 13057

 

 

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