# [bldg-sim] plenum temperature and roof heat transfer using eQuest

sjudson at noresco.com sjudson at noresco.com
Tue Sep 20 08:27:30 PDT 2005

```If there are a large number of samples, why would the windspeed be
overstated by sampling at 15 minutes before the hour?

-----Original Message-----
From: bldg-sim at gard.com [mailto:bldg-sim at gard.com] On Behalf Of Jeff
Haberl
Sent: Monday, September 19, 2005 11:52 PM
To: bldg-sim at gard.com
Subject: [bldg-sim] plenum temperature and roof heat transfer using
eQuest

FYI.

You must also enable CWFs, and have properly layered roofs and walls or
the hourly temperature profiles can be meaningless. Even with this it
remains difficult to match meas temps from an attic without manipulating
a proxy variable such as infiltration.

Jeff
BB 8=!  8=)  :=)  8=)  ;=)  8=)  8=(  8=)  :=')  8=)  8=)  8=? BB

Jeff S. Haberl, Ph.D.,
P.E.............................jhaberl at esl.tamu.edu

Professor......................................................Office
Ph: 979-845-6507

Department of Architecture.......................Lab Ph: 979-845-6065

Energy Systems Laboratory.......................FAX: 979-862-2457

Texas A&M University..............................77843-3581

College Station, Texas, USA.......................URL: www-esl.tamu.edu

BB 8=/  8=)  :=)  8=)  ;=)  8=)  8=()  8=) 8=?  8=)  8=)  8= BB

-----Original Message-----
From: bldg-sim at gard.com <bldg-sim at gard.com>
To: bldg-sim at gard.com <bldg-sim at gard.com>
Sent: Mon Sep 19 11:31:24 2005
Subject: [bldg-sim] plenum temperature and roof heat transfer using
eQuest

Glenn,

Thank you for the trick. I will try it out. the problem is I don't have
complete data on measured peak attic temperature for all the cases I
want to study, i.e. with different insulation level, different climate
zone, etc.

Guo.

On 9/19/05, Glenn Haynes <glenn.haynes at rlw.com> wrote:

Guo,

Accurate treatment of radiant heat transfer in attics, etc., is
too cumbersome for an overall building simulation code like DOE2 (maybe
future generations with faster computers...).  A little trick I
discovered to help compensate for the underestimation of attic
temperatures is to put a little glass in the roof deck.  If you get the
right amount, it tends to correct for both summer and winter attic
temperatures.  How much glass depends on a number of variables, but if
you have some idea what that peak temperature is (measured data
indicated about 118-122 degrees F. in St Petersburg, Florida), you can
find the right amount by trial and error.  I found that about 5% was
sufficient to obtain the result I desired.  If you have enough attic
temperature data under differing conditions, you can experiment with
emissivity, U-value, etc.  I just never had enough time to explore those
variables, but it seemed that the right glass area was the most
important variable.

Glenn Haynes

________________________________

From: bldg-sim at gard.com [mailto: bldg-sim at gard.com
<mailto:bldg-sim at gard.com> ] On Behalf Of Guo Zhou
Sent: Friday, September 16, 2005 2:47 PM
To: bldg-sim at gard.com
Subject: [bldg-sim] plenum temperature and roof heat transfer
using eQuest

Dear All,

I'm using eQuest 3.54 to model a simple 5 zone (perimeter +
core) big box retail building with 4' plenum in Fresno, CA. Roof
insulation = R-11, Wall insulation = R-19. Ceiling is not insulated. not
much glazing.

The following are the findings:
On hot summer days(outside dry bulb above 100 degree F), when
the rooms are controlled to maintain 75 degree F:

1. with R-11 roof insulation and no ceiling insulation, the
plenum temperature is very close to room temperature( about 2 degree F
higher) during the day.

2. with R-11 roof and R-19 ceiling, the plenum temperature is
5~8 degree F higher than room temperature

3. with no roof insulation and R-19 ceiling, the plenum
temperature can reach 93 degree with outside is 103 degree.

4. in all above 1,2 and 3 cases, the plenum temperature results
from return-air-path = plenum-zones and duct are identical.

I think the actual plenum temperature would be much higher than
the simulation results. Especially in case #3.

causing it?

As a result, the cooling load from the roof being largely
underestimated...

Thanks.

Guo

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