Glenn,<br>
<br>
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.<br>
<br>
Guo.<br>
<br><br><div><span class="gmail_quote">On 9/19/05, <b class="gmail_sendername">Glenn Haynes</b> <<a href="mailto:glenn.haynes@rlw.com">glenn.haynes@rlw.com</a>> wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">Guo,</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">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.</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">Glenn
Haynes</span></font><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"></span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<div>
<div style="text-align: center;" align="center"><font face="Times New Roman" size="3"><span style="font-size: 12pt;">
<hr align="center" size="2" width="100%">
</span></font></div>
<p><b><font face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma; font-weight: bold;">From:</span></font></b><font face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma;">
<a href="mailto:bldg-sim@gard.com" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">bldg-sim@gard.com</a> [mailto:<a href="mailto:bldg-sim@gard.com" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">
bldg-sim@gard.com</a>] <b><span style="font-weight: bold;">On
Behalf Of </span></b>Guo Zhou<br>
<b><span style="font-weight: bold;">Sent:</span></b> Friday, September 16, 2005
2:47 PM<span class="q"><br>
<b><span style="font-weight: bold;">To:</span></b> <a href="mailto:bldg-sim@gard.com" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">bldg-sim@gard.com</a><br></span><span class="q">
<b><span style="font-weight: bold;">Subject:</span></b> [bldg-sim] plenum
temperature and roof heat transfer using eQuest</span></span></font></p>
</div><span class="q">
<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
<p style="margin-bottom: 12pt;"><font face="Times New Roman" size="3"><span style="font-size: 12pt;">Dear All,<br>
<br>
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.<br>
<br>
The following are the findings:<br>
On hot summer days(outside dry bulb above 100 degree F), when the rooms are
controlled to maintain 75 degree F:<br>
<br>
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.<br>
<br>
2. with R-11 roof and R-19 ceiling, the plenum temperature is 5~8 degree F
higher than room temperature<br>
<br>
3. with no roof insulation and R-19 ceiling, the plenum temperature can reach
93 degree with outside is 103 degree.<br>
<br>
4. in all above 1,2 and 3 cases, the plenum temperature results from
return-air-path = plenum-zones and duct are identical.<br>
<br>
I think the actual plenum temperature would be much higher than the simulation
results. Especially in case #3.<br>
<br>
Can anybody please tell me what you think about it? What's causing it?<br>
<br>
As a result, the cooling load from the roof being largely underestimated...<br>
<br>
Thanks.<br>
<br>
Guo</span></font></p>
</span></div>
</blockquote></div><br>