[bldg-sim] plenum temperature and roof heat transfer using eQuest
Guo Zhou
guozhou2005 at gmail.com
Fri Sep 16 11:46:35 PDT 2005
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.
Can anybody please tell me what you think about it? What's causing it?
As a result, the cooling load from the roof being largely underestimated...
Thanks.
Guo
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