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

[Guo Zhou]

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] *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.
> 
> 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
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20050919/93ba3449/attachment-0002.htm>