[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[EnergyPlus_Support] Re: Problem with very thin high conductivity construction
Some thoughts:
Do you know there is a third approach. You can overwrite the zone volume in the zone object.
If your ceiling tiles are unpainted, I may believe the 1 mm thickness.
Yes I have also reached limitations, but usually found a work around like changing the material properties somewhat.
If you have a de-presurized ceiling space because you are using it a air distrubution or extraction system, then model the seperate zone. Otherwise, I wouldn't.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "smporritt" <mail@...> wrote:
>
> I have come across a problem with modelling thin metal ceiling tiles and wonder if anyone can shed any light on the issue.
>
> I am modelling retrofit options for an airport terminal building, which consists of a large low zone (30m x 20m, ceiling height 2.7m), glazed along one long wall, with metal ceiling tiles (steel: thickness 0.001m, conductivity 50 W/mK, density 7800 Kg/m3, specific heat 450 J/KgK). Above the ceiling tiles is a cavity to an insulated metal deck roof.
>
> I have tried two modelling approaches, the first being to build a single zone with a flat roof construction consisting of the metal tiles, an air gap and the insulated metal deck (called my integrated roof version). I have also built a version with a separate semi-exterior unconditioned zone above the occupied zone to represent the roof void to allow control over ventilation to the roof cavity, which I need to do later in my modelling (separate roof version). In both cases the zone volumes were kept the same.
>
> The results for annual heating and cooling energy use using the two construction methods are very different, with the separate roof construction method using over 40% less cooling energy. However, if I replace the metal ceiling tiles with other lower conductivity materials, such as conventional ceiling tiles or plasterboard, the differences between the modelling methods are small (around 1%). Even if I reduce the thickness of the plasterboard to 0.001m the difference in cooling energy is less than 3% when comparing the integrated roof version to the separate roof version.
>
> I have tried many tests, including building new models from scratch, EnergyPlus v6 compared to v7, CTF vs CFD, different timesteps and algorithms and reducing the roof air cavity to a very small depth to minimise differences between the modelling approaches. In all cases I am not getting any errors (e.g. convergence) reported by EnergyPlus. Using CFD I have also looked at node temperatures to see if anything odd is happening (oscillating at timestep), but apart from the temperatures being very different there is nothing odd happening.
>
> If I increase the thickness of the metal ceiling tiles to 0.008m or more the results from the two methods converge, likewise if I reduce the conductivity of the metal tiles to around 10 W/mK or less the results converge. I also tried splitting the metal tiles into 2 x 0.0005m layers and adding a very low resistance no mass material layer between them and in that case the results were very similar for the two modelling approaches.
>
> Is anyone aware of any issues with EnergyPlus modelling very thin high conductivity constructions? I have searched the forums and EnergyPlus documentation and can find no mention of this being an issue. Any help or thoughts gratefully received, thanks.
>
------------------------------------
Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/EnergyPlus_Support/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/EnergyPlus_Support/join
(Yahoo! ID required)
<*> To change settings via email:
EnergyPlus_Support-digest@xxxxxxxxxxxxxxx
EnergyPlus_Support-fullfeatured@xxxxxxxxxxxxxxx
<*> To unsubscribe from this group, send an email to:
EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/