# [EnergyPlus_Support] Re: Outside Surface Temperature - Conduction Finite Difference Method

```Diwanshu,

You are correct. The Solid green line in the Sketchup Axes is the true north. If your outside surface is facing in that direction your wall is facing true north with zero degree rotation. And you would basically rotate your building with respect to that direction (i,e with reference to the solid green axis). Thanks for clarifying it further.

Sincerely yours'
Niraj Poudel
Clemson University

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Shekhar, Diwanshu" <diwanshu.shekhar@...> wrote:
>
> Niraj,
>
> I am a little confused about what you meant by true north. May be we both are on the same page. But here is how I have understood the coordinate system in Openstudio Sketchup plugin. Solid green line is north. Dotted green line is south. Solid  red line is east and the dotted red line is west. (For example: if an outside surface is facing towards the dotted green line, the surface is a south facing surface). I can understand how this can be confusing. A visual would help understand  but I can't seem to find any. I just thought of a better way to understand this. Put yourself inside the building and look towards a direction, say South (towards dotted green line); the outside face towards that direction would be the south facing surface.
>
> Please correct me if I am wrong or let me know if you meant the same.
>
> Diwanshu
>
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Niraj Poudel
> Sent: Friday, June 17, 2011 9:37 AM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Subject: [EnergyPlus_Support] Re: Outside Surface Temperature - Conduction Finite Difference Method
>
>
>
> Dear Ooi,
>
> The reason why I am using CFD as opposed to CTF for my simulation is because I intend to place PCM (Phase Change Materials) in my test hut. And as Dr. Li pointed out, I am working on a research project therefore am trying out different algorithms. Initially I did run the simulation using the CTF algorithm.
>
> However, to get back to the original topic. I apparently made a mistake in naming the walls in OpenStudio. So, as a result I was getting higher outside surface temperatures on the North Facade as opposed to the South Facade. Apparently the true north in GoogleSketchup Openstudio is the negative Y-axis (Cartesian Co-ordinates). Eg. Your north face will be facing towards the Negative(-) y-axis if you set your rotation to zero(0). It makes sense, because if you look at your building in plan view, true north will point upwards, which is the negative y-axis if you look at it from a perspective point of view. (I hope my rambling made some sense here)
>
> Anyways, thank you both, Dr. Li and Ooi for your responses.
>
> Sincerely yours'
> Niraj Poudel
> Clemson University
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>, YuanLu Li <yli006@> wrote:
> >
> >
> > When one is doing resaerch, it is logical to try different algorithm used for calculation.
> >
> > CTF and CFD should provide the same result, within their limitations.
> >
> > Outside surface temperature calculation is TARP based and it should not be different with the two different algorithm for the material.
> >
> > The above is for discussion only, and I welcome more information on this topic..
> >
> > Dr. Li
> >
> >
> >
> >
> >
> >
> > To: EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>
> > From: ooi_kb3@
> > Date: Thu, 16 Jun 2011 08:37:51 +0000
> > Subject: [EnergyPlus_Support] Re: Outside Surface Temperature - Conduction Finite Difference Method
> >
> >
> >
> >
> >
> >
> > Hi,
> > May i know why you do not use Conduction Transfer Function? Thank you. i would only use CondFD if (1) one of the material in the construction of the wall is phase change material or (2) i want to know the temperature within the construction.
> > ooi
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>, "nirajpoudel@" <nirajpoudel@> wrote:
> > >
> > > Dear EPlus users,
> > >
> > > When I run a simulation using the ConFD algorithm of a test hut (3m by 3m by 3m - 0 degree North orientation) located in Greenville, South Carolina. The outside temperature of the north facade during first two weeks of July comes to be 25-30 degree Celsius more than the corresponding South Outside surface temperature at 12:00 Noon. I have checked the sun path diagram of GreenVille for the first two weeks of July and it looks to me that the south wall outside surface temperature needs to be considerably more than the North wall. Unless, there is a considerable Heat conduction from the east and west walls towards the North. (From the east wall during the morning and from the west during the evening). Am I missing something here?
> > >
> > > Thanking you in advance,
> > > Niraj Poudel
> > > Clemson University
> > >
> >
>

------------------------------------

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.

<*> 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/

```