Re: [EnergyPlus_Support] Re: Trying to explain temperature differences in a room with conduction

Sarah,

In case you might have missed it. Since a new chain has formed in the support group for your query. Jeffrey has a really good strategy for you to test your model.

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Jeffrey Spitler
Sent: Thursday, August 15, 2013 11:18 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: Trying to explain temperature differences in a room with conduct

Have you set the exterior surface thermal absorptances to zero or a small number like 0.001? That will effectively turn off radiation exchange with the environment regardless of what the sky model is doing.

Jeff Spitler

That sounds like a very simple and effective strategy!

James V Dirkes II, PE, BEMP, LEED AP
www.buildingperformanceteam.com
Energy Analysis, Commissioning & Training Services
1631 Acacia Drive, Grand Rapids, MI 49504 USA
616 450 8653

On Thu, Aug 15, 2013 at 10:06 AM, ilikemyselfmore <ilikemyselfmore@xxxxxxxxx> wrote:

Niraj,

I'll try to change the sky temperature in the .idf file, I didn't think of that before. Thanks. I'll keep you posted.

Attached is a copy of my .epw file if you want to have a look but I doubt it will be interesting.

Sarah

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Niraj Poudel <nirajpdl@...> wrote:
>
> Sarah, could you attach your .epw file so we can have a look at it? I think
> you might also have to change the sky temperature in your .idf file to stay
> constant at a certain value to prevent the heat loss to the sky. If I
> remember correctly, the sky temperature defined in the .idf file takes
> precedence or overwrites horizontal infrared radiation. You might have to
> look into the documentation for the answer to that.
>
> Niraj
>
>
> On Thu, Aug 15, 2013 at 8:17 AM, ilikemyselfmore
> <ilikemyselfmore@...>wrote:
>
> > **

> >
> >
> > Thank you all for your answers.
> >
> > I did change the solar variables in the weather file. And I also thought
> > about energy exchange with the sky, but I didn't find a way to reduce its
> > effect. The value for the horizontal infrared radiation is already 0 in my
> > weather file. Do you have any other suggestions?
> >
> > Sarah
> >
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Niraj Poudel <nirajpdl@>
> > wrote:
> > >
> > > I totally agree with Jim. I had performed such a study about 2 years ago
> > > when it was possible to set the convective coefficient of walls to really
> > > minuscule values. Now, I dont think Eplus allows you to set such low
> > > convective coefficient values without generating a warning or error of
> > > sorts.
> > >
> > > The radiant exchange with the sky during the night, on the other hand, is
> > > considerably high and that explains the -5 oC temperature on the roof.
> > If I
> > > remember correct the radiant exchange is tied to the infrared solar
> > > radiation (or the horizontal infrared radiation) data in the .epw file.
> > > Manipulating that value could help your cause.
> > >
> > > Niraj
> > >
> > >
> > > On Wed, Aug 14, 2013 at 6:34 AM, Jim Dirkes <jim@
> > > > wrote:
> > >
> > > > **
> >
> > > >
> > > >
> > > > Oops. I missed the description "no wind and no sun on these surfaces".
> > > > I'm not sure how you can model without sun unless you also changed the
> > > > solar variables in the weather file, but I doubt you can model without
> > > > radiant energy exchange to the sky.****
> > > >
> > > > ** **
> > > >
> > > > *James V Dirkes II, PE, BEMP, LEED AP**
> > > > **www.buildingperformanceteam.com*<
> > http://www.buildingperformanceteam.com/>
> > > > *
> > > > **Energy Analysis, Commissioning & Training Services**
> > > > *1631 Acacia Drive, Grand Rapids, MI 49504 USA
> > > > 616 450 8653****
> > > >
> > > > ** **
> > > >
> > > > *From:* EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:
> > > > EnergyPlus_Support@xxxxxxxxxxxxxxx] *On Behalf Of *Jim Dirkes
> > > > *Sent:* Wednesday, August 14, 2013 7:23 AM
> > > > *To:* EnergyPlus_Support@xxxxxxxxxxxxxxx
> > > > *Subject:* Re: [EnergyPlus_Support] Trying to explain temperature
> > > > differences in a room with conduction****
> > > >
> > > > ** **
> > > >
> > > > ****
> >
> > > >
> > > > And radiant energy exchange with the sky
> > > >
> > > > Jim Dirkes II ****
> > > >
> > > > Building Performance Team****
> > > >
> > > >
> > > > On Aug 14, 2013, at 7:10 AM, "ilikemyselfmore" <ilikemyselfmore@>
> > > > wrote:****
> > > >
> > > > ****
> >
> > > >
> > > > Dear Group,
> > > >
> > > > I am currently trying to simulate a room with no internal loads
> > (people,
> > > > lights and electric devices), no convection (no wind, no ventilation
> > and
> > > > infiltration). I am trying to show only the conduction effects through
> > the
> > > > walls, so I also tried to reduce the effects of the radiation.
> > > >
> > > > To make sure that my simulation would work, I created an EPW file with
> > a
> > > > constant Dry Bulb Temperature at 5°C. Normally, the operative
> > temperature
> > > > in the room after a few weeks/months should also be 5°C. However, after
> > > > running the simulation, I got 0.5°C in that room. All the 6 surfaces
> > are
> > > > made of 20cm thick concrete, and they are towards the outside. There
> > is no
> > > > wind and no sun on these surfaces.
> > > > I observe that the roof outside surface is -5°C and that the floor
> > outside
> > > > surface is +5°C, but I am not sure how to explain these differences.
> > Does
> > > > anyone have an idea?
> > > >
> > > > Thanks for you attention,
> > > >
> > > > Sarah****
> > > >
> > > > ****
> > > >
> > > >
> > > >
> > >
> > >
> > >
> > > --
> > > *Niraj Poudel, Architectural Engineer.*
> > > *PhD student, PDBE Program.*
> > > *Clemson University, Clemson, SC.*
> > > Linkedin: http://www.linkedin.com/pub/niraj-poudel/19/1ba/568
> > >
> >
> >
> >
>
>
>
> --
> *Niraj Poudel, Architectural Engineer.*
> *PhD student, PDBE Program.*
> *Clemson University, Clemson, SC.*
> Linkedin: http://www.linkedin.com/pub/niraj-poudel/19/1ba/568
>

Niraj Poudel, Architectural Engineer.

PhD student, PDBE Program.

Clemson University, Clemson, SC.

Linkedin: http://www.linkedin.com/pub/niraj-poudel/19/1ba/568