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

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@xxxxxxxxxxxxxxxxxxxxxxxxxxx> 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
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@xxxxxxxxx> 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