Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page
Ask Your Question
1

Unexpected Negative Conduction on Hot Day

asked 2025-06-30 04:21:55 -0500

Twose10's avatar

updated 2025-06-30 10:23:28 -0500

Hello everyone,

I am having logic issues with some results on energyplus cooling load simulation (15 August). The main issue is that my exterior walls are showing negative Surface Inside Face Conduction Heat Transfer Rate while Outdoor Surface Temperature (37ºC) is above Interior Surface Temperature (21ºC).

Simulation is showing Peak Load at 7:30am from one NE space, which makes sense. What does not make sense is having negative conduction when outdoor surface temp is hotter. Following you can see graph of these hourly day simulation.

image description

Thanks in advance, Hope you make me see the light in this phenomena analysis

edit retag flag offensive close merge delete

1 Answer

Sort by » oldest newest most voted
1

answered 2025-06-30 08:27:16 -0500

Twose10's avatar

SOLVED:

The unexpected results were due to the significant impact of radiation on heat transfer within the space. In the Surface Heat Balance equation: Surface Conduction to Exterior = Surface Received Radiation – Convection to Zone Air, the result turned negative because the incoming radiation exceeded the convective heat transfer to the zone air.


Notes:

  • This was confirmed by reducing the solar absorptance and thermal absorptance of the interior material to near zero, which minimized the effect of radiation.
  • It was also observed that as the windows of the space begin to receive sunlight, surface conduction progressively decreases. This confirms that increased radiation reduces conduction—potentially enough to make it negative.
  • To better understand the phenomenon, the following outputs were compared: Surface Inside Face Conduction, Surface Outside Face Conduction, and Surface Heat Storage.
  • An image showing the comparison and supporting the explanation is attached.

image description

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Training Workshops

Question Tools

1 follower

Stats

Asked: 2025-06-30 04:21:55 -0500

Seen: 43 times

Last updated: Jun 30