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

How does CSE deal with low mass surfaces when using forward-difference

asked 2022-12-18 16:48:14 -0600

cmui's avatar

updated 2022-12-18 19:00:57 -0600

I've been reviewing the code for CSE and haven't been able to find an easy answer to the following question -

How does California Simulation Engine avoid numerical instability while using euler forward difference surface models with fixed time steps (usually 2 mins)? Thin exterior layers that see solar are particularly problematic.

Are there adaptive time steps, or are exterior layers treated as massless?

edit retag flag offensive close merge delete

2 Answers

Sort by ยป oldest newest most voted
2

answered 2023-01-04 13:01:45 -0600

Chip Barnaby's avatar

My recollection is that fictious mass is added to lightweight layers to ensure numerical stability. Note that this approach can handle massless materials (ideal resistances) in addition to real light materials.

However, I could not find the details in the code with a bit of poking around.

If you make and send an example file with some cases that might cause trouble, I can trace through the code and find how the adjustment is made.

edit flag offensive delete link more

Comments

Thanks for the reply Chip! The test case here has 9mm wood siding in CONSTRUCTION lw_wall. Could be a good way to see this code path.

https://github.com/cse-sim/cse/blob/main/test/1ZAttic.cse

cmui's avatar cmui  ( 2023-01-05 15:53:02 -0600 )edit
1

answered 2022-12-23 11:08:15 -0600

CSE performs adaptive discretization of the material layers in order to ensure numeric stability. This discretization is performed once for each material layer in the simulation based on the timestep and the thermal properties of the material.

edit flag offensive delete link more

Comments

Thanks! That's helpful. Do layers ever get merged in nodal representation if their time constant is too small. Ie. 9mm of wood siding on the outside of a wall construction, perhaps getting merged with the stud and fiberglass properties of the layer behind it.

cmui's avatar cmui  ( 2022-12-25 13:44:34 -0600 )edit

Your Answer

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

Add Answer

Training Workshops

Careers

Question Tools

Stats

Asked: 2022-12-18 16:48:14 -0600

Seen: 130 times

Last updated: Dec 23 '22