Question-and-Answer Resource for the Building Energy Modeling Community
Get s tarted with the Help page
Ask Your Question
2

Adiabatic (asymmetrical) walls in Eplus

asked 2016-11-07 08:08:19 -0500

Elbaek gravatar image

updated 2016-11-08 15:47:11 -0500

Hi.

I've been reading up on how Eplus handles the adiabatic boundary condition. Documentation says: "EnergyPlus will apply the same boundary conditions to each side of the construction so that there is no temperature difference across the surface."

I get why this would work well for symmetrical walls, but what if you have a typical concrete slab floor with insulation and wood on top? As far as i can tell, wouldn't that cause potential heat exchange/loss to that construction element?

Hope that was clear. :)

edit retag flag offensive close merge delete

1 Answer

Sort by ยป oldest newest most voted
2

answered 2016-11-08 14:19:17 -0500

Archmage gravatar image

There can be plenty of heat exchange in and out of all kinds of surfaces with "Adiabatic" boundary condition regardless of symmetry in the construction. The same boundary conditions get applied to both faces of the surface, but the surface still can have heat capacity and it is likely to be hotter or colder than the surroundings at times. An asymmetrical construction might not end up with symmetrical surface temperature results at the faces at any given time, but over time it will average out. It is just a temporal artifact of how thermal storage charging and discharging happens.

edit flag offensive delete link more

Comments

Hi Archmage.

I'm aware that adiabatic walls still contribute to thermal mass (as they should). What i'm not convinced entirely of is that you can be sure no heat is 'lost' through these walls when they are not symmetric.

The same boundary conditions on a symmetric wall would create an adiabatic layer directly in the middle of the wall, where heat from each zone would never diffuse through. For assymetrical walls (eg. 100 mm insulation followed by 100 mm concrete) in buildings where temperatures are fluctuating - can you be certain of the creation a truly adiabatic layer?

Thank you, Rasmus

Elbaek gravatar image Elbaek  ( 2016-11-09 04:20:49 -0500 )edit

Your Answer

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

Add Answer

 

Question Tools

1 follower

Stats

Asked: 2016-11-07 08:08:19 -0500

Seen: 166 times

Last updated: Nov 08 '16