Modeling a simple basement?

[jamesmustillo]

I can't seem to find how to model a typical basement in any of the WUFI or PHIUS manuals (or elsewhere online).

I am modeling a typical two story house with a conditioned, but unfinished, basement below grade. There is no insulation or air barrier between the basement and the first floor; it falls within the thermal envelope.

Right now I have put the basement wall and slab details into the "Foundation Interface" tab and I have it as a separate Simulated Zone (Upper Floors=Zone 1, Basement=Zone 2). However, it seems like the basement will be counted twice when modeled like this: once in the Foundation Interface, once by the Simulated Zone.

So my question: how should the basement geometry be modeled, as an Attached Zone or a Simulated Zone?

If it is an attached zone, how do I figure out the Temperature Difference Reduction Factor?

J

[woodenrings]

I don't believe you draw the unheated basement but rather set it up in the foundation tab https://youtu.be/0oLvRNKt-Hs

[hbreaux]

If the basement is within the thermal boundary, it should be modeled as a zone...not as an attached zone. An attached zone is for those that abut against and are not contained within thermal boundary. The foundation interface needs to be set for every project so it should not be double counting.

[Graumlich]

Reading this thread, am I seeing consensus in that one should both model the basement AND set it up as a basement in the "foundation interface" tab? And that such an input does NOT doublecount anything?

I'm running into a similar issue as above where I've fully modeled my heated basement as part of the primary building zone. But when switching the foundation interface from "on grade" to "heated basement", I'm losing an extra 1000 kBtu/yr during the heating period and 1000 kBtu/yr in my cooling period. Which, as one might expect, is a problem, and I want to make sure I understand the above conversation before I chase my tail for a day or two.