I had a question yesterday regarding heat transfer through interior walls.
I think this comes up on the list fairly frequently - why is my LS-C (or
LS-B) report showing no heat transfer across internal surfaces when I know
my garage or attic is colder than the adjacent spaces. Is this heat loss
really being reflected in the model - and if so, why isn't it in the LOADS
reports?

Here was my answer - (corrections & clarifications are welcome):

What you are doing to model the effect of insulating the floor between the
garage and the ground level is correct. eQUEST will calculate the heat loss
across that interior surface floor and show the impact of the insulation.
The main issue is finding it. I imagine you are looking at the LS-C or LS-B
report which show no internal conduction. The issue here is how the
calculations are sequenced in DOE-2. In the LOADS, we are calculating the
envelope heat loss then in SYSTEMS we are calculating the HVAC response.
But, until the HVAC response is calculated, we don't know what the space
temperature is so we can't calculate the envelope heat loss as we don't know
the delta-T between inside and outside. So, for LOADS, we give the space
temperature an initial guess - keyword Temperature in the SPACE. By
default, all spaces have their temperature set to 70F - this is why you see
no internal heat loss in the LS- LOADS reports as the temperature is the
same for all zones. You could set the annual average temperature down in
the garage so that the heat loss shows here but it is not that important.
As long as in the zones, the keyword SIZING-OPTION is set to ADJUST-LOADS
then in SYSTEMS, the actual space temperature will be used to recalculate
the heat loss.

So, the heat loss is there - you can reassure yourself of this by creating
an interior wall of nearly infinite resistance, apply it as a parametric
run, and see the space heating in the adjacent zones go down. You can also
create hourly reports that look at the parameters of the zones. One of the
hourly variables (23) at the zonal level is "Contrib to the zone load due to
conduction from adj zones (Btu/hr)" -- this is where you will see the
actual hourly heat loss using the actual hourly space temperature for the
zones.

I hope this helps clear up what you are seeing. Please feel free to ask
more if I am not being clear.

Kind regards,

Brian