[esp-r] about creating back-to-back surfaces in esp-r

[Jon Hand (clcv10)]

A follow-up to recent comments on creating internal mass in zones...

>
> Where do I create a back to back surface? How do I make columns  
> hanging in the mid air?
>

In the geometry menu there is a item to manage surface edges
and in that item the add surface choice has an option to
create either a vertical or horizontal rectangle (you provide
the origin of the rectangle and its two dimensions).

An approach adopted by a number of users is to ensure
that internal mass does not touch or penetrate the
bounding surfaces of the room and does not share
vertices with the bounding surfaces of the room.

Once the new surface has been added, attribute it with
a construction which represents the mass (see below)
and give it a name that reminds you that it is internal
mass.

The next step is to use the add surface function a 2nd time but
this time choose the copy surface in this zone option.  Select
the new rectangle you just created as the surface you want
to copy and then choose the invert edges option.  This will
create the opposite face of the internal mass.

The last step is to attribute the boundary conditions of
each of these new surfaces.  There are two schools
of thought:

- the traditional approach is to assign an
adiabetic type to both surface.  Thus they act as a
thermal sponge, but no heat crosses from one face
to the other.  In this approach the constructions used
should each represent half the thickness of the actual
mass of the entity.

- an alternative approach is to treat the two surfaces
as partitions (i.e. connect each to the other).  This
approach allows heat to flow from the front to the back
of the surface as well as acting as thermal mass. For
this to work well use a shorter timestep.

If internal mass has been added to a room it interacts
just as any other surface in terms of longwave and
shortwave radiation and convection.  Consider whether
radiation viewfactors should be calculated and also
whether you should include a shading/insolation
analysis so that sunlight falling on the mass at specific
times is properly recorded.

-ESRU