I am seeking opinions on the validity of my method of
calculating internal mass for a model I am studying.
My building has a core zone surrounded by unoccupied shell
zones that include glazing (the glass is diffusing). I must condition the
shells to avoid high surface temperatures from solar gains on critical
components in the shell zones (I can’t change the building, only the
conditioning air). I ran an initial series of models that included: no
internal shell mass, an assumed internal mass, and double the assumed internal
mass to get a feel for the internal mass impacts.
The interior mass for the trial analysis was a 6mm steel
plate exposed on both sides. Having internal mass improved my shell zone
performance. Double the mass by increasing thickness made further
improvement, but double the mass by increasing the surface area made even more
of an improvement. Consequently I determined that I need reasonable internal
mass surface areas for this model to work properly. My initial mass
estimate (area and mass) is only a fraction of what I have in the actual
building shell zone.
The actual internal mass is not a wall but a space frame
structure composed of round tubular steel members. I have created internal
mass objects with the exterior surface area of the tube (the part that “sees”
the zone) and double the wall thickness (the inside of the tube looks at itself
and does not exchange with the zone directly). I have also been conservative
in calculating internal mass by using only the primary members of the space
frame (about 95% of the total space frame weight) and not including additional
cladding attachment steel in the total.
If you have experience with similar modeling and actual building
performance I would appreciate your opinion on the potential simulation
accuracy.
Thanks in advance…
Ned
Lyon
Staff Consultant
SIMPSON GUMPERTZ & HEGER
| Engineering of Structures and Building Enclosures
41 Seyon Street, Bldg. 1, Suite 500
Waltham, MA 02453
781.907.9000 main
781.907.9350 direct
781.907.9009 fax
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