Does anyone have any experience with changing the Furniture Weight and
Fraction of Floor Area options?
I think most people don't include alterations in furniture mass in an
eQUEST simulation, so it's usually left as default with the assumption that
it covers a typical building. And I think anyone designing a passive style
building would opt for a different tool other than eQUEST to optimize the
building characteristics, but I'm interested to know how the model affects
our day-to-day simulations.
After reading the help files, it's not obvious as to why there needs to be
both a "floor weight" and a "fraction of floor covered" as both are used to
define a square footage of furniture in relation to the floor area. What I
found from the engineers manual is that the floor weight is used to define
the surface area of the furniture (including top, bottom, and sections
facing the walls) which can exchange radiant and convective energy with all
other surfaces in the room, while the fraction of floor area is used to
calculate the percent of the floor covered by furniture looking down and is
used to estimate the percent of a radiant pulse from a source (solar,
lighting, occupants) that would normally strike the floor which is shielded
by the furniture.
According to this definition, I would expect the surface area as defined by
"floor weight" to be greater than or equal to the surface area defined by
"fraction of floor area". And since DOE2 models furniture as a very thin
(2-3 inch) slab, I would expect the surface area to be around twice the
fraction of the floor area. (i.e. the furniture will be able to exchange
energy from the top and bottom sections of the slab, while only the top
intercepts a radiant source to block it from reaching the floor.) However,
I found this not to be the case with the defaults in eQUEST. From the
engineers manual, the "Heavy" type furniture has a Characteristic Weight of
20 lbs/sf of floor area, and with the default Weight of 2.00 lbs/sf this
gives a surface area of 10% of the floor area. The default value for the
fraction of floor area is 20%. This seems to be modeling a situation which
is physically impossible--an object with a surface area of X cannot then
have any cross sectional area of 2X. By default, should we be using a floor
weight closer to 8.00 lbs/sf for a 20% fraction of floor area?
These values are not used on an hourly basis, but they are used to
determine weight factors which are used to calculate hourly loads. In a
building I'm working on, increasing the furniture surface area to twice the
fraction of floor area decreased the peak load by 1.6%, so in the grand
scheme of things, I guess it's not that important. But if anyone has any
insight, I'd appreciate your comments.
Aaron
