Dear all,
I performed a simulation of my baseline building over the 4 rotations.
The difference between the lowest consumption and the highest one out of
the 4 runs was only 1.33% (1,312,500 to 1,329,200 kWh).
Is this a normal value? This is my first project but I thought I would
have a bigger number.
Any advice out of your experience is greatly appreciated.
Many thanks,
Omar Katanani
Omar,
Simulation for 4 rotations value will be small difference only, in some of the cases it will be same also. it all depends upon the building location & orientation.
Regards
Soham
Small rotational differences are typical of buildings with similar
surface areas on the east, west, north, and south elevations. I would
only expect a significant difference if you have a very "long"
footprint, or one side of your building is largely unconditioned along
the perimeter. Conceptually, I suppose we're being "rewarded" for
choosing an optimal orientation rotation on the building site - but if
anything we're really being rewarded for designing "long" building
footprints as they can have a larger difference against the averaged
baseline...
That said, if an architect asks me at a conceptual design stage, the
most thermally efficient building shape considering exterior surface
area is theoretically a hemisphere - barring that a "cubic," compact 3D
shape is better than any "long" shape with larger surface area for the
given volume/footprint. If the goal is to maximize LEED points
(relative baseline performance), you might suggest a thermally
inefficient, but optimally-oriented "long" shape that will do better
than it's averaged baseline... (I wouldn't!) If the goal is to reduce
energy consumption/utilities however for the end-users, reduce the
building shape surface area.
NICK CATON, E.I.T.
Interesting hypthesis.
I think it depends. Longer, thinner footprints work better if you are trying to daylight you building. They also wotk better with other passive strategies and natural ventilation. In terms of heat balance, high internal load buildings sometimes shed loads better with more skin.
That being said - it really depends on climate and usage. Balanve point temperature is a good way of studying this.
Vikram is absolutely right...
I've received a few other direct emails, and I'm afraid in creating an
example/illustration I may have been a bit broad in my brushstrokes!
The essential point I was trying to convey is, all other things being
equal, smaller envelope surface areas are generally preferable to larger
surface areas if you're trying to improve building energy performance.
I don't mean to infer a high-surface area building shape is inherently a
bad idea. Design variables including (but not limited to) glazing
placement, building/site shading, ventilation strategy, climate,
daylighting controls and other building automation can all play a
significant part in addition to the variable of envelope surface area,
and can definitely make a non-cubic building shape make a lot of sense -
but only if done with consideration. Re-iterating, I was also making
the point that 90.1's Appendix G "baseline rotation averaging" rule can
be misleading on the design side of things.
Simultaneously, external loads are often a good thing for at least part
of the year, as is having a degree of "thermal breathability" with the
exterior. Free tools like Sketchup + the free IES-VE plugin are great
for quickly experimenting with a variety of building shape tweaks, and
I'd encourage anyone in the position to experiment with this process to
give it a go - you can learn a lot quickly just playing with different
tweaks and observing the effects.
Also, I was very curious to learn about this Mr./Ms. Banlave's work...
but after a bit of googling I suppose you meant balance =)?
NICK CATON, E.I.T.