ASHRAE Journal - March 2014 - 96

Column energy Modeling
By Javad Khazaii

Modeling Real vs. Imaginary
By Javad Khazaii, Ph.d., P.E.

Building an energy-efficient building often begins with an energy (cost)
comparison between a design building and an imaginary baseline building as
defined in ASHRAE/IES Standard 90.1, Appendix G. Even though this method
has contributed to higher performance of buildings and systems, I believe we
can do better than that.
I think the current approach made good sense a couple
of decades ago when we did not have a thorough and
reliable database for the energy consumption of various types of commercial buildings in different climate
zones. Now, we have access to a plethora of information gathered by the U.S. Department of Energy (DOE)
regarding the average energy consumption per square
foot per year of existing commercial buildings.
For example, we can find the average energy consumption of educational buildings in a particular climate zone
in the United States by looking in the DOE's Buildings
Energy Data Book. This is actual data that can be a useful
performance indicator for us, and our energy modeling
target.
Let's assume we have changed our method of rating
the building performance and instead of comparing
two deterministic simulations for the design building
and our imaginary building (giving 1 to 20 points if our
design building is between 12% to 49% better than the
imaginary building performance [cost]), we are comparing between a risk-based simulation for our design
building and the current deterministic industry average
energy consumption per square foot per year in our specific climate zone. (Of course, before anything else, commercial software needs to be developed that is capable of
risk-based energy modeling.)
For example, if we set our new standard requirements
to: If the results of the risk-based analysis of the design
building shows that there is at least x% chance that our
x
design building performs a minimum of y% better that
the industry average it can score 1 point, and if there is
at least x% chance that our design building performs a
x
minimum of 2y% better that the industry average, it can
2y
score 20 points. Likewise, each incremental additional
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ASHRAE JouRnAl

ashrae.org

March 2014

point between y and 2y% improvement will score an
2
additional incremental point between the limits of 1 and
20 points.
For me, the most obvious advantage of this alternate
method is that constructing a baseline using a real
industry-proven value, means that we are working
toward make a building perform better than an actual
benchmark. Using this alternate method, we do not
(only) state that the building is performing m% better
than if we designed it using the standard method, but
instead we state that the building is performing n% better than the average of existing buildings with similar
functionality in its particular climate zone.
In addition, we can communicate the analysis results
simply with anyone in the industry, especially the owner
who needs to understand exactly what he will receive for
his investment.
Most importantly, by using the alternate method, we
are encouraging more innovation in building design
and technique. For example, let's assume an architect
designs an unusual geometry for a building that is
very energy efficient compared to most other building
shapes. Based on guidelines of the current method, he
has to simulate both design and base buildings with the
same unusual building geometry. Therefore, the current
standard method will not give him a full credit for his
innovative design.
However, in the alternate method, its performance
is only compared to existing buildings. This means an
innovative geometry has a chance to outperform the
average existing buildings' energy consumption by a
higher percentage.
Javad Khazaii, Ph.D., P.E., is an associate engineer with Newcomb & Boyd Consulting
Engineering Group in Atlanta.

ASHRAE Journal - March 2014

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