Give Me Options!
Tim Griffin, PE, LEED AP, IDEA USGBC Liaison
Editor’s Note: “LEED® + District Energy”
is a quarterly column providing information about the U.S. Green Building
Council’s LEED rating system and how
it applies to buildings served by district
2004 for LEED Version 2. 2 and 10 percent
reduction over ASHRAE 90.1-2007 for
LEED Version 3.0).
The USGBC’s real goal is to
encourage building design teams to
reach energy reduction targets well
beyond average performance. To this
end, the USGBC provides points toward
LEED certification for increases in energy
savings beyond the minimum target in
incremental steps (a maximum of 10
in Version 2. 2 and 19 in Version 3.0).
This is a powerful incentive for building
designers, as no other rating category
comes close to offering this number
of points, making it difficult to achieve
more than a basic certification without
addressing the building’s energy use.
To meet these requirements,
however, building designers only have to
run one model to verify that they met the
energy prerequisites and to determine the
number of points achieved. Unfortunately,
this does not apply currently to buildings
connected to district energy systems.
The march toward a new and improved guideline for evaluating district energy systems within
the U.S. Green Building Council’s
(USGBC) LEED (Leadership in Energy
and Environmental Design) rating system
continues. The proposed new guideline
contains many well-thought-out
modifications that are intended to make
the assessment process easier and will
help capture district energy’s benefits.
However, it appears the final District
Energy Guidance Document version,
originally planned for release last
October, will require more time to
get a few last details wrapped up.
The latest and perhaps final
discussion has dealt with the most
complicated piece of the program itself
for new building construction projects:
energy modeling, which has many
ramifications for district energy systems.
Therefore, I am devoting this quarter’s
column to a review of the improvements
the USGBC is making.
Energy modeling is a tool used by
designers to create a computer model of
a proposed building’s hourly energy use.
By shifting building orientation, changing
fenestration or applying different
equipment selections (with their energy
load profiles and costs, etc.), a design
team can compare numerous options to
determine the best configuration from a
lifecycle cost standpoint.
Applying Modeling to
Determining how to model a facility
connected to district energy is not
straightforward. The problem is twofold:
First, if a building has no choice but to tie
into a district energy system, the USGBC
does not want to penalize the owners’
efforts to achieve a LEED rating just
because they could now not meet the
minimum energy prerequisite. Otherwise,
tying into a district energy system whose
energy performance is poor will exclude
the building itself from a chance to earn
LEED certification. On the other hand, if
a facility has access to a district energy
system with excellent energy performance,
the USGBC does not want to allow the
facility’s designers to gain the maximum
number of points just by tying into that
system without applying any energy
savings features to the building itself.
To solve these challenges, the
USGBC created a two-step process just
for buildings connected to district energy.
In Step 1, the building’s modeler has to
hold the district energy services supplied
to the building cost-neutral. As a result,
all the energy reduction can only come
from the building itself. To understand
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