the challenge this creates, see figure 1. In
this chart, if the total pie represents 100
percent of the energy (in dollars) used by
the proposed facility during a year, then
modelers have much room to work to
find the smaller slice of pie that must be
removed to meet the prerequisite.
Figure 1. Total Building Energy Use.
Energy
reduction
Building energy
Source: RMF Engineering, Inc.
However, if the building is tying into
district energy, then, as shown in figure 2,
there is a certain portion of the pie – the
cost-neutral portion – attributed to the
district energy system, in which no energy
savings can be achieved. Therefore, the
energy reduction slice can only come from
the building itself.
Figure 2. Total Building Energy Use
Connected to DES.
Energy
reduction
DES energy
Building energy
Source: RMF Engineering, Inc.
This has created significant challenges
for some district energy customers. In
fact, the way energy cost is calculated, the
actual rate charged the building customer
is applied. As a result, the district energy
system portion of the annual energy use
consumes an artificially higher percentage of the pie. In contrast, in a building
with its own cooling and heating plant,
some of the energy reduction can come
from the plant and some from the building. Therefore, in meeting the prerequisite,
energy system designers have much more
flexibility when a plant is not connected to
a district energy network.
There’s a second problem: Even if
modelers successfully exceed the energy
prerequisites with their Step 1 model, they
cannot earn any points with that model
under LEED NC Version 2. 1 and 3.0 and are
limited to 2 points under LEED NC Version
2. 2. Instead, they have to run a second
model under the next step. For Step 2,
they have to run the model with the district
energy system included and then compare
that against a model of the proposed building with its own plant that meets the minimum requirements of ASHRAE 90.1. Only
then can they determine if any points can
be achieved for energy efficiency. However,
there are limitations here as well. The points
achieved in the Step 2 model often cannot
all be applied to the LEED point total. The
points are capped at a certain amount over
those earned in Step 1.
Confused Yet?
Complicated? The USGBC even thinks
so. In fact, it is changing the guidance
for district energy in an attempt to both
simplify the process and make it less
burdensome on both project designers
and USGBC’s reviewers. Two models take
more time for designers to create and
for reviewers to analyze. In addition, a
lot of the problems reviewers find with
LEED applications come from the models
created in Steps 1 and 2.
So, how do you simplify the process?
The USGBC wants to provide options. In
fact, it has proposed that Step 1 and Step
2 be renamed Option 1 and Option 2. The
intent here is to require building modelers
to build only one model, either a the Step
1 or Step 2 model, to demonstrate they
both meet the energy category prerequisite
and to determine how many points they
can achieve. There are several advantages
for district energy systems in this scenario:
• Under Option 1, the modeler follows the
previous requirements of Step 1; but any
point achieved with this model can be
applied to the project without having to
also run Step 2.
• If the modeler cannot meet the
prerequisites under Step 1, there is more
flexibility to do so under Step 2. Due
to the limitations discussed previously,
this could enable some buildings on
a district energy system to apply for
LEED certification that may have been
prevented from doing so in the past.
Tim Griffin, PE, LEED,
AP, is IDEA’s liaison with
the U.S. Green Building
Council and serves on
IDEA’s board of directors.
He is a principal and
branch manager with
RMF Engineering Inc., a firm specializing in
district energy system design and
commissioning. A registered engineer and a
LEED Accredited Professional, Griffin has a
bachelor of science degree in mechanical
engineering from North Carolina State
University and a master of business
administration degree from Colorado State
University. He authored the book Winning
With Millennials: How to Attract, Retain,
and Empower Today’s Generation of Design
Professionals. He may be reached at
tgriffin@rmf.com.
