output of the baseline model determines
the number of points earned toward the
building’s LEED goals.
Modeling of buildings, and its impact
on district energy, is an important topic
for IDEA members to understand; but it is
too complex to tackle in detail as a part of
this quarter’s column. Stay tuned for an
article and companion column coming in
the fourth quarter of this year dedicated
to the subject. For this quarter, I want to
focus on how costs come into play.
Why Dollars?
Everything seems straightforward so
far (I hope), but as mentioned previously,
the challenge comes in figuring out how
to compare different energy sources. In
our industry, we certainly understand
that converting different energy types
into their Btu content is not an apples-to-apples proposition. For instance, a
Btu of steam and a Btu of natural gas
are not the same in that they are in
different usable forms. This applies in
varying degrees to all energy sources.
Therefore, ASHRAE and USGBC had to
come up with a way to compare them.
The answer? Dollars. They decided that
converting the cost of the source energy
needed to heat or cool a building into
dollars was, while not perfect, a relatively
simple and effective method to take all
a building’s annual input energy sources
and convert them into a metric that fairly
represented the percentage of real energy
each source provided. Thus, dollars
become a surrogate, or stand-in, for
energy use.
As an analogy, think of how you
use heat in your home. A Btu may be a
Btu, but it is much cheaper to use natural gas instead of electricity as an energy
source, primarily because of the efficiency
advantage. With the cost of natural gas
dropping like a rock even while the cost
of electricity climbs, this difference is
amplified. When building a home four
years ago, I insisted on natural gas furnaces, ovens, water heaters, fireplaces
– even a natural gas grill for my deck.
Unfortunately, I let the builder talk me out
of a gas clothes dryer. Today, with four
teenagers, it would have already paid for
itself. (Don’t listen to your builder when
trying to keep your utility cost low.)
Why is it important to have all
the energy sources converted into a
comparable metric? Doing so is necessary
when analyzing a building’s total annual
energy use. If they are not converted,
then building systems that use sources
in the raw form, such as natural gas and
electricity, will have a smaller impact on
the analysis than sources of energy, such
as steam and chilled water, in a more
usable form.
The USGBC cares about
encouraging the selection of
the most energy-efficient and
environmentally friendly systems,
regardless of the costs.
However, the fact that dollars are
used does not mean that the USGBC is
concerned about the costs of installing
or operating the proposed systems. It is
not! Instead, it cares about encouraging
the selection of the most energy-efficient
and environmentally friendly systems,
regardless of the costs. So, how does this
method prevent a relatively inexpensive
energy source such as coal, which the
USGBC considers to have many negative
environmental impacts, from gaining a
favorable comparison in the LEED rating
system because of its low cost per Btu? It
does so by requiring energy modelers to
use the same fuel, and corresponding fuel
rates, in both the proposed model and the
baseline model.
Here’s a recent example. One of our
IDEA members working in the interior of
Alaska (told you this work had taken me
to some interesting places) called me when
he had a problem with his LEED application
on a large building. The building received
steam from a district heating plant that
used coal as the input fuel. In his baseline
energy model, he used furnaces that
burned propane as prescribed by ASHRAE
90.1. For his proposed model he used the
actual district energy plant and coal as the
input fuel. Because of the cost advantages
of coal, the model suggested a fair number
of energy points would be achievable
even though the relative efficiencies of
this particular district heating system
were poor.
