ASHRAE Journal - February 2022 - 49

COLUMN ENGINEER'S NOTEBOOK
FIGURE 1 Major Categories of Whole Life Carbon Assessment. Inner ring shows
a typical distribution of carbon emissions by category when natural gas is used
for heating, whereas the outer ring represents emission category sizes for an
all-electric approach.
All Electric
Embodied:
Construction
Operational
Off-Site
Mixed Fuel
Operational
On-Site
Potential Emissions
Embodied: End of Life
Embodied:
In Use
in McConahey.4 The goal of embodied carbon emissions
reduction is to use less material fi rst, use recycled or biobased
products when possible and then to specify low
carbon materials by examining carbon content of materials,
processing and transport before resorting to offsets
for residual emissions.
Operational carbon includes primarily energy either
burned on-site or purchased from an electrical utility, as
shown in the inner ring of Figure 1. The outer ring in the
diagram refl ects a shift away from on-site combustion
of fossil fuels to full electrifi cation of heating sources, as
discussed in Ho;5 Rumsey, Le Garrec, and Levasseur;6
and Gill.7 Operational carbon also includes fugitive
emissions from refrigerants and any wastewater treatment
on-site as well as carbon emissions from off-site
water sources, as discussed in McConahey,8 which is
why a sliver of operational carbon on-site remains in
the all-electric scheme.8 The goal of operational carbon
emissions reduction is to use less energy fi rst, reuse it
when possible and then to look for renewable energy
sources before offsetting residual emissions.
The conversation around whole life carbon starts
with acknowledging the fact that construction and
operation of a building will emit carbon. The goal is to
emit as little carbon as possible through good design.
With 24/7 carbon-free renewable energy sources,
operational net zero carbon can be achieved, but
there will almost always be residual emissions associated
with embodied carbon. These can be balanced to
achieve net zero carbon emissions if carbon offsets are
purchased.
We have been introduced to the idea of a net zero
building previously in an eSociety news article9 and
even in an ASHRAE Journal podcast.10 Most of our effort
Embodied:
Construction
FIGURE 2 Whole Life Carbon Emissions and Offsets Versus GHG Scope Category.
Each of the three outer rings maps the extent of coverage for each scope within
the GHG Protocol and how balance within the same scope coverage area is typically
achieved.
Scope 3
Scope 2
Scope 1
All Electric
Mixed Fuel
Operational
Off-Site
Operational
On-Site
Potential Emissions
Renewables & Offsets
Carbon Offsets:
Construction
Renewables
On-Site
Green Power
Purchase
Embodied:
In Use
Embodied: End of Life
Carbon Offsets: End of Life
Carbon Offsets:
In Use
as designers, contractors and manufacturers focuses on
the building up until the point of construction, then it
becomes the owner's responsibility to operate under net
zero carbon principles. It's also the owner's responsibility
to " pay off " the residual carbon emissions through
green power purchases and carbon offsets. The intention
of most net zero commitment frameworks is to
encourage intelligent design choices to reduce the burden
of these persistent carbon reduction costs.
Figure 2 envisions how initial emissions and their logically
paired carbon reduction methods can be matched
by considering the GHG Protocol's scope categories of
emissions. As noted in McConahey,11 Scope 1 refers to
on-site direct emissions, including fugitive emissions
of refrigerants. Scope 2 refers to off-site emissions from
energy providers. Scope 3 covers all other scopes.
When we consider whole life carbon, the years
2030 and 2050 represent the most crucial milestones
on the time line based on global initiatives. The
Intergovernmental Panel on Climate Change advises
that multiple sectors of industry need to align their
movements this decade if we are to limit global warming
to less than 1.5°C (2.7°F) or even 2°C (3.6°F) by the end of
the 21st century.12
As noted earlier, a whole life carbon assessment looks
not only at the carbon emitted Day One but also that
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ASHRAE Journal - February 2022

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