ASHRAE Journal - March 2022 - 72

COLUMN SOLVING PROBLEMS
temperature, " he said. " For example, the 99.6% heating
temperature for Chicago is 1.9°F (-16.7°C), but the
50-year extreme temperature is -23°F (-30.6°C). The
electric heating source must provide the required heat
at these extreme conditions. Multiple-day electric grid
outages like those experienced in Texas last year also
need to be considered. These issues do not typically
manifest themselves in mild climates but can present
life-threatening consequences in cold climates. "
" We can reduce refrigerant needs with passive design
strategies to reduce active heating and cooling. Heat
pumps are beginning to transition into natural (R-744)
or low-GWP hydrocarbon refrigerants (e.g., R-32,
R-452B). This transition will help reduce greenhouse gas
emissions from refrigerants in heat pumps. Evaluating
alternatives to large refrigerant distribution piping
systems can also help minimize refrigerant charge and
leakage, " Peterson said.
Scoggins said a common question she's asked when
speaking on decarbonization centers on why engineers
should worry about building emissions when the electric
grid is " dirty. " " We do have a dirty grid-in some places it
is worse than others-but we have to start somewhere, "
she said.
It is also a common misconception electric buildings
alone will get the built environment to its carbon-neutral
goal by 2050, said Peterson.
" Electrification can help decarbonize the buildings
sector if the electric grids are able to decarbonize. The
current electric grids will not be able to handle the
increase in electric loads without substantial energyefficiency
improvements. The electric grids will need to
quickly transition to very low carbon or carbon-free to
reduce these indirect carbon emissions, " he said.
Much of the transition is forecasted to be heavily
influenced by solar and wind energy sources. " As these
become a higher percentage of the total supply, we will
see large deviations on carbon intensity by season and
time-of-day. Carbon intensities will be lowest when the
sun is out and the wind is blowing. Grid storage will be
part of the solution, but buildings will also need to integrate
energy-efficiency measures and demand response
to create flexible building electrical loads for electrification
to fully reach its full carbon reduction potential. "
Another challenge is some ASHRAE members are not
familiar with the impact of embodied carbon as compared
to operational carbon, said Peterson. " Embodied
72
ASHRAE JOURNAL ashrae.o rg M A R CH 2022
carbon impacts can be very significant, 250 kg/m2 to
1000 kg/m2, when constructing a new building. While
the past focus has been on major embodied carbon
structural elements, embodied carbon of MEP system
elements is now being considered. " 1
Net Zero Carbon vs. Net Zero Energy
Besides electrification, many decarbonization strategies
align with net zero energy strategies, said Peterson.
" Building heating and cooling loads can be reduced
with passive efficiency strategies and optimizing waste
energy. "
Critical energy-efficiency upgrades can include
improving the building envelope, measurement tools to
provide insight into energy use and software to optimize
energy use. Active energy-efficiency measures can further
reduce annual energy consumption.
But low carbon strategies are different from net zero
energy strategies, he said, because hourly electrical
carbon emission rates vary widely throughout the year.
" The difference between net zero carbon and net zero
energy is the latter refers to generating energy that
exceeds annual demand but does not necessarily result
in annual energy that is net zero carbon. Net zero energy
strategies do not account for when energy is created or
used by the building. Low to zero carbon buildings will
need to be demand responsive to electric grid carbon
signals by utilizing thermal and/or electrical storage at
the building, with smart controls that boost energy efficiency
and lower emissions. "
Peterson said control systems integrated into buildings
can help coordinate supply and demand and shift
energy use. Demand-side management systems can
help save costs by optimizing use for when and where it
is most needed, but they can also improve decarbonization
by shifting energy use to times of the day when zero
carbon energy is highest in the grid mix.
" Low carbon buildings will also focus on embodied
carbon, while net zero energy strategies have focused on
only operational energy, " he said.
Peterson recommended using a carbon metric (CO2e)
on each project to help owners and design teams understand
the carbon impacts of design decisions. " Using
whole carbon life cycle assessment (LCA) on projects will
allow owners and design teams to make informed decisions
on trade-offs between embodied and operational
carbon for new construction projects. "
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