Decarbonization for Dummies

Decarbonization has become the new buzzword of the built environment community. This is not to say the concept or concern is new, it’s just now coming to the forefront. Talk about a misunderstood concept. In full disclosure, I am one of them who did not clearly understand what it truly meant. Throughout my entire engineering career, I’ve always designed projects with energy conservation in mind, almost solely having dedicated the last decade and a half of my career to saving energy. In the new lexicon, I was completely focused on reducing operational carbon (OC).

I was recently asked to speak at the local American Institute of Architects (AIA) chapter on this subject. While preparing, or “cramming for the exam,” so to speak, I learned decarbonization is much more than just reducing the energy consumption of a building, or what I previously denoted as OC.

FIGURE 1. Comparing and contrasting embodied and operational carbon.
Image courtesy of Stacy Smedley/Skanska

To fully understand the concepts, this new terminology must be defined.

Carbon is greenhouse gases (GHGs), which are gases in our atmosphere that trap heat.
Decarbonization is essentially both the journey and the destination: reducing, then eliminating, the embodied carbon (EC) and OC of a building through:

Increased building design/construction and operational efficiency;
On-site renewable energy generation; and
Off-site greenhouse gas (GHG) emission offsets.

Embodied carbon (EC) is the CO₂e¹ associated with the building construction, including the extraction, manufacture, and transportation of building materials as well as its ultimate demolition.
OC is the CO₂e associated with operating and maintaining the building throughout its lifetime. Most of this CO₂e is associated with the energy used in building operations.
Net-zero carbon buildings use renewable energy production and other GHG offsets to reduce their CO₂e to zero.

One can imagine how this threw my perspective into a minor tailspin. Once I started talking with some of my peers about how I felt, admitting I’d missed this complete concept, I discovered I wasn’t alone in this “lack of understanding.” During these conversations, I found many mechanical, electrical, and plumbing (MEP) engineers and architects, like myself, have only been focused on lowering OC (i.e., making buildings more efficient).

To fully understand this concept, one must understand the impact each component has as a whole and individually. First, one must be able to define what a metric ton of CO₂ is. To supply some tangible scale, I used the EPA’s equivalencies calculator² for some examples. The examples have been broken down by what emits it; what can be done to avoid it; and, lastly, what can be done to have it sequestered.

Examples of 1 Metric Ton of Emitted Carbon

112 gallons of gasoline consumed (i.e., 2.6 Hummer fill ups @ 15 mpg average);
1,101 pounds of coal burned;
40.6 home BBQ propane gas cylinders; and
188 therms of natural gas burned.

Examples of 1 Metric Ton of Avoided Carbon

43 trash bags of waste recycled instead of landfills (i.e., using for an anabolic digester which emits methane); and
27 incandescent bulbs switched to LEDs (based on 60-W bulbs converted to 10-W LEDs).

Examples of 1 Metric Ton of Sequestered Carbon

First, one must define carbon sequestration. Carbon sequestration is simply a way of removing CO₂ from the atmosphere;
Approximately 17 tree seedlings growing for 10 years or approximately 165 planted seedlings per year; and
1.2 acres of forest in one year.

Unfortunately, there is no way society can simply “plant its way” out of this dilemma. A power plant emits 1 metric ton in almost the blink of an eye. For some perspective, per the EPA, one average natural gas fired power plant emits 397,959 metric tons per year². That’s the equivalent of 45.43 CO₂e per hour or 0.76 CO₂e per minute. And, coal-fired plants emit almost 10 times those amounts.

FIGURE 2. Total carbon emissions of global new construction from 2020 to 2050.
Image courtesy of Architecture 2030/EIA

Let’s now address each carbon type individually and how we can all help. Since most have an understanding of what OC is, let’s start with EC.

According to Architecture 2030², EC will be responsible for almost half of total new construction emissions between now and 2050. The associated graph indicates the 30-year “Time Value of EC.” As you can see, it clearly indicates that at year 10, 74% of the total carbon in new buildings is still EC, and almost half (49%) of the total carbon emissions over the last 30 years came from EC.

FIGURE 3. Sources of embodied carbon by industry.
Image courtesy of Greengage Environmental

So, how can EC be reduced in the built environment? First, one must understand where EC comes from. According to a Greengage Environmental Study⁴ (Figure 3), most of it (42%) comes from the building super structure (concrete, steel, aluminum). Additionally, an extensive study performed by Thornton Tomasetti⁵ concluded that, regardless of the project type (commercial, educational, or domestic), approximately 43%, on average, comes from the concrete flooring in a building, followed not so closely by walls at approximately 20%, on average. Irrespective of anything when we evaluate what materials goes into constructing a building, such as aluminum, fiberglass, or even glass, everything plays a part in the overall EC footprint. Some materials have a greater carbon footprint than others. For example, aluminum’s EC is 11.5 tons of CO₂ for every 1 ton of aluminum created. Glass is 0.9 ton of CO₂ for every 1 ton of glass created.⁶ This created the need for a life cycle analysis (LCA) of how carbon is used in buildings and resulting decisions on how to lower it. Pay attention to a building’s cladding, which is glass and aluminum. The phrase “carbon LCA” returns many results when punched into a search engine.

FIGURE 4. A majority of embodied carbon comes from a building’s superstructure (i.e., concrete, steel, aluminium, etc.
Image courtesy of Thornton Tomasetti

The best way to the reduce EC is, much like everything else, to start with the end in mind. Goals can’t be met if they are not set, plain and simple. But, to achieve these goals, everyone must play their role in this macabre play. For example…

Architects can lower the buildings EC by using less glass. Many consider this blasphemy, I know, but it also has a side effect, as it also reduces the OC.
MEP engineers can suggest and fight against the heavy equipment (i.e. chillers, cooling towers, generators, etc.) being located on the roof. Thereby, reducing the amount of building structure and, consequently, the amount of EC.
Structural engineers, the folks who make up 43%, on average, of a building’s EC footprint, can aim to reduce the EC in concrete slabs, foundations, and columns, which differ in quantity, depending on the building structure (i.e., hospitals, data centers, high-rise building, etc.).
Designing sustainably is another worthwhile option. The United States Green Building Council (USGBC) estimates that green buildings, on average, reduce energy use by 30% and carbon emissions by 35%, which generates cost savings of 50%-90%⁷.

FIGURE 5. More than 66% of the global building stock will be buildings that exist today.
Image courtesy of Thornton Tomasetti

A Simple, Basic Plan to Reduce EC

Build Nothing or Less

Adaptively reuse existing buildings. (Much of America’s building stock is existing buildings anyhow.); and
Use existing assets more efficiently.

Build Effectively

Optimize structural design;
Use LCA and a whole life cycle approach; and
Specify use low-carbon or carbon-positive materials (i.e., timber construction for buildings due to the lower EC properties).

Build Efficiently

Reduce transportation; and
Reduce construction fuel emissions and waste (i.e., incorporate better building practices, such as a no-idling policy on job sites).

Achieving net-zero carbon is a simple but crucial concept. Well, conceptually it is simple; however, in actuality, it is not simple. Here is a simple but enlightening definition.

“Achieving net-zero emissions means that some greenhouse gases are still released, but these are offset by removing an equivalent amount of greenhouse gases from the atmosphere and storing it permanently in soil, plants, or materials.”⁸

So conceptually design, build, and operate very efficiently to lower CO₂ emissions as outlined above. Then, add the measures needed to remove the remaining CO₂ emissions. There are two ways to try and achieve this: biogenic sequestration and direct air capture.

Biogenic sequestration uses plants through photosynthesis. The biogenic carbon cycle centers on the ability of plants to absorb and sequester carbon. Plants have the unique ability to remove carbon dioxide (CO₂) from the atmosphere and deposit that carbon into plant leaves, roots, and stems while oxygen is released back into the atmosphere.
Direct air capture (DAC) is a modern technology that grabs CO₂ from the air and turns it into something that can be converted into a form that can be sequestered. Sequester means to take out of the air in such a way, so it is not readmitted. However, as of this article’s publishing date, this is not cost-effective. (Biogenic CO₂ feedstock costs range from $15 per tCO₂ to $30 per tCO₂, where DAC CO₂ capture costs range from $135 per tCO₂ to $345 per tCO₂⁹)

Now, let’s return to my main forte, reducing OC emissions. Keeping with that direction in mind, I’m going to illustrate one possible “design path forward” for operational decarbonization. Like almost anything else, there are many approaches that can be taken. The following multistep process is mine.

As stated earlier, start with the end in mind. Keep that as a guiding principle. Achieving a decarbonized building must be the focus of the project designer. Every campaign needs a leader, be that person.

FIGURE 6. A comparison of buildings based upon their energy usage.
Image courtesy of TLC Engineering Solutions

First, convince the owner to embrace this idea, as it’s the right path to take. Without the owner’s support, the process and ultimate end goal will not be achieved.
During initial design phase, introduce to the project any architectural and MEP design strategies that will lower the ongoing building’s overall energy use (i.e., OC).
Next, concentrate on the equipment that will be designed into the building and make sure it only uses electricity, so that fossil fuels are no longer burned on-site, creating emissions locally.
Finally, focus on how electricity gets to the building and how it is generated (renewables, etc.).

And, finally, pursue beneficial electrification (or strategic electrification), which is a term for replacing direct fossil fuel use (e.g., propane, heating oil, gasoline) with electricity in a way that reduces overall emissions and energy costs.

How can some of this beneficial electrification be accomplished? One of the more common paths being promoted is really a no-brainer: Convert electric resistance heat to a heat pump-type system. To gauge its impact fully, first evaluate it from the building energy side (site energy). As an example, if a building has a required heating load demand of 350 MBH (100 KW), and it is converted to a heat pump system with a simple coefficient of performance (COP) of 3, it will only now require 33 kW to satisfy the same demand. What impact will that change have on the power plant energy side (source energy)? Again, based on our assumptions of 1,500 pounds of CO₂ per hour emitted for 100 kW, then it’s only 500 pounds of CO₂ per hour emitted for the heat pump for 33 kW.

If this same 100-kW heating load was served by a series of split DX ≤ 5-ton units, based on the new 2023 energy regulation requirement of a COP of 8.8, that 100 KW is now approximately 11 kW of site energy and a source energy of 166 pounds CO₂ per hour emitted.

There you have it, my Reader’s Digest version examining the carbon conundrum. Or, as I believe it appropriately named, “Decarbonization for Dummies.” This article was meant only to whet your beak in the thirst for knowledge. Don’t make this your last stop. Remember, its up to all of us to make a difference.

Editor's Note: Al LaPera will be presenting at 2023 CxEnergy, May 2-5 in Dallas/Fort Worth. For more information, visit www.cxenergy.com.