By Jon Mohle, Senior Product and Market Manager, Clark Pacific
From construction to operations, the built environment accounts for more than 38 percent of carbon emissions in the U.S. Amid increasing concerns over climate change, public sector demand for more sustainable buildings, and growing awareness of social responsibility, the construction industry is grappling with how to reduce its environmental impact and play a role in a more sustainable future.
As recently as 10 years ago, sustainable buildings were viewed as experimental but today, are becoming more feasible. And still, owners and project stakeholders are often forced to choose between sustainability and cost. An owner may have ambitious sustainability goals, but if the cost of bringing them to life is too high, they may be out of reach.
I’ve seen this happen time and again. Designers, engineers, and contractors work to accommodate an owner’s environmental goals, but run into problems when pricing comes into play. Often, green features push the project over budget and realizing the building can’t generate enough rent to satisfy the proforma, the owner askes the team to come up with a less costly option. In doing so, green features are cut one by one until the project is within budget, but far less sustainable.
Progress Through Innovation
Through advances in technology and innovative approaches to construction, sustainable buildings today don’t have to cost more. Beginning in the earliest design phase, all the way to operations, sustainable buildings are becoming a reality without breaking the bank through:
Waste in the construction industry has been an ongoing problem. However, through early engagement, whether during predesign or schematic design, owners, architects, engineers, and contractors can reduce rework and wasted materials. Constructible BIM solutions and collaboration platforms make it easy to share real-time project data across teams. Using these solutions to work together throughout the design and construction process, problems that could lead to higher costs and opportunities to improve the environmental performance of the building are identified and implemented early while the design is still flexible.
Building Performance Analysis
Recent advances in building performance analysis tools allow design professionals to explore the energy impact of various design features. For example, they can quantify the energy savings exterior shading elements on the windows or electrochromic glass may provide. The ability to test concepts at the beginning of a project and collaborate with the entire team to find sustainable options that are also withing budget can eliminate the need to choose between cost and sustainability.
Additionally, considering how a building will be occupied can eliminate unneeded systems and space and thus, reduce the amount of energy required to cool, heat and light it. These cost savings can then be invested in sustainable features such as lighting controls or exterior sun shading devices.
Whole Life Carbon Assessment
Whole Life-Cycle Carbon (WLC) are the carbon emissions resulting from the materials, construction and operation of a building over its entire life, including demolition and disposal. A WLC assessment provides a complete picture of a buildings true carbon impact.
Carbon assessment is still in its infancy as researchers are racing to understand and document the impacts of the materials and equipment used in the built environment. Carbon assessment to date has been almost wholly focused on energy savings with concepts such as Net-Zero Energy, which is an energy accounting principal where 100 percent of the energy used by the building is offset by sustainable sources, often using onsite renewables such as solar PV.
Recently the design community has begun expanding its focus to embodied carbon, the carbon emissions generated from constructing a building. This includes all emissions from the extraction and processing of the raw materials, transportation and their final placement in the building. As you can imagine it is a highly complex task to track carbon through a building’s entire supply chain, so most teams narrow their definition to include the largest contributors, which are typically the structure and façade of the building.
Mechanical systems to date have been mostly ignored due to the highly complex nature of quantifying the impacts, however, there is an interplay between structure, façade, mechanical and energy that cannot be ignored. Recent research has begun to focus on the environmental impacts of mechanical systems and their refrigerants. One such study is “Refrigerants and Environmental Impacts: A Best Practice Guide by Louise Hamot.” In this guide, Hamot not only discusses the large impacts that refrigerants can have on the environment, but also best practices for quantifying and controlling those impacts.
As an example, Variable Refrigerant Flow (VRF) heating and cooling systems have gained popularity in the U.S. due to their high energy performance and simple installation. When this system is evaluated on energy performance alone it is quite favorable. However, when considering the WLC impact of the system, it doesn’t fair as well. Unlike most systems that use a combination of air and water to transmit heating and cooling throughout the building, VRF uses refrigerant to transmit thermal energy. Because a VRF system can include miles of refrigerant piping, it leaks far more refrigerant into the atmosphere than conventional system which only uses refrigerant in the chiller or heat pump. The impact of this is staggering. A conservative estimate of refrigerant leakage alone has roughly half the environmental impact as the energy used to operate the heating and cooling system.
Progressive design teams are rapidly adopting WLC analysis to make more informed decisions about our built environment’s impact. With embodied carbon of structure and façade well established and mechanical systems’ embodied carbon rapidly approaching mainstream, expect other major systems, such as electrical and interior finfishes, to follow, offering a more complete assessment of a buildings true impact.
Offsite manufacturing, also known as prefabrication, has grown in popularity for its ability to deliver cost and schedule certainty, but could it also help deliver more sustainable buildings? Building off-site in a controlled environment reduces material waste and a streamlined manufacturing process is more energy and labor efficient. Advances in prefabrication not only change how structures are constructed, but also optimize their core integrated systems to maximize energy efficiency and performance, and occupant wellness and comfort.
Heating, cooling, and hot water account for nearly half of global energy consumption in buildings. Recent research conducted by the Center for the Built Environment demonstrates how heavy thermal mass radiant heating and cooling (radiant in concrete floors) can leverage milder water temperatures to considerably reduce the energy needed to heat and cool buildings.
In a heavy thermal mass radiant solution, heating and cooling energy are delivered to the slab using water. This water heats or cools the slab. The slab then radiates this heat or cool into the surrounding space.
Concrete is great at storing and holding energy. If you’ve ever spent a summer evening on a slab that was in the sun all day, you know that hours later, it still feels warm. Unlike traditional systems that are designed to maintain comfort during the worst hours of the worst day, a heavy thermal mass radiant system can leverage the mass of the building itself to store heating and cooling energy and release it slowly into the space. The system essentially turns a building into a battery.
This opens up a world of green opportunities. By storing energy in the slab, a building operator suddenly gets to choose when to use that energy. For example, if the goal is to use solar energy to cool the building, only run chillers during hours of sunlight. If the aim is to halve the size of all-electric heating and cooling plants, equipment is sized for the average heating and cooling demand over the day and the slabs store the excess until it’s needed.
Accelerating the Path to Zero
Industry conversations around embodied carbon have increased tenfold in recent years and for good reasons. Building materials represent nearly a third of the construction industry’s embodied carbon. When it comes to materials, concrete isn’t always viewed favorably. In fact, cement, the glue that holds concrete together, is alone responsible for 8 percent of the worlds CO2 emissions. At the same time, concrete is the most widely used man-made material in the world. While concrete is often characterized as our biggest problem, it may actually be our biggest opportunity. Concrete is durable, long-lasting, and its thermal stability can lead to more energy efficient buildings and facades.
Low carbon solutions for concrete exist today. In fact, some have been used successfully for over 40 years. These solutions make use of materials called Supplementary Cementitious Materials (SCMs), which are often post-industrial waste products such as flyash (a by-product of the coal industry) and slag (a by-product of the steel industry). These materials, which can replace a portion of the cement in concrete, are not burdened with high amounts of CO2 and actually improve the concrete’s performance. The only downside is that SCMs can slow down the curing process, causing the concrete to gain strength more slowly.
Historically, the construction industry has refined building design with only a single driving variable – cost. In efforts to simplify formwork, structurally inefficient systems emerged that save labor but use more material. Efforts to accelerate construction lead the development of mixes that can achieve high strengths in only a few days. These practices combined result in buildings that use more concrete and concrete mixes that use more cement.
Today, the industry must consider a second variable in building design – CO2. As the industry optimizes designs around this new two variable system (cost and carbon) it can’t simply take a traditional design, toss in some SCMs and call it sustainable. It’s time for the industry to completely rethink the way it builds.
In 2018, Clark Pacific did just that. Starting with a blank canvas, the company established a two variable approach and evaluated dozens of potential designs for cost and carbon. Concrete volume was carved out by thinning slabs and adding ribs to achieve the same strength with less. Ribs were made wider to reduce the early strength requirements of the concrete and enable higher SCM mixes. Offsite fabrication allows for the use of a form heating system that accelerates early strength gain. This allows for the removal of up to 70 percent of the cement from mixes. The heating system removes roughly 20 times the carbon from the mix than it created while heating the forms.
This aggressive approach removes roughly 20 percent of concrete from a building and the remaining concrete has 45 percent less carbon when compared to 2019 National Ready Mix Concrete Association Baseline mixes for similar strengths.
The system also incorporates an offsite manufactured heavy thermal mass radiant heating and cooling system built integral with the floor system and delivered to the site complete with distribution piping and controls. The overall solution results in removal of half the carbon from the concrete, 30 percent less electricity over traditional all electric air-based solutions at a price that is competitive with conventional low performance buildings.
As individuals and industry professionals, we should all consider the fundamental design, whether it’s concrete, steel, timber or precast, with both cost and carbon in mind. The advances in technology, materials, systems and processes captured here are encouraging first steps. Together, we can all pave the way to a greener, more sustainable future.
This material appears in the December 2021 issues of the ACP Magazines:
California Builder & Engineer, Construction, Construction Digest, Construction News, Constructioneer, Dixie Contractor, Michigan Contractor & Builder, Midwest Contractor, New England Construction, Pacific Builder & Engineer, Rocky Mountain Construction, Texas Contractor, Western Builder