Article Source: ASHRAE
Buildings account for 40% of carbon dioxide emissions, and many jurisdictions are implementing low-carbon and net zero policies that affect new building design and construction and require retrofits of existing buildings in efforts to decarbonize. How will decarbonization affect the industry and engineers, and what are some of the challenges that we need to think about today so we can be ready to address them tomorrow?
“Building decarbonization raises the bar for the technical proficiency required of building design professionals,” said Daniel Nall, P.E., BEMP. HBPD, Fellow/Life Member ASHRAE, a member of the Vision 2030 Built Environment team focusing on decarbonization. “Energy modeling and other forms of technical analysis are required to evaluate the effectiveness of proposed strategies. Construction must be more exact [and] building operation must also be more exact.”
ASHRAE Journal spoke with Nall to help explain how decarbonization fits into the Vision 2030 initiative, define relevant terminology and explain the implications of building decarbonization.
How does decarbonization fit into the Vision 2030 initiative?
Decarbonization is very much a part of the Vision 2030 Initiative. The Built Environment component of Vision 2030 explicitly calls out both embodied carbon and operational carbon as components of net emissions and signifies ASHRAE’s commitment to leading the way both in defining zero carbon buildings (ZCBs) and in advancing techniques for evolving our building stock—both new and existing—toward the ZCB goal.
What are operating carbon and embodied carbon?
Carbon emissions directly resulting from the operation of the building are aligned to the reporting organization and are organized, by international consensus, into three scopes:
- Scope 1 emissions are direct greenhouse gas (GHG) emissions that occur in the building from sources that are controlled or owned by the reporting organization, e.g., emissions associated with fuel combustion in boilers, furnaces and equipment. Scope 1 also includes fugitive GHG emissions, such as refrigerant leaking from HVAC or commercial refrigeration equipment.
- Scope 2 emissions are indirect GHG emissions associated with the purchase by the reporting organization of electricity, steam, heat or cooling for use in the building.
- Scope 3 emissions are the result of activities from assets not owned or controlled by the reporting organization, but that the organization indirectly impacts in its value chain, both upstream and downstream of own activities, including carbon emissions outside of the physical footprint of the facility. These emissions include embodied emissions within resources consumed by the organization—paper used, waste produced, coffee consumed—and also the emissions of any suppliers, which are especially important to organizations that produce physical products.
Embodied carbon is the sum of all the GHG emissions—mostly carbon dioxide—resulting from the mining, harvesting, processing, manufacturing, transportation and installation of materials that are incorporated as a part of a building or some other long-term fabrication.
What are some common atmospheric greenhouse gases (GHGs), and how are they measured?
The atmospheric GHGs most associated with buildings include carbon dioxide, methane and many refrigerants. GHGs are characterized by a metric called global warming potential (GWP) that compares the global warming impact of a mass unit of a given material to the same mass unit of carbon dioxide.
What constitutes a ZCB?
I think a slight modification of the Canadian Building Council’s definition is the best definition I have seen: “A zero carbon building is a highly energy-efficient building that produces on-site, or procures, carbon-free renewable energy or high-quality carbon offsets to counterbalance the annual carbon emissions from building materials and operations” and which, over time, offsets the carbon emissions embodied in the original construction process of the building.
Is there a need for a single definition of ZCBs?
A single definition of ZCBs will enable the entire building industry to seek the same goal and allow comparison of strategies to get to that goal. Agreement on a single definition of ZCBs—with respect to carbon emissions factors and the scope into which various types of emissions fall—would better enable comparison of strategies for carbon reduction. For example, much of the controversy around electrical storage involves different ways of calculating the embodied carbon of battery materials and thus the amount of beneficial use of the battery required to offset the embodied carbon.
Diving Into Decarbonization
How is decarbonization affecting the HVAC industry and HVAC engineers?
Currently decarbonization is directly affecting HVAC engineers in only a few regions of the country, such as California and New York City, where carbon emissions regulations are planned. The HVAC industry, on the other hand, has recognized that decarbonization is an upcoming trend and is focusing on developing products, such as high-efficiency, high-lift heat pumps to accommodate this trend.
In what ways can decarbonization efforts create jobs and opportunities for HVAC&R, construction materials and design sectors?
Building decarbonization raises the bar for the technical proficiency required of building design professionals. Energy modeling and other forms of technical analysis are required to evaluate the effectiveness of proposed strategies. Construction must be more exact. Building operation must also be more exact and must be attentive to concurrent weather, occupancy conditions and grid carbon emissions at all times.
One of the biggest opportunities in the HVAC&R industries will be the requirement for more technically sophisticated operating techniques, which will involve more extensive data gathering and analysis and utilization of digital tools, including digital twins of buildings to inform operation. The need for enhanced continuity among the design, construction and operations phases of building life may overcome the current disconnect between these phases and provide opportunities for new services to enhance that continuity.
What trends are we seeing regarding decarbonization practices and policies—particularly regarding the balance between decarbonization and saving energy?
We have just begun to recognize that zero energy buildings are not necessarily ZCBs. The GHG emissions factor for the electric grid varies both with location and time. A true ZCB recognizes that emissions factor and behaves so as to minimize the GHG emissions from the electricity that it consumes. While saving energy is good, reducing GHG emissions is even better. From a global warming standpoint, all Btus are not equal. A Btu of photovoltaic-generated (PV-generated) electricity is far different from that of a Btu of electricity generated by coal-fired power plants. Zero carbon analysis recognizes that difference.
One of the biggest challenges for building decarbonization is the inadequacy of current incentives. The GHG emissions potential of different forms of energy are not reflected in the costs of energy, so building owners still legitimately choose higher GHG emitting energy sources because of lower prices.
What are some challenges engineers may face while implementing decarbonization practices and policies with both new building design and construction and retrofitting existing buildings?
One of the biggest challenges for building decarbonization is the inadequacy of current incentives for decarbonization. The GHG emissions potential of different forms of energy are not reflected in the costs of energy, so building owners still legitimately choose higher GHG emitting energy sources because of lower prices. In general, electric heating equipment is either much more expensive in terms of operating costs (electric resistance) or in terms of first cost (heat pump technologies). These cost issues mean that fossil fuel energy sources are still economically competitive with electric energy sources. Currently, zero carbon emissions delivered fuel (biogas, biodiesel, solid biofuel chips) has limited availability and sometimes dubious GHG emissions validation.
A major challenge for engineers is that many of their clients do not understand decarbonization and may be uncomfortable with design solutions that address the problem. Arguably, the three most important strategies for decarbonization—electrification of building heating requirement, energy recovery and energy storage—are often seen as complicated, high-cost, low-return luxuries.
Resiliency can be an issue with respect to ZCBs in that the electric grid is more vulnerable to natural interruption than gas pipelines or fuel truck delivery schedules. Even so, the combination of on-site renewable generation, on-site electrical storage and appropriately sized fuel powered standby generation can reduce outage risks to levels comparable to conventional building energy sourcing. If anything, the flexibility in operation required for ZCBs benefits emergency management. As mentioned above, on-site renewable generation and energy storage provide zero carbon reliable emergency energy sources. Load-shifting capabilities can also be repurposed to provide load-limiting capability better to enable the building to continue operation during certain types of emergencies.
How can engineers overcome some of these challenges?
The biggest short-term challenge for building decarbonization is that it likely entails additional first cost and additional operating costs. One strategy for overcoming that challenge is to design systems that can accommodate phased decarbonization. An example would be a hydronic heating system that can utilize very low-temperature hot water (100°F). Such a system—in the short term—could be served by a gas-fired boiler, but its low temperature capability would allow it to be served by air-to-water heat pumps in the future.
Another strategy is to make use of currently accepted technologies that already incorporate some of the decarbonization technologies described above. A good example of this strategy is the utilization of variable refrigerant flow (VRF) multi-split systems with refrigerant phase heat recovery. These systems enable the efficient recovery of building internal heat gains to meet space heating requirements.
Another important strategy for the engineer is to develop and refine the story about decarbonization and the techniques required to achieve it. Good communication with clients is the best path to implementing building decarbonization techniques. Case studies, simplified diagrams and descriptions of ownership and operational issues all can help owners become more comfortable with these technologies.
Are there any cities currently implementing decarbonization efforts or any particular buildings that may serve as examples of how building professionals can move forward in their learning/practices?
New York City is currently in the midst of creating rules for the implementation of Local Law 97 that will limit GHG emissions for most buildings larger than 25,000 ft2. This process of rulemaking involves finalizing a number of definitions of how carbon emissions are calculated and what are appropriate exceptions and allowances for buildings that have specific requirements and limitations related to their function.
The 2022 Zero Code for California is a ZCB energy standard for new nonresidential, high-rise residential and hotel/motel buildings—the prevalent building types being constructed in cities today.
The practice of adapting building designs to these standards is in its infancy. Systems in compliant buildings, whether new or retrofitted, must be both energy efficient and flexible. Load shifting, either by modifying schedules or by storing energy, is required. Energy storage strategies include both electrical and thermal storage. Schedule modification may take advantage of the inherent thermal mass of the building or the flexibility of functional requirements. For those of us in the design professions, we are at the beginning of a great adventure, exploring how buildings may be configured to use energy when the GHG emissions implications of consumption are lowest and to avoid using energy consumption when they are highest.