Operational Carbon

Our approach to energy efficiency and operational carbon reductions for the Case Study focuses on key strategies that: 

  1. Reduce energy demand through climate responsive passive and active strategies. 

  2. Electrify and decarbonize. Eliminate all fossil-fuel consuming equipment and appliances to provide higher efficiency and improved indoor air quality. Supply electricity through clean renewable energy sources either on-site or off-site. 

  3. Decentralized, modularized and distributed systems to allow for low-cost off-site preassembly, reduced piping lengths and penetrations, high efficiency energy recovery, and individual occupant control over energy consumption. 

  4. Transition to low-GWP refrigerants 

Early-stage energy analysis was used to benchmark the building design, inform design decisions, and balance cost and long-term benefits over the entire building life-cycle. The proposed design achieves a 32.5% energy use savings when situated in San Francisco, CA and a 46.7% when situated in Atlanta, GA. 

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Additional design strategies to maximize energy efficiency include: 

  • San Francisco (Heating only region): Compact modular in-wall heat recovery ventilators (HRV) with electric resistance heating. 

  • Atlanta (Heating and cooling region): Compact integrated heat pump based domestic hot water and energy recovery ventilator unit. 

  • Highly insulated building envelope with low air infiltration, operable windows for natural ventilation when suitable. 

  • Building envelope: 

  • Walls: Total Assembly R-25 (R-15 for Atlanta) 

  • Roof: Total Assembly R-30 

  • Operable windows 

  • Rooftop is designed to support on-site solar photovoltaics if local clean energy is not available or additional building energy resilience is desired. 

SPEED and tallyCAT

 

Whole life carbon reduction, materials transparency, and human health and wellness are at the heart of our approach to whole-systems regenerative design. That's why we developed SPEED, an in-house energy modeling tool for early design. We’ve partnered with Building Transparency to pilot the Embodied Carbon in Construction Calculator (EC3) Tool and are co-creating a new open-access tool called tallyCAT. These tools are at the forefront of research-informed practice. They help us to reduce operational and embodied carbon through the design process, deliver better buildings, and transform our industry.

Refrigerants

While often not accounted for, overlooking the impact of refrigerants can result in a design that results in a higher overall carbon footprint over its lifespan. The Case Study’s modular and distributed heating and cooling systems reduce the amount of refrigerant charge per unit by approximately 50%. In addition, we are constantly advocating and working with equipment manufacturers to eliminate all CFC-based refrigerants and push the use of natural low GWP refrigerants such as CO2.

Renewable Energy

The current design doesn’t prioritize the use of on-site solar photovoltaics to maximize construction economy. As an all-electric building that eliminates fossil fuel combustion, the ability to eliminate operational carbon emissions can be immediately realized by procuring clean energy from local utility provider at a small premium. However, the rooftop is designed to accommodate solar if the local utility provider does not have a clean energy option, or if additional building energy resilience, or demand reduction is desired.

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Grid Emissions

The power supply of a locality has an immense effect on the operational carbon of buildings. Some states, such as New York, California, and Washington already have very low emissions from the generation of electricity. In 2021, eight states committed to have zero carbon emissions from electricity generation by 2050 or earlier. More states are soon to follow. In 2020 80% of all new electricity generation was renewable. The market for new coal and natural gas power plants is crashing. Over 280 carbon intensive coal plants have been closed in the US. Fossil fuel power generation is struggling to stay competitive with renewables. Because of growing consumer demand, some utilities now allow choice of generation so that building owners or tenants can choose offsite 100% renewable generation.

All electric buildings are inherently lower emissions than gas buildings. With each passing year that difference is more pronounced. Operational carbon in all electric buildings can be eliminated today with a combination onsite and offsite renewables.