In the past three months, Sam Rashkin, chief architect of the U.S. Department of Energy’s Building Technologies Office, has been traveling non-stop, speaking at meetings and conferences about the expansion of zero energy buildings in the United States. While accustomed to an exacting traveling and speaking schedule, the demands on his time likely accelerated with word that Rashkin will retire from the DOE and his role as chief housing-efficiency advocate at the end of the year. Insulation Institute recently caught up with Rashkin for an assessment on zero energy building today and where it’s headed in the future.
Zero by the numbers
All signs point to an impressive movement for zero energy buildings, according to Rashkin. A self-professed “housing guy,” Rashkin is buoyed by the growth in residential zero energy buildings in the U.S. and Canada.
“They report over 350 percent growth between 2015 and 2018, to more than 22,000 homes, according to a Team Zero report,” Rashkin notes. “This tracks with DOE’s experience, where we’ve seen a doubling of Zero Energy Ready Home certifications of the past three years, with approximately 4,500 home certifications.”
Impressive growth in Zero Energy Ready Homes has been boosted by a strong commitment by local governments, including 19 mayors globally and six in the U.S. that have signed carbon pledges for new construction buildings by 2030 and all buildings by 2050.
“Cities in the U.S. are actively promoting zero energy initiatives, including Lancaster, CA, Palo Alto, CA, Bloomfield IA, and Montpelier, VT. In addition, some states are also leading the way with building code targets moving to zero, including California, New Jersey, and Washington. Many other states have plans for adopting the latest 2018 International Building Code, and others have stretch codes that keep ratcheting up the rigor of enclosures so that they are ready for zero energy performance.”
The accelerating pace of Zero Energy Ready Home adoption demonstrates that it is the future of building, but that doesn’t mean that everyone understands the requirements.
Getting to Zero
“The building blocks for ‘zero’ are very simple,” according to Rashkin. “First, optimize for energy efficiency. This is achieved with highly efficient enclosures that include advanced insulation practices, airtight construction, and high-performance windows.” Regarding advanced insulation, DOE is agnostic on the type of insulation used to achieve zero, with fiberglass among the various options that can help achieve Zero Energy Ready Home performance.
“With a highly efficient enclosure, the heating and cooling loads become so small that the components inside the homes now account for more than half of the total energy consumption. So, energy-efficient equipment, appliances, lighting, and fans are also critical to minimizing total energy use,” Rashkin stated.
“Highly efficient building enclosures create their own challenges with moisture management, comfort, and indoor air quality. Thus, the second building block calls for high-performance systems to ensure [the builder] ‘does no harm.’”
Raskin explained that highly insulated envelopes, airtight assemblies have much greater wetting potential (e.g., colder surfaces on the inside face of construction cavities) along with reduced drying potential (less thermal flow with better insulated air-sealed assemblies). “Thus, Zero Energy Ready Homes require bullet-proof bulk moisture control to keep water out of the assemblies.” Details like flashing, weather resistive barriers, and capillary breaks are all part of the bulk moisture management system.
“Comfort is an issue because highly efficient enclosures result in substantially reduced heating and cooling loads with significantly lower airflow and longer swing seasons,” Rashkin explained. “As a result, the common practice of ignoring proper duct design is more likely to result in incomplete mixing of conditioned air. The common practice of not addressing relative humidity control becomes a much bigger problem with longer swing seasons. This is because the accidental dehumidification from air conditioning is no longer available during this time to address the latent load.”
Rashkin said the common practice of installing HVAC ducts in unconditioned attics is more detrimental to small duct systems with reduced airflow. “Zero Energy Ready Homes require much more attention to duct design, latent load control strategy, and optimized duct location.” Indoor air quality is a challenge as well.
“Because significantly airtight construction minimizes dilution of contaminants with natural infiltration, Zero Energy Ready Homes require a comprehensive strategy for indoor air quality, including source control, to minimize contaminants, effective dilution with whole-house ventilation, and filtration with high-MERV filters in HVAC systems.”
The final building block to get from a Zero Energy Ready to Net Zero home uses solar-ready construction in locations with a meaningful solar resource to ensure zero energy performance is available in the future with no cost penalty or disruption. Rashkin said this is achieved with low- to no-cost details and practices during construction. He noted that DOE is also agnostic on whether homes achieve zero energy performance with onsite solar or choose an option for offsetting onsite energy consumption, such as purchasing utility renewable power, joining a micro-grid system, or purchasing offsets. “The approach to Zero Energy Ready Homes is so powerful because it means all buildings can participate in a zero energy solution regardless of available roof area, local shading, or solar resource limitations.”
Zeroing in on the Future
“At the rate we’re going, I fully expect, Zero Energy Ready Homes to become the norm by 2030, when tens of thousands of homes are certified each year or constructed under codes representing zero energy performance,” Rashkin noted. “DOE’s Zero Energy Ready Home program is effectively contributing to the future in a way that ensures that energy efficiency comes first, high-performance is a mandatory requirement to ensure we do no harm, and solar-ready construction provides an opportunity for homeowners to experience zero onsite, whenever they believe it makes the most sense,” he said.
The upside to that achievement is that homeowner savings would be significant. “DOE analysis shows that transforming to Zero Energy Ready Homes by 2030 can result in approximately $150 billion in U.S. homeowner savings on their utility bills and about 1 million jobs. This is years of work that cannot be outsourced.”
In addition to the economic benefit, the environmental benefit would be enormous, with an estimated 1.1 million metric ton reduction in carbon emissions. All good news for the nation.
“The zero train has left the station, and we’re in for a great ride.”