By Kessie Avseikova 

California recently endured a punishing heat wave in the beginning of September that shattered temperature records and had residents see back-to-back Flex Alerts issued by the California Independent System Operator to avert rolling blackouts amid historic high demands. “This is an extraordinary heat event we are experiencing, and the efforts by consumers to lean in and reduce their energy use after 4 p.m. are absolutely essential,” stated Elliot Mainzer, the California Independent System Operator’s president and CEO. Extreme heat is likely to become the norm for the state amid a warming climate (Petek 2022), and futureproofing built environments will be one of many strategies to reduce grid strain while minimizing the discomfort experienced by occupants. Passive House construction offers both comfort and efficiency.

So, what is it that makes Passive House design special?

The foundation of Passive House design lies in its implementation of super-insulated construction, effectively eliminating the need for traditional heating and cooling systems, even in challenging climates. The core design principles also integrate high-efficiency fenestration and dedicated ventilation, which result in ultra-energy-efficient buildings with thermal mass properties that can store heat and cold and release it steadily and slowly. Homes built to the Passive House performance standard do not succumb to daily temperature swings, offering predictable and consistent performance with their ability to maintain comfortable indoor temperatures for hours without operating heating or cooling equipment.

California has always been at the forefront of utilizing building codes and standards to encourage energy-efficient construction; however, the state does not have its own guidelines or standards for Passive House construction as it is not part of the current building code. Instead, builders and contractors look to two Passive House certification organizations for reliable standards: the Passive House Institute/Passivhaus Institut (PHI) of Germany and Passive House Institute US (Phius) a Chicago-based non-profit. Each organization offers a standard which has a unique set of performance metrics and required energy modeling solutions. Regardless of the distinctions, both PHI and Phius standards aim to achieve specific building performance criteria using core concepts (Phius 2022):

  • Thermal Control. Thermal control helps keep Passive Homes cooler when it’s hot outside, and warmer when it’s cold outside. A Passive House utilizes a self-contained layer of continuous insulation that minimizes the transfer of hot or cool air through the building shell. Thermal bridge elimination minimizes risks of air transfer and mold growth.
  • Air Control. A Passive House achieves low air infiltration rates by maintaining an uninterrupted air barrier. With an airtight enclosure, balanced ventilation is critical to maintaining indoor air quality. Passive buildings continually exhaust air from kitchens, bathrooms, and any other high-moisture or odor-producing spaces with stale air and supplies fresh air to living areas utilizing a heat recovery ventilator (HRV). During this process, it transfers heat from the exhaust air into the incoming air without directly mixing the airstreams together to minimize heat loss. A Passive House HRV needs to recover at least 75% of the exhaust air heat.
  • Radiation Control. Passive home design employs high-performance widows and doors while using shading and daylighting strategies to minimize or exploit sun exposure and radiant heat.
  • Moisture Control. Due to their design, Passive Homes require special attention during their design to account for vapor and moisture within the enclosure and mechanical systems and to maintain humidity for occupancy comfort. Occupancy comfort is so integral to the Passive House concept that PHI has integrated a “comfort equation” to its building process.

At its core, Passive House is a performance standard, not a set of prescriptive guidelines, which enables architects and designers to pursue a variety of pathways to achieve the required performance of both extremely comfortable and hyper energy efficiency. Our research suggests that customers looking to build Passive House–compliant homes are inclined toward energy conservation and decarbonization. This includes implementation of heat pump technology, energy-efficient appliances (such as induction cooktops), renewable generation (rooftop solar and wind), and storage integration. And that hyper efficiency translates to not only long-term energy saving for the homeowner, but also the potential to provide much needed load reductions for the grid. Operating a reliable electric grid requires balancing electric supply and demand almost instantaneously. Balancing supply and demand requires that the grid respond immediately to changes in load, which requires sufficient flexible generation resources that can quickly increase and decrease production as load changes. Maximizing the efficiency of the electric grid requires flat, reliable load that is easy for the grid operator to balance, and our research indicates Passive Home design has the potential to provide those benefits.

How exactly can building design make a difference?

The steepening ramp associated with the infamous “duck curve”—a phenomenon wherein midday solar generation and the afternoon peak combine to create an abrupt ramp in net electricity demand—is exacerbating the challenge of managing supply and demand on the California grid by increasing the need for additional flexible generation to maintain reliability. In response, California is pursuing multiple avenues for “flattening” the duck curve such as increasing demand response program participation and introducing time-of-use rates for load shedding and shifting as well as building out clean energy generation and battery storage. The Passive House standard supplements these efforts and presents the opportunity to deliver several important benefits to new building construction demand for energy:

  • Reduced Peak Load. Passive Houses have long “thermal time constants,” which means they don’t react to daily temperature swings. One case study showed 40% lower winter peak load for a Passive House building than for a baseline building defined as the Building America 2009 benchmark. We compared available consumption data for the two Passive Houses built in Sunnyvale and Alamo California (Barry 2021) to consumption data for similarly sized Zero Net Energy (ZNE) homes (Allen et al. 2020). The comparison showed pronounced differences between the two home types during the peak hours for both the cooling and heating season. The Passive House load was between 36% and 46% lower than the ZNE load between 4:00 p.m. and 9:00 p.m. in the summer and 0% and 46% lower between 5:00 a.m. and 8:00 a.m. in the winter.
  • Flatter Load Shape. Engineering modeling simulations of typical California homes show Passive Houses have between 3% and 46% lower ramp rates than code-compliant homes depending on season and climate zone. Additionally, the an simulations suggest Passive House buildings having a less “peaky” load profile than code-built housing (Gracik and Sanborn 2017). Load “peakiness” is generally represented by the load factor, which is defined as the ratio of the average load divided by the peak load in a given time period. Based on Gracik and Sanborn’s simulated neighborhood-scale electric demand and system load factors across 100 code-compliant ZNE homes and 100 Passive Houses, the Passive House standard has been shown to achieve higher load factors than code-compliant ZNE homes in nearly all scenarios.
  • Increased Load Flexibility. Passive House design can enable on-demand change in the load curve and deliver load shifting benefits. By deploying precooling or preheating strategies during the day, Passive Houses can leverage daytime solar generation and enable the building’s thermal mass to maintain cooler or warmer temperatures respectively during evening hours and into the night without incurring any additional cooling or heating load. Such interventions can be automated and, when applied at scale, could act as a reliable and dispatchable grid resource that reduces peak load by acting as energy storage for off-peak daytime solar generation.
  • Reduced Rooftop PV Overgeneration. Neither Passive House standard has a requirement for solar PV, but both recognize and encourage integration of solar into Passive House design. Our research confirmed that rooftop PV is almost always included in Passive House design in practice. Results of our literature review suggest Passive Houses require fewer solar panels than non-Passive House residential new construction. One study showed Passive House construction requiring up to 50% smaller PV arrays.

Each of these benefits can impact system-level electric grid operation if deployed at scale, offering distribution grid benefits. This is particularly true for new developments of Passive House communities. Potential grid benefits resulting from widespread deployment of Passive Houses include reduced and avoided costs:

  • Avoided Grid Investment Costs for New Developments. Passive Homes have lower total electric consumption, lower peak load than code-built homes. Therefore, a substation and feeder serving a Passive House community can serve more homes than the same substation and feeder could serve if the community was built to-code. Furthermore, Passive Homes have more consistent load shapes than to-code homes. Together, the reduced demand and lower uncertainty associated with new Passive House communities can lower the costs associated with building electric infrastructure for new developments.
  • Lower Costs to Operate the Grid. Together, the benefits of widespread Passive House deployment could theoretically lead to substantially lower operating costs for the grid. While the amount of these cost savings for Passive Homes specifically has not been quantified in the literature, a whitepaper from the Sacramento Municipal Utility District examined the impact of halving air conditioning load during peak periods and found that the capacity value alone was estimated to be several thousand dollars per home.

With a goal to decarbonize the built environment, Passive design is a holistic approach that reaps benefits for both homeowner and grid operator. According to Phius, the upfront cost to build a passive home is currently slightly higher than the cost to build a conventional home but those costs tend to be nullified with reduced utility bills and less maintenance over time as many of the interior and exterior finish materials used in Passive House design (including the high-performance windows and doors and the elimination of a furnace or other conventional HVAC system) are virtually maintenance-free. Recent legislation such as the Defense Production Act on Electric Heat Pumps may make the technology behind Passive Home design more readily available and affordable in the immediate future.

Passive Homes offer a two-prong solution to current grid resiliency needs with immediate gains in potential load reduction as well as reduced load impacts during peak times or extreme weather events. The California Public Utilities Commission (CPUC) Energy Division has an interest in how widespread deployment of Passive House construction could offer further energy savings and grid benefits above and beyond the current Energy Code requirements. While the quantitative assessment of grid benefits is ongoing and is planned for release by Opinion Dynamics and the CPUC later in 2022, the results from the first phase of our current study offer strong evidence of the Passive Houses’ potential in supporting a more resilient and flexible grid.

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