Successful in Europe, the Passive House Movement Seeks to Achieve Carbon Nuetrality Through Insulation, Airtight Construction and Extreme Energy Efficiency
Imagine being able to heat an entire house with the energy of a hand-held hair dryer. Or, put another way, picture a house that uses up to 90 percent less energy than its conventional alternative, has no traditional furnace and its mechanical system can fit into a small linen closet. Sound implausible? Far from it, as one design and construction team in Sonoma, Calif., is demonstrating as it nears completion of what is expected to be one of the first “Certified Passive House” retrofit projects in the country. The project is being monitored by the United States Department of Energy (DOE) as a prototype home in its demonstration “Build America Program.”
Located just blocks off the historic downtown Sonoma plaza, the O’Neill residence passive house retrofit stands as an example of a growing movement to design and build super efficient structures that take energy savings to a whole new level.
Well established in Europe over the past two decades, the passive house movement is now garnering increased attention and interest in the United States— and for good reason: passive house offers a practical, performance-based approach for dramatically slashing a building’s carbon footprint and energy use. It is centered on a scientifically-based modeling system, the use of relatively simple, preferably locally available materials and good old fashioned construction techniques that emphasize careful attention to detail and quality workmanship. “It is just essentially bringing back the lost art of really good carpentry, having attention to detail. It’s kind of ennobling the profession again,” says Prudence Ferreira, principal consultant with Integral Impact Inc. and president of the organization Passive House California. “It’s not about doing anything exotic; it’s about working with what we have here locally.”
Tried and True: Passive House’s Roots in Europe
The passive house concept draws on the ideas of super-insulation, low energy and passive solar projects from North America and Europe in the 1970s and ’80s. Professors Bo Adamson of Sweden and Wolfgang Feist of Germany created the first passive house (dubbed “Passivhaus” in Europe) in the early 1990s in Darmstadt, Germany. In 1996, Dr. Feist founded the Passivhaus Institut in Germany, fostering a growing trend that led to the design and construction of an estimated 20,000 passive house projects to date, predominantly in Europe and Scandinavia.
The passive house approach has been applied to both residential and commercial projects, including multifamily housing, retail stores, factories, schools, churches and government buildings in addition to private residences. As recommended by European Parliament in January 2008, the energy efficiency standard achieved by the passive house will be required for all new public building construction throughout European countries beginning in 2011 and beyond.
Just more than a decade after passive house debuted in Europe, German-trained architect Katrin Klingenberg designed the first certified passive house in North America — a 1,200-square-foot home in Urbana, Ill., constructed in 2003. Klingenberg established the Passive House Institute U.S. (PHIUS) in Urbana with builder Mike Kernagis. In January 2008, the Passivhaus Institut in Germany authorized PHIUS to be the official and sole certifier of passive houses in the United States.
How Does It Work?
The passive house is a super insulated, virtually airtight structure that uses passive solar gains and the heat created by occupants living in the space, along with the building’s appliances, electronic devices and more, to heat and cool the structure. In lieu of conventional “active” heating and cooling systems, a passive house uses a mechanical heat recovery ventilation system, which transfers the temperature and moisture from a home’s outgoing air stream to an incoming fresh air stream. In effect, the building’s exhausted air is reused to heat or cool the incoming fresh, filtered air — providing superior indoor air quality as a result.
Given a passive house’s air-tight construction, proper ventilation is critical and can be achieved either by a heat recovery ventilator (HRV) or energy recover ventilator (ERV), which differ primarily based on the way the heat exchanger works. With the ERV, the heat exchanger transfers some water vapor along with heat energy, while the HRV only transfers heat.
A passive house achieves its extremely high degree of energy efficiency by aggressively combining high levels of structural insulation, airtight construction and heat or energy recovery ventilation along with passive solar gains achieved through high performance, triple paned windows, solar orientation, shading and various other features. Particular attention is given to eliminating thermal bridges, which result when building materials that are poor insulators come in contact, allowing heat to flow through the path created and escape from a structure.
The only strictly performance-based building certification system currently in use, the passive house approach is based on three primary criteria: air infiltration, Btu consumption and kwh usage. The basic standard for building performance in those areas breaks down as follows:
1) A building must consume no more than 15 kilowatt-hours (kWh) per square meter in heating energy per year. (Equivalent to no more than 4755 Btu per square foot annually.)
2) The total primary (source) energy must not exceed 120 kWh/m2/year, or 38,000 Btu/ft2/yr. This includes water heating, lighting and plug loads. Source energy encompasses the energy required to produce and deliver energy to the site; it can be offset with solar thermal and other measures, including photovoltaics.
3) The building must not leak more air than 0.6 times the house volume per hour at 50 Pascals of pressure.
Designing and Certifying the Passive House
The passive house is modeled in the Passivhaus Planning Package (PHPP), a Microsoft Excel energy calculation tool. The program performs its calculations, taking into account virtually every component of the structure, from the site weather patterns and solar orientation, to the construction mode and materials, to the ventilation system design and everything in between. This modeling program is essential to the design process; the space heating requirement of 15 kWh, for example, can only be verified by modeling the proposed design within PHPP. In order to be certified, a structure must demonstrate (via compliance reports generated from the PHPP modeling software) that it complies with the rigid passive house energy consumption requirement. An on-site blower door test conducted by a third party is also required to verify that that the building performs to the extremely rigid passive house airtightness standard of 0.6 ACH50, which is about 10 times tighter than the average house.
The passive house concept represents a paradigm shift from the traditional design approach for the mechanical system, according to architect Jarrod Denton with St. Helena, Calif.,-based Lail Design Group, the firm involved with the Sonoma passive house remodel. The house is designed for the heating core, rather than the heating core being designed to fit the leaky house.
“Conventionally, you build a building and then size your mechanical system to that building,” he notes. “Here, we figure out the ventilation rate; we know how much heat will be carried through that air flow, and then we design the shell to accommodate that.”
At its core, the passive house concept is “elegantly simple,” Denton says. “It’s building better; it’s durability. There are very simple principles involved that allow the design team and the contractor and everybody involved to pool their resources together.”
The O’Neill Home – The Road to Passive
For the companies involved in the O’Neill passive house retrofit project in Sonoma, pooled resources were key to the project’s success, as the team worked to meet the targeted completion date of July 2010. “This is probably the best example in my history of a collaborative effort; everybody involved with the project has had to be on the same page, pulling toward the same goals,” Denton says.
The project team includes Denton; contractor Rick Milburn, owner of Napa-based Solar Knights Construction, who is the first builder in California to be certified by the PHIUS; and certified passive house consultant Graham Irwin of Essential Habitat Consulting of Fairfax, Calif., along with several other key consultants.
From the outset, owner Cathy O’Neill expressed her desire to create a comfortable and environmentally friendly home. After learning about the advantages of passive house, she decided to make hers a model home that set a new benchmark for energy efficiency in America.
The existing house that was selected for the transformation offered strong potential, including its proximity to downtown and it direct access to a “pocket park” off the back yard, among other features — but it also offered some formidable challenges, according to Milburn.
Constructed in the 1960s, the O’Neill residence was originally two structures linked by a covered breezeway. It was set on an un-insulated slab foundation that provided little option for adding insulation underneath. This required the extra insulation to be layered on top, while adequate floor-to-ceiling heights still had to be maintained. “This was the worst case scenario for a passive house in Northern California,” says Milburn. “This is as bad as it will get.” The remodel updates and unites the two structures, converting the breezeway into a framed kitchen and expanding the final floor plan to around 2,400 square feet, wrapped around a Mediterranean style courtyard.
Ultra Low Energy Design
Designed to achieve “site net zero” electrical usage, the complete overhaul project included, among other things, the addition of extensive amounts of insulation, ultra efficient windows and doors, new roofing made from recycled content, new flooring, the addition of a passive solar thermal hot water heater and a new mechanical ventilation system featuring the energy recovery ventilator, the “UltimateAir™ Recoup Aerator®”, manufactured by Stirling Technology, Inc. of Athens, Ohio. This system runs on the equivalent of a 100-watt light bulb in normal usage. A small backup heating and cooling system is also included.
A full 100 percent of the structure’s electrical needs will be met from the ultra-low energy design combined with a dozen grid-tied photovoltaic panels. Among the numerous other sustainable and energy efficient features are high efficiency lighting and appliances; locally fabricated casework, as well as salvaged and recycled finishes used throughout; drought resistant landscaping; and rainwater harvesting via a catchment system under the driveway that will capture an estimated 25 to 35 percent of the irrigation water needed for the residence. The contractor was able to retain approximately 40 percent of the existing exterior wall framing on the structure.
While Irwin says the house is modeled for a minimum 70 percent total energy reduction from a standard California house, he points out that the solar hot water system that will also contribute to space heating is not factored into those savings and will likely bring the total savings closer to the 80 to 90 percent range. The actual savings will be measured and tracked in the coming years as a part of the U.S. DOE’s Build America program.
The Passive House Premium
As with most new building systems, passive house design and construction in the U.S. does cost more upfront — a premium estimated at anywhere from 10 to 20 percent over the cost of a conventional approach when it comes to a residential remodel, according to Milburn. He estimates the cost premium of new residential construction at “less than 10 percent” and perhaps even less for commercial and multi-family projects after the initial learning curve about passive house is met. “The first project is going to cost in education, but after that we should be able to match what they are doing in Europe, which is no additional cost,” Milburn says.
As for the Sonoma project, “right now we’re within our 20 percent delta of what it was going to be to retrofit this house (conventionally),” Milburn says. However the savings achieved through reduced life cycle and operating costs of the structure will help balance that initial output over the long term. And the passive house project is built to last, reducing the maintenance and repair costs in the long haul. “All of the materials in a passive house are selected either for recycled content, longevity or durability,” Denton notes. “This performance level has to be maintained for a period of 20 to 50 years.” The airtight standard in passive house, combined with its ventilation system effectively keeps out moisture, eliminating the problem of mold that has spawned a growing number of lawsuits in the residential and commercial building sectors in recent years.
Meeting the 2030 Challenge
Cost premium or not, the need to dramatically reduce energy consumption and stem CO2 emissions in the built environment is becoming more critical with each passing year. The state of California Public Utilities Commission, following California’s “Global Warming Solutions Act of 2006” (AB 32), has mandated that by 2020, all new residential construction must achieve net zero energy, with a similar requirement for all new commercial construction by 2030. This follows along the lines of the “2030 Challenge,” in which the nonprofit organization Architecture 2030 called for no fossil fuel use for buildings by that target year.
Carbon neutrality is the ultimate goal and it may be mandated — but is it doable? “With passive house, I think absolutely it is realistic,” Ferreira says. “Without passive house, I don’t think we have much of a chance of getting there. There’s no other codified system that will deliver consistent results in place at all.
“We’ve got increasing population and increasing demand for energy,” Ferreira adds. “We are essentially stuck in a situation where we realize that we can’t get to where we need to be by looking at increasing supply; we have to decrease demand and then we have a fighting chance of meeting our goals.”