Passive House Design Brings Simplicity to Energy Efficiency

Modern-Day Science Meets Old-Fashioned Methods of Weatherization

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Posted: Wednesday, January 16, 2013 5:13 pm

Do you think investing in the latest high-tech HVAC and on-site renewable energy systems is the only way to create an energy-efficient building? Well, architects in Europe are suggesting you think again.

Passive House, a standard for green design and construction developed in Germany, is now being applied in the U.S. as a simplified and less mechanized approach to meeting rigorous standards of energy efficiency.

Collaboration among affordable housing developers in the U.S. is helping it achieve more recognition on this side of the Atlantic.

The Passive House Building Energy standard applies modern-day science to old-fashioned weatherization techniques, depending largely on super-thick insulation, triple-paned windows and air-tight construction to create green buildings that are customized for the local climate.

A tour of Passive House buildings in Germany convinced a community-oriented developer in Pennsylvania that using the passive approach makes the most sense when developing affordable housing.

“The real benefit to us as people who are building for low- to moderate-income families and households,” said Linda Metropulos, “is if we can find a way to lower utility bills substantially, we're enabling them to have much more money in their pockets at the end of the month.”

Metropulos is a senior real estate officer for ACTION-Housing, a Pittsburgh-based nonprofit developer of affordable housing.

While Leadership in Energy and Environmental Design (LEED) has become the standard for green building in the United States, the Passive House approach is less known here. In western Pennsylvania, at least 125 buildings have some type of LEED certification, according to the U.S. Green Building Council, but until last year, no certified Passive Houses existed in the area.

So Metropulous became a pioneer, spreading the idea to her organization and collaborating with others in the nonprofit housing industry who had also taken the tour in Germany.

Building a Prototype

The first Passive House in western Pennsylvania came to fruition after damage from Hurricane Ivan in 2004 led to a county program that purchased and demolished flood-prone properties, and enabled participating municipalities and developers to build new housing elsewhere. Allegheny County financed the Passive House, located on a formerly blighted property in Heidelberg Borough.

When considering Passive House standards, Metropulos described the local government entities as both cautious and supportive.

“In general, government agencies have to be prudent and cautious with what is done with the money they are investing in communities,” she said. “But they were supportive and just wanted assurances that the people moving into the house would be warm when they needed to be and cool when they needed to be.”

With the 1,800-square-foot house constructed and on the market, everyone is eager to track its energy performance over the first few years, Metropulos said.

“I think everyone believes if you can demonstrate that you can really reduce energy consumption, it's a good thing,” she said. “And if you can do it aggressively without costing a whole lot of money and putting on photovoltaic and geothermal systems, it's even better.”

In that way, the prototype house in Heidelberg, a suburb of Pittsburgh, is a game changer. Its total energy usage – heating and cooling, domestic hot water, and electricity – cannot be more than 38 kBTU per square foot per year by Passive House standards. An average house located in the northeastern states consumed about 50.7 kBTU per square foot in 2009, according to the latest available data from the Energy Information Administration.

Passive House criteria limits heating and cooling loads to 4.75 kBTU per square foot, less energy than it would take to power a 1,500 watt hair dryer.

Heating and cooling a house accounts for nearly half of its energy consumption, according to Energy Star, followed by lighting at 13 percent, water heating at 12 percent, and clothes washing and drying at 7 percent.

Heating and cooling the Passive House in Heidelberg is projected to cost an average of $25 per month. The remainder of the bill depends on occupant usage of appliances and other plug-ins.

Using proprietary energy-load software, architects modeled and designed the house to be 68 degrees in cold months and 77 degrees in warm months. A Heat Recovery Ventilator exchanges the air completely every three hours, pre-treating the outside air for temperature and moisture. It also replaces the need for a more energy consuming conventional HVAC system. Not having a furnace might raise eyebrows in a part of the country where it snows, but the Heat Recovery Ventilator can handle the job because a super-insulated shell and airtight envelope minimizes heat loss.

The airtight envelope must pass a blower test as part of requirements for certification.

Passive House standards focus on the thermal barrier between the inside and the outside of the building, requiring less money to be spent on mechanical systems that will eventually wear out, said Metropulos.

Thick insulation lines the walls, which explains why the house’s window sills are about one foot deep. Triple-paned windows, the only materials specially purchased from Europe, provide better insulation than double-paned.

“We're actually using a more durable window, better insulation, better siding material, and a thicker wall with a standard palette of materials,” said Laura Nettleton, president of Thoughtful Balance in Pittsburgh, the green architecture firm that designed the house.

When ACTION-Housing approached the architects to design the Heidelberg house, they asked for about 2,150 square feet. Instead, the architects proposed a smaller 1,800 sq. ft. house, shifting more money toward materials. For the same price at the expense of size, the house also has bamboo flooring, ceramic showers, and solid surface countertops.

To construct the 1,800 sq. ft., 3-bedroom, 1.5-bath home, the developers didn’t have to break the bank. It cost about 13 percent more to construct using Passive House standards, not including the detached garage.

“As long as upfront costs don't become so ridiculously large that it's hard to justify, there's a lot of support across the board” for creating a higher-efficiency home, said Metropulos.

Architect as Energy Geek

While Thoughtful Balance has worked on many LEED projects, they had to become experts in Passive House, too. One architect on staff went through the training and certification. Since then, a second architect has been trained and is awaiting certification.

The process is different than LEED in that the software enables the architect to make calculations that used to require a mechanical engineer, giving immediate results on factors such as passive solar orientation and insulation thickness. Local climate input enables the software to tailor the model for the region, automatically adjusting the insulation and window values, for example.

Those decisions, such as adding an extra inch of insulation, are in the hands of the architect. For typical construction in the Pittsburgh area, R-19 is the recommended thickness. For the Heidelberg house, the architects used R-62 for the walls and R-105 for the roof.

“It's really overkill in terms of insulation, but insulation is so much cheaper than what energy is today,” Nettleton said. However, they can’t always do the same for retrofits like the gutted brick YMCA building the firm is currently converting into 84 Single Resident Occupancy (SRO) units. The county approached ACTION-Housing to work on the project.

"It's very challenging. We're aiming for Passive House," said Nettleton. “We're not sure we'll be able to. The rating is very tough, but because it's a retrofit, there are slabs that touch the wall, and we can't insulate.”

Still, by improving the envelope and tempering the water with a geothermal loop, the retrofit will pay for itself, she said. Currently the YMCA pays about $65,000 a year on energy. That should come down to between $20,000 and $25,000 after the retrofit is complete, she said.

“We’ve blown it out of the water in terms of energy efficiency,” said Nettleton. “The owners were telling me I couldn’t make the numbers work as it is. But we put them in the black.”

While the firm specializes in environmentally-friendly buildings, Nettleton said high-tech systems aren’t always the best solutions. They may be eye-catching, she said, but using more mechanical systems creates more maintenance expense for the owner down the line. The exceptions might be larger office buildings and multifamily housing complexes. When the old YMCA is converted to SROs, the building will have a geothermal system.

“If you think about geothermal systems, they’re pretty low tech. We’ve been able to reduce the size of our equipment to a fraction of what it would be” without using Passive House design, she said.

She describes her discovery of Passive House “a little bit like a gold rush.” Last fall, she attended a conference in Colorado with 400 other “energy geeks.”

“To us, Passive House is kind of the wave of the future,” she said, “It’s really exciting because it’s simple.”

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