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Precast concrete enables net-zero homes

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by Korky Koroluk last update:Sep 2, 2014

BY KORKY KOROLUK - Constructing buildings that produce at least as much energy as they use is still a new concept, especially when working in a cold climate.
Precast concrete enables net-zero homes

 

Although no longer rare, such buildings are not common and builders are still experimenting with materials and technology.

Now two young families are living in a duplex in Edmonton that utilizes the thermal-mass heat-storage properties of precast concrete as an aid to achieving a net-zero energy building.

The duplex was built by Habitat for Humanity Edmonton, and was under construction for two years — largely because as well as being a residence for two families, the structure is also a research project that is still underway.

Using precast for net-zero housing is an idea that Habitat president Alfred Nikolai heard of one morning over breakfast.

“I wish I could take credit for thinking of precast,” said Nikolai, president for Habitat for Humanity Edmonton. But the credit lies with some people from Lafarge, the large multinational building-products producer.

Staff members at Lafarge had some people up from the United States and they invited Nikolai out for breakfast.

“They said they were looking at doing two precast homes,” he recalled in an interview, “one in Atlanta, in a warm climate, and one in Edmonton, in a cold climate. And they asked if we were interested.”

A precast concrete wall section is lifted into place for the net-zero duplex built in Edmonton, Alta.

Lafarge was talking about just one home in Edmonton.

But, Nikolai told them that Habitat doesn’t build single-family homes any more.

It would, however, be interested in a duplex, he said.

When Lafarge agreed, the ball was in motion.

Lafarge got Stantec Inc. on board, and between them, the two companies got “a whole bunch of other companies” involved.

Lafarge had wanted to do a residential job using precast, said Don Zakariasen, director of marketing for concrete products for Lafarge Western Canada.

“We were especially interested in the thermal mass side of things.

“Early on, we thought we could just model a net-zero project and glean a whole bunch of information.”

But, the company came to realize that modelling wasn’t the way to go.

“It’s when you build it that you know every challenge that you’re going to face becomes a reality,” he said.

“With a model, the situation might never actually occur, and you’ll delude yourself into thinking that you’ve got a total understanding of it, when you don’t.”

Zakariasen said Habitat was a natural fit for the project.

“We deal with Habitat on a global basis,” he said, noting Lafarge’s long-standing interest in affordable housing.

They also agreed to have sensors installed in the building system so energy use could be monitored for research purposes.

“We were interested in validating the benefits of concrete thermal mass,” he said.

“In the past there has been modelling done to validate it, but no one has done actual tests where you have independent validation, and that’s what we wanted to do here.”

As a result, sensors were installed.

They regularly log on to a site at the Massachusetts Institute of Technology (MIT), and upload information on things like temperature, humidity, and energy use.

The process will continue for two years and will yield a body of hard data that will be verified by researchers at MIT.

Designing the duplex was done by a multidisciplinary team using an integrated design process, where meetings were held to discuss all aspects of the project and how each element interfaces with all the others.

Besides Lafarge and Stantec, the team included Kassian Dyck Associates (structural engineering), Vital Engineering (mechanical engineering), Dow Chemical Canada (rigid insulation), and other specialty firms that aren’t heard of as often.

They included Landmark Solar Productions (photovoltaic panels on the roof), Clark Ecoscience and Sustainability (horticulturalists), and Patching Associates Acoustical Engineering.

The structure has a lot of sustainable features.

Ground-source heat pumps provide heating and cooling.

A photovoltaic array on the roof provides hot water and augments the geothermal system.

A forced-air system circulates internal air.

A green roof was considered, but rejected because of worries about providing access and security.

Energy modelling was based on projected annual needs of 10,000 kilowatt hours.

That led to R-44 insulation in the walls and R-98 in the roof.

Windows are triple glazed.

Modelling also showed that, because the building would be so energy-tight, heat loss through the basement floor became an issue.

Insulation was installed under the cast-in-place slab, something rarely done in residential construction.

Edmonton’s low wintertime sun was a problem.

“So, in the winter we’re (using) the electrical grid as a battery because the solar panels won’t generate enough power,” Zakariasen said.

“But, in the summer months we’ll far surpass the energy needed and we’ll be able to put it back into the grid.”

With the grid serving as a battery to balance the peaks and valleys in the building’s energy performance, achieving net-zero energy over the course of a year became possible.

last update:Sep 2, 2014

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