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The Rise of Net-Zero Homes

Posted: 07/01/2014 2:07 pm

A net-zero home is more than just a place to hang your hat - it's a super-efficient, solar-powered look into the future.

It was Le Corbusier, the Franco-Swiss modernist and founder of brutalism who coined the term "buildings as machines for living." The net-zero home is far more deserving of the term than the bare concrete structures that "Le Corbu" made famous.

Over the course of a year a net-zero home will generate as much energy as it consumes. They've been around for less than 10 years, but these buildings and the thinking behind them are taking North America by storm. 

Net-zero history
Net-zero homes started as a glimmer in the Canadian Housing and Mortgage Corporation's eye. They developed a pilot program back in 2004 and it led to the Riverdale net-zero project being completed in Edmonton, in 2007.

Peter Amerongen built the Riverdale house, one of the first net-zero homes in Canada, with the help of a team of 45 professionals and volunteers. Amerongen has been building homes for more than 40 years and has been interested in energy efficiency since the oil crisis in the '70s.

The Riverdale project is a duplex with a large solar thermal array that aimed to cover the house's space heating needs. Getting it built was a key first step in making net-zero mainstream. The lessons learned on their first epic project bled over into the next, a more modest net-zero project with a smaller budget-the Millcreek net-zero house.

Simpler systems, solar photovoltaic awnings and a dedication to passive solar and thermal mass were an evolution in net-zero design. They were able to get close to net-zero by maximizing the free heating energy from the sun with large, quality south-facing windows and storing that energy in a thermally massive concrete floor, all thanks to a pesky client.

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"He [Conrad Nobert] brought me a copy of CMHCs Tap the Sun book and he went behind the back to my structural engineering friend Andy Smith," says Amerongen.
"You can add a bunch of mass to that house really cheaply by pouring a 2.5 inch concrete overlay on the floor. So we did and we found when we did the modelling that we were awfully close to net-zero and that we could in fact get there by maximizing the passive solar potential."

More passive solar energy means fewer complicated and expensive mechanical systems and a lower cost house. Since that first house in 2007 interest in net-zero homes has grown rapidly.
Amerongen says there are two game changers that have really made net-zero possible - drastically reduced solar prices and a super efficient air source heat pump that works in the cold climate of Canada. This combination means Peter is developing affordable net-zero homes on lots that don't even have ideal solar access.

How to build your own net-zero home
So if this whole net-zero thing catches your fancy how do you do it? We spoke to half a dozen architects, engineers and homebuilders and if you want to build a successful net-zero project it comes down to three key points:

  • Energy conservation

  • Passive solar design

  • Renewable (solar) energy production

Energy Conservation: Your net-zero home needs a high quality building envelope. You need super insulated walls and ceilings, quality energy efficient windows and it all has to be sealed up tight to prevent heat loss. Mike Turner is an engineer at Manasc Isaac Architects who built his own net-zero home: he put R70 insulation in his roof, R50 in his walls and he used quad-paned R8 windows.
The home needs to be far more airtight than the average Canadian home.  An average home has 4.4 air changes per hour - you should be shooting for 0.5 air changes per hour.
Use energy efficient electric heating systems such as an air source heat pump made for cold climates. With no natural gas hook-up you will probably use a high efficiency electric hot water heater.
And needless to say your house has to use as little electricity as possible. That means buying energy efficient appliances, killing phantom loads and being generally mindful of the electricity that you use.

Passive Solar Energy: The site and orientation of your house is key. Face it south and install lots of high performance windows. Build the right sized overhangs that keep out direct summer sun, but still let the lower winter sun shine in. Use a concrete floor for thermal mass to store heat after the sun goes down. Your goal here is to harvest and retain as much free energy as possible.

Energy Production : Once you have created the most energy efficient home you can and harvested as much free passive solar energy as possible then you need to produce the energy you require. Solar photovoltaic panels are the simplest most cost-effective solution for the home today. They have dropped drastically in price over the last few years and your investment will protect you from future electricity prices increases for 25 years.
Buildings and electricity production together account for nearly a quarter of Canada's greenhouse gas emissions. In one fell swoop the net-zero home addresses a significant chunk of Canada's greenhouse gas emissions. In a world facing climate change and a volatile energy market the net-zero house is the house we need.

This is part one of a four part series called Chasing Net-Zero. In Part 2: Net-zero beautiful we explore the evolving aesthetics and technology of net-zero homes.

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  • Net-zero homes pioneer, Peter Amerongen

    Peter Amerongen of Habitat Studios led the team of 45 professionals that built the first net-zero home in Edmonton, Alberta in 2007. This makes him a pioneer of an idea that is taking North America by storm. Photo David Dodge, Green Energy Futures

  • First net-zero home

    This is the Riverdale net-zero home in Edmonton, one of 12 that was built as part of the CMHC equilibrium program set up to prove net-zero homes can work. Many of those first net-zero homes were technological marvels, but the idea worked and started a revolution in the design of the efficient, sustainable homes of the future. Photo David Dodge, Green Energy Futures

  • House gets half of heat from passive solar

    In seven short years Peter Amerongen’s super energy efficient homes evolved rapidly. This Belgravia net-zero home, built just five years after the first gets half its heat from passive solar energy, has no furnace, no gas hook up and a very simply mechanical room that contains only a standard electric hot water heater, an air exchange system that preheats air and 7.6 kilowatts of solar photo voltaic modules to power all of the homes needs. Photo David Dodge, Green Energy Futures

  • Solar squared - net-zero harvests passive solar and solar PV energy

    In Peter Amerongen’s second net-zero build, the keep-it-simple maxim was already in play. By maximizing south facing, efficient windows, including plenty of solar photovoltaics and incorporating a heat storing concrete floor this home is much simpler and more affordable. Photo David Dodge, Green Energy Futures

  • Net-zero infill - produces as much energy as it consumes

    This is the front view of Conrad Nobert’s Mill Creek net-zero home, Peter Amerongen’s second effort at building net-zero homes. From the front it looks like a regular infill home, the only difference is this home produces as much energy as it uses over the course of year. Photo David Dodge, Green Energy Futures

  • Save energy + passive solar + solar PV = Net-zero home

    Mike Turner built his net-zero home incorporating solar photo voltaics, passive solar design and a ton of energy efficient systems to minimize energy wastage. Photo Photo Garth Crump

  • Solar PV key to net-zero homes

    The Turner home incorporates 8.2 kilowatts of solar photovoltaics (PV) on the home and four more kilowatts on the garage for a total of 12.2 kilowatts to help his home reach net-zero energy use over the course of a year. Photo Garth Crump

  • Solar garage

    Mike Turner added four kilowatts of solar photo voltaic modules to his garage, in addition to 8.2 on his home, to help supply all of the net energy required by this home located in North America’s most northerly large city, Edmonton, Alberta. Photo David Dodge, Green Energy Futures

  • Solar powered home

    Mike Turner on his back porch. The 8.2 kilowatts of solar photovoltaic modules are mostly on the back part of his two-tiered roof, barely visable from the street. The solar modules are very affordable now, which in turn provides predictably priced electricity for 25 years, the life of the system. Photo David Dodge, Green Energy Futures

  • South facing captures passive and solar PV energy

    Effect Homes built this net-zero home following the early lessons of net-zero incorporating optimized passive solar energy using south facing windows, just the right overhang protecting it from summer sun and a concrete floor to store heat by day, releasing it in the cool of the night. Photo David Dodge, Green Energy Futures

  • Air source heat pumps are game changer

    Keep it simple! Les Wold of Effect Homes shows their version of a net-zero home’s mechanical room. It has an electric air source heat pump heating system, an air exchange system that pre-warms the air and on-demand hot water, all powered by electricity generated by a solar photovoltaic system. Photo David Dodge, Green Energy Futures

  • Get to net-zero using a heat pump

    This is a larger cold-climate air source heat pump that helps homes get to net zero energy use even without optimal southern exposures for passive solar energy. It’s a game changer for net-zero homes. Photo David Dodge, Green Energy Futures

  • Induction stove uses half the energy

    Rule one: conserve as much energy as possible with a well insulated home and energy efficient appliances. This induction stove uses half the energy of a conventional stove top and can boil water in less time than a microwave. Photo David Dodge, Green Energy Futures

  • Thick insulation helps get to net-zero

    Insulation is perhaps the most important energy conservation step to take in building a net-zero home. These 16 inch (40.5 cm) walls provide R56 insulation, a big help in reducing the amount of energy you need to heat your net-zero home. Photo David Dodge, Green Energy Futures

  • Quad-paned windows save energy

    Mike Turner installed quad-paned windows in his net-zero home. At R8 they offer three to four times the insulation of a conventional window. Windows are a double-edged sword – they help harvest passive solar energy, but they also are a key place energy is lost. Photo David Dodge, Green Energy Futures

  • Concrete floor stores passive solar energy

    According to Amelie Caron, a high-performance building consultant, passive solar’s secret sauce is a concrete-topped floor that provides a thermal mass to store passive solar energy during the day and slowly release it at night. Using the thermal mass with big south facing windows, good insulation and correct overhangs can help you capture half your heat from passive solar energy. Photo David Dodge, Green Energy Futures

  • Pre-warmed fresh air for air-tight homes

    Mike Turner opens the hatch to an air exchange unit used to save energy by preheating incoming fresh air and a the same time ensure there is enough good quality fresh air in home that is so tight it gets only 0.5 to 1 air exchanges per hour. An average Canadian home gets 4.4 air exchanges per hour, thus wasting energy. Photo David Dodge, Green Energy Futures

  • Electric hot water heater part of a solar powered net-zero home

    As part of the keep-it-simple and affordable strategy many net-zero homes are using efficient and electric hot water heaters that work well with a home that gets all of its energy in the form of electricity from solar photo voltaic modules. Photo David Dodge, Green Energy Futures

 

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