Made for each other: Net Zero and Passive House
Net Zero Energy building is hot in North America these days; that’s where people put enough grid-connected solar panels on their roof so that over the course of the year they produce as much energy as they use. Elon Musk is building factories and roofs are sprouting panels like mad. It’s a wonderful trend, creating a lot more energy supply. But it is also much easier to achieve if you reduce energy demand.
That’s the key point being made in a new free e-book, Net Zero Energy Buildings: Passive house + Renewables, written by Mary James and just released by the North American Passive House Network.
Passive House, or Passivhaus as it is known in Europe, is a standard of construction that sets limits on energy consumption and air leakage. It is achieved through five key factors:
- An optimal level of thermal insulation
- High quality windows, usually triple glazed with insulated frames
- “thermal bridge” free construction; “Thermal bridges are weaknesses in the building envelope’s thermal barrier that allow more heat to pass through than might be expected. Following the path of least resistance, heat travels from a warmer space toward a cooler one.”
- An airtight building envelope, also to reduce heat loss
- Mechanical ventilation with heat recovery .
The performance of these buildings is not their only important feature. Most notably, the Passive House Standard is a standard defined by occupant comfort. It replaces the typical view of energy reduction from a punitive construct based on deprivation and compromise to one based instead on a vision of the possible: a life-affirming solution of comfort, durability, and health that just happens to deal squarely with the challenge of our century: carbon emissions reduction.
The Passive House Standard is not without its critics; Some say that the standard is too rigid, requires unjustifiable amounts of insulation, and doesn’t take climate variations into account. In the USA some are trying to develop a new standard to deal with these issues. Others, like the author and proponents of this book, are sticking to the original formula that they claim has worked rather well in all kinds of climates.
© Trent Bell/ Belfast Co-housing by GOLogic
Michael Anschel, a Passive House critic I admire, summarized his objections in a comment to a recent post, Should we be building like Grandma's house or like Passive House?
Buildings should be designed around occupants. That's who they are for! They should be comfortable, full of light, grand or quaint, they should resonate with our souls. Passivhaus is a single metric ego driven enterprise that satisfies the architect's need for checking boxes, and the energy nerd's obsession with btu's, but it fails the occupant. Leave airtight structures to the army corp of engineers and their apple sheds.
I repeat it here because the demonstrations of Passive House shown in the book clearly show buildings that are indeed comfortable and full of light, and might resonate even with critic Michael’s soul, if he has one. From the European examples that tend to be what Bronwyn Barry hashtags as #BBB (boxy but beautiful) to American ones ranging from Maine to California that are not boxy at all, with many different styles and climate-appropriate designs.
© Orchards at Orenco/ Ankrom Moisan Architects
Finally, the author lists “10 Reasons why the Passive House Standard is the Ideal Foundation for Net Zero Energy Buildings.” Number one of which is:
The use of the Passive House approach reliably succeeds in delivering highly energy-efficient buildings. The low remaining energy demand can be met by using renewable energy sources on a long-term basis.
This is the key point; I wish the book went into even more detail. British Architect Elrond Burrell went further in his explanations of why Net Zero (or as they call it in Britain, Zero Carbon) is not as good a target as Passive House:
Stringent space heating and cooling energy targets along with comfort targets ensure that the building fabric has to do the majority of the work. The building fabric, which will last the lifetime of the building, will be highly energy efficient and ensure a comfortable building by design, regardless of how and where the required energy is generated.
That’s the beauty of Passive House + Renewables: You deal with the building first. Then going Net Zero for the balance of your energy requirements is not a big deal at all; you just don’t need very much.
© R 951 Passive House/ Paul Castrucci
Passive House is often hard to explain to North Americans; It is a confusing name, there are not a lot of them to show, and as critic Michael noted, it seems complex and attracts data nerds. Net Zero, on the other hand, is an easy concept to understand and to sell; you see gizmos on your roof and your electric bill going down. In fact, they were made for each other.
Learn more in the free flip book here.
UPDATE: A reader has complained that he doesn't like Flash, and would prefer a PDF. Here is a link to a PDF version.