I’ve been looking, apparently in vain, for a good book (that’s not in German!) detailing Passive House building and modeling techniques. The best I’ve been able to do so far is Toward a Zero Energy Home, and it must have been pretty good, since I read it cover-to-cover in less than 24 hours. It’s not particularly dense or detailed, but it was a nice quick overview of low energy building systems, with lots of pretty pictures, and a dozen case studies from all over North America, including a couple right here in Boulder.
The goal that the authors have chosen to highlight — “Net Zero” — means that the buildings in question produce as much energy as they consume on an annually averaged basis. This necessarily means that they all have some on-site production, wind, PV, solar-thermal hot water, etc. However, to keep such projects reasonably cost effective, it’s necessary to focus first on energy efficiency measures. Most important among these is a very tight building envelope, much more insulation than code requires, and appropriate glazing for passive solar gain. Then the internal power loads need to be minimized, by using energy efficient appliances and LED or CFL lighting. Only after doing all that is it financially worthwhile to start adding on-site renewable generation, capable of meeting the overall annual energy demands of the dwelling. Financially worthwhile, that is, if you have already decided that you want to create a Net Zero building.
In the introduction the authors talk a little bit about their motivation for choosing Net Zero as the goal they want to focus on, but I don’t think their arguments really hold together. Based on the introduction, you’d think that the best justification for increasing building energy efficiency is high and volatile oil prices. They repeatedly mention the 2008 spike in oil prices, and talk about the people in the Northeast that locked in winter fuel oil prices at what turned out to be very high prices. However, even in the Northeast, where heating oil usage is most prevalent, it represents only a small minority of household energy use. The overwhelming majority of oil use is within the transportation sector. The only fossil fuel that most buildings consume directly is methane (natural gas), for heating, domestic hot water, and cooking purposes. Overall, the majority of building energy consumption is in the form of electricity, which is primarily produced from coal and natural gas. The US Energy Information Administration sucks just as badly as everyone else at forecasting energy prices, but they do a great job of collecting retrospective data. Their Residential Energy Consumption Survey details all this stuff. So oil prices have virtually nothing to do with building energy costs. Coal is catastrophically abundant, and shows every indication that it will remain quite cheap for many decades to come. Natural gas prices are somewhat volatile (again, just ask the US EIA), and correlated with oil prices, but nowhere near as scary to most people as $5 gasoline.
If high and volatile oil prices should motivate anything, it’s a re-arrangement of our land-use policies, toward dense urban development that prioritizes the comfort and convenience of people over motor vehicles. Unfortunately, out of 12 case studies only one is a multi-family dwelling: an awesome 7 story apartment building in the East Village designed by Chris Benedict and Henry Gifford that uses 75% less energy than comparable buildings, and which cost nothing extra to build. Three others are in urban contexts (Berkeley, Boston, Chicago), five are in towns or suburbs, and three are totally inaccessible without a car. Extreme energy efficiency is actually easier and cheaper to attain in a multi-family context, because such buildings have much less skin exposed to the elements, for the amount of living space they provide. It was nice to see that the case studies included a few retrofits instead of being all new construction. If we can’t figure out how to make our existing buildings much, much more efficient, then because it takes a long time to turn over building stock we’re going to be wasting a lot of energy in buildings for decades.
The motivation for choosing Net Zero as the goal clearly isn’t just financial. Vastly higher energy efficiency than code requires is usually a good investment from a purely financial point of view, but since most building projects (and all of the case studies so far as I could tell) are grid-tied, the energy prices that make sense to be concerned about are electricity and natural gas. Absent subsidies (and often even with them) small scale wind and solar PV sadly still don’t make economic sense. Net Zero taken by itself also can’t be justified on the basis mitigating climate change, because it doesn’t take into account all of the embodied energy and other climatic consequences of the materials used to build the buildings. Cement production alone accounts for 5% of global CO2 emissions. The spray-foam insulation that works so well for air-sealing buildings is mostly petroleum based, and in some cases uses HFC blowing agents which are spectacularly powerful greenhouse gasses, as does much of the rigid foam insulation (XPS) used to prevent thermal bridging on the outside of buildings. If you care about the climatic impact of your building, then you have to take that kind of thing into account, in which case the bulk of your insulation usually ends up being blown in cellulose fluff, which is cheap, non-toxic, and usually made from recycled materials. It’s not as good an insulator or air-sealer as the plastic, so you need more of it, and you have to be careful about retarding airflow in other ways, but it works. There are also non-petroleum based foams, and new blowing agents that aren’t greenhouse gasses. Even if they chose not to focus on these considerations, I would have appreciated it if the authors had pointed out that they exist.
They repeatedly acknowledge the Passive House movement for many of the innovations in building envelopes, super-insulation, high-performance windows, and heat recovery ventilation, but they also (like many in the building industry, in the US and elsewhere) make the extremely strict standard out to be a little bit overzealous, and potentially not compatible with the extremely cold temperatures which are common in the upper midwest. In leveling this criticism, I have to imagine that people don’t fully understand the motivation behind Passive House. The standard isn’t based on what’s convenient or necessarily financially attractive, it’s based on an analysis of how much energy one can reasonably expect to have access to in an economy which only uses renewables. That number doesn’t change based on whether you live in Fairbanks or Phoenix. If you can’t make passive buildings work in Fairbanks, then you can’t ethically live in Fairbanks (though to be fair at most arctic population densities, firewood becomes a potentially renewable resource). Of course, with enough insulation, you can theoretically make a passive building work anywhere, you just might have to live inside a giant thermos bottle! The Passive House standard is not extreme; what is extreme is our expectation of energy availability, warped by a couple of centuries of easy access to fossil fuels.
Another interesting optimization that they talked about in the book concerned the use of ground-source heat pumps. Instead of digging wells or long trenches especially for the heat pumps, they just made the trenches for utilities somewhat deeper, and laid them there along with the wires, or embedded them in the area excavated around the below-grade portion of the building. I’d like to learn more about heat pumps, the heat recovery ventilators, and the combined so-called magic box appliances that are available in Europe, combining pretty much all of a building’s heat management functions into one unit. They seem fantastically expensive at the moment, but the market is small. They don’t appear to be particularly exotic machines, and it seems like there would be good cost-reduction potential. We’ve got to create a market for this stuff in the Americas or it’s always going to be fabulously expensive, and involve unnecessarily pouring money into somebody else’s economy. Or maybe they could be made in China, along with everything else, including Spanish and Danish wind turbines.
Nearly all of the homes and techniques discussed in the book focused on homes in heating climates, while lots of the US uses most of its building energy for cooling — all across the South and the low-elevation Southwest, and increasingly even in climates like Colorado, where you really don’t need anything more than a ceiling fan in the summer, people are installing air conditioning anyway, because we’ve forgotten how to shade our windows effectively in the summer. Much more seriously, the vast bulk of humanity lives in hot places. Southern China, India, sub-Saharan Africa, Indonesia, Brazil. These aren’t cold places. They will benefit little from the particular low-energy building techniques that have been and are being developed by white people in Northern Europe. But who in Mumbai or Jakarta or Guangzhou won’t want air conditioning once they can afford it? The city of Mumbai alone has as a quarter the demand for air conditioning as the entire United States. Which helps explain why India is planning to build 200 new coal fired power plants in the next ten years, and why even though China has been drastically improving the efficiency of its energy sector, their overall CO2 emissions have been increasing pretty much linearly for the last two decades, and more than linearly in the last 5 years. Which is scary. The one case study the book covered in a hot places was in muggy Florida, and it was a single family ranch house. We desperately need comfortable high density passive architecture for hot climates that are also economically accessible to these newly affluent people of the world.
Economic accessibility isn’t just an issue for the developing world either. Many of the projects detailed in the book cost around $200/square foot, which is common for higher end custom homes, but a far cry from any kind of mass produced housing. They did include a couple of Habitat for Humanity houses though, with costs more like $100/square foot, which would be much more generally accessible in the US. They were built in a collaboration with NREL here in the Denver area. It might be interesting to volunteer on the construction of more houses like that if the project is ongoing, just to see how all this stuff works first hand.
Reading back over this review, it seems much more critical than it should be. Most of my criticisms are just of degree. All the building techniques they talk about are vast improvements over current code, and many of them make dollar sense even if you don’t care about climate. If you do care about climate, then the same practices simply need to be applied even more vigorously. It looks like they’ve got another book more focused on the building techniques themselves, Green From the Ground Up, and it looks like it’s checked in at the Boulder Public Library.
Hopefully I’ll be able to get some sleep tonight!
4 thoughts on “Toward a Zero Energy Home by David Johnston and Scott Gibson”
Interesting post. Regarding passive housing for warm areas, are you familiar with wind towers such as those used in the (Persian) Gulf?
My understanding is that these can be surprisingly effective even somewhere like the UAE, which experiences painfully hot and humid summers.
I have seen those, and they’re a simple, elegant solution for dry climates — they’re essentially passive evaporative coolers, pulling air in from below over the qanat. Powered evaporative coolers work great too, and should be standard all over the sunbelt and the inter-mountain west. They use much less power than air conditioning. I have no idea why people in Phoenix insist on AC. I grew up in central California with a swamp cooler, and it was fine, even with 40°C (105°F) summer temperatures. If they’re working somewhere like the UAE, with high humidity, then my guess is its because the air is being pulled through the cool sub-surface, and not because of the evaporation, as evaporative cooling breaks down pretty quickly. You can’t use a swamp cooler in Houston or Mumbai. “Earthtubes” that pull ventilation in through subsurface conduits do the same thing, but can’t scale up to dense urban uses. The heat pumps mentioned above can also be used for cooling loads, but again, at some point you saturate the soil — you can only pull so much energy out of it before the system doesn’t work any more. I’d be curious how well it scales up. The Power Tower in Linz is the largest Passive House style building to date — a 19 story glass curtainwall high rise — and it uses a bunch of ground-source heat pumps that are almost like “roots” for the building, sent down wells drilled beneath its foundation hundreds of feet.
A blog on building a kit passivhaus in wisconsin.
And definitely check out the Cold Climate Housing Research Center‘s sustainable northern shelter pages. The nice folks there are doing amazing things – building homes in arctic villages for half what anybody else would, while having them use a fraction of the energy to maintain and actually listening to what the local people want in a home. Of course, the yupik and inupiat used to live in semi-subterrainian homes that were so warm with a single seal-oil lamp that they would pretty much be naked inside, in the winter. More or less anyway. No foam, no plastic vapor barrier, but of course the trick is meshing with the parts of the modern world that are desirable – and CCHRC is doing that.
Still all cold-weather, heating climate applications though – I can’t imagine wanting to live anywhere where it gets above 80F in the summer 🙂 Even Wisconsin and Fairbanks (both of which get warm due to being so far inland) would broil me!
Whoa, apparently randomly Green Building Advisor has a post on Net Zero Energy vs. PassivHaus today.