In addition to saving energy, net-zero technologies offer a plethora of health, safety, and environmental benefits; but achieving zero energy can be prohibitively expensive. In this interview, Lucas Alm and Dan Handeen describe how they and their students successfully partnered with Habitat for Humanity to design and build the Net-Zero Northside House in a low-income Minneapolis neighborhood.
Anna: What drew you to affordable housing?
Lucas: Dan and I agree that if we can implement these designs affordably, it has huge implications for our region. If you have enough money, you can make net-zero happen. But does that really impact society? You can throw money at it… but are there ways to intrinsically rethink how we build to make net zero approachable and feasible for folks that aren’t wealthy? The affordability piece was crucial to applying these technologies while helping people.
Anna: What are the key technologies and design of a Net Zero home in our climate?
Lucas: It’s twofold: there’s the building envelope, which has to be as robust as you can afford it to be; and there’s the renewables.
Dan: A robust building envelope, plenty of insulation, and efficient appliances. Reducing your load makes the best return on investment before you start investing in renewables or some other power source.
There are examples of specific technologies in both the homes we built. The Princeton home has a dual heat source water heater. It’s a slab-on-grade, modest 1,000 square foot house; but it uses solar thermal panels on the roof to precharge the heat in its large water heater. And it has a gas-fired backup. And so it uses a dual fuel source - if there’s a week without sun, this enables its inhabitants to meet their heating needs.
We were really looking to the future and asking: what is a more sustainable energy source? We thought about diversified generation sources, different distribution systems or models, and the ability to have on-site electricity generation; and we went with an all-electric heating strategy for the Northside Net-Zero House.
Lucas: These homes are super tight. So the heat recovery ventilator is paramount to improve indoor air quality. It’s also a low-velocity way to distribute heating and cooling throughout the house.
Dan: One other technology isn’t installed in the house, but definitely drove our design. We used the passivhaus planning software. The students learned it, and a passivhaus consultant helped them develop iterations that really optimize the home’s design.
An additional challenge is that our climate is pretty demanding. It’s dry and 70 below wind chill; and then it’s 90 percent humidity and 110 degrees in the summertime. We have to manage these two ridiculous extremes somehow. Our homes need extra insulation and robust heating and cooling systems to meet our basic comfort levels. The famous rationale for going to high performance was, if you beef up your envelope enough you can change or reduce the expense needed for your HVAC system. We’re not finding this in Minnesota. In the summer, dehumidification is energy-intensive. And we’ll see that continue with increasing dewpoints, it’s already happening.
Anna: Do you find yourself at a limit for how big a net-zero house can be?
Dan: It can be challenging to really make use of passive solar gain if the size gets too big. However, the smaller a single-family home, the more surface area ratio to the volume enclosed - or the area you’re able to occupy. So there are benefits to getting larger: if you minimize the amount of surface area that bleeds out heat, you’ll have a more comfortable space.
Lucas: I think it’s good to mention passive solar. Sometimes we see these South-facing windows as free heat, basically furnaces with a view. But of course on urban lots, the window’s either in the front yard or the back yard. Do you really want that amount of glass there?
Anna: What other lifestyle factors did you consider?
Lucas: The students were aware when they designed affordable housing that these families may have different cultural mores, even down to how they set the thermostat, than what they’re used to.
Dan: We can design it to be net-zero, but if you leave all your windows open in the middle of the winter time, and have all your tv’s on all night…
For example, the Minnesota Sustainable Housing Initiative did a study of a townhome with side-by-side identical units. One was underneath their projected their hot water and energy, and the other one was roughly twice what they expected. It came down to the number of people living there: one side had extended family members staying with them for a long period of time, so of course their use was higher.
Anna: So what assumptions do you make about plug load and occupant behavior?
Lucas: The default on the software is an energy-conservative European. We know Americans use more energy than that, so we fudge those numbers up a fair amount to make them more realistic.
What’s great about the Northside project is that Habitat worked with the family, so they’re aware that their house is unique and they can do things to make it more advantageous. The family actually had to write an essay about why they want to live in a net-zero house. They understand that they could potentially have no utility bills on an annual basis.
Anna: What non-energy benefits can they expect from the house?
Lucas: Air quality for sure, and comfort is huge.
Dan: Over the next few decades, I think we can anticipate greater variability in created effects on our infrastructure and our energy resource supply chains - both electricity and natural gas.
This design allows us to embody "passive survivability." If your power goes out for three days in January, this house will retain heat and stay above freezing. You may need to light some candles, but other people might have to move out of their house to stay warm. It allows that kind of buffer in the home’s design. That’s a really important factor to consider for new construction moving forward. This design also has a more robust structural system, providing greater resistance to extreme weather events from the outside.
We don’t currently value durability and survivability economically. Instead, we look at the payback using current energy practices. But we don’t really know what that’s going to be in the future. Net-zero provides good insurances against that.
Anna: If it’s not feasible to make all construction net-zero today, how do you see its role in the clean energy movement?
Lucas: I don’t know if I agree that it’s not feasible - I think we need to rethink how we build. Take building layout - students embraced the idea of an open plan, with few partitions and very simple direct finishes. But it may be very aesthetically or formally different than what people expect to see in a house, and so we’re hopeful that some of those ideas or conceptions of what a house is will start to change. It’s difficult to do, but as energy codes become more and more stringent…
Dan: And it’s not necessarily about alternative energy sources. It comes down to getting the loads down - if it can’t be zero-energy, it can be zero-energy ready.
Lucas: The Northside house is a great example. We had no idea that Habitat was going to provide solar, but the students designed it to be net-zero ready.
Dan: That’s what it is - being prepared. Maybe you can’t afford to do the solar right now, but as technology improves and cost goes down, maybe there will be that opportunity in the future, with state incentives. And more distributed generation, not necessarily on every single house, is a viable model.
Lucas: Or if there’s a community solar farm. Minneapolis has lots of mature trees. So putting in renewables on every single house gets to be very complicated, and in some cases completely impossible.
Anna: What other assumptions should we rethink?
Dan: Lucas brought up the notion of what we think of as a "house." The formal implications aren’t minor. The Northside net-zero house, for example, is really tall. That puts the solar up above the trees on the boulevard and maximizes our passive solar gain. But it looks different than the other houses in the neighborhood.
We worked closely with the neighborhood housing committee. From an energy perspective, they were all excited. But when the students started sharing their renderings of proposals, we saw some pretty strong reactions against it. They weren’t fans of the look. But as we spoke more about why certain formal gestures were made, whether to maximize solar energy or make extra space, they really became enthusiastic about the design. They loved it in the end.
I think we can really see that shift culturally. For example, the Tiny House Blog is wildly popular. At the same time, technologies are becoming so efficient that people can make much smaller changes to their behavior and still save energy.
Lucas: I think it’s important that we pay tribute to the students. They were amazing, especially when they realized this wasn’t for their grades, but for families. And unlike studio work for a critique, projects like the Net-Zero Northside House continue and connect to a community.
Dan: And this was the first time that many of them got to work in a real-world environment as part of a team setting. Of course we helped guide the process, but they had to rely on each other to get this done
Lucas: And we all know that to achieve sustainability, we need that collaboration.
Photo credit: College of Design, University of Minnesota