When workers finish their work retrofitting a 1920s-era house near Harvard’s campus in Cambridge, Massachusetts, the house will look essentially the same as it did before from the outside–but it will run on almost no energy.
The renovation of the former single-family home, now the headquarters of the Harvard Center for Green Buildings and Cities, is an attempt by the HouseZero project to demonstrate that it’s relatively easy to transform ordinary houses to eliminate their carbon footprint. Homeowners might think that making their homes more efficient will require huge renovation costs for little energy (and cash) savings. This project is hoping to prove otherwise, and be a model for other projects to emulate.
After a few years of intensive research–including reading hundreds of studies–on what was possible, the HouseZero team landed on several goals. After the redesign, developed with the architecture firm Snøhetta, the house should no longer need electric light during the day. The tiny amount of electricity used can be provided by rooftop solar panels. Instead of a standard system for heating and cooling, the house will use ventilation and tweaks to the design to stay comfortable passively; on the coldest days, a geothermal system will provide extra support. The house will also produce zero carbon emissions–including emissions from the “embodied” energy in the materials used in the new construction.
All of this is going to be accomplished using existing technology that homeowners can purchase now. “We could have done something that’s futuristic,” says Ali Malkawi, professor of architectural technology at the Harvard Graduate School of Design, director of the Harvard Center for Green Buildings and Cities, and the founder of the HouseZero project. “But what we chose to do is use existing ideas and technologies, put them all together, and see what we can do and push and reach goals that no one has reached before in terms of retrofits.” (One small, separate section of the building will test a more advanced design that could go even further.)
The building is in a historic district, which added another layer of difficulty to the design. The appearance from the outside had to stay essentially the same, though the renovation has enlarged the windows slightly to let in daylight–no one should have to switch on a light until the sun goes down.
The windows are also key to making the building comfortable without traditional heating or air conditioning. Using sensors that monitor humidity, temperature, and air quality, the windows will automatically open and close throughout the day and night, using algorithms to predict what actions it needs to take to keep the building warm or cool the next day.
“If you want to open the window yourself, you can,” says Malkawi. “But at the same time, the building by itself knows its need for ventilation, and it adjusts itself and opens up in relation to occupant health. If there’s a need for ventilating the building, it will automatically open the windows.”
Since adding mass to a wooden building can help it retain heat in the winter and stay cool in the summer, the redesign includes new concrete floor slabs to increase mass. A solar vent draws air up from the basement to help keep the building ventilated. The new windows, which are triple-glazed, are tightly sealed, so when they are closed, they also help keep the temperature comfortable. In extreme weather–during a deep freeze in February, for example–the building can use heat from a new geothermal heat pump installed beside the house.
Solar panels on the roof will generate enough electricity to offset the little that is used to power computers and other equipment, as well as offset the energy used in the materials in the retrofit, so the building has no carbon footprint.
The building’s performance will be measured through a network of sensors and studied so the results can be shared with homeowners who want to do the same thing or use some of the ideas. “If a homeowner wants to see the importance of the geothermal, we’ll be able to quantify that and they’ll be able to use that portion only if they don’t want to use the ultra-efficiency that we have,” says Malkawi.
Though the researchers haven’t quantified the costs yet for homeowners (or how quickly those costs could be offset by savings on energy bills), they plan to share the the full budget of the retrofit. The HouseZero project will be more complicated than a project at a typical home because it’s also converting the space to work well as an office and lab; Malkawi says that cost for homeowners should be affordable. “This can be done in a relatively inexpensive fashion,” he says.
For homeowners, making similar retrofits would save money–collectively, U.S. property owners spend more than $230 billion a year heating, cooling, and powering homes. The retrofits could also curb a major source of climate pollution. While it’s easier to make newly built houses ultra-efficient, most homes in the U.S. already exist–and buildings account for nearly 40% of carbon emissions in the country, more than any other sector.