The HouseZero project is an extreme retrofit of an existing building, the home of The Harvard Center for Green Buildings and Cities at the Harvard University Graduate School of Design (GSD). According to the press release it will “demonstrate how to transform this challenging building stock into a prototype of ultra-efficiency that will use no HVAC system, no electric light use during the day, 100% ventilation, almost zero energy, and produce zero carbon emissions, including embodied energy of materials.”
“Before now, this level of efficiency could only be achieved in new construction,” said Ali Malkawi, professor of architectural technology at the GSD, founding director of the Harvard Center for Green Buildings and Cities and the creator of the HouseZero project. “We want to demonstrate what’s possible, show how this can be replicated almost anywhere, and solve one of the world’s biggest energy problems — inefficient existing buildings.”
Now I like this project and do not want to be an argumentative curmudgeon but really, lots of people have achieved this level of efficiency in renovations. But let's leave that for now.
The subhead of the press release online says it “ requires no HVAC or electric light”, corrected on the PDF version to say “requires no HVAC or daytime electric light. Instead,
The HVAC system will be replaced with thermal mass, and a ground source heat pump for peak (extreme) conditions. A solar vent will instigate buoyancy-driven ventilation and triple-glazed windows will employ natural cross ventilation through a manual and automated system that monitors for temperature, humidity and air quality….Rather than approaching the house as a “sealed box,” the building envelope and materials of HouseZero are designed to interact with the seasons and the exterior environment in a more natural way. Much like a layered approach to clothing, the house is meant to adjust itself seasonally, and even daily, to reach thermal comfort targets.
This looks like a fascinating project, with TreeHugger favourite Snøhetta as lead architect; they designed the remarkable Powerhouse in Norway and certainly have the experience.
There is not a huge amount of information available about this house, but I have a few problems with it. Certainly, the house is full of ideas and principles that we promoted on Treehugger, from putting on sweaters, to celebrating thermal mass to using natural ventilation- ten years ago.
Let’s start with the subhead: Extreme retrofit of its headquarters requires no HVAC or daytime electric light.
HVAC is an acronym for Heating, Ventilating and Air Conditioning and of course it requires this, and it has it. There is a ground source heat pump connected to piping in the floors, providing radiant heating and possibly cooling. Radiant heat is what just about every house in Europe and many older houses in America have with radiators. It doesn’t have a conventional North American ducted heating system, but that is really not unusual.
The heat or cooling from the heat pump is supplied to the radiant floor which has a lot of thermal mass, “thereby slowing thermal inertia to buffer both daily and seasonal changes in thermal conditions.” But this is Boston, which doesn’t get huge swings between day and night, which has cold winters and hot summers. And, the thermal mass is inside an improved envelope with insulation and reduced air change, so there's almost no swing.
And there is a ventilation system, exactly the kind I have promoted for years, using natural ventilation, “maintained through smart window technology which uses internal and external monitoring to automatically open and close windows as needed for a healthier interior environment.”
But it can get hot and humid in Boston. Can natural ventilation cut it in the summer? It can get cold in winter. Can you open the window in January? There are many questions about ventilation that I am sure will be answered in greater detail, but as shown on the sketch, I am doubtful that it can work.
There is the question of it’s 100 Percent Daylight Autonomy. “no artificial light is required during daylight hours on non-cloudy days.” (hardly 100% autonomy) Roof and window treatments are custom shaped to allow maximum light admission during the winter and limit direct sunlight during summer.”
Again, 10 years ago, in the days of incandescent and crappy compact fluorescent bulbs, I would have thought this is wonderful. But is it today, when we have super-efficient LED bulbs? With every window that is providing light, there is also heat gain in summer and heat loss in winter. At what point does that actually consume more energy that the LED bulb?
Don’t get me wrong, this is a wonderful project, testing out all the ideas that architects and builders promoted in the seventies and that I promoted ten years ago. It’s what was known in the seventies as “mass and glass”. And as building expert Joe Lstiburek noted,
We were here in the late 1970s when ‘mass and glass’ took on ‘superinsulated.’ Superinsulated won. And superinsulated won with lousy windows compared to what we have today. What are you folks thinking?
That’s when I had to write that Everything I ever knew or said about green sustainable design was probably wrong, and the real epiphany, Should we be building like Grandma's house or like Passive House?
I quoted Martin Holladay of Green Building Advisor and concluded:
…high thermal mass floors are not particularly comfortable, that south facing windows as an energy source are counterproductive and “should be limited to that necessary to meet the functional and aesthetic needs of the building.” That careful orientation doesn't really matter any more because nobody needs that extra solar gain.
Alex Wilson has also complained about in-floor radiant heating, noting that..
..it's a great heating option for a poorly designed house…. A radiant floor heating system also has a very long lag time between when the heat is supplied to the floor and when the slab begins radiating heat....If there is a component of passive solar heating in the home, it will cause overheating because you can't turn off the slab when the sun comes out.
There is also the Solar Vent, "that uses sunlight to draw air from the basement spaces offering robust ventilation at times of higher levels of occupation". It really is That Seventies Show all over again here, a complicated system that works only when the sun shines. We learned long ago that really simpler is better.
Finally, there is the complexity and cost of the stuff going into the HouseZero project that makes me question whether it is actually viable. Ali Malkawi says “We want to demonstrate what’s possible, show how this can be replicated almost anywhere, and solve one of the world’s biggest energy problems — inefficient existing buildings.”
But it is really difficult to retrofit old houses with concrete radiant floors, I have tried it. It cannot be replicated almost anywhere; between the additional loading, the concrete finding its way through every crack and the huge amount of moisture that is driven off as it cures, it was an expensive mess. Automating windows is also expensive, especially since replacing windows has the worst bang for the buck of just about anything you do in renovation. And ground source heat pumps? Not many people are doing them anymore in efficient houses, because they are so expensive and air source heat pumps have got so efficient.
I want this house to work; it is a high-tech version of Grandma’s house. I am hoping that as more information comes out that all my concerns will have been addressed.
But I worry that it is too expensive, that it is not really replicable, that it doesn't scale, and that people are not willing to put up with the discomfort of natural ventilation in summer, and the need for ventilation in winter. And really, we know how to renovate houses to be energy efficient and net energy positive, it is not a wheel that we have to reinvent again, we do not have time. We have watched this movie before and know the ending: improve the thermal envelope.
I would love to write once again that Everything I have learned about green building in the past ten years was wrong. But I do not think it is going to happen.