A Zero-Energy Community: Part 2
Not for the faint of heart: the ultimate spreadsheet. We spent three long meetings just figuring out what were reasonable lifestyle assumptions for the zDwellers, and this was the result. At the end of the day, achieving zero net energy will be up to the residents.
More design integration at work—here we’ve pursued deep daylighting into the homes, with a high clerestory in each unit. This was taken on a very cloudy, rainy day on one of the north facing units. The home is completely comfortable without lights on, providing obvious living and energy benefits.
Our R-38 wall section. Rockwool insulation is placed in the 2x6 cavity, and 3.5 inches of continuous expanded polystyrene insulation is screwed to the outside of the oriented strand board shear wall. A benefit to this exterior insulation is that the thermally conductive bridge of the wood studs is broken by insulation. Even a thin layer of exterior insulation can make a big difference.
A mechanical marvel, our ground source heat pump. We’ll go more granular on this in a future blog. I show it here because it’s our single most important conservation item.
LED lights have really come of age in just the last year or so. When we were in schematic design they didn’t seem like a very cost effective technology for us, but when it came time to spec the lights, we were really amazed to see how far they had come. The light quality is outstanding, and really hard to differentiate from halogen bulbs.
Even small things matter. Here we’ve installed switched outlets, color coded black, to make it easier for residents to turn off phantom loads—those things that continue to draw power when they are turned "off." No more cluttery power strips!
One of the core environmental benchmarks of zHome is achieving zero net energy and zero net carbon emissions. We are achieving this with a number of conservation technologies which reduce energy use by about two-thirds of that of a typical townhome. We then offset the remaining third with solar panels mounted on each zHome roof. The extra energy these panels generate during the summer will offset the amount of supplemental energy the units will need during the cold, dark Northwest winters.
Figuring out how to get to zero net energy and zero net carbon emissions at a cost accessible to the mainstream market was not an easy task. A subgroup of our design team wood-sheded for many hours in a series of meetings at the David Vandervort offices. The stars of the show were Tom Marseille, WSP Flack and Kurtz managing principal, energy expert, and Cascadia Green Building Council board member, and Chuck Murray, then of the WSU Energy Program and now with the State of Washington Department of Commerce, where he leads updates to the State Energy Code.
The design that emerged through those hours combined two core conservation strategies that cut our energy use in a one-two punch: thick, highly insulated, very tightly sealed walls (R-38 walls and R-63 ceiling for you techies), and a ground source heat pump system that is three times more energy efficient than the best forced air furnace.
A sprinkling of other things round out the picture, including 100% LED and fluorescent lighting, in-home energy monitors, heat recovery ventilators, super efficient appliances, hydronic in-floor heat distribution, and natural daylighting. And then of course the solar panel production completes the package.
At the end of the day what I am most impressed by is how relatively simple this all ended up being. None of the technologies are avant-garde. What is perhaps most innovative about zHome is the bringing together of all these things under one roof to meet a profound and world changing benchmark—zero net energy and carbon neutrality. Zero-carbon buildings for the mass market are possible today, and they will only get easier in the years to come. I strongly believe it’s time for us to stop fretting about how we’re going to deal with climate change and ocean acidification, and move forward positively and hopefully with the solutions we have at hand. We can do it!
Performance-testing the home with a blower door and sealing it well is perhaps the lowest hanging fruit in the world of building energy efficiency. The blower door depressurizes the house and helps to find leak points. We sealed our homes to nearly twice what is required by code.
Tom Marseille, one of our energy leads and nationally known energy expert, thinking deep thoughts about a zero-carbon future.
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