This year, the U.S. DOE Solar Decathlon moved from its historic location on the Washington , D.C. Mall to Irvine, California — a very prescient move considering the current government closure of the Mall. The Decathlon concept has expanded to a Solar Decathlon in Europe in 2012 and China in 2013, and the recent U.S. event was open to overseas contestants. Among the many university teams vying for a chance to compete, teams from Austria and the Czech Republic succeeded in securing spots among the 20 finalists.
The goal of the competition is to design, build, and operate a solar-powered house, which is judged on cost-effectiveness, energy efficiency, and design aesthetics. Projects are also scored on engineering, communication and home entertainment.
The AIR House is meant to be a prototype for an affordable (A), innovative (I), and recyclable (R) house. It has become a media darling — reviewed by Architect magazine, Inhabitat, Ecobuilding Pulse, and likely a few more before the contest is over. The AIR house appeals on many levels. It has a very light environmental footprint, due to its low-waste prefab process, the net-zero operating costs, and the design for disassembly and recycling at the end of the service life.
Flex spaces and multipurpose rooms
Of course, it has all the expected technology — a solar thermal system, PV, and a heat-recovery ventilator — as well as the unexpected technology, such as a radiant chilled ceiling system and a graywater system that feeds into the garden.
Designed for retired seniors, it does not make any of the concessions of starter houses and manages instead to neatly package full functionality and comfort into the small footprint by optimizing the spacial layout. The multipurpose room has lots of built-in closets and functional flex spaces. Sliding glass doors provide the flow onto a deck, where a small vegetable garden continues the visual link to the outdoor landscape.
Wood louvers make a house-within-a-house
But the most interesting aspect from the perspectives of both design and energy is the “house within a house” concept. The mechanical room is at right angles to the main living space, and the two wings create an “L” shape that defines the patio. This entire rectangle of indoor/outdoor living space is nested within a second structure of wood louvers that extend over the roof and around three walls. These walls are spaced far enough away from the primary structure to create a surrounding deck that has some degree of privacy, yet offers filtered views of the outside.
This wooden canopy gives a bit of the sense of living in a treehouse, protected from winds and filtering the sunlight. The effect of this soft boundary is very organic, as if the house “breathes” through the louvers. And it immediately calls to mind a lush tree garden landscape setting, almost as another layer of this design.
Many architects have experimented with double skin faÃ§ades
Double skin faÃ§ades (DSF) are not a new invention. It might be said that the brush shelters built over the top of Navajo hogans are a type of double roof. In the U.S., there was renewed experimentation in the 1970s with double walls and extracted air systems based on the principles of passive solar thermal chimneys. In some designs, the buffer space was large enough for a greenhouse accessed from inner windows. Of course, the realities of such designs were complicated by humidity build-up, air not moving at predicted rates of speeds, and the difficulty of keeping the space free of bugs, critters, and greenhouse debris.
In general, the DSF technique is more typically used in commercial construction, where a secondary exterior glass skin can provide maximal daylight, a sound buffer, and insulation separate from the structural exterior wall. DSFs are categorized by the direction of the air flow: they can be buffers of supply / return air (from indoor air or outdoor air), or a space for exchanging air from inside to outside, or outside to inside.
One of the best references for double-skin faÃ§ades is the Oesterle book by the same name, documenting many of the existing uses of DSF in Europe. This technique is also gaining popularity in Asian cities, in the glass building skyscraper cities. But the cost and degree of difficulty in accurately modeling the effect of the two thermal envelopes and the air flow remains a major roadblock to mass market adoption.
A boring shape becomes interesting
There is beauty in the simplicity of the louvered shell used in the AIR House. First of all, this is a very easy way to spruce up a very boring box-shaped house, trailer, or even a shed. The basic design can be customized with a bit of creativity in the slat design, keeping in mind the orientation needed for the summer shading. A variation might include plants trellised up the side walls, and the careful selection of plantings in the prevailing wind paths to provide cooling, or even scents of flowers.
In this approach to double-skin faÃ§ades, the exterior air flows freely through the slats into the buffer space. Here, it is cooled and as the temperatures change, it continues to flow. This would create a nice ventilation effect of continuous moving air. The slats could also be positioned to capture regular wind patterns, to channel them to or from the house as desired.
This application was actually put to the test at the Solar Decathlon site, as the shell protected the house from the worst of the Santa Anna winds and dust. A careful design specific to the site would optimize the passive solar capabilities for summer shading and thus moderate the heat load on the building envelope. But in any case, since the air buffer is not contained in any way, the risks of this DSF approach are low. It seems unlikely to create problems of mold or humidity build-up, and there is nothing mechanical to break. It is very site-specific, but it would seem to be easily modifiable and tweaked to provide the most benefits.
A place to socialize
The Czech entry has particular appeal to me, not only because of my Czech roots (in the land of tennis stars, Vaclav Havel, and great beer) but because I find the design is a breath of fresh air in this contest (pun intended).
The design recognizes that human comfort comes not from a show of technology, but rather from a connection to the natural environment and to other people. It seems to have become a favorite gathering spot for dinner parties, and the space easily accommodates these social activities. We’ll keep our fingers crossed (or as they say in Czech, budeme drÅ¾et palce, or “hold one’s thumbs”) and wish Team Czech Republic the best of outcomes in their first Solar Decathlon.
[Editor’s note: The results are in: The Czech team won the Architecture category and placed third overall.]
Dr. Vera Novak was recently awarded a PhD in Environmental Design and Planning by Virginia Tech. Her work is dedicated to increased depth and breadth of sustainability in construction, by leveraging the points of greatest potential impact. She is currently working on optimizing corporate sustainability practices to support regenerative design, as well as adapting a lean thinking process for smaller scale projects. She also writes the Eco Build Trends blog.
Get building science and energy efficiency advice, plus special offers, in your inbox.