Lessons from Phoenix Part 2 - Passivity

At any trade show, it’s usually worth it to barge in to a random event, feel awkward for a moment in exchange for a free drink and a chance to encounter new perspectives. So after a long day of seminars at Greenbuild, I found myself making small talk among a group of well dressed facilities managers involved in the LEED for Existing Buildings side of things. This is actually a very important part of the sustainability equation, since the operational energy of a commercial building will surpass the embodied energy used to make that building a few years after the building opens.

As I made my rounds, I spotted a small group near the food table that definitely did not look like facilities managers, wearing tee-shirts and jeans and engaged in some very serious conversation. They turned out to be from New Mexico like me, and had carpooled out together for the conference. Among them was Mark Chalom, an architect and designer of sustainable homes from way back, who built a good number of passive solar homes in my neighborhood.

Passive heating and cooling are like the holy grails of sustainable design, but they are also a bit of an anachronism. Unlike other technologically driven forms of conservation, passive strategies are low hanging fruit – they cost, in theory anyway, nothing, and vernacular buildings often have these principals embedded in their forms. But in today’s practice, passive design is often overlooked or gets cut out of building projects when other concerns arise. Before passive design can come back to the mainstream, there is a bit of history to overcome.

In the 1980’s the community I live in, Eldorado, NM, could claim the largest concentration of passive solar homes in the country. As I’ve roamed around and visited neighbors, I’ve noticed that some of these homes were a bit overzealous, with large south facing windows that maximized the solar gain for heat in the winter, but caused overheating in the shoulder seasons of May and October to the point of discomfort. Then there is the awkward triangular roof form caused by those tall south facades, antithetical to the low slung rectangular masses of our local traditional architecture. While we still have passive solar advocates in Eldorado, stylistic concerns , sunsets and mountain views have increasingly dictated building form and orientation over the last 20 years. Even the local elementary school is about to get a second story addition on top of its passive solar, saw-tooth roof, which never really worked that well anyway.

Passive strategies for schools and other commercial buildings do present a different and more complex set of challenges. Even in the colder parts of Northern New Mexico, these building types will typically need more energy for cooling then for heating because of all the people and equipment inside. The secret to passive temperature control here is having transitional spaces, where a wider range of temperature fluctuation can be allowed, so outside air can be used to cool the building during many parts of the year. With south facing atriums and corridors, thermal mass can store heat or draw air in for cooling as required, which can then be circulated mechanically or by simple convection vents to other parts of the building. Add to this strategy superior insulation, sophisticated controls and careful modulation of direct sunlight through external shading devices, and you have a commercial building that reduces its energy consumption by a very significant amount. There are even buildings out there with net-zero energy use (i.e. they produce more energy than they consume), and the challenge to make this equation work more efficiently looms large on the horizon.

The dumb logic of shading devices in Phoenix is so clear they have become commonplace in new commercial buildings, where the 120 degree days require as much shade as you can muster. But serious passive thermal design requires a series of small and synchronized steps in order to really work, especially in more diverse climates like New Mexico. If the sunshades are not precisely aligned or even the wrong color, you can get too much heat gain, glare, or the need to retrofit manual blinds, which will often be left closed all day in an office environment. Transitional spaces like public atriums are worth the extra square footage, providing a place where you can open the windows without ruffling your office papers. And thermal mass helps immensely in the high desert; buildings with concrete structure (or adobe!) don’t react as quickly to our wide daily fluctuations in temperature. Most importantly, computer energy simulations are now being produced for buildings, which can predict the effects of passive strategies and allow designers and owners to consider the cost and comfort benefits of each strategy before they build.

These are old lessons, anachronistic even, but they will continue to taunt us and demand our attention in their new virtual form. Well worth the awkward moment, no?

Passive Solar Design
http://www.nmsea.org/Passive_Solar/Passive_Solar_Design.htm

Eldorado, NM
http://www.santafenewmexican.com/Local%20News/Passive-solar-building-rat...

Measures of Sustainability
http://www.canadianarchitect.com/asf/perspectives_sustainibility/measure...

Net Zero Buildings
http://zeb.buildinggreen.com/