Shopping only for local produce, or growing all of your own, sounds great until you remember one thing: avocados. And then tangerines, mangos, papayas, passion fruit — fresh-squeezed orange juice. Banana smoothies.
There’s a long list of covetable fruits and vegetables that won’t grow in Colorado’s climate, and in a world where those invested in sustainable living look to decreasing reliance on fossil fuels, trucking them in or even growing them here in greenhouses has a carbon footprint that’s simply too big.
But bananas weren’t really what was on Marc Plinke’s mind when he started designing green.
“I had this dream that from before I was 18 to be able to live sustainably or live in a way that it wouldn’t take away from our kids — just this idea that we can actually leave the planet better than we found it,” he says. He spent a year and a half remodeling his house, built in 1961, to make it beyond net zero, he says, before starting on other projects. “The idea was, well, the next thing besides making our houses more efficient is to eat more locally and ideally food you can grow yourself, so that’s where the motivation comes from.”
In Colorado, eating fresh fruits and vegetables all year round takes some serious intervention — like a greenhouse. But while a normal house heats for $.10 per square foot, a greenhouse often costs more like $3 to $4 per square foot — and consumes a colossal amount of fossil fuels in the process.
Greenhouses lose heat through the ground, through necessary leakage and ventilation and convective and radiant heat losses, and consume energy in electricity needed to run fans to move the air and pumps to move water and, in many cases, to add heat.
Plinke started dissecting the traditional models of greenhouses — often all Plexiglas with little insulation, leading to fluctuations in temperature and a shut-down of the growing season in Colorado’s coldest months. By replacing some of the glazing with insulated panels, he stabilized some of the fluctuating temperatures. He’s also created a ground-to-air heat transfer system, a temperature-triggered system for circulating air that makes use of the thermal storage capacity of the greenhouses’ soil.
The same principles of using thermal storage, increased insulation and the glazing in the right places have been in discussion for the last 35 years among those looking to create successful passively heated greenhouses, according to a 2003 paper from the University of Missouri-Columbia Southwest Research Center that details the construction of a solar-heated greenhouse in Mount Vernon, Mo. That greenhouse has provided cool-season crops, including leafy greens, vegetables and flowers, since its construction in 1988.
Plinke and his team started Ceres Greenhouse Solutions in 2011 to build or renovate existing greenhouses using those passive solar designs with a few of his own flourishes. The end results look more like houses with large windows faced with reflective shutters to maximize light than hoophouses. Plinke mentions some people use them as home offices or simply a refuge from the cold, dry months in Colorado.
Even in February, their interiors are a warm, humid environment ripe with the scent of fresh earth and a hint of a breeze from the fan used to keep air circulating — necessary turbulence both for pollen and strong plant stems.
A Ceres greenhouse, put to the test at 10,800 feet in Leadville, was yielding summer squash, tomatoes, basil and figs through the winter while temperatures dropped to minus 20 at night.
So who says you can’t live sustainably and have your papaya, too?