Unintended consequences


The saying goes that there’s no free lunch, but I’m not sure that applies to weasels.

I’ve had the much-hated animals in my chicken coop lately, with their usual pattern of mass carnage. We’ve also been seeing foxes around and hearing coyotes. Now that we know a bit more about what kind of predator pressure we are facing here, there are measures that can be taken. The chickens are currently in a temporary lockdown in my solid steel dump trailer with a plywood lid. Protection from the smallest weasels, it seems, requires eliminating any holes larger than three-quarters-of-an-inch.

Looking ahead at building a new coop, I’m trying to balance the idea of using half-inch hardware cloth (expensive and heavy) with the idea of a highly mobile, open-bottom chicken tractor that allows our birds access to the pasture and bugs that they love and make them healthy. And doing all that on our bumpy, rocky, stump-ridden pasture. So the wheeled chicken tractors preferred by the YouTube authorities are out.

Increased security will come at a cost of decreased mobility; saving costs on lost chickens will mean spending on latches and hardware cloth and the lot. There’s no free lunch, and hopefully that will soon include weasels.

In buildings, we’ve been hearing lately more detail about how things that we think are a good idea cause problems elsewhere.

Triple-glazed windows may save more energy than double-paned windows, but a recent study conducted by U.K.-based consulting firm Inspired Efficiency and "footprinting" expert Circular Ecology finds that in terms of their life-cycle carbon footprint, they don’t necessarily come out ahead.

Researchers determined that the embodied carbon of an average triple-glazed window is 51 kilograms greater than a double-glazed window with the same frame type because of the carbon dioxide emissions that are released from extraction, refinement, transport, and processing of the additional layer of glass and pocket of gas between the panes. It would take almost 20 years for a triple-glazed window to pay back this additional embodied carbon -- longer than the lifetime of many windows.

That doesn’t mean you shouldn’t specify triple-pane glazing; there are other benefits, including operational cost savings, construction cost savings from smaller mechanical systems, improved thermal comfort, and acoustics to name a few. Furthermore, if customers are seeking to reduce their carbon footprint, frame choice has a far larger impact, according to the researchers. Choosing wood over PVC saves 25 kilograms of carbon -- 10 years’ worth of operational savings -- so over 20 years, a triple-pane, wood-framed window will have a lower carbon footprint than a double-pane window with either a PVC or aluminum frame.

We care about this in part because carbon has a time value. We need to reduce carbon emissions now to forestall global warming. Waiting 20-plus years for carbon savings to kick in on efficiency measures is not ideal.

In other news, research from Arizona State University suggests waste heat ejected from air conditioners is raising nighttime temperatures -- at least in very hot and dry cities -- contributing to an even greater need for cooling.

In a computer simulation of 10 days of extreme heat across the Phoenix metropolitan area, researchers found that the waste heat put out by air-conditioning systems did not have a significant effect on air temperatures during the day when it was typically already above 106-degrees Fahrenheit. However, during the night, when temperatures dropped to around 80-degrees F, heat expelled from the indoors warmed the city air almost 2-degrees F in some locations.

With extreme heat projected to increase this century, this positive feedback loop could prove a public-health concern or put further strain on electrical grids; in Phoenix, energy used for cooling already sometimes rises to half of the region’s total electrical consumption.

While I do my best to take care of the chickens, both of these stories were reported on by my colleague here at BuildingGreen, Candace Pearson.

Thanks as always for reading and keep your questions and comments coming to Tristan@BuildingGreen.com.

Tristan Roberts is Editorial Director at BuildingGreen, Inc., in Brattleboro, Vermont, which publishes information on green building solutions. You can learn more at www.BuildingGreen.com. You can reach Tristan at Tristan@BuildingGreen.com.


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