Human World

Energy audit by Sanjay Sarma: the first citywide

An energy audit – an assessment of how well a home holds in its heat or cooling – typically takes hours for just one house. But MIT engineer Sanjay Sarma’s new method can conduct an energy audit of a building in only seconds. His team uses special heat-sensitive cameras mounted on a car. He said:

It took us a few seconds per house, because we basically drove past the house

In fact, over the winter of 2010, Sarma’s team conducted an energy audit of an entire city: Cambridge, Massachusetts – the first of its kind. The car-mounted cameras took pictures of the temperature of Cambridge’s roughly 25 thousand buildings. He told EarthSky:

When a building leaks heat, there is a particular frequency of light at which you can see it, it’s kind of a color that’s beyond our visible range, it’s called infrared. And on a winter’s day, if the outside of the building is hot, it means the building isn’t doing a great job of holding the heat in.

Dr. Sarma designed a special program to compile all his infrared images. He’s still analyzing the temperature data, but he believes that about 20% of Cambridge’s buildings, with simple fixes, could cut their energy bills by up to a third.

Our findings are actually quite specific. As in, “Hey, your door sill has a leak, or your window is cracked, or your roof line has a leak”.

Dr. Sarma added that about 10% of all energy consumption in the United States goes to heating and cooling buildings. He said that the point of this sort of technology is to offer precise fixes to building- or homeowners.

What we want to do here is conduct precise interventions, to offer a specific fix, if the homeowner wants to take it, to fix the problem. The analogy I use is that if we know there is a high rate of heart disease in a town, we don’t want to ask everyone to take aspirins, right? We try to figure out what people have the heart condition, and so on. Unfortunately, our approach to energy these days tends to be broad spectrum. What this allows you to do is be much more specific.

Some energy leakage problems make more financial sense to fix than others said Sarma. For example, if is house is quite old, or poorly constructed – that is, it leaks heat all over – that leakage might not be worth tackling. But, if it’s a only single window that’s leaking, it makes good sense (money and energy-wise) to take care of the problem. He also clarified this is true for cooling, as well as heating:

There’s really no point on wasting money on problems that are going to take a lot to fix. IF the problem isn’t focused, like a single leak you can fix, it’s hard to actually invest money in that problem. So what this does is it prioritizes homes and buildings so you can go and fix thermal problems. It can also help you distribute subsidies, and determine subsidies a particular area needs.

Infrared cameras can also be used for defense, and also security purposes, to detect if a human is present in a classified area. Sarma noted that a number of people had privacy concerns about what they perceived as the invasive nature of infrared in energy analysis. He said:

Any scanning technology, even, for example, Google Streetview, there are privacy concerns that come up. The good news is that infrared light is a low frequency light. It doesn’t see through a wall, it only sees the surface of a wall. It doesn’t even see the wall, actually – it seems the temperature of the surface of the wall. So it’s actually very fuzzy, which actually made our research difficult. But it’s something we’re going to continue to think about, and deal with in a very realistic way, because I’m a big believer in individual privacy, when it comes to any technology.

April 12, 2011
Human World

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