Volkswagens, Homes and the Limitations of MPG Assessments

The recent Volkswagen emissions scandal is a tragedy on many levels, and it has highlighted some of the flaws in the systems we use to evaluate the efficiency of our cars and trucks. In particular, the use of standardized laboratory tests to measure emissions and fuel economy has proven troublesome. Sadly, it’s not difficult to imagine other automobile manufacturers taking similar actions or engineering their vehicles to perform exceptionally when new in order to excel in laboratory tests. If the goal of the system is to produce cars that score well in testing scenarios, that’s what will be produced.

Many experts in the residential energy efficiency space like to use the MPG analogy to make the case for one-time standardized building efficiency tests. I expect the analogy has lost a bit of luster with the VW action, but the idea is that these standardized tests can be used as an “asset” assessment of homes in order to create MPG-like ratings that can be shared with homeowners, homebuyers and renters.

I don’t mind these analogies (I’ve made them myself), and I fully support the use of asset assessments – they are extremely important in helping us understand structural efficiency and providing information that can be used to differentiate homes (and new automobiles when everyone is playing by the rules).

What’s missing from these assessments however, is the actual performance of the home or vehicle over time. What happens to efficiency (and emissions) when parts in our car start to wear, we don’t maintain the heating and cooling equipment in our home, or different occupants and drivers enter the equation?

Generally speaking, we don’t know the answer to these questions, and this is a problem. If our goal is to reduce emissions and energy consumption, how can we test a car or home once and assume it’s efficient as long as it’s functional? We can’t, which is why we need to evaluate the performance of our homes and vehicles throughout their lifetimes.

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