I would like to add, at the same time, that passive and renewable-energy strategies are gaining popularity, and that they are often integrated with mechanical systems. We should therefore keep in mind that “not all Btu’s are created equal”, as a wise professor once said. While an absolute carbon metric could potentially solve this, I’m finding that “tons of carbon” seems to be an abstract notion among our clients and even in our office (not to mention the confusion introduced by the alternative expression, “tons of CO2″). In any case, we will soon need an equally robust way to distinguish between a wind-powered, electrically heated building and a gas-heated building with an EUI half its size.

A related concern is our ability, as designers and engineers, to evaluate the contributions provided by passive systems in mechanical contexts; this seems to be much-needed information among our clients. A sunspace providing passive solar heating, for example, might require more glazing, and glazing with greater thermal conductivity, than would otherwise be used, incurring a nighttime heat loss penalty. Even though entire building’s EUI may diminish, the solar contribution is challenging to assess, both in models and in real performance, since the “no-sunspace control” is either limited by model simplifications or absent altogether. For this reason, it is essential that we all contribute to building performance databases so that consensus impacts of specific energy-saving strategies, within diverse spatial and programmatic contexts, can emerge.

Thanks again for a great post!