Measuring how much power is consumed in a place, whether it's a Google data center or an office building or a single-family home is easy. Breaking it down another step can be done, too.

Knowing just what work goes on with that power – finding an electrical energy equivalent of miles per gallon – is another task altogether.

Data centers have been delving into the issue, but it's applicable across the spectrum of energy-using buildings. Google, with detailed records of its energy usage, knows that 12.5 megawatts of its 260 megawatt daily consumption is used doing searches, CIO Magazine reports on its website. But how much per unit of work – and what is a "unit of work" anyway?

"The idea of quantifying the kilowatts of energy required to perform a useful unit of work is now considered the holy grail of data center metrics," CIO said.

Building owners and managers may face a similar challenge in trying to understand what is a unit of work for HVAC or lighting in an office building.