If you’ve ever walked into your office building on a weekend, you’ve probably experienced one of the most easily identifiable energy-efficiency problems.

Chances are good that the empty building was as warm or cool as it normally is on the weekday when the building is at full occupancy -- sucking all that electricity to keep the building comfortable for no one except you. Lucky you.

So is that inefficiency the fault of the building manager who doesn’t just simply turn the air conditioning down on Friday evening? Or is there are bigger problem with the building or HVAC system that needs to be fixed with an equipment retrofit?

FirstFuel, a Massachusetts-based company that analyzes energy consumption in buildings, thinks that the first problem -- operational improvements through changes to behavior -- is the primary driver of the problem.

The company remotely examined utility data for 60 million square feet of commercial buildings across the U.S. When it analyzed the sample buildings, it found that slightly more than half of energy efficiency opportunities could be realized with simple operational improvements. For example, the data showed that 60 percent of HVAC systems were fully running an hour before a building was occupied. It also showed that 60 percent of buildings were running equipment out of sequence, with less efficient systems' heating and cooling units running when they didn’t need to be.

FirstFuel says fixing these simple problems with tweaks to behavior or small automation changes would save a total of about $12 million across the facilities sampled -- or roughly $17 billion if applied across the entire U.S. commercial building stock.

That’s a compelling case for operational changes. But what does it mean for how building managers should consider efficiency improvements?

For companies with a stake in helping facility managers make those decisions, the answer depends on the business model.

“I'm a huge fan of what these companies are doing. And I don’t see it as exclusively one or the other -- an operational change or a retrofit,” said Jon Guerster, CEO of Groom Energy Solutions, another Massachusetts-based efficiency company that focuses on retrofits for commercial and industrial facilities.

“Operational change is a crucial piece that provides a high-volume and low-cost way to allow building owners to figure out how to spend their time,” said Guerster. “But it’s the first step in the process.”

Groom Energy comes at the problem from a slightly different perspective. Like FirstFuel, Groom performs remote audits of sites, as well as on-site equipment retrofits. But its primary focus is on equipment retrofits for commercial and industrial buildings that require a lot of energy.

Simply changing behavior in a commercial office building could have a major impact on energy use. But in an industrial building or a hotel -- facilities with far more complex needs -- installing new controls and equipment is often needed, said Guerster.

Groom’s latest project was a “multi-measure” retrofit at the crating manufacturer Atlas Box. Along with working with the building manager on operational improvements, the project featured installation of software-controlled LED lighting, upgrades to the compressed air system, and new controls for the vending machines. It will eventually include new controls for the HVAC system and variable frequency drives that help run a conditioning unit’s motors at a lower speed when needed. Groom expects the retrofit to reduce Altas’ energy use by 55 percent.

“There’s an opportunity for both scenarios. You can remotely monitor a building and tell a facilities manager about energy issues. However, in some cases, they can't act on it without new equipment. The world is moving toward intelligent analytics to help change behavior, but often you need the controls and systems to execute."

In presenting its analysis, FirstFuel isn’t arguing that operational changes are the only solution. It is merely pointing out that reducing onsite energy use can be far more simple than installing a bunch of new equipment. Indeed, its analysis showed that behavior shifts can represent half of savings in commercial buildings.

But like any efficiency project, the solution is site-specific and is usually not an either/or choice.