What do you get for the multi-billion-dollar property trust that’s already squeezed millions of dollars in energy efficiency out of its buildings?

That’s the question that Malvern, Penn.-based Liberty Property Trust was asking itself earlier this year. The $7 billion real estate investment trust had already earned a 2012 Energy Star Partner of the Year award in March, having certified more than 89 buildings with the U.S. EPA program and cut some $3.4 million from its energy budget over the past four years.

Liberty had also taken a step beyond most REITs by developing a proprietary building wide area network to track and display real-time energy use for its property managers, Marla Thalheimer, director of sustainability, said in an interview this week.

At that point, the company started asking itself, where else could it find waste across its hundreds of properties? In other words, “We hit a bit of a plateau,” she said.

It’s a common situation for building owners that have replaced the lights, tuned up the HVAC systems and taken care of the other low-hanging fruit in the building energy efficiency game. What’s left over is much harder to pinpoint, particularly when the scope of possible effort spans lots of buildings across different regions.

Enter Retroficiency, a Boston-based startup with a technology a platform that combines public and proprietary data to create building energy models -- ones it says can shed light on where energy is being wasted without even entering the building.

In the case of Liberty, Retroficiency was able to take an energy assessment process that could have taken a team of engineers weeks to process, and squeeze it down into one day, Thalheimer said. In the process, it identified about $2.3 million more in energy savings potential, ranging from lighting and HVAC to building controls and plug loads, as well as helping to prioritize just which buildings and systems were likely to pay themselves off most quickly.

Buildings waste a lot of energy, and much of that waste is theoretically very easy to fix and keep fixed. A study from Deutsche Bank and the Rockefeller Institute found a $279 billion investment opportunity in U.S. commercial building efficiency over the next decade, with the potential to return more than $1 trillion, or nearly four times the investment, over that time.

But building owners and managers have a lot of other things to worry about, such as tenant attraction and retention, property improvements and upgrades, and other competing priorities for investment, Thalheimer noted. Any money spent on efficiency needs to show a clear payback over a known period of time, she said. Simple lighting replacements deliver very clear cost reductions -- but investigating beyond those simple projects opens up a lot of variables that are hard to quantify, she said.

“The challenge for building owners is, you have to get the biggest bang for your buck,” she said. “Retroficiency’s recommendations are very useful, because they tell you things you haven’t looked at yet.” While Liberty hasn’t yet fixed all the energy-wasting problems that Retroficiency’s scan caught, it’s on a path to do so, both in terms of prioritizing high-value projects and providing individual building managers access to the data to set their own goals, she said.

It’s important to note that Retroficiency doesn’t do energy efficiency retrofits or building controls itself. That’s more the realm of building controls and energy services giants like Honeywell, Siemens, Johnson Controls and Schneider Electric, as well as startups such as SCIEnergy, SkyFoundry, BuildingIQ and many others targeting various aspects of the built environment.

Retroficiency, on the other hand, is a tool for the parties involved in that process, whether they be property owners, big management firms like Liberty or customer Jones Lang LaSalle, or building energy control and service vendors like SAIC and Schneider Electric.

Retroficiency, funded with $3.3 million in VC from Point Judith Capital and angel investors, isn’t the only company targeting this analysis and insight portion of the building energy efficiency process. Another is FirstFuel, a Lexington, Mass.-based startup with $12.5 million in VC and customers including the U.S. Department of Defense and several unnamed state government agencies, large U.S. utilities and European utilities.

FirstFuel uses utility interval meter data to gain its insights. Retroficiency started out approaching the data-crunching challenge from the property data side, then expanded into interval meter data with its acquisition of Nexamp last year.