Will building energy efficiency be the next greentech boom sector — and does that mean it’s becoming a bubble? Yes, and yes, are the answers from a Lux Research report this morning that predicts a boom next year, and a bust by 2015, in the building energy efficiency IT sector. The McKinsey Curve teaches us that energy efficiency is the cheapest, most cost-effective green investment out there. But with the real estate downturn and economic malaise, building owners want cheap and scalable solutions, not big retrofit projects — and software, sensors and systems integration technologies are just the ticket. That’s led to a spate of acquisitions in the space — for example, Schneider Electric bought two French building software startups last week and Siemens acquired HVAC-room occupancy optimizer Site Controls in October. The same goes for the IT giants getting into building energy controls — Cisco started its EnergyWise and Building Mediator business line by buying Richards-Zeta Building Intelligence last year, for example. Who’s next to be bought? Lux names a few building efficiency IT startups it likes, including Microstaq, Cimetrics and Optimum Energy.