Indian Wells, Calif. -- SureGrid is probably the only green company out there to be inspired, at least in part, by spin bikes.

The company has created a cloud-computing-based building management system that attempts to curb energy by fine-tuning the HVAC system. The system examines weather data, room occupancy, traffic and use patterns and turns the chillers up or down accordingly.

It can also be hooked into demand response systems. Ultimately, SureGrid will likely sell the system to utilities or independent service providers.

So what's the carbon dioxide/exercise angle? "CO2 is the best occupancy sensor there is," president Mike Frost told me during a break. CO2 dissipates quickly; thus, changes in CO2 levels can serve as a proxy to determine how many people are in a room.

"It is better than a motion sensor," he added.

The company discovered this through management systems in health clubs, particularly rooms with spin biking classes. Spin rooms are generally kept at 70 or 72 degrees. But when classes begin, the heat rises and the air conditioner needs to kick into a higher gear. People also breathe more heavily, which also highlighted the CO2 connection.

"Health clubs have saved a lot of money" by kicking the AC back down once the CO2 levels drop, he said.

Although building management remains (and likely will remain) dominated by big vendors like Johnson Controls and Honeywell, opportunities for building applications and services that can ride on top of these existing systems and make them more responsive to events like changing weather or easier to operate have emerged in recent years. Since the technology is often the same, the big differentiation between many of these startups and new entrants comes down to customer wins. When large acquirers try to expand in the market, that will likely be the principal criteria.

Optimum Energy -- which has a cloud application for dynamically controlling the water chillers in commercial AC systems -- says it can cut the power consumed by running the chiller by 35 to 50 percent. Adobe, for instance, adopted Optimum in its headquarters. EnerNoc acquired Cogent Energy to get into building management last year and landed a deal to study the efficiency of Morgan Stanley's New York offices.

SureGrid, meanwhile, has put its systems into the Michael's chain of hobby and craft supply stores. While current customers use the system to adjust the HVAC to balance comfort with energy efficiency, they remain a bit nervous about demand response. Assume it's a hot weekend day in a resort town, Frost posits. A utility wants to declare a demand response event and curb AC units. But if a wedding reception is underway, the hotel won't want to cooperate.