In an effort to diversify its portfolio of services, EnerNoc has bought SmallFoot, a Colorado company that specializes in ZigBee- and low power-based equipment for managing energy in buildings.

The deal marks the third in a series of recent acquisitions for the company. It bought Cogent Energy in December to accelerate the push into building management and it purchased eQuilibrium Solutions, a carbon accounting company, before that.

Historically, EnerNoc has garnered its revenue from demand response services sold to utilities. It's a growing business. EnerNoc currently has control over 3.5 gigawatts of power that it can deliver to utility clients. However, demand response companies are wholly dependent on utilities -- that is who pays the bills. There are only around 2,100 utilities in the U.S. and some of them move incredibly slow. Some also want to control their own demand response services; Tendril Networks CEO Adrian Tuck has theorized that software developers could start to displace demand response service providers.

By moving into building management, EnerNoc can sell its software, hardware and services to a wide array of corporate clients and businesses.

In fact, if you put the three acquisitions together, EnerNoc now has networking equipment for controlling appliances (SmallFoot), software to manage the process (Cogent) and more software to see if the first two things are really worthwhile (eQuilibrium).All three were fairly small before EnerNoc gobbled them up.

What will the company buy next? It's hard to say, but one could imagine EnerNoc trying to buy companies with particular specialities, such as Optimum Energy, which makes software that controls air conditioner chillers, or Lumenergi, which has an application and equipment for dimming those hard-to-dim fluorescent tube lights.

Competitor Comverge, which has historically concentrated on providing demand response services to small businesses and homes, is also diversifying into providing software to utilities.

EnerNoc reported $190.7 million in revenue for 2009, compared to $106.1 million for 2008. It went public in 2007 and had its first profitable quarter in the third quarter last year.