The last month brought a few new venture rounds for startups developing monitoring hardware and software analytics to make buildings smarter.

This morning, the building analytics company FirstFuel announced a Series C round worth $23 million to expand into Europe and build its offerings in deregulated U.S. markets. That round was the biggest for an American company in the sector so far this year, coming in second overall to the $115 million round closed by the French networking startup Sigfox in February.

Since early March, three other U.S. smart building companies have cumulatively picked up nearly $10 million in venture capital and seed funding.

Lucid, the maker of a universal operating system for buildings, added $5.9 million to its previous Series B round closed last June, according to SEC filings filed in late March. The Series B round was led by Formation 8 Partners with a follow-up investment from Zetta Venture Partners.

Lucid's last venture round was in 2009. Since then, the company has focused on profitability through sales -- only now deciding to go back to investors for growth capital. 

BuildingIQ, a startup with predictive analytics for HVAC systems, also closed a $2.7 million round in March as part of a $10.6 million offering, according to SEC documents. This follows BuildingIQ's $9 million venture raise in early 2013, which included Aster Capital, Paladin Capital Group and Siemens' venture arm.

The company says it grew recurring revenue by 96 percent in 2014 and is now serving close to 20 million square feet of buildings with its analytics software.

Last October, a startup called Persistent Efficiency emerged with a stick-on submeter that reads magnetic fields from circuit breakers and reconstructs them into current, load and power factor. This week, the company said it had closed a $1.1 million seed round from angel investors, including Peter Rumsey, who previously backed Building Robotics. 

Persistent Efficiency CEO Jason Trager says the "Power Patch" can monitor power quality and energy consumption at a fraction of the cost of a traditional submeter. The company is looking to apply "assembly-line principles" to monitoring building energy use, and eventually build more analytics capabilities on top of its novel device. 

These investments follow an $14 million round closed by Blue Pillar in February to expand its monitoring capabilities for microgrids and critical backup systems in buildings. 

"Among the markets we're tracking, building energy management is second only to energy storage in terms of VC interest so far this year," said Andrew Mulherkar, a grid analyst with GTM Research.