A venture capital unit of German industrial giant Siemens said Thursday it has invested $5 million in indoor-air software firm 75F, bringing the Minnesota company's first round of venture capital investment to $28 million.

Siemens' Next47 VC unit joins Bill Gates' Breakthrough Energy, the Oil and Gas Climate Initiative and WIND Ventures in putting money into the Bloomington-based company.

The Siemens investment closes out 75F's inaugural VC round.

CEO Deepinder Singh declined to say what the recent investment implies about the overall value of 75F or whether Siemens, which has been acquisitive in the building-energy field recently, may be a prospective acquirer.

75F's technology is complementary to Siemens' other acquisitions, Singh said.

"My belief as an entrepreneur has always been that we should turn market leaders into partners," Singh said. "By doing this, we can accelerate the adoption of truly innovative technology."

Henning Sandfort, CEO of building products at Siemens Smart Infrastructure, said the company's investment in 75F reflects its interest in technologies that make it easier for customers to reap savings from energy efficiency.

"75F's wireless solution is easy to install and implement, offers fully-integrated AI and analytics, and can help get companies large or small on a path to meeting their energy or carbon-reduction goals," Sandfort said in a statement.

Singh, a computer scientist, started 75F after becoming frustrated by the inability to control the temperature throughout his large old house in Mankato. The company has won the Minnesota Cup and several other entrepreneurial and green-technology competitions since 2015.

Singh said 75F's business today is equally divided between North America and the Asia-Pacific region, primarily Singapore and India.

Singh said 75F expects to triple its 2020 revenue this year, though he didn't disclose a precise figure. The company employs 130 globally and has 33 jobs open. Its sweet spot is commercial buildings of 10,000 to 250,000 square feet, but it has installed its systems in structures of up to 1 million square feet.

"We make dumb buildings smarter," Singh said. "We provide a complete 'stack' that allows people to be more comfortable with better indoor air quality while saving energy."

Steve Case, an early internet pioneer, AOL co-founder and CEO of Revolution, the venture firm behind the Rise of the Rest Seed Fund that targets businesses outside of Silicon Valley, was an early 75F investor.

"We have entered the Third Wave of the Internet, where it is no longer the Internet of things, it is the Internet of everything," Case said in a statement. "Companies like 75F are so compelling because they are building on that trend with a focus on what I call the three Ps: Partnership, Policy, and Perseverance."