ElectraTherm, which specializes in low-temperature waste heat recovery, landed $5.4 million in venture funding, bringing the total amount raised to over $10 million. Last year it raised $2.6 million.

Waste heat is one of the larger untapped, but proven and economical, sources of energy around today. The U.S. consumes about 100 quads (quadrillion BTUs) of energy a year and around 55 to 60 quads get dissipated as waste heat because of energy conversions, line losses, and inefficient machinery. Pick up your laptop brick and put it on your lap: Feel the power of waste heat. Better yet, wear a sweater on a factory tour.

Various companies have emerged to tackle the problem. Some, such as Cypress Semiconductor, Promethean Power and Alphabet Energy, are developing thermoelectric devices – i.e., semiconductors that can convert heat into electricity and vice versa. ARPA-E, the high-concept research division of the Department of Energy, recently awarded grants to a few startups and universities to experiment with figuring out way to develop nanotubes and nanowires to convert heat to power.

More traditional companies like ElectraTherm and Recycled Energy Development, meanwhile, capture heat mechanically that allow customers to re-use the energy locally. The heat can be converted into electricity (RED has a project to produce 45 megawatts of power from the waste heat inside a large silicon factory) or as heat. Panasonic, meanwhile, has begun to market co-generation fuel cells for homes in Japan that produce both power and heat.

Low in ElectraTherm's case is a relative term. The company's Green Machine requires a liquid heated to about 200 degrees, but that is less than half the temperature required by conventional systems. The Green Machine takes the liquid and runs it through a heat exchanger. On the other side of the heat exchanger is a volatile refrigerant. The heat converts the refrigerant from a liquid to a  gas to create pressure inside the refrigerant tubes, which is then exploited to turn a turbine. In a sense, you have three technologies in one: waste heat capture, heat exchangers and pressure-driven turbines.

It recently completed field tests at Southern Methodist University.

ElectraTherm's standard Green Machine can provide 50 kilowatts of power and several can be strung together. Larger units are also available, but the company will not likely cross the 1-megawatt line. After that, other alternatives such as fuel cells begin to undercut its advantages.