DIY waste heat capture


in Economics, Geek stuff, The environment

We have discussed the issue of waste heat before, in the context of both incandescent lightbulbs and the cogeneration of heat and power. For those interested in a more hands-on treatment of the subject, there are instructions for building a thermoelectric unit which allows you to charge electronics using waste heat from appliances. The same page also shows how to make a LEGO car powered by electricity produced using the heat from a small tea candle.

Using this system while heating your house doesn’t make a lot of sense, but similar devices may have some practical value inside buildings that are being cooled or outdoors. Of course, the cost and complexity of the thermoelectric unit also demonstrates why a lot of waste heat goes uncaptured, since it is cheaper to use more electricity or fuel than to improve system efficiency.

{ 3 comments… read them below or add one }

. June 4, 2009 at 5:45 pm

Stirling Engines

An external combustion engine. Or a no-combustion engine, powered by the heat from the sun, or in my case, from the heat of the network switch it is sitting on, or the wood stove in the living room.

. March 14, 2010 at 7:02 pm

Technology Quarterly

Heat scavenging
Stealing the heat
Energy: The idea of recycling paper, glass, metal and plastics has become commonplace. New technologies allow heat to be recycled, too

Mar 4th 2010 | From The Economist print edition

“By constructing a computer rack similar to that used in the office test, the researchers were able to provide the greenhouse with badly needed heat. A short while later, the rack was joined by three more racks that today provide the greenhouse with enough heat to cut its gas bills by $15,600 a year—while simultaneously saving Notre Dame $38,000 in cooling costs.

Another way to recycle heat that is being explored is to capture infrared with photovoltaic cells similar to those used in solar panels. Photovoltaic cells depend on packets of light (photons) knocking electrons free from atoms. They then employ the electrons so liberated to create a current. Photovoltaic cells are usually most responsive to photons in the visible and ultraviolet parts of the spectrum, but they can also respond to high-frequency infrared photons. Objects at a temperature of 1,000-1,500ºC produce plenty of such photons.

But only those that are travelling at a near-perfect right-angle to the surface of the hot material can escape and travel outwards. Photons travelling at any other angle within the material are reflected back inside when they reach the surface. As a result, photovoltaic cells placed near hot objects have only been able to generate around 0.02 watts per square centimetre. By contrast, photovoltaic cells absorbing sunlight can produce about 20 watts per square centimetre, provided the light is carefully concentrated using mirrors.

So Dr Hagelstein and his colleagues changed the design of the cell, adding tiny metal wires to the usual sandwich of semiconductor materials in order to pick up the liberated electrons and allow them to be carried off to create an electric current. Although the new device is still at an experimental stage, the team’s calculations, published in a paper in the Journal of Applied Physics in November, suggest that it could convert heat to electricity at a rate of 100 watts per square centimetre. Installed on a laptop, it could recycle heat from the microprocessor and extend running time by around 20%. One way or another, it seems likely that the abundant reservoirs of waste heat are about to be tapped.”

. October 17, 2013 at 10:30 pm

Scavenging heat
Hot property

SEATTLE’S South Lake Union used to be peppered with low-slung, ageing industrial buildings. In the past few years, however, it has begun to change. Amazon moved its headquarters to the neighbourhood in 2010. Microsoft’s co-founder Paul Allen has been developing 60 acres (24 hectares) of land he owns there. But perhaps an even bigger transformation is the result of Seattle’s embrace not of modern technology but of an old one, albeit with a new twist.

The old technology is so-called district heating, whereby heat is generated at a central plant and distributed to buildings, which no longer need to run their own heating systems. The new twist is that the heat would be scavenged from data centres, which produce lots of it.

District heating was once prevalent in many American cities (and continue to be in many European ones). Since the 1970s, however, many utilities have lost interest in heating networks, which are costly to maintain. But its efficiency and green potential has stoked renewed interest.

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