Harnessing Waste Heat for Improved Efficiency in Diesel Trucks

[Loren Booda]

How much energy could be saved by users turning off their computers during long idle times? Were California's brownouts last summer due in large part to inactive computer electrical consumption? Is there an advantage to keeping computers on (overnight, say) that overrides immediate energy conservation? Is it a priority in the industry that new computers be designed to use less energy?

 

[Elledan]

The energy used by computers in most parts of the US is dwarfed by the electricity used by ACs, TVs and many other home and business appliances.

However, at a time when Intel introduces a new CPU (Prescott) which uses a grand total of 103 Watt, something does have to change, if only to make cooling future PCs somewhat less a hassle. AMDs Opteron and Athlon64 CPUs, for example, draw about the same amount of power as Athlon XP CPUs: around 86 Watt. IBM PowerPC CPUs use around 45 Watt, I believe. VIA C3, EDEN and Transmeta Crusoe CPUs are happy with less than 10 Watt, allowing those to be cooled passively.

It seems likely that after the rapid increase in processor speed we'll see a decrease in power used by those components, possibly followed by GPUs (videocards).

Shutting down and starting a computer has one big disadvantage: thermal expansion and contraction of components, leading to premature failure.

 

[russ_watters]

I design for 200W for a typical computer (HVAC engineering), but actual use can vary a lot. In any case, the math for an individual computer in your home looks like this:

200W
12hr/day not in use
$0.12 / kWh

200*12*30/1000/.12= $8.64 per month

In the winter, some or all of that can be subtracted from your heating bill, in the summer you quadruple it to air condition it.

There are probably a good 10 million computers running in California at any given time. At 200W each, that's 2,000 mW, or roughly two nuclear reactors. Not insignificant if you're a business looking for an easy way to cut costs, but not a major issue for the power grid.

And no, switching your computer on and off twice a day will not harm it.

With Prescott burning 100W, heat dissipation is going to become a huge issue for computer makers in the next couple of years. We're not far from needing water cooling in mass-produced pc's.

 

[Nice coder]

With a modification to the PSU and a few peltiers, you can get the computer to recycle some of its wasted heat.

You could also turn your computer off while not in use.

 

[chroot]

Originally posted by Nice coder
With a modification to the PSU and a few peltiers, you can get the computer to recycle some of its wasted heat.

Eh?

- Warren

 

[russ_watters]

Originally posted by chroot
Eh?

- Warren

Eh, eh? Sorry, Nice Coder: no. Since a computer doesn't use heat for anything, there is nothing have it do when you recyle it. All heat in a computer is waste. A peltier adds to the total energy usage of a computer.

 

[Loren Booda]

Does the entropy of a computer increase with its density of gates, given an equal overall energy input?

 

[hitssquad]

Peltier junctions as thermoelectric couples

Originally posted by russ_watters
Eh, eh? Sorry, Nice Coder: no. Since a computer doesn't use heat for anything, there is nothing have it do when you recyle it. All heat in a computer is waste. A peltier adds to the total energy usage of a computer.

Peltier junctions produce voltage when placed between two heat sinks of different temperature.


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power generating modules
 HZ-2   2.5  watts output  
 HZ-14  14   watts output  
 HZ-9   9    watts output  
 HZ-20  19   watts output

--
http://www.hi-z.com/


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Hi-Z has built a 1kW generator to utilize the waste heat of the engine of a class 8 diesel truck. This thermoelectric generator can be employed as a substitute for the truck engine alternator.[/color]
--
http://www.hi-z.com/websit07.htm



Though all peltier junctions produce voltage from temperature difference, some are better at it than others. Given peltier junctions tend to be only good at one of the two types of peltiers tasks, meaning they are effectively specific to either 1.[/color] producing electricity; or 2.[/color] using electricity to produce a heating/cooling effect.


The best energy-production-specific peltiers currently turn ~4.5 percent of their input heat into electrical energy. Breakthroughs are still being sought, and even 20 percent is thought to be possible...
http://www.hi-z.com/websit30.htm#Quantum

...but even the current relatively-low level of efficiency has been good enough, so far, to beat out other high-reliability heat-engine competitors (such as stirling-cycle heat engines) for the space-probe market:


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Thermoelectric Generator for Space

For Space Exploration missions, particularly beyond the planet Mars, the light from the sun is too weak to power a spacecraft with solar panels. Instead, the electrical power is provided by converting the heat from a Pu238 heat source into electricity using thermoelectric couples. Such Radioisotope Thermoelectric Generators (RTG) have been used by NASA in a variety of missions such as Apollo, Pioneer, Viking, Voyager, Galileo and Cassini. With no moving parts, the power sources for Voyager are still operating, allowing the spacecraft to return science data after over 25 years of operation. [/color]
--
http://www.its.caltech.edu/~jsnyder/thermoelectrics/history_page.htm



FYI, a few years ago there was a company marketing a peltier-equipped woodstove to the off-the-grid-market. It could produce a maximum of 100 watts of 60-cycle, 110-volt AC power when there was a fire going inside of it. They called it the Midnight Sun -- appropriately enough, since the target market was solar panel users who needed a way to produce power after dark.


Apparently another company appropriated the name and is using it for a somewhat-similar-in-concept photo-cell-powered, external-combustion, heat engine product:

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JX Crystals in Issaquah Washington, has created a product - Midnight Sun - primarily for use on sailboats. The 14 centimeter wide by 43 centimeter tall cylindrical heater, powered by propane gas, can produce 30 watts of electricity and is targeted as a means of recharging batteries that run navigation and other equipment. The unit not only provides electricity but acts as a co-generator, supplying space heating for the boat cabin. It uses a partially selective radiator made of magnesium aluminate and has gallium antimonide photovoltaic cells connected in series.

Although its current $3,000 price tag makes it more expensive than a conventional diesel generator, Midnight Sun runs silently and is expected to be more reliable, because it lacks any moving parts. [/color]
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http://educate-yourself.org/zsl/zslthermophotovoltaics19sep02.shtml





-Chris

 

[Loren Booda]

The first I heard of a Peltier was to keep cool one's auto-borne six-pack!

 

[russ_watters]

hitssquad, that's all very nice, but in a compter, peltiers are used the opposite way from which you describe. A voltage is applied to create a temperature difference as so to assist in cooling. If used the way you describe, a peltier would add to the cooling requirements of a pc.

Important spec:

The best energy-production-specific peltiers currently turn ~4.5 percent of their input heat into electrical energy.

Does the entropy of a computer increase with its density of gates, given an equal overall energy input?

No: its all entropy either way.

 

[wimms]

Originally posted by Loren Booda
Does the entropy of a computer increase with its density of gates, given an equal overall energy input?

Not sure if that applies to your question, but to the matter of computer energy consumption it does:
http://www.zyvex.com/nanotech/reversible.html
http://www.nature.com/nature/journal/v406/n6799/box/4061047a0_bx1.html

 

[hitssquad]

Improving efficiency by tapping waste heat

Originally posted by russ_watters

Peltier junctions produce voltage when placed between two heat sinks of different temperature.

but in a compter, peltiers are used the opposite way from which you describe. A voltage is applied to create a temperature difference as so to assist in cooling. If used the way you describe, a peltier would add to the cooling requirements of a pc.

As with anything else, peltiers are used whatever way one would like. Using a peltier for active cooling, as you describe, causes the total energy use of the computer to go up.

Conversely, using a peltier (or any other type of heat engine) for generation of electricity from the waste heat of a computer, as I described, causes the total energy use of the computer to go down.


Here is an example involving the tapping of waste heat from a diesel truck, in order to improve efficiency:

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Hi-Z has built a 1kW generator to utilize the waste heat of the engine of a class 8 diesel truck. This thermoelectric generator can be employed as a substitute for the truck engine alternator. Power to the driveshaft increases by three to five horsepower, which increases fuel efficiency and reduces emissions. [/color]
--
http://www.hi-z.com/websit07.htm





-Chris