Quote from: mwizard on September 10, 2014, 02:08:21 PM

Quote from: Nagle on September 10, 2014, 08:46:52 AM

You can't extract much energy from low-grade heat. Maximum efficiency = (T2-T1)/T1, where T2 is the temperature of the low-grade heat (exhaust from the computer system), and T1 is the ambient temperature of where you dump the heat. All temps are absolute (K). Typical chip surface temps are 60-80C, and 70C is about 343K. If your cold end is a cool day (say 15C), then T1 is 288K. The maximum energy you can recover from that heat is 19% of the input. That's a theoretical upper limit. Actual heat engines don't do that well.

It is even worse than the above calculation. The maximum energy that can be extracted between temperatures Thot and Tcold is (Thot - Tcold)/ Thot. The above equation should be (T2-T1)/T2 rather than (T2-T1)/T1.

For the above example of 70C and 15C the maximum possible efficiency is 16% rather than 19%. In reality the efficiency is likely to be between 5 and 10%.

Trying to extract any power from a small temperature difference is very inefficient. Large power stations get better efficiency because the difference between high and low temperatures is around 500C, not 50C. Power stations need the biggest possible temperature difference - that's why they need cooling water or cooling towers.

In summary part of the confusion in this thread seems to be because there are 2 very different ways proposed in this thread, and on the 3xergy site, to use the heat.

1) Simple use the heat as heat. This is efficient. Simply use the heat from a miner to heat a room or heat water. This seems to 'first generation' proposed at the www.3xergy.com site and appears to be nothing more than using a miner's excess heating to do space (or water) heating. There is nothing new or unusual with this proposal.

2) The second way to use the heat is to use the small temperature difference between the miner and a cool point to extract power, for example to generate electricity or to power refrigeration. As shown above this is very inefficient with small temperature differences. Extracting power from the heat (temperature difference) and distributing excess heat via the electrical grid, as proposed on the www.3xergy.com site, is extremely unlikely to be cost effective. I won't call it a scam but it may be wishful thinking. It can be done but is rarely worth the effort. If you want more information see Carnot's principle or the second law of thermodynamics.

1) is exactly right and very simple

2) is missing the point, were not generating electricity from heat - that is too many energy conversions and way too inefficient to be viable. We are talking about using heat to create cold so we don't need to use electricity to make cold. Almost 100% of the energy that goes into a computer makes heat - (if you can point me to some peer reviewed literature that claims otherwise I would love to see it!) 100% of that heat (minus thermal leakage) can be used for other purposes. Given heating and cooling our spaces are two of the very largest consumers of energy on the planet and that making cold from heat is a very, very well proven from a technology perspective this is a pretty easy thing to do. The harder thing to do is making enough heat from computation - we're working on that, it is a hurdle we can overcome.

We're not distributing heat BTW - that is crazy and left for the likes of NYC's district heating plants to do with horrible inefficiency. We're talking about distributing computation to make heat where it is needed. Its not a scam or wishful thinking and it falls squarely within the current boundaries of both physics and today's technology. Its sitting right next to me now, as I type, putting my answers to you on the internet at 180f in the loop.

"Extracting power from the heat (temperature difference) and distributing excess heat via the electrical grid, as proposed on the www.3xergy.com site, is extremely unlikely to be cost effective." Boilers used to run chiller plants are used all day every day around the planet to extract energy from heat, most big buildings on the planet are doing it right now. We are already making the temps these systems typically do - again, with off the shelf parts. We are not shipping power over the grid.

Any help you guys have on improving the website so people don't immediately jump to 'scam!' would be a great help. We need people to see the simple elegance of the solution, not worry that its a scam.