4 ms·
You're not going to achieve an over-unity system. Assuming no other losses, you'll be using 100% of heat energy from the stove. The equation is missing a -1% te
by waterheater 3y ago
You're not going to achieve an over-unity system. Assuming no other losses, you'll be using 100% of heat energy from the stove. The equation is missing a -1% term somewhere.
- Retric 3y agoYou’re allowed to make use of the same energy at different points in time. The 1% used by the fan is the same 1% that’s heating your room. A computer converts 99.9% of the electricity to heat a room just like a space heater. However, you can play video games on the PC while it’s heating your room.
- pishpash 3y agoThat's why all electric heating should be devices that do work or compute. Do not waste the Gibbs free energy of the universe.
- andbberger 3y agothis was the only sane argument for blockchain mining but it was never competitive with heat pumps
- Scoundreller 3y agoDepends how cold it is outside, but yes, heat pumps usually win.
- Scoundreller 3y agoI want a cottage industry of aluminum smelters in cold climates. Pick up a pile of aluminum oxide from a depot, electrolyze it into aluminum at home, and drop off the finished aluminum at the depot for a cheque that covers your electricity. "The theoretical minimum energy requirement for this process is 6.23 kWh/(kg of Al), but the process commonly requires 15.37 kWh." https://en.wikipedia.org/wiki/Hall%E2%80%93H%C3%A9roult_process https://en.wikipedia.org/wiki/Hall%E2%80%93H%C3%A9roult_proc... That's quite a few kWh of heat per kg of finished product. You're going from Al2O3 to Al, so your returns will weigh less than your pickups. Comparable to coal or oil heat: "With a complete combustion or fission , approx. 8 kWh of heat can be generated from 1 kg of coal, approx. 12 kWh from 1 kg of mineral oil" https://www.euronuclear.org/glossary/fuel-comparison https://www.euronuclear.org/glossary/fuel-comparison
- Retric 3y agoNeat idea. Aluminum smelting isn’t really hands off enough to make this viable at home. It might make sense at industrial scale while pumping waste heat to nearby office buildings or something. But even slightly higher electricity costs would be a huge issue.
- leoedin 3y agoThe problem is that heat pumps exist, so resistive heating is never the best option. An aluminium smelting at home heating solution would have a maximum CoP of 2 (as you're reducing the energy usage of the smelter by the same amount). A heat pump could easily have a CoP of 3 or 4.
- Scoundreller 3y agoThat’s a lot more efficient than an industrial aluminum smelter. The use of electricity as an input is inescapable for this process, so may as well use the waste heat as directly as possible.
- Retric 3y agoYou have that math backwards. A smelter turns ~1/2 the energy from electricity into chemical energy and releases the remaining 1/2 as heat thus the COP would be 0.5 not 2. However smelting is profitable because aluminum oxide is less valuable than aluminum which more than compensates for the waste heat having zero value at the smelter. Thus various schemes for combined heat and power etc which take the valueless waste heat and use it for some other purposes like warming homes or greenhouses etc. So while the COP would be 0.5 the electricity would be subsidized by the smelling process. https://en.wikipedia.org/wiki/Cogeneration https://en.wikipedia.org/wiki/Cogeneration Where such schemes fail is generally economies of scale.
- grvdrm 3y agoI should mine BTC in my heatless basement! Love it.
- NavinF 3y agoYou misunderstood. For comparison, a typical cheap AC has an efficiency (coefficient of performance) of 300%. For every 1W consumed, the AC moves 3W.
- pishpash 3y agoThat's an AC. This is a heat engine run normally. You're not getting >= 100%.
- deleted 3y ago[deleted]
- thsksbd 3y agoThe "over 100% efficiency" is technically incorrect, but the OP is right. Carnot limits the efficiency to make work from a thermal process (much less then 100%, in fact). Carnot does not prohibit you from enjoying the inefficiencies as waste heat.
- deleted 3y ago[deleted]
- pishpash 3y agoThey didn't miss anything. They're just double counting utility. Same thing would happen to get warm next to a computer. You pay for electricity once, and use the computer while getting cozy.