7 ms·

The most important take away from this is that electrical energy can be easily "multiplied" into thermal energy by using it to move around the almost unlimited

• harperlee 6y ago
  But this is not a takeaway that’s specific to this process, that’s how ubiquitous heat pumps work in residential HVAC. The article takeaway is that iron powder is a surprising electricity—>heat battery.
• IgorPartola 6y ago
  The other way to put it is that your efficiency is proportional to 1/(delta T). In other words if your heat pump is working between two environments with very close temperatures then the heat transfer is very efficient (for example 19 degrees C outside, 21 inside). But if you are trying to heat your house to a livable temperature while it’s -20 outside, your efficiency is terrible. This is why for example you see heat pumps installed all over the place in homes in the southern parts of the US where you also need little heating all around, while places up north where you do spend quite a bit on heating cannot really take advantage of heat pumps due to winters being too cold.
  • Reason077 6y ago
    > "But if you are trying to heat your house to a livable temperature while it’s -20 outside, your efficiency is terrible." Heat pumps are designed so that their "efficiency" (performance) is never less than 100% (COP >= 1). In very cold conditions, they may not be more efficient than resistive electric heating, but they will never be worse. > "places up north where you do spend quite a bit on heating cannot really take advantage of heat pumps due to winters being too cold." You're talking about air-source heat pumps here. In colder regions, it's better to use ground source/geothermal heat pumps. Ground temperature is consistent year-round even in very cold climates.
    • IgorPartola 6y ago
      True. Geothermal heat pumps will always be better but given that you can get an air source heat pump for 10^3 to 10^4 dollars while a geothermal setup will cost you 10^4 to 10^5, geothermal becomes prohibitive for most residential setups.
      • bluGill 6y ago
        Depends on your timeframe of investment. Your air source heat pump will need to be replaced in 7-10 years. The really expensive parts of a geothermo system will last basically forever, the other parts may need to be replaced every 7-10 years, but the costs is about the same as replacing a air source heat pump, and geothemo is more efficient in general. Thus if you live in the same house for 30 years geothermo may pay off.
      • dharma1 6y ago
        Your upper limit for geothermal seems a bit high, typical installation is 20-30k. But commercial viability depends on typical outside temperature and time frame for payback
      • jabl 6y ago
        Over here in northern Europe, for a typical single-family house, replacing an oil-fired boiler with an air-water heat pump (that is, the heat pump uses outside air to heat water that can be run through the existing radiators) costs around 10k-15kEUR, replacing the boiler with a ground-source heat pump (incl. borehole drilling, the whole shebang) is around 15-25kEUR. So the price difference is not huge. In southern parts of the country, and for older houses with less expected life left in them, air-source pumps have proved more popular, whereas further up north and for newer buildings ground-source pumps are more often the choice.
  • JackC 6y ago
    > But if you are trying to heat your house to a livable temperature while it’s -20 outside, your efficiency is terrible. Amazingly (to me), there are now air source heat pumps that stay > 100% efficient down to -20C before regular electric heat takes over: https://www.nordicghp.com/2017/01/heat-pump-effective-temperature-range/ https://www.nordicghp.com/2017/01/heat-pump-effective-temper... Though apparently you'd be better off with a ground source heat pump if your average temperature during heating season was below freezing or so. [Edit: I mention this because I've heard that "you don't see heat pumps in the north" was true in the past but is now outdated -- they've made sense in warmer climates for a while but have only recently crossed over for colder climates, so it will take a while until they're common.]
    • dragontamer 6y ago
      > heat pumps that stay > 100% efficient down Note: there are two popular "efficiency" measures, and its important to realize that they're incompatible. Air conditioners are commonly "energy moved / energy used", which can reach greater than 100%. If you move 150W of heat using only 100W of electricity, you have 150% "efficiency". --------- I don't know the term for the other kind of efficiency (I'm not a physicist), but lets call it "inverse engine efficiency". This is "energy out / energy in", which ends up being pretty close to "energy moved / (energy moved+electricity used)" Under this measurement of efficiency, 150W moved with 100W of electricity is 60% efficient. This follows the more standard physics rule of thermodynamics (you can never go above 100% efficiency: it will always take some number of energy to move heat around). Note: Car air-conditioners are funny systems. They use the heat from the combustion engine to move heat from inside the cabin to the outside world. So you are literally using heat to move other heat.
      • greesil 6y ago
        Isn't this just the coefficient of performance?
      • Reason077 6y ago
        > "Note: Car air-conditioners are funny systems. They use the heat from the combustion engine to move heat from inside the cabin to the outside world. So you are literally using heat to move other heat." Car air-conditioners are not powered by heat from the combustion engine. They are powered mechanically by a belt ("serpentine belt") connected to the engine. Or, in some cases such as battery electric vehicles, powered electrically with the compressor turned by an integrated electric motor. The extra heat produced is just a byproduct (thermal inefficiency) of producing and transmitting that mechanical/electrical energy.
  • nojokes 6y ago
    Are you talking about air source or ground source heat pumps?
    • IgorPartola 6y ago
      Either. I am talking about heat pumps. The efficiency formula is exactly the same. The difference is that ground water stays at a consistent 12-15 degrees C IIRC. That is close to what we as humans like to live in, so the efficiency is relatively high heat round. In the meantime air temperature fluctuates by quite a bit. The main drawback of using ground water as your heat source/sink is that it is expensive and costly to maintain relative to a resistive coil with electricity running through it.
  • kurthr 6y ago
    Water heater heat pumps (other than the complexity) do an excellent job of maintaining 40C temperature differentials (eg Vermont or Maine) with better than 130% wall plug efficiency. I think ideal efficiency is proportional to Tcold/dT (T in Kelvin) so it could go as high as 400% if there weren’t fluid, pump, and insulation losses. The real challenge is reliability and cost of electricity. If your power goes out and you have heating oil you can still live for a week. Brewing water temperatures peak at ~100C (pressurized steam is dangerous) and even with 20C water that’s an 80K difference so you’re down to 350% ideal, which probably puts you close to breakeven with pump losses. It’s the complexity that kills it.
    • jabl 6y ago
      > The real challenge is reliability and cost of electricity. If your power goes out and you have heating oil you can still live for a week. At least over here, all oil boilers I've seen use mains electricity driven pumps, injectors etc.
  • maerF0x0 6y ago
    >But if you are trying to heat your house to a livable temperature while it’s -20 outside, your efficiency is terrible. For air source, in the north (at least in canada) they use ground source ones put below the frost line. So the ambient temperature down there is >0C .
• Retric 6y ago
  Brewery’s need high temperatures simply as a way to quickly heat a large volume of liquid. Most recipes involve boiling the mixture for around an hour, and you want to reach boiling quickly. If your heat pump is only at ~120C you would need a lot of surface area which makes cleaning difficult. On top of this reaching 120C via heat pump is already inefficient and the heat pump ends up being expensive compared to resistive heating.
  • hinkley 6y ago
    Breweries need multiple temperatures, and that's an area where heat pumps could still be applied. I think the common mistake is either/or solutions and you're making it here. Water has a high thermal mass. Starting with ground temperature water and heating it up greatly increases the number of BTUs. And then after you've cooked it, you need to chill it down to around room temperature. Where you dump that heat could make a huge difference.
    • Retric 6y ago
      It takes vastly more energy to start and maintain a rolling boil for an hour than to reach 50c. If we where talking a giant scale industrial process then optimizing this stuff via heat exchangers would be a major consideration. However for a Dutch brewery located in such a cold area it’s much harder to justify such specialized investments with associated maintenance costs. Remember this inherently allows them to load shift and thus get much lower electricity prices as well as reducing peak demand.
• socialdemocrat 6y ago
  Yes but in a renewables world Electricity will not necessarily be ready on demand. In that case the multiplier is irrelevant. Nor may it be available locally. With iron burning you could theoretically create iron using solar power in Sahara and then ship that to the Netherlands for use in breweries. Thus you can decouple where and when power is generated from usage.
  • julesnp 6y ago
    Wouldn't any heat energy gains be negated by the energy needed to ship the heavy iron from the Sahara to the Netherlands?
    • fpoling 6y ago
      The energy cost of sea transport is like 50 less per distance traveled than on land and it has being like that for the last 3000 years. So the cost of shipment to Netherlands is just a cost of transporting to the nearest sea port from Sahara.
    • ohyes 6y ago
      you need to run your ship on iron fuel as well. I guess that is the test though, can it ship itself?
      • Ichthypresbyter 6y ago
        I think an iron-powered ship would have to be a steamship. There are still a small number of steam-turbine-powered merchant ships being built- specifically LNG carriers, where gas that boils off from the cargo can be used as fuel.
        • benibela 6y ago
          In Lensmen, they build iron-powered spaceships They are far more powerful than other kinds of spaceships
      • deleted 6y ago
• maerF0x0 6y ago
  > So we are looking at on order of magnitude more heat for the same electrical consumption 40% vs 400% efficiency. Instantaneous renewable energy prices are low, but rarely that low. Wouldn't this imply that when heat is the goal we should always use these pumps? What is the limit of usefulness of these pumps? (eg, what if a whole city did it for all its heat needs?)
  • whatshisface 6y ago
    For one thing, heat pumps are more expensive than heaters. A heat pump is basically an AC unit that runs in reverse - way more expensive and complicated than a fire or a long thin wire.
  • gnopgnip 6y ago
    It depends how much of a temperature delta you need. In cold climates often the efficiency is comparable or worse than resistive heaters
  • bluGill 6y ago
    The big limit is temperature differential matters. The smaller the better!. 40C differential is about the max modern equipment can do with enough efficiency to be worth bothering with. Your home freezer might do more than 40C in extreme cases, but it isn't efficient (We also don't have many other options for this mode, for heating we have other options that work)
• m463 6y ago
  I can see that heat pumps can only move a certain amount of energy and to a similar extent electricity. I remember looking at on-demand hot water heating. It's easier to do with natural gas. But for electricity it would require something like a 100+amp electrical circuit and would have limits on flow rate and/or temperature increase. for a heat pump, it just wouldn't work. So for hot water the most common solution is to trickle charge a thermal battery - a hot water heater - and release it fairly quickly during a hot shower. I can see the same sort of thing happening here.