For those looking for the details, I think this is the patent: https://patents.google.com/patent/FI128161B/en
Large-scale ‘sand battery’ goes online in Finland
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Re: Large-scale ‘sand battery’ goes online in Finland
#42Why sand? - water has 5x the specific heat capacity of sand - water can be pumped around easily - water can be used directly for district heating
Presumably, because sand can be heated to above 100C. Given Newton's law of cooling, it's not entirely clear to me why you want your thermal battery to be heated to above 100C... But I'm not an engineer - I only play one on TV.
Sand (much denser = sinks in water) has low thermal conductivity, and isn't much more expensive.
Simply put, in two bodies of equal volume and 'heat capacity', the one that's hotter stores more heat.
Sand properties: [https://material-properties.org/sand-density-heat-capacity-t...]
Re: Large-scale ‘sand battery’ goes online in Finland
#43> It has a particularly strong use case in Finland which sees long and very cold winters, and was recently cut off from Russian gas supplies over a payments dispute.
Well I guess that's one way to characterize war-related sanctions and their side effects.
Re: Large-scale ‘sand battery’ goes online in Finland
#44Alberta has a neighborhood that stores heat in the summer for winter use: https://en.wikipedia.org/wiki/Drake_Landing_Solar_Community
its only ~50 homes
Re: Large-scale ‘sand battery’ goes online in Finland
#45Why sand? - water has 5x the specific heat capacity of sand - water can be pumped around easily - water can be used directly for district heating
Presumably, because sand can be heated to above 100C. Given Newton's law of cooling, it's not entirely clear to me why you want your thermal battery to be heated to above 100C... But I'm not an engineer - I only play one on TV.
Newton's law of cooling just says that your loss is going to be proportional to the temperature difference. But 1) the capacity of the battery is also proportional to the temperature difference, so the loss as a percentage of total energy stored should be roughly a constant. 2) If the application is home heating, you can't heat the home to a higher temperature than the battery itself, and you also can't easily group together the energy into a higher temperature. You would on the other hand want a high temperature for the heat to transfer quickly from the convection medium to the actual houses. So starting hot would make a lot of sense despite the downsides?
Re: Large-scale ‘sand battery’ goes online in Finland
#46As an American it completely breaks my expectations that district heating not only works can be more efficient that decentralized heating. The amount of heat lost just moving water from the water heater on one side of the house to the shower on the other is ridiculously high in houses here. The idea that you can insulate well enough to efficiently move heat across a city is amazing to me.
Volume to surface area: for every doubling of diameter you have 1/16th the losses, before factoring in insulation.
1/16th probably sounds high, but the extra halving is because flow rate increases as radius^4, not cubed as one might guess.
Re: Large-scale ‘sand battery’ goes online in Finland
#47Alberta has a neighborhood that stores heat in the summer for winter use: https://en.wikipedia.org/wiki/Drake_Landing_Solar_Community
its only ~50 homes
> Optimal community size would be 200-300 homes to realize the economies of scale. The number of systems would remain the same; only the number of boreholes would need to increase
Decentralized systems like this one are cheaper and faster to build so it makes sense that the number of households served is on the low end. That doesn't mean it's not useful tech.
Re: Large-scale ‘sand battery’ goes online in Finland
#48Earlier quoted context omitted.
As a German living in a city with mandatory district heating... the end result is to be that people seem pay more for heating than they would with a decentralised system. I think that's mostly due to the high upkeep costs of the system, though, the transmission loss is quite manageable, I think. Of course there are arguments to be made that when accounting for the cost of installing a heating system, and the space it…
> As a German living in a city with mandatory district heating... the end result is to be that people seem pay more for heating than they would with a decentralised system. So, in America, it is very common for hot water tanks to suddenly fail, leaking water everywhere and causing massive amounts of property damage and even creating health hazards through mold. In a not-insane world, all hot water tanks would come wi…
If they changed the anode rod on the water heater periodically it might last longer. Also the reality is that HVAC and water heater might need periodic inspections.
Re: Large-scale ‘sand battery’ goes online in Finland
#49No post body was provided.
Re: Large-scale ‘sand battery’ goes online in Finland
#50As an American it completely breaks my expectations that district heating not only works can be more efficient that decentralized heating. The amount of heat lost just moving water from the water heater on one side of the house to the shower on the other is ridiculously high in houses here. The idea that you can insulate well enough to efficiently move heat across a city is amazing to me.
Many American universities use district heating for the whole campus. Also, as made famous by the many steam vents in NYC movie shots: https://en.wikipedia.org/wiki/New_York_City_steam_system . More info: https://en.wikipedia.org/wiki/District_heating#United_States
As the first dorm on the loop my freshman year, I’d get back from crew practice, go into the bathroom, turn on all three showers, and flush the three toilets about three times each to flush all of the hot water out of the cold water line so that I wouldn’t burn myself when taking a shower.
I never heard if anyone got hurt when I took a day off and slept in.