Large-scale ‘sand battery’ goes online in Finland • Hacker News Board

Re: Large-scale ‘sand battery’ goes online in Finland

#161

Post by arka2147483647 » Thu, Jul 07, 2022, 6:32 AM UTC

gamegoblin wrote: post #14

pavon wrote: post #8

As 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

From finnish point of view, those seem small.

In finnish, the term is ”kaukolämpö”, literally ”far heat”.

You dont heat a ”district”, you heat the entire city. I mean, electricity wires go everywhere, why not heating pipes.

And so the network for Helsinki looks like this: https://twitter.com/energiahelen/status/1511998227008176129?...

The red lines is the heat pipe network, it covers the entire city.

When Americans talk about ”district heating” they miss the scope of the thing.

Re: Large-scale ‘sand battery’ goes online in Finland

#162

Post by fulafel » Thu, Jul 07, 2022, 6:40 AM UTC

aaaaaaaaaaab wrote: post #17

Why sand? - water has 5x the specific heat capacity of sand - water can be pumped around easily - water can be used directly for district heating

It seems to be about buffering heat energy for district heating in a CHP (combined heat and power) generation station, in presence of fast electricty market swings (think wind power). So would allow the CHP plant to ramp up generation quickly to supply electricity at a high hourly price, while buffering the produced heat peak to be more slowly drained to the district heating network.

Against this background it seems relatively cheap to build for the small size of plant in the picture, vs water tanks, and less risky (water entering the DH network has to be >100 C which means pressurization which in a big tank means a risk of a big boom).

It's true that water is pretty great for this also due to high heat capacity and that's why most existing heat batteries in cities are using water, that's why this is "novel" and "patented"...

Re: Large-scale ‘sand battery’ goes online in Finland

#163

Post by pastage » Thu, Jul 07, 2022, 6:42 AM UTC

dwighttk wrote: post #105

jefftk wrote: post #103

Earlier quoted context omitted.

Why was the cold water line hot?

It was next to the hot water line and not insulated (enough) and it had pretty much just been sitting there all night.

Lucky you didn't get legionella. That is not up to spec, cold water lines should always be below 25°c. I have never seen such an installation, even in development countries it was done correctly.

Re: Large-scale ‘sand battery’ goes online in Finland

#164

Post by cinntaile » Thu, Jul 07, 2022, 6:47 AM UTC

kgeist wrote: post #136

konschubert wrote: post #15

Earlier 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. True, my sister's family lives in a house with centralized heating and they pay 3-4 times more (!) per month compared to our home which simply uses an on-demand heater.

That sounds like way too much. Individual metering can't explain such a huge difference but I do wonder if they use that?

Re: Large-scale ‘sand battery’ goes online in Finland

#165

Post by thombat » Thu, Jul 07, 2022, 6:50 AM UTC

mulmen wrote: post #92

gamegoblin wrote: post #14

Earlier quoted context omitted.

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

The University of Idaho uses district heat. The pipes run under the sidewalks so the waste heat keeps the sidewalks clear in winter.

By German standards that's still poor insulation. In winter in Leipzig the district heating pipes have snow sitting on them.

Re: Large-scale ‘sand battery’ goes online in Finland

#166

Post by GistNoesis » Thu, Jul 07, 2022, 6:51 AM UTC

UkrainianJew wrote: post #142

WalterBright wrote: post #113

Earlier quoted context omitted.

How can it not be efficient? The heat to heat a rock is 100% recovered when the rock cools back down. A tank of water works, too, but tanks rust, mildew, and leak.

Heat keeps leaking out. The amount of stored heat is proportional to the cube of the linear size, the leak rate is proportional to the surface area (square of the linear size). Hence, the bigger the storage, the higher the efficiency. Same why a flea can jump >10x its height, and a human cannot (square growth of strength, cubic growth of weight).

I'm not sure if the leak is really proportional to the surface area. (It's probably even less due to how the heat equation works).

The equation for the thermal resistance of a cylindrical system is explained in https://youtu.be/6x-jdCGWuHI?t=801

The thermal resistance is the sum of 3 (or more) terms, and while the outer terms are indeed proportional to surface area, I'm not sure if the physical constants of the system aren't designed so that the middle heat conductive terms of resistance R=ln(r2/r1)/(2pikL) is the dominant factor.

Re: Large-scale ‘sand battery’ goes online in Finland

#167

Post by Fatnino » Thu, Jul 07, 2022, 6:55 AM UTC

osigurdson wrote: post #127

1123581321 wrote: post #97

Earlier quoted context omitted.

Disagree with all of this. Hot water leaks are very rare. Water heater failure usually manifests as cold showers and a quick replacement unit from a plumber. Drain pan with a hose is a more reliable protection than a sensor. Sensors are much more likely to give annoying false positives than to prevent damage; you can see from Rheem discussion forums that they’re not appreciated.

I think the real problem is how susceptible houses in US/Canada (maybe elsewhere) are to water leaks of any sort. Drywall, wood, MDF, insulation, etc., are all immediately destroyed with water in a short amount of time. A typical house lasts for 100 years or more and will likely experience many water leaks of various kinds over the course of its lifetime.

Houses last 100 years? They can, but typically after 20 years it starts to make economic sense to scoop the remains of the house into a dump truck and build a fancier house on the now much more expensive land under it.

In my neighborhood (admittedly, originally built in the 50s) every single sale I can remember from the last 15 years has resulted it a complete teardown and rebuild bigger. And one of those rebuilds recently changed hands and is undergoing extensive remodeling for over a year now.

Re: Large-scale ‘sand battery’ goes online in Finland

#168

Post by treerock » Thu, Jul 07, 2022, 6:58 AM UTC

WalterBright wrote: post #93

I've proposed several times on HN a "box of rocks" at the house level to store heat/cold when electricity is cheap, and release heat/cold when electricity is expensive. It was ridiculed every time. I should have patented it :-)

Maybe at a smaller scale, but that sounds like a storage heater I had in an old flat.

https://en.m.wikipedia.org/wiki/Storage_heater

Re: Large-scale ‘sand battery’ goes online in Finland

#169

Post by Fatnino » Thu, Jul 07, 2022, 7:00 AM UTC

WalterBright wrote: post #95

com2kid wrote: post #40

Earlier 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. 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…

> 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. I've had them fail and leak many times. But I had the water heater put in the basement next to a floor drain, and the floor slopes slightly towards the drain. No damage whatsoever from leaks, and it wasn't an emergency to get it fi…

When my parents got their house one of the requirements my mom had was to move the water heater out of the hall closet and into a lean-to outside the kitchen door.

When I was a baby we lived in my aunt's basement for a few months and the water heater flooded the basement and my mom swore she would never live in the same house as one of those again.

Re: Large-scale ‘sand battery’ goes online in Finland

#170

Post by 2Gkashmiri » Thu, Jul 07, 2022, 7:02 AM UTC

fulafel wrote: post #159

pavon wrote: post #8

As 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.

Traditionally when using combustion plants the great advantage in nordic countries comes from CHP (combined heat and power), you can extract much more energy from the fuel this way vs having separate electricity and heat plants. But yep great insulation in the network is a requirement.

i have been thinking about getting a solar water heater>heat pump>radiator to warm up my home but the costs just dont make sense because of the heat pump. i am told the life expectancy of a good heatpump is like 10 years, that amount divided by only 10 winters it is expected to see is more than what we currently pay for electricity in winters, accepting that we don't currently have whole house heating, (we rely on personal hot water bottles/electric blankets in bed)