Large-scale ‘sand battery’ goes online in Finland | Hacker News Reader

Large-scale ‘sand battery’ goes online in Finland

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287 pointsbobse287 comments

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.

You're omitting a very important point: the heat sources themselves. The heat for the entire city doesn't come from a single power plant. It is distributed over many heat generation plants throughout the city, some dedicated solely to district heating. I don't think any spot on that map is more than a few km from a heat source.

To be fair, the vast majority of Helsinki's district heating system is powered by three combined heat and power (CHP) generation plants in Vuosaari, Hanasaari and Salmisaari. You're right that there is also 11 dedicated water heating plants to supplement the CHP supply in very cold weather or times of high demand, but they are supplementary.

More people live in New York than in the whole of Finland.

You can sort of tell from the other responses, but really the core of this argument is not the one you think it is: You think this means it is less appropriate for New York because of this fact. It is the opposite. Your population density is higher, so these types of solutions are easier and more cost-effective. This makes the fact that you don't already have it seem even more incompetent, which is the opposite of what you wanted to achieve.

Consider it's a nation that reinvented a crappy version of a metro with bunch of teslas in a very unsafe tunnel, I don't think you can expect reasonable answers. /sarcasm

I know it's hard to develop actual efficient solutions due to the cost of buying land, creating new infra. So you go for the cost efficient route instead of the practical efficiency.

I believe the parent was responding to “seems small” in regards to NYC’s steam heating system, which is the largest in the world.

Which only makes more sense for the New York to be heated by a network of pipes.

Portions of NYC are heated by pipes. ConEd operates the largest commercial steam system in the world.

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

>Today, Consolidated Edison operates the largest commercial steam system in the world (larger than the next nine combined).

Huh, neat.

A series of tubes, you say?

I never understood why it was so funny. For me it was good first order of approximation of how internet works.

We actually do pipe some stuff around and it flows from one place to another.

Is the series of tubes so hilariously unimaginable for Americans?

It’s not a truck.

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.

This is most unfortunate but in proper district heating systems the scalding hot district circulation water never touches your house's heating / warm water. A heat exchanger is employed to insulate the different circulation systems. For example, my house has district heating and the warm water side is capped at +65C to protect against burns.

It's still pretty damn hot of course but I've never had any problems like you described, and I've lived in a dozen different houses in my city - all with district heating. Probably the system in the dormitory was somehow badly designed or incorrectly tuned.

I’m not positive I would have been scalded if I didn’t do that, but I do know that just turning on the cold line would yield at least uncomfortably hot water.

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.

> That is not up to spec, cold water lines should always be below 25

Yikes, that's tough. In my city, the cold water pipes are buried close enough to the surface and the brutal sun that it comes out of the tap about 27-29c during the day.

same, been in two developing countries with similar heating system, never seen such a problem. sounds disturbing

It's possible there's a faulty faucet mixing valve somewhere in the building causing hot water to mix into the cold line.

The hot water from the cold tap reliably went away once the water started running which is what made me think that it was sitting still next to the hot water that caused it

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.

Sometimes this is intentional to keep paths clear. Idaho is much colder than Leipzig in winter.

You want to do that with the cooler water that is coming back to the power plant after the heat is delivered to the customer. Thus you use lower value heat to melt the streets. Assuming you do combined heat & power, as a bonus you get a small benefit on the power cycle as you get colder water into the pwrturbine cooling.

The sidewalks are actually the tops of tunnels that carry power and steam in both directions.

The historic averages don't look very different:

https://www.timeanddate.com/weather/germany/leipzig/climate

https://www.timeanddate.com/weather/usa/moscow/climate

though Moscow gets rather more snow

When the sidewalks are melted, it becomes waste heat. The rest of the year, it is waste heat. No matter how cold it is, if you accidentally leak heat it is wasteful - even if the side effect is something you may otherwise want.

Idaho summers are very hot. The district heat only runs part time. It is all waste heat from the power plant. There’s ample hydroelectric and wind power in the region as well. I’m not sure if the plant does demand shifting over the course of seasons but it could only run in winter because it runs on biomass and employs students. Many campus facilities are essentially jobs programs for students. The mission is experiential learning. I got a B.S. in business that included welding.

That sounds pretty cool

It was actually a great experience. It’s a land grant university that does a lot of really good research and has solid mechanical engineering, business, law, and architecture schools. I worked several on-campus jobs like janitor and IT support. They set me up with good internships over summers and decent mentors. I wouldn’t be where I am in life without the University of Idaho.

Great. How much energy do you spend clearing paths?

It's a fun set of optimisations: to get the path-clearing effect do you run the pipes on less optimal routes (greater capital costs), or do you using varying grades of insulation (less effective under paths to get the clearing effect, more effective on the short-cuts between paths), and so on. I hope Idaho uses these scenarios in their maths lessons, in place of the hoary "the phone company needs to put a line across a property that includes a river where it costs three times as much per metre..." that I teethed with.

Well the shortest distance between two points is a straight line. Pipe and sidewalk routing have similar objectives and constraints.

Not all sidewalks are heated. It’s more like they paved the top of the service vaults.

I don’t recall this problem specifically but the university employs a lot of students and alums.

Probably less than you lose in energy from heating the paths all year round.

As I explained they aren’t heated year round.

University of Minnesota still has it and has been upgrading it:

https://cpm.umn.edu/combined-heat-power-plant

St. Paul also: https://www.ever-greenenergy.com/project/district-energy-st-...

Texas tech in Lubbock does it. Blew my mind then and now.

Yet anytime it snows/freezes somehow the school shuts down. There is no drainage for runoff to accumulate so it just sits on the roads. Alum from 2012

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 takes, the premium paid for district heating is not that high.

But still... if district heating is so smart, why ain't it cheaper?

What's nice about it, and maybe hard to quantify, is how this limits air pollution in the city. However, people are still allowed wood burning ovens... which they are now all turning to since the district heat is getting really, really expensive..

> 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 with moisture meters (you can buy them at the hardware store, $20 maybe) that would alert when the tank started to fail. But no, instead, American's are just accustom to the idea that about every 10-15 years, they will have to fix some large amount of water damage.

The condo complex I used to live in had a huge line item for water damage very year, insurance companies charge a large deductible because they know the damage is going to happen. Recently the condo association has taken to enforcing manual inspections of hot water heaters and requires they be replaced after 10 years, due to the large number of insurance claims that were being made.

(I did suggest they just enforce the use of moisture detectors...)

Oh and in condos, the hot water tanks are supposed to be hooked up to a drain so this flooding isn't an issue. But, well, apparently most of them were not hooked up properly. :/

FWIW I've seen this same issue in multiple places I've lived, apartment complexes have issues with hot water tanks going out all the time.

So anyway, my point is, Americans are really bad at moving hot water around.

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.

Water heater failure is also easy to avoid by annual or seasonal flushing of any accumulated sediment and checking the anode. As long as the anode is replaced, the water heater should be fine.

I would expect a large condo association's maintenance staff to be able to handle this sort of thing very easily.

The ceramic lining of a water heater cracks due to thermal stress over time.

Pure stainless steel water tanks don't have this flaw, but they aren't they common.

That is what the anode is there for, to be the sacrificial corroding element.

Depends a lot on how corrosive/nasty the water is in an area though. Some are just nuts.

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.

20 years!? That's absurd.

It never makes economic sense to tear down a house if you're paying for it (above the land value). It depends on building codes in your area and such but my house is nearly 40 and it's not even close to end of life. Hell, the house I grew up in is still there and it's gotta be approaching 80.

> It never makes economic sense to tear down a house if you're paying for it (above the land value).

The land value is the key. Often, houses in the 50s-80s were built in what was suburbs or actual small villages back then, with enormous land surrounding them because land was cheap. Nowadays, the urban areas have grown and grown, and with them the desire for space for people to live on - even here in Europe, in Munich for example, land values exploded over the last 20-30 years. Think of like the land price not only doubling or tripling, but increasing tenfold or more since the houses were built.

Say you have land with a house that was worth 50.000 $ when it was constructed... and now, the land alone can be worth millions. So you tear down the existing house that's in the middle of the plot, build four new houses on it, each one bigger than the old one, and sell three of the four houses to pay for your new home and a nice chunk of cash. Or you rent the houses out for absurd amounts of money and never have to work a day in your life again.

And that happens not just with houses 50 years or older. Here in Munich, I've seen this happen with houses younger than me, simply because land values went up so immensely.

20x in Munich? That is new to me.

European houses are usually built out of bricks and concrete on proper foundations instead of wood and drywall, which means the substance lasts a lot longer itself and it becomes actually economical to do upgrades like heat insulation, PV energy and the likes. Also, we don't have regular extreme weather events like hurricanes that devastate entire countries (and thus make it uneconomical to build expensive houses).

> instead of wood and drywall

Wood doesn't get any weaker with age. Assuming no water damage, 200 year old timber houses are just as durable now as when they were built. In fact 200 year old timber houses in America are more durable than anything you can build now because the quality of wood 200 years ago, even 100 years ago, is better than what you can get now, and the quality of wood 100 years ago in America is better than anything Europe has had for multiple hundreds of years!

Also drywall is a nice material for many reasons. Need a new wall? One day of work. Want to remove a wall? If there isn't a support beam, not an issue. American houses can be reconfigured as the needs of family and society change. My 1950s house has had walls removed and added throughout its life and owners, which is why it has an up to date flow despite what was a very constricted original floor plan.

Also dry wall is easy to fix and paint.

Water is an issue, yes. That part sucks.

Finally, in regards to natural disasters, wood construction can withstand earthquakes far better than stone construction!

Water is always an issue no matter what type of construction. Concrete and masonry? Water and freeze thaw cycles will eventually destroy it.

Most common major structural work with stick built houses is jacking them up and replacing the foundation. That's because the concrete or masonry foundation has deteriorated but the wood framing is in good condition.

My anecdata doesn't align with yours. I've had a water tank fail and I've known a bunch of other people with the same experience.

> 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 fixed, either.

It's stupid simple and cheap to do this, I dunno why I've never seen any other dwelling with such a setup. My house has a number of things like this, making it cheap to maintain.

P.S. I'm an American.

The BC Building Code mandates a floor pan under the HWH, draining into the wastewater system. The floor will be sloped as well, and the drain within X distance of the heater. I expect it’s a Canadian national standard.

The plumbers are always surprised to find my setup. It's the same for the washing machine, which has also saved me from very expensive water damage.

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.

At least in California it’s mandatory that it be this way.

A good idea, but not sure it it’s code, is to do the same with the clothes washer.

Flood sensors (there are ones with auto water shutoffs too) for the clothes and dish washers are a good idea too.

This comment is wrong on many levels. Hot water heaters should last a lot longer, and when they fail it’s probably a faulty thermostat or short. Still, water heaters get a drain pan to catch leaks. Lastly, installing a leak detectors are trivial and common. Your condo may have been a bad install or not installed to code.

America moves hot water just fine.

EDIT: yes water heaters can fail. Usually due to bad install, people store stuff on the pipes or on top of the unit treating the mechanical closet like a utility storage closet for brooms vacuum ironing board stuffed in, or subjected to a freeze. Nothing wrong with the device itself, everything to do with improper install or maintenance.

> Lastly, installing a leak detectors are trivial and common.

I've told about a dozen people in my life that leak detectors were a thing, and they were all shocked at the info. From what I gather, their existence is not common knowledge.

> Still, water heaters get a drain pan to catch leaks.

Initial leaks yes, but eventually hot water heats fail in a dramatic fashion and spew water everywhere.

> Your condo may have been a bad install or not installed to code.

Literally every apartment complex I've lived in has had this same issue. The apartment complex's my friends live in, same issue. I figure that commercially ran complexes would be motivated to install leak detectors, but apparently not.

> Hot water heaters should last a lot longer, and when they fail it’s probably a faulty thermostat or short.

Should, sure. The warranty is 10 years on higher end models, and the last ($2000!) water heater I had fail on me failed at 9 years and 6 months.

I've seen older hot water heaters, sure, but the expectation is failure after 10 years. All the plumbers I've ever talked to have repeated exactly that. They also say that a large # of tankless units they have seen encounter motor failures after 10 years and also have to be replaced.

Tanks don't fail unless the anode gets depleted.

You seriously need to tell your condo association to get their maintenance people to flush the water heaters regularly (seasonally or annually) and check/change the anodes. If they're gas-fired heaters, the burner and air intakes should be getting cleaned.

If this isn't being done, it's probably because your maintenance is being done by plumbers, who have convinced everyone that "they just fail, you know?"

Replacing a tankless water heater because the motor has failed is silly. You replace the motor. And tankless heaters don't fail very often unless, again, they don't see regular maintenance. As in: flush/descale annually and water/air filter cleanings.

100 unit complex, no onsite maintenance, each owner is responsible for maintaining their own unit. All exterior entrances, so common areas are outdoors and maintained by contractors.

How does an anode help against a thermal expansion crack in the wall?

1) there should be a thermal expansion tank in the system to stop major pressure cycles. If you don’t have one, you’ll have dangerous high pressure spikes in the system.

2) anodes stop heavy corrosion in the system by sacrificing themselves.

Are you saying its not common for water heaters to fail and cause water damage? Maybe I'm an outlier, but several people have told me that this happened in their homes.

We have several hot water heater apologists in this thread. It's rather amusing.

But I think there must be a regional difference. Maybe hot water tanks fail more depending on the climate or water acidity or something...

One problem is that people never replace their sacrificial anode. Most people don't even know it exists.

They last as long as the expected tank life these days. Tanks with longer life rating use powered rods.

>They last as long as the expected tank life these days.

Kinda seems like a self-fulfilling prophecy or one could even say planned obsolescence.

It does. Unfortunately, homeowners have no interest in paying for premium units or investing in maintenance. So manufacturing precision goes into exceeding the 8-10 year warranty and little more. My hope is that the current and upcoming electric and natural gas pricing increases will lead to more awareness of heat pump water heaters, which last quite a bit longer.

Or an accurate estimate???

I don't really get how you can extract a conspiracy out of something lasting as long as the manufacturer expected it to last.

I commonly find it's blocked by the installation. My last house it was blocked by the vent stack and one of the water lines.

They leak because the sacrificial anode rod corrodes away. The difference between a 5 year warranty and 12 year warranty water heater is a few inches of metal.

There’s a cheap ($20?) add on for our water heater that adds a conductivity sensor in the drip pan, and a shutoff valve on the inlet.

There’s a slightly more expensive variant from another company that supposedly looks at flow for the whole house, and cuts water off due to slow leaks or burst pipes.

I’m shocked that the water heater cutoff valve isn’t required by code. In contrast, plumbed drain lines for water tank flushing have a much worse payoff per dollar and are required by code around here. (When I’m feeling cynical, I assume that the codes here are designed to subsidize contractors while maximally screwing over home owners.)

Edit: the plumbed lines don’t actually help with leaks; so they do nothing that a garden hose would not accomplish.

> There’s a cheap ($20?) add on for our water heater that adds a conductivity sensor in the drip pan, and a shutoff valve on the inlet.

Oh I know, they are awesome. They should come standard, and more people should know about them. It is one of those things I try to bring up in conversations at random, because holy crap the # of people I know who have had water damage from their water heating dramatically failing is too high. Heck it happened to my family twice while I was growing up.

> the plumbed lines don’t actually help with leaks; so they do nothing that a garden hose would not accomplish.

Why not? I've seen places where with a drip pan angled towards a hole connects to a pipe that drains outside.

It should work for slow leaks. Doesn't do anything if the tank bursts of course...

The drip pan is for slow leaks , not for flushing or a gusher - but most gushers start as slow leaks, and it’s easy for a drip to cause massive damage if it goes unnoticed for months.

What’s the name of this 20 dollar device?!

Just a water tank moisture detector, e.g. https://a.co/0ujkOuD

Did you manage to realize any insurance savings? Or do the BigCo's just not care if you monitor it right?

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.

I was thankful, and shocked, the one year of my life that my HVAC system didn't break down in some fashion.

Hot water heaters should have leak detectors on them. They often don't. The higher end models do. Product differentiation strikes again.

Last water heater I had, the anode was A-OK, I had it checked about a year prior to the water heater failing.

Thermal stress destroys stuff.

Anode rods are consumable. Did you personally see the rod itself during the inspection?

They also don't repair damage. A really mean thing to do would be to replace the anode on a nearly-dead water heater right before selling a house. The minute the anode finishes rusting away, the heater could let go.

I've... Never had a problem that was catastrophic in my adult life. Only real issue we've ever had was someone hit the ac unit with their car.

Curious what sort of load you put on yours to have such terrible luck.

I had one catastrophic failure and several minor ones. Now I have a tankless water heater.

Where I'm from mostly installations have a 2 inch deep drip pan which you place a water detector. It emits a very loud noise if the bottom of it gets wet

ex. https://www.homedepot.com/p/Basement-Watchdog-Battery-Operat...

This doesn't help for catastrophic failures but for leaks it should.

> one year of my life that my HVAC system didn't break down in some fashion

Something’s wrong here. I’ve only seen 1 partial failure (a refrigerant leak reduced efficiency by 5x, but the AC still worked) in the last 15 years across several houses. You’ve got an order of magnitude more failures.

Do you live on a boat? :P

Hydronic heating system[1] (hot water running under the floors) that was incompetently installed. No expansion tanks, wrong pipes used (no oxygen barrier so oxygen seeped in and rusted the cast iron pump), pressure wasn't balanced, just tons of issues.

My current house's HVAC system was also done piss poorly in places and there can be a 15 degree difference between rooms, so that's going to be 10k+ to fix. Fun times.

[1]Despite the obscene maintenance costs, the luxury is worth it. Warm floors are really nice!

Last year, one of the district heating pipes in my fairly new apartment block (7 years old) start leaking where it enters the building. Once discovered someone from the heating company came to turn off our supply, and then the next day they came to dig up the pavement outside and fix it.

On a side note, it seems like a very bad design choice to have that place be the room where all the electrical meters are. However even where there were large puddles of water over the floor it didn't cause any issues.

You kinda offer a solution by telling us about the annual inspections. There are also water alarms that go in the pan under a water heater for slow leaks.

I've also seen them placed in areas with tile floors and a drain just in case. Sounds like much of the decentralized system damage from water heaters is customer neglect.

Here in Norway we generally pay LESS when we have district heating.

Here in Poland we pay much LESS with district heating than decentralized one. If I would have to pay for decentralized heating of my flat, I'd need to use natural gas. But even before nat gas proces went to the moon, it was at least Here in Poland we pay much LESS with district heating than decentralized one 2x more expensive than district heating

Weird - natural gas was, up until last year, the cheapest of all options in Austria. My father used to pay more in base fees and taxes than the actual gas. For some people, prices now went up by x8, so it’s now the most expensive option. Many are looking into heat pumps + solar right now.

Polish district heating is mostly coal, hence the cost savings vs imported gas.

I think from what I heard the problem with district heating in Germany is quite complex and as said probably not one of energy efficiency. It very much is as I understand a problem for a non-functioning market and problems with centralised planning. Often people e.g. need to subscribe to a higher energy base amount than they need. As there is only one player in the market and consumption is mandatory, there is few incentives to drive down cost structures and scale better with demand.

I find district heating in Copenhagen to be good value, and it seems to be a good deal greeted.

https://celsiuscity.eu/district-heating-prices-highly-compet...

One reason Denmark has very affordable district heating is that it is based on "waste heat" from power plants, and "waste heat" is exempt of energy taxes (because those are paid on the primary energy sale, i.e. the electricity).

This comes with some perverse incentives in an age of renewables:

1. If the power plants use surplus electricity to provide district heating it is no longer a "waste product" and consequently taxed. Since the power plant cannot run without generating electricity, this leads to periods of negative power prices.

2. Cooling water from e.g. data centers is too cold for district heating, but it would be energy efficient to use heat pumps to extract that energy. This is not done, because the product would be subject to full energy taxes as it is not a waste product.

Wood burning ovens for heating in city area should not be allowed, that is just idiotic. The amount of deaths and health issues that is going to cause is really nasty.

Is your claim still true when air filters are installed in the chimney?

Wow, I never knew that chimney air filters existed. I guess I had assumed it would be impractical for a residential size chimney.

>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 some terrible bureaucracy coupled with some hybrid privatisation. I would be livid if my politicians allowed some company to profit off their de facto monopoly on a central heating grid.

The story of an efficient centralized system costing more than an inefficient decentralized one replays itself throughout the lives of Germans, resulting in impoverishment of the average German.

Germany is a very rich country with the poorest people in Europe. Germany has a huge amount of political and corruption problems and they are covered up well. You will be shocked by the tax rate too if you tried to earn an income. Median German households are the poorest in all of Europe. Don't just take my word for it either.

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

> What's nice about it, and maybe hard to quantify, is how this limits air pollution in the city.

It should be simple to quantify. If gas is used for heating I can't think there would be any improvement.

Local heating with a heatpump would be an improvement if the power supply mix is greener than gas only, maybe worse if the power is all coal.

So if the district heating system operates on as a "quasi business" (and AFAIK most Stadtwerke do even though they are publically owned), wouldn't it make sense to price close or at the price it would cost to use other heating. That maximizes the profit.

Yeah I'd hate having District heating. A friend had this in the past and she couldn't even regulate it. The house was way too hot for her.

It would not work for me as I usually have the house around 16 degrees C in winter. Needless to say my energy bill is very low :)

> Yeah I'd hate having District heating. A friend had this in the past and she couldn't even regulate it.

Interesting because I could regulate mine after all the radiators were replaced around 20 years ago.

And I kind of had to because the workers installing them made a mistake and I got the radiator meant for the living room, so it was grossly oversized for the space it heated.

That being said it's usually mandatory to keep them at least half-open considering that the heat is shared with other apartments.

I now live in a building from the early 90s and the knobs are all functional but I don't use them because the city pumps heat according to the weather outside.

> That being said it's usually mandatory to keep them at least half-open considering that the heat is shared with other apartments.

Yeah that was kinda the thing. She could technically close it but then the neighbours would complain.

I would hate that as most of the time I use no heating (or cooling) at all. Also, I wouldn't like to pay for it if I don't even use it.

PS: I live in a nicely mild-climated mediterranean coastal city so I can imagine "not using the heater" is not really a done thing if you live in Finland :)

That's only the case with really old apartments. I live in a fairly new apartment with district heating (7 years old) and each room has its own thermostat to control the underfloor heating.

This does not sound right. You can regulate district heating when it enters your house.

I have seen this several times in 1950s/1960s eastern bloc apartments.

I was only visiting, so I don't know if it was the original design, or if the valves have jammed.

This was standard in the Sowjet Union. If you think it’s too warm, you open the window.

In Finland, which this news article is about, typically in apartments, each radiator has a thermostat so you have very precise control. Also in houses. Further, each building has a heat exchanger.

Offices have multiple thermostats per floor.

That's not a thing here, everyone has controllable thermostats (Finland).

It really shouldn't stop from regulating temperature. It is basically two heat exchangers. One for local central heating which is then controlled by what ever thermostats you have connected and one for hot water...

Ofc, it the thermostats used are bad there might be problems.

District heating is a regional monopoly in Germany.

American here.

Most household water pipes really aren't insulated, or aren't insulated well enough. Plus, moving water under the frostline means that the ground it's moving through might be upwards of 55 degrees F.

My house came with an outdoor wood boiler (it's more a rural cabin than a house, really). It moves 180*F water from the boiler 50 feet underground into the house, where it runs through an air exchanger in the central air system and pipes it back out to be reheated.

Newer models of these things can get upwards of 98-99% burn efficiency, and ~85% heat transfer efficiency- as good as or better than you can get with standard efficiency furnaces.

My hometown has a power plant in city center. During winter it uses the entire downtown area as a heat sink. It's great. Power plant gets cooling for its hot water, city residents get cheap heating for their homes.

Best part is you don't even care about heat loss because you're trying to get rid of all that heat anyway.

This scheme has been inplace since the 60's. https://en.wikipedia.org/wiki/Ljubljana_Power_Station

District Heating is quite popular in much of the world. USA built the first such system back in 1853. https://en.wikipedia.org/wiki/District_heating

Given how much health problems are caused by coal power plants, not sure it is that great to live near one.

But if you have to have coal, it makes good sense to harvest the energy rather than wastefully pumping the steam into cooling towers.

I mean it’s already there and has been for 60 years. I’m sure its polution pales in comparison to the 200,000+ cars driving in the area daily.

Back when the coal power plant was built it was pretty normal to live near coal burning things.

Unless it has a lot of flue scrubbing, it's likely to be far, far worse than 200,000 reasonably modern cars in terms of things like fine particulate matter emissions, NOx and SOx emissions, etc. which are the real bad ones for health issues.

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)

My father works in that field. In his opinion heat pumps (with today prices and optimizations) are way overrated. The initial investment and the energy spent (it’s way more than advertised) doesn’t make sense for the average family.

i dont mind the energy spent on a day to day basis because i already have a 5.5kwh solar off grid array. i generate around 30 kwh during a good summer month and a fraction during winters but it gets offset from the grid also.

the grand scheme as i wrote above does not seem cost effective only because of the heat pump. if it were cheaper, i would definitely buy it because radiators/solar water/solar panels are low/no maintenance while heat pump does have it.

that can't be true. In Germany it is quite a trend now, but they are installed for many years. What I can read in the boards is not that discouraging. Where does this 10 year number come from?

https://www.racold.com/heat-pump-water-heaters

>Our heat pump water heater comes with a 2- years warranty and a dependable service for the inner tank.

this is like the premium heat pump contract manufacturer. good brand with a good reputation.

roughly 10 years is what the installer told me. refrigerators in india come with a 5+10 year warranty usually so this 2 year warranty is indicative.

The internet tells me that split-ac systems (basically small heat pumps) have a life expectancy of 10-20 years. That's not too bad, for example an oil-based heating system (as we have in our german basement) also only has a life expectancy of 20 years and has way less moving parts.

My oil based system is 45 years old but no part in it is the original one anymore, so with a certain maintenance cost spread over the years you keep it living indefinitely. Does the ship of Theseus concept apply also for heat pumps, or there you have to throw it away after 10 years?

Cost wise it only makes sense if you have photo-voltaic on the roof. In Germany there is more acceptance of paying more if there is a (possibly perceived) environmental benefit.

You can actually use an absorption heat pump that multiplies your solar thermal collector heat flux by 2~3 to lift outside ambient/ground source temperature to inside levels.

> But yep great insulation in the network is a requirement.

Indeed, even with "free" heat from CHP you can get an economic net loss.

Every house connected is a lot if piping, most of it unproductive — heating empty space, and losses in piping. So CHP district heating work best with large apartment buildings, and worst with single family housing.

This way Danish 65C° district heating for detached housing may be the worst example of district heating adoption.

And even if you do have only commie block style apartments, you may still end with having to add extra heat from local boilers in very cold climates. There regions in Russia where heating eats 1/3 of regional GDP.

But an overall, does district heating makes sense? Hell yes, and it must be made mandatory in the West one way, or another, along with policies to prevent counterproductive outcomes.

For USA, district heating made sense in the coal power era. Today, why burn natural gas at a central plant and then have to manage a complex steam distribution network with associated losses when you can simply distribute natural gas instead and get 98% AFUE at the point of use? Even better is a heat pump with gas backup at point of use. Triumph of technology.

Also, You dont really insulate the steam distribution pipes, you just count the loss bug as a feature “heated roads and sidewalks to melt snow!”

Lastly, district heat doest work in American low density

District heating can use cogeneration in nearby power plant, so it essentially reuses waste heat from electricity production. There are even district heatings that use heat from nearby nuclear power plant.

Also note that modern systems does not use steam distribution, but high-pressure hot water distribution.

If you burn the gas in a power plant you turn something like 40% into electricity. You can deliver something like half of the remaining Joules as heat to homes, raising the overall efficiency to 60% or so. You can then use the 40% you have as electricity to run heat pumps, which put out something like 2-5 Joules of heat per Joule of electricity. In total this gives you a lot more Joules of heat per unit of gas than just burning the gas in the homes directly.

That assumes the power plant is near the people. In many places the power plants are in another state.

District heating of course only works when the power plant is near some district where people live.

Here in Netherlands, districted heating is considered green because the centralized heat is not generated using coal or gas. Instead the heat comes from burning trash or other industrial waste heat.

Geothermal makes so much sense conceptually. It seems ridiculous to run natural gas pipelines everywhere when there is a limitless supply of heat under every house provided one drills down far enough. Hopefully the process can be simplified and costs can be reduced significantly.

> Today, why burn natural gas at a central plant and then have to manage a complex steam distribution network with associated losses when you can simply distribute natural gas instead and get 98% AFUE at the point of use?

- efficiency of gas heaters, both with tanks and without, is definitely not 98%. Only the most modern condensing boilers can achieve over 90% efficiency, and the utter majority of heating systems are old clunkers [2].

- a central plant can/has to install exhaust and condensate filtering systems, whereas decentral heaters just pipe their exhaust into the environment

- gas lines are a massive fire and explosion risk

- decentralized heaters that are based on burning anything are carbon monoxide risks - in Germany alone, it's usual to have a dozen people or more die due to CM poisoning by a defective heater [3] each year.

- a district heating system can be adapted to different fuels (anything from trash over oil to gas or geothermal energy can be used), whereas a switch of the heat source is completely out of the question in a decentralized system (which is a real big issue here in Europe at the moment, as alone in Germany half the heat is generated by gas burners [4])

- a central plant can also use energy to power electricity generators, thereby improving total efficiency

> You dont really insulate the steam distribution pipes

Of course we do. Right around the corner where I live there is a centralized heating in construction, and these pipes are heavily insulated.

[1] https://en.wikipedia.org/wiki/Condensing_boiler

[2] https://www.effizienzhaus-online.de/zwei-drittel-aller-heizu...

[3] https://www.focus.de/immobilien/wohnen/wohnen-13-tote-durch-...

[4] https://www.bmwi-energiewende.de/EWD/Redaktion/Newsletter/20...

Australian here.

The idea that anything can be insulated at all is fucking novel.

New construction has minimum standards these days, but that does nothing for the majority of older house which have single glazed window, iron roofs, and no insulation whatsoever and, if you're renting, lucky to have a heat pump.

And yeah, no insulation on the hot water piping means massive loses from water heater to tap.

As a Swede, I've never been as cold as in Australia in winter! My Australian friends can't believe -20 degrees is survivable, but the thing is that our houses have a different temperature on the inside ;)

In Hobart I once lived in a place that had radiators. I made the mistake of keeping the place comfortable and it cost me $700 of cheap hydro power in a fortnight.

Yup, we got a ways to go. Insulation is simple and cheap. All construction should friggin' max it out.

Double glazing is now not heinously expensive anymore. But still seems to have the Australia Tax.

I have a hot water recirculator installed and love it. It's even faster than on demand.

Faster hot water incentivizes hand washing. Just think about how many more people would wash their hands at the airport if they didn't have to wait 2 minutes (or forever) to get hot water.

I'm looking at going this route before I finish the basement. The master shower is the furthest point from the heater, and it takes a solid 2-3 gallons to get hot water in the morning. The math didn't make sense until I put in a heat-pump water heater. Now I average $170/year to heat my water, and the recirc should only add ~$30/year. My pipes are well insulated, but I'm in a colder climate so loosing heat into the walls just lowers my heating bill.

I installed a recirculating pump and had it on the timer. But then for some reason, I switched it to always on and it's so much nicer. Hot water is always hot.

I’ve been tempted to do that. Sometimes I wake up at odd hours when it’s not running.

I wash my hands with the cool water that initially comes out?

Cool water? What about freezing water in the winter?

I am still waiting for the freezing water to come out of the tap.

Assuming your pipes are between the tap and the water heater, and the pipes run indoors, the water temperature will be close to room temperature - nowhere near freezing.

Which was a problem in NL because the bathroom of the airbnb was not well insulated. And there wasn't a hot water option because... NL.

It is cost effective, efficient and saves on emissions. Nowadays, all major cities and towns in Sweden have district heating systems. Stockholm also has a distric cooling system, although not as developed.

More info “District heating and cooling in Sweden” https://www.sciencedirect.com/science/article/pii/S036054421...

I once visited a geothermal plant about 20km outside Reykjavik that supplies hot water for heating the city. Even in the depths of Icelandic winter, the temperature only drops 1 deg C between the plant and the city. A lot of Rockwool around the pipe IIRC.

I live on a small island in Iceland, too far across the sea to pipe Geothermal water to, so the town heats water electrically and pipes it to homes instead. It's not very efficient, and it is rather expensive. It's kind of interesting because there just aren't hot water heaters for sale here, and Icelandic homes are built with that assumption.

I'm on the far side of the island from the plant, and in winter you can absolutely tell the difference in water temperature. In summer months there's an anti-scald unit in every home that's necessary to prevent it being too hot, but in winter sometimes you end up with rather lackluster showers.

Is that because of heat losses getting to you, or because enough heat is being used to heat the houses that the overall temp is lower?

I would have to imagine heat loss in transit, as it's not a problem anywhere else other than the far side. The plant itself has a lot of waste heat and not boiling too much water is a concern.

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.

Naively, I would have guessed flow rate to increase as radius^2 (cross sectional area).

Guessing the reason for extra increased flow is some edge effect / turbulence mechanisms?

Center flow at a given pressure is also square the radius.

Well, if you want to hear from the darkside... Romania.

Badly maintained infrastructure (as an American you're probably familiar with the idea). Keeps breaking down. Not enough money invested to bring it to modern standards. Pipes are not well insulated, they break down constantly, huge leakages and losses.

Cost of heating is so high that about 20% or more of the entire Bucharest city budget (I've just checked, budget: ~$1.8 billion, subsidies: ~$450 million; Bucharest has about 2.2 million people) is spent on subsidizing heat for poor families. Heating/hot water sometimes go down for hours or even days in random districts.

In many districts district heating is mandatory because everyone who can pull out does so and that makes the system even more inefficient, which would cause the collapse of the entire system, hurting poor families even more.

How can anyone function if their heat is down for days? Bucharest isn’t in a tropical climate!

They do try to fix it and in the vast majority of cases it's a bunch of hours. If it's longer than that, people have electric heaters, some use their gas stoves... you can kind of handle that for a short while.

And it's usually quite localized, some blocks don't have it, obviously if it affects large chunks of the population priority goes up.

Well there is district steam in New York. Another thing may be density: you will lose less heat due to distance travelled for central parts of New York than for a less dense(?) European city which is itself much much denser than a typical American suburb-city

This is actually a really good business for natural gas utilities to switch to if they want to survive in the future.

They have tons of experience with pipes, they can swap gas furnaces for heat pumps and exchangers.

And it turns out that the areas that district heating works well with are really comparable to where it makes sense to pump natural gas. Yoi don't necessarily need heated pipes, just using the ambient temp in the ground is usually good, with very small bits of storage/heating.

> The idea that you can insulate well enough to efficiently move heat across a city is amazing to me.

It only works well when heating is 'free' - such as when you're using waste heat from a nuclear power plant, or from overproducing solar/wind plants.

Klamath Falls, OR uses geothermal heat for municipal hot water including warmed sidewalks! https://www.klamathfalls.city/232/Geothermal

Even just adding a little inuslation to a pipe will drop the heat loss down to a few watts/ft when dealing with a pretty large delta T. If you’re using 20k+ watts to heat a home the losses on the pipe are minimal. And I’m guessing these homes are all pretty close together. Not a mile apart.

I wonder how far out one can scale a cooling, rather than heating, system. Probably not worth it making it city-wide, but then - who knows? If it works for heating...

There are district cooling systems as well, there don't seem to be any scale problems in the engineering. It's more attractive if you have a body of cool water nearby for the heat pumps.

But the users need to have different heat exchangers than just radiators, if you just put cold water into radiators they'll start sweating precipitation and you'll get mold etc damage.

> 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.

It's factual. The gas supplies in question were not covered by sanctions, but Russia tried to unilaterally switch to being paid in roubles and were told to go batter sand (bada bum tssh).

> gas supplies in question were not covered by sanctions, but Russia tried to unilaterally switch to being paid in roubles

I don’t think this is a very honest characterization:

Russia demanded payment on their terms only after they were kicked out of SWIFT and their reserves frozen by foreign banks.

I don’t think I’d describe that change in payment terms in response to bank sanctions as “unilateral” or unrelated to sanctions.

> Russia demanded payment on their terms only after they were kicked out of SWIFT and their reserves frozen by foreign banks.

If only there was something Russia could do to stay in SWIFT and not be hit by sanctions....

Why stay in SWIFT when it's been demonstrated that they can be cut off from global supply on the whims of the US administration? That one decision did more for the death of the American empire than any other.

I don't think "whims" means what you think it does.

What do you think China and India think it means?

What do you think it means?

It was a joint decision, taken by the US administration, the EU council, the UK and Canada in response to the Russian invasion of Ukraine -- not just something the Americans came up with.

Just restate the obvious: Russia has invaded Ukraine.

Russia's invasion of Ukraine was the unilateral issue here, everything else was a response to that. But either way I'd characterise this as a 'payment dispute' because the issue was how Russia wanted to be paid, not that Finland was barred from paying them at all.

There is nothing unilateral in two imperialist powers fighting. Just like there was nothing unilateral in WW1 or WW2.

Sure, the start of World War 2 was very multilateral: Poland wanted not to get invaded, Nazi Germany and the USSR both disagreed.

The parallels with the current situation are left up to the reader.

What about https://en.wikipedia.org/wiki/Munich_Agreement

Do you really think that WW2 happened over whether Poland would be invaded? I think you are confusing cause and effect.

Same as thinking that WWI happened due to the assassination of Archduke Franz Ferdinand.

I remember in a different way.

Gas related banks were not included in first SWIFT sanctions, other banks were.

They were only after Russia pretended to be paid in rubles. Of course that demand was driven by sanctions.

If fact that gas related banks were left out of first sanctions was quite controversial, many saw that as a weak european move as europe is still unable to live without russian gas.

"only after they were kicked out of SWIFT and their reserves frozen by foreign banks."

This is a response to an invasion of another country. Maybe I'm reading your tone wrong but "only after" seems to imply this was unjustified or at the least had no reason behind it.

I think their point was less to assign blame, but whether or not it was war related.

The parent's use of "only after" doesn't sit right

It implies a forced (no choice) reaction to an unjust or unexpected cause. A more neutral tone would have just said "after"

"I ran from the police after they pulled me over for speeding"

"I ran from the police only after they pulled me over for speeding"

I think your example negates your point.

I don't read that as the speaker being forced to run, or that being pulled over was unjust.

It describes the order of operations. The fact that someone ran only after being pulled over could be very relevant.

That's fair. Maybe it's because I only qualify "after" with "only" if I'm making some point.

I agree that there is a second part, conditionally. It Implies that you would not have run if you had not been pulled over- which is true!

The same holds true for Russia. They would not have demanded payment in rubles if they had access to Swift.

The problem is that people confuse conditionality and moral justification.

I would not have run if they never pulled me over is no more of an excuse then I would never have shot him if he didn't look at me weird.

Something can be conditional and true but still a bad reason.

Gazprombank is still in SWIFT

Given reports that the Russian military may be paying soldiers through Gazprom, that probably won't last much longer.

https://www.rferl.org/a/ukraine-gazprombank-sanctions-funds-...

It’s possible to be factual and dishonest at the same time.

> war-related sanctions and their side effects.

Tick

In a similar vein, I find it quite curious/strange/amazing is that Russian gas has continued to flow through Ukraine during this war. Russia wants the cash and Ukraine does not want to shut off Europe from the gas until Europe does not want the gas to flow. I believe that Russia is still paying Ukraine gas transport fees. Realpolitik in action.

That is nature of things. The spice must flow.

Alberta has a neighborhood that stores heat in the summer for winter use:

https://en.wikipedia.org/wiki/Drake_Landing_Solar_Community

Read the Wikipedia page, might be missing something, but seems like the system works in summer and winter, but don’t see anything about summer production being used in the winter.

> The borehole thermal energy system (BTES) is located underground to store large quantities of heat collected in the summer to be used in the winter.

Basically they heat up the soil and rock beneath their park during the summer using hot water/glycol from their solar arrays, and then during the winter they pump cold water through it which soaks that heat back up.

What's amazing is that it apparently took 4 years to fully saturate the area with heat energy.

And there isn't a massive amount of heat loss with that? It's a cool idea, what surprises me is that it actually works

Yes, appears so; after looking around, found three additional documents.

(1) 10 year report on the project, which has detailed charts on the performance of the system:

https://www.dlsc.ca/reports/swc2017-0033-Mesquita.pdf

(2) More mathematical explanation of the dynamics of the system, specifically: “Because of their construction principle, BTES are not thermally insulated to the bottom and the side; only a top insulation layer reduces the losses to the environment. As the thermal conductivity of underground material is rather moderate, in a range of 1–5 W/m·K, heat losses can be kept low if the total volume is large enough to achieve a good surface-to-volume ratio. Size is important because heat losses are proportional to the storage surface while the storage capacity is proportional to the volume.“

https://www.sciencedirect.com/topics/engineering/borehole-th...

(3) What is the specification W/mK

https://forum.digikey.com/t/what-is-the-specification-w-mk/3...

London Underground originally was kept cool because of its thermal mass. Over the last 100 years, it has now turned into a giant heat store, and there is an emerging airconditioning problem. I believe its the resistive heating from the trains passing through, over time, plus the sweaty exhalation of millions of people.

TL;DR ground heat is remarkably persisting and takes years to dissipate, if deep enough. Coolth, the absence of heat, is really the same in this regard, because the heat transport through the ground is not rapid.

This is also why deep hot rocks need fracking to get thermal energy working unless its happening naturally. Rocks all around the place "down there" are hot. Very hot. A lot of ground water comes out hot. Bath (uk) for instance. its hot. So how come the rest of bath is cold and wet? Because ground heat doesn't move fast.

From Wikipedia, “When the tunnels were built the clay temperature was around 14 °C; this has now risen to 19–26 °C”

According to the same page though, the tunnels only add 4% to the heat and humans add 7% — remaining 89% comes from the trains; unless I misunderstood something.

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

From the Wikipedia page:

> The borehole thermal energy system (BTES) is located underground to store large quantities of heat collected in the summer to be used in the winter.

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.

It’s interesting. 7 million in support to supply 97% of annual heat for 52 homes isn’t that far off being reasonable for an early R&D project. An 80% price drop at modest scale, say 100 different 300 home subdivisions actually seems achievable.

I think it’s largely a question of how dependent this is on local geology.

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 :-)

HVAC engineer here. At the residential level this is already achievable with hot water storage from either solar thermal and/or heat pumps. Plus you get to use the hot water (assuming you've sized the tank correctly!)

Storing heat in rocks or sand doesn't make sense from a thermal efficiency standpoint unless the temperature is high and that isn't economically viable unless you have large volume storage - typically district or precinct level.

Article says they heat sand up to 500C, which is not very possible with water.

They have to heat to 500C, because recovering the energy is slow unless you have those high temperatures. The advantage of water is that it's easy to extract the heat energy and transmit it to where you want it.

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.

Thanks for the answer. I suppose the answer is a decent insulation on the box. It only has to last for a few hours.

Of course, some engineering would have to go into optimizing the size of the rocks and the surface area / mass for the expected use.

The other issue is ‘heat quality’ (or temperature deltas). It’s easier to recover a given amount of heat from very hot sources than from only luke warm sources, and smaller heat stores will have a very pronounced difference very quickly, resulting in control issues.

Basically, if you only have a small amount of sand, it’s harder to keep it warm for longer (more surface area for the mass, so more insulation required), and harder to deal with effectively (fan needs to blow much harder when it’s only warm, much less when it’s hot), etc.

So like, sand?

I'm not an engineer, but I've been following the various rock storage projects, like this one

https://www.stiesdal.com/storage/

for some time, and water tanks are simpler.

When you set up a water tank, you just pump water into it to get the storage medium, and when you need to extract heat, you can pump out actual storage medium and do the heat exchange directly. With a rock storage, you either need pipes in them or move air through the rocks, which requires a much beefier overall system since it's harder to extract the heat. Does that make sense?

Rusting tanks sounds like a problem with either badly engineered mismatched piping, or badly engineered tanks. Ideally, you'd have a well-engineered tank as a closed system with a heat exchange unit next to it.

By the way, I live in a town with a wide district heating system, and there's no storage at all in the individual houses here, only a small heat exchange unit. They are building a 200.000 cubic meter water storage system in the other end, though. I don't know about this particular project, but there are other projects where the water storage is large enough and insulated well enough that they actually do store cheap solar heat from the summer through the winter - and it's cheaper than using gas, even before the current price spikes.

Hot water heaters are always rusting and then leaking. Corrosion is always a problem with water and metal, along with sedimentation and the growth of slime.

With the box of rocks, yes you'll need to duct hot air in to heat them, and duct cool air in to extract the heat and blow it through the house. I don't know that this needs a beefy system, if you've got central air there is already most of the duct work in place.

Interesting idea. Something I do on cold nights when camping in the back country is to put some rocks in my fire and bury the firepit when the coals are hot and sleep on top of that. Usually keeps me warm enough to at least get 4 or 5 hours of comfortable sleep during cold nights.

Yup. When I watch "Alone" where the contestants are supposedly survival experts, I often wonder about their ineptness around fire, fireplaces, chimneys, etc. None seem to have hit on the idea of putting a rock in the fire, then wrapping it in some insulation then putting it in the sleeping bag.

Some make themselves sick from the smoke (inadequate chimney), more than one burned down their shelter.

(I have no idea how to hunt & fish, but I bet I could build an adequate shelter and fireplace.)

Well, those old storage heaters were pretty much that. And they went away for a reason

Doesn't mean the idea can't be implemented better, of course.

In fact I do think there's a lot of low-hanging fruit that remains to be explored in energy production.

The reason they went away was cheap energy 24/7. Houses stopped being built to fit in with the local environment with the advent of cheap heat and A/C.

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

Did people think it wouldn't work? Your basically describing a modern version of a Russian stove, which was invented like 700 years ago.

Don't listen to other people.

I never have :-) Sometimes to my detriment, but most of the time it works out in my favor.

The ‘sand battery’ explained: Insulate a lot of sand and heat it with an electrical element (300-500°C). When you need the energy back, pump air into it and you get hot air to power generators and heat buildings.

It's important to remember with most of these thermal batteries is that they are limited in efficiency by the laws of thermodynamics, both when putting the energy in and then again pulling it back out.

The net round trip total power loss is usually well above 50%.

I'm no thermodynamicist, so I can only take you at your word about the power loss. But still:

* Suppose you can effectively and consistently get 40% of the energy you put into this kind of battery.

* Suppose you can make enough sand batteries to cover your overall power consumption (this is a big ask, but for the sake of discussion let's assume we can achieve this).

* Suppose that you have an energy source that's non-uniform across the day. For simplicity suppose that it produces 2N MegaWatts for 12 hours and 0 MegaWatts for 12 hours, i.e. N MegaWatts on average.

* Assume that electric power consumption, not including the batteries, is uniform across day and night (It isn't; it would actually be lower when power is generated if we're talking about solar).

* suppose we want a uniform power source when considering the batteries.

------

Now, let delta be the fraction of our power output which we divert towards batteries, which are only charging during the 12 hours in which that is possible. Solving for uniformity,

  fraction not diverted to batteries = fraction recovered from batteries
  (1 - delta) = 40% \* delta
  1 = 1.4 \* delta
  delta = 1/1.4 = 5/7 ~= 0.7143
  1-delta ~= 0.285

So, you get a power source that's uniform over the entire day at 0.285 * 2N = 0.55 * N MegaWatt, i.e. over half of your average power output of the unstable source.

That's not great, but it's pretty damn good!

Thats for electrical power, if all you want to do is extract heat, you only major loss is thermal cooling over time and in the pipes. You should be able to get most of your energy back from a well-insulated system

Exactly, for just storing heat the theoretical limit is 100%. Imagine putting hot water in a insulated thermos when you have some, waiting 6 months, then pouring it in your bathtub when you do want it. Nothing is lost

From other articles, the key is that, if the energy recovery happens during cold months and the residual energy in heat form is used to feed municipal heating networks, efficiency can be up to 90%.

If someone prefers video format + founders answering questions... https://www.youtube.com/watch?v=tm7spMG0ch8

What's the round trip efficiency of something like this, and what's the rate of loss to the environment? There's been a couple of these posted in the last few days and I have no feel for these numbers.

Data from Drake's Landing in Aberta has a COP of 30 (30kw of heat per kw of electricity)? The heat stored is waste heat - otherwise lost to the atmosphere, so storing it until use is should be compared to typical heat pump COP of 2-4.

https://www.dlsc.ca/

https://en.wikipedia.org/wiki/Drake_Landing_Solar_Community

The key here is: this isn't a battery.

It's electricity powered thermal storage for municipal heating.

Which, in my opinion, is a smart idea. Why bother converting the heat back to electric to end up being used to generate heat in homes.

You could use this as a heat sink at the home attached to a high efficiency heat pump for 6:1 thermal efficiency.

We could do with municipal heating here in Tasmania

The concept seems to be similar to the "Gridscale Storage"[0] system sold by Stiesdal technologies[0], which claims a round-trip efficiency of 55-60%.

The important insight here is that per Carnot's law[1], the higher the storage temperature the higher the theoretical max efficiency for thermal storage. Stiesdal had an initial concept that stored at even higher temperatures (1000C) and used a standard power plant steam turbine for converting back to electricity. But these turn-key solutions are probably more realistic.

If you are interested in realistic renewable energy, do browse the Stiesdal pages: Henrik Stiesdal [2] was pretty much the inventor of the modern wind turbine (sold the upwind 3-blade design to Vestas, CTO at Siemens Wind Power): He seems to have a superb intuition for industrializing heavy machinery. I am keenly following his advances into electrolysis and floating offshore wind power.

[0]: https://www.stiesdal.com/storage/the-gridscale-technology-ex... [1]: https://en.wikipedia.org/wiki/Carnot_cycle#Carnot's_theorem [2]: https://en.wikipedia.org/wiki/Henrik_Stiesdal

This was the question I came to pose... This is such an exciting field but when the CORE most important variable is missing, I tend to assume the worst - in this case being that the value is atrociously low.

The RTE of turning electricity into heat (or hot water into hot sand into hot water) is pretty good, most of your problem will be environmental losses between the heating station and the end-users.

It's not going to be as good as a heat pump, but they don't work very well in very cold climates, and storing electricity (or energy that you turn back into electricity) is expensive/lossy/difficult.

The sidebar on this article claims efficiency "up to 99 percent". OK, but what is typical?

https://www.dailymail.co.uk/sciencetech/article-10982885/Wor...

For those looking for the details, I think this is the patent: https://patents.google.com/patent/FI128161B/en

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

Sand is non-corrosive and doesn't expand significantly at 500C (it takes temperatures ~3x that to get it to melt). That doesn't answer the "why" completely, but those are probably some of the factors.

Edit: the article doesn't explain how the "battery" works, but my intuition is that the sand doesn't move. It's likely merely heated and then passively heats whatever actual transportation medium is used (likely water).

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?

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...]

From your link, sand has much worse heat capacity than water at 800 J/kgK vs 4000 for water.

Water also boils at STP at 100C, which limits upper energy storage.

My guesses: - Water would either require a tremendous sized reservoir, or infrastructure capable of withstanding the pressure of superheated steam - superheated steam, and even water to an extent, has corrosive chemistry. Sand is basically inert.

Those are just guesses though. I'd love an engineer who works on this to break down the real reasons.

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"...

That's useful. It's storing low-grade heat, which is fine for home heating but not useful for electricity generation.

Curious, can this be used in reverse, to keep sand cool and use it to cool down houses?

Would bring down a lot of AC usage in tropical countries.

A major problem would he that the temperature delta for storage will be way smaller. There isn't really space for the same 500C below ambient in that direction :)

Normally they just pump sea water since that's usually below 20 C anyway.

https://en.wikipedia.org/wiki/District_cooling

From this article it seems like they are using the sand to store heat that would otherwise go to waste due to temps too low to otherwise turn it into other forms of energy.

At least that’s what it seems like. They aren’t very specific, but it explains why they aren’t using something more akin to pumped water energy storage.

How about putting a thermoelectric device in orbit- you know one of those things that generate electricity from a temperature differential- the sun facing side is hundreds of degrees above zero,the shadow side is hundreds of degrees below zero. Beam the energy to earth with a maser

It is hard to radiate heat in space and maintain the low temperature side. Also, thermoelectric materials are notoriously dense and heavy

Dupe?

https://news.ycombinator.com/item?id=31999241

I am really intrigued as to how some posts for the same (or similar) story get to the front page and others don't rate a mention.

The whole thing seems so inefficient but I am not an expert.

Can anyone here expand on this?

There are times in Europe during the summer when power is free, due to excess wind and sun power. Meanwhile winters are dark and cold. If you could keep the heat for 6 months that is very useful.

They are using waste heat that otherwise would just disappear. 50% efficient is still better than 100% not used.

They are not using waste heat but low-cost electricity. A system heated to 500C is not running on waste heat.

You can sink solar power into it in the summer and use the heat in the winter.

With intermittent power like solar and wind you probably want to be able to sink it somewhere useful.

It has 80 hours of storage - that's not enough summer/winter shifting. At most it's day/night.

If it discharges continually, it will discharge for 80 hours. 8000kWh / 100kW, capacity divided by discharge rate

This is a different number than the amount of energy lost when it is not discharging. However I would suspect that this particular unit is not designed to store heat for six months.

However there are plenty of underground systems designed for seasonal storage, and the storage capacity is relatively cheap. The problem is getting enough neighbors together to meet the minimum scale.

There are lots of websites online that explain it more like:

https://www.bbc.com/news/science-environment-61996520

are we not already running out of sand?

https://www.bbc.com/future/article/20191108-why-the-world-is...

We are running out of angular sand, not desert sand. Angular sand can be used for building materials like concrete but desert sand is smooth so doesn't work well for it. For this battery, I would expect either sand would work (but I didn't see any details in the article)

We are running out of a special kind of sand. This isn't the one.

Strange they heat the sand instead of moving it around like a pumped battery

Moving sand (an abrasive grit) around is challenging at room temperate, doing it at 1000°F (500-600°C) seems impossible. It makes far more sense not to subject things to that kind of abrasion, and just flow air or water/steam through it.

It's possible. NREL's ENDURING system does just that.

https://arpa-e.energy.gov/sites/default/files/2021-03/07%20D...

Quick stats: stores heat in sand at 1200 C, round trip power->power efficiency of 54%, LCOS of $0.05/kWh for 100 hour storage. Heat is transferred from the sand to the gas for a Brayton cycle by direct contact in a fluidized bed heat exchanger. Babcock and Wilcox is expanding this now to the pilot stage under an exclusive license.

That is a very elegant work around. {They never convey the particles while hot, only after they've given up their heat, or before they get heated and then fall into hot storage}

I'd be happy with 54% round trip efficiency, it's way better than losing renewable power by not being able to store it.

A thermal battery is useful in concert with a heat pump.

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