I'm about to retire from this very trade, so here's my 2 cents.
In my city the boilers run at 600psi.(Not near any salt water, however if we decided to use it if we could, removing all the impurities from the feed-water would be to expensive. At our psi the feed-water must be clean and deaerated to protect the boiler tubes.)
I'm a plant operator so I don't fix leaks in the field, these steam leaks are just that, small leaks that develop in the steam supply piping or the condensate return piping. (True, some lines aren't insulated properly in the maintenance boxes, so you do get some pulverized condensate.)
The steam generated from the main plant is used for all kinds of applications. Heating of course, whether live steam or heating water using a heat exchanger. Also it is used to power steam turbine chillers to create chill water, which cools a significant amount of office buildings and manufacturing plants. (These chillers use refrigerant, usually 134a, to cool down the water being pumped through them, which is then pumped to where the cooling process is needed. Sometimes these pumps are steam driven, but are usually electric motor driven. Water temp leaving the chiller is usually 38 degrees, but may be around 42 by the time it arrives to where it is used.)
My plant uses natural gas to create steam. Many electrical generating power plants still use coal or nature gas to heat treated water to create the steam to spin the turbines which spin generators to create the electricity. (Sorry, I’m not a very good writer.)
There are many other applications for steam boilers, and no matter what they are, there’s always the threat of leaks. The cleaner the system, whether steam of water, the better the chances of not corroding the piping. This is done by using chemical treatments to destroy the oxygen or rust inhibiters.
If it’s the same as NYC then the steam you see is generally from water evaporating off the outside of the pipes (not steam escaping from the pipes). The pipes are very hot, so any outside water that touches them quickly turns to steam.
That means the whole thing is incredibly wasteful. I always wondered why nobody seems to care about the huge amounts of energy being wasted in NYC in this way.
There's an invisible component which is the efficiency of the furnace used to create the heat. Suppose every building uses a small furnace which is 30% efficient, then there's no visible waste heat in the streets. On the other hand, suppose a bunch of buildings use a single furnace which is 50% efficient and pipe the heat with 10% waste from piping. You're still substantially less wasteful to use the central furnace. There's no such thing as a system that doesn't generate waste, and the visibility or invisibility of the waste doesn't tell you how wasteful the system is.
What does it mean for a heating furnace to be less than 100% efficient? Efficiency is normally measured in terms of how much waste heat you generate. If your goal is to produce heat, it isn't possible to produce any waste heat.
Releasing heat into the air is the entire point of the building furnace. For the heat to get lost, it would have to leave the building.
There's a more obvious argument that leaking steam into the streets is a waste of heat, but that still depends on your goals. You might like having warmer streets.
> Releasing heat into the air is the entire point of the building furnace
You're thinking of forced hot air systems, but these do not vent combustion exhaust into living space. There are fuel remnants and combustion byproducts in the exhaust which would smell bad, and kill people.
Combustion exhaust, and all of the heat it contains, goes up the chimney and is lost. The living space air is heated by proximity to the combustion chamber, but circulates in a separate closed loop.
Also, in a forced hot water system, there is no air circulation at all. 100% of the air involved is heated and goes straight up the chimney.
Aside: Some people call FHW systems "boilers" instead of "furnaces", but this seems to vary by region. Where I'm from, "boilers" are steam systems only -- which seems reasonable, since water is not boiled in a FHW system.
> Also, in a forced hot water system, there is no air circulation at all. 100% of the air involved is heated and goes straight up the chimney.
Without disputing your other points, this isn't right. I'm not thinking of any particular style of system. The point of every heating system is to release heat into the air. The problem people experience is that the air they occupy is too cold, and the solution is to heat that air. The point of a system that circulates hot water through your building, or your apartment, or anywhere, is that the hot water will release heat into the air there. Heating the air is the only goal regardless of whether the system involves circulating any air.
The point that you can lose heat by venting hot combustion waste to the external atmosphere is well taken.
I think we were talking about furnace efficiency. This is measured without respect to the heating distribution elements. You don't need to have a distribution system connected to measure furnace efficiency.
So when I said that 100% of the air involved in a forced hot water system is used for combustion and exhausted, I mean the air at the furnace, not the air that is indirectly heated in the living space.
Agreed that the goal is to heat the living space though, including the air. A forced hot air system does that directly (pushing heated air into living space), and forced hot water does so indirectly (pushing hot water into radiators in living space, which heat the air by convection).
Radiant floor heat is another example where there's no air at the heat source.
Furnaces are almost 100% efficient because you're literally producing heat. There's very few ways to burn fuel and not get that fuel to produce heat.
This kind of argument works for power stations, but it doesn't work for heat because it's obviously not more efficient to heat 13 miles of piping in addition to your building rather than just burning stuff in your building.
An old but common oil-fired furnace for a forced-air system will be about 70% efficient at heating air which will be delivered to the living space. This is measured at the egress point of the heating chamber, which is distinct from the combustion chamber. It is not measured at the living space, because there are other losses in distribution (uninsulated and/or leaking ductwork, etc).
The rest (almost 30%) goes up the chimney, or radiates out from the furnace itself. It's heat, thermodynamically speaking, but it is not useful heat.
(Some is also lost to light energy, and some fuel is not fully-combusted. These account for a small but measurable loss.)
In NYC the steam is from co-generation facilities which produce electricity first, so the steam is essentially waste product to begin with – in most coal plants for example you'd just have giant steam stacks to condense the water again. But yes, it's all very normalized waste.
So what's up with maintenance? The leaks seem trivial to locate and visibly waste both heat and water.
How is it more economical to have enough leaks that people start talking about it instead of doing proper maintenance? Especially since this situation seems fairly unique, I've never seen this outside the US, and could only name San Francisco and New York as places where this happens. So what discourages maintenance in those places compared to everywhere else?
Steam leaks is a big indication that you've made it as the downtown of a metropolis. I've witnessed it in Seattle, pretty sure in Chicago and not sure about Milwaukee.
Doing proper maintenance requires opening the streets, which is expensive and causes confusion and delay, so there's some amount of acceptable leak before it's a good idea to fix it. There's always a chance of finding unmapped critical infrastructure when you dig, which adds more risk. Plus, when you fix it, you lose the street cred.
I live in a town with teleheating, frankly I never saw it steem. I would say the upkeep in the US of the infrastructure is just bad.
This reminds me that in Paris you can pretty often see water flowing on the street, it seems that the Paris water supply has a tendency to leak that I just don't see in other towns (but then, i am really walking for kilometers through the city when visiting paris so maybe I just have more opportunities to spot leaks).
Paris regularly cleans its streets with the non-potable water supply of its two-stream h2o distribution system. Probably an antiquated practice back from when not everyone had sewer connections and would dump their waste pots on the road, but they still do it.
As long as a service provider can pass those costs onto customers and there is no alternative service, it can't be economical to make repairs. You'd be expending capital to decrease revenue.
But everyone is facing roughly the same forces here. You either spend money on maintenance, or you lose money in leaks. It's a tradeoff, but any place outside SF and NYC seems to determine that the best place in that tradeoff produces barely any leaks that a pedestrian would notice.
Water distribution works the same way. Large systems lose like 10% of their supply through leaks in the system but just pump more through the system to make up for the losses. Just like drug smugglers.
The energy market in California is highly regulated and the prices consumers pay are fixed by the California Public Utilities Commission (CPUC), and are designed to cover the utility's costs, plus a "reasonable" profit.
If it was an absolute free market with no barriers to entry sure. I've never lived anywhere that energy, water, or sewer was a free market.
My natural gas supplier for example (which is used primarily for heating where I live) routinely raises prices and always flouts state law. My only option would be to discontinue use of natural gas, which would cost me even more money.
I’d think there would be some sort of safety system for venting pressure. Or even condensation around the hot pipes (which seems to be why the same thing happens in New York which also has a steam network)
Other parts of the world with district heating don't leak steam. Is it just because they use (liquid) water and not steam?
The water is still plenty hot enough for steam to form in leaks, so there's perhaps some factor that makes leaks more tolerable in steam systems? Different corrosion concerns perhaps, air leaking in is less corrosive?
Steam based systems are just obsolete, steam under pressure leaks easily unless you do plenty of maintenance. Most district heating systems use liquid water in a closed loop. In fact most operators today are looking to further reduce temperatures to reduce losses and improve efficiency. You only let this much steam escape if you really dont care about saving energy/money
The issue is generally for these large historic systems, the capital cost of replacement is larger than the savings. Because the streets of New York had many utilities laid out very early, there’s poor mapping and everything underground is haphazard, and disrupting somebody else’s utility system will get them to sue you.
Well it's more a infrastructure policy issue than a technical one. Steam systems are so wasteful its hard to lose money upgrading them. As you say though, if you have different utilities under different ownership, some state owned and some not, it's more a problem of managing the upgrade as part of a long term infrastructure program if its not coordinated through a central utility provider.
That, and that even if there was a central utility, documentation was not a priority at the turn of the 20th century, and so the locations of infrastructure are either not even mapped or incorrect.
I have a fun tangential story about when steam doesn't rise.
In college I would walk past a steam stack on campus every day, because I could see it was always on the verge of making rings (pretty much any cylinder with steam or smoke passing through it or around it is, I've seen rings from incense, boiling rice [the cylinder here is the column of steam bubbles], dropping food coloring into water - if you look for them you start finding them. The craziest example I've seen, which works much like the food coloring, is an airplane contrail.). I thought if I kept it up, one day the wind would blow in just right right way and there would be a beautiful train of rings.
I never did see it. But on a hot day[1], I saw the steam settle into the narrow alley next to the building. It formed into a tiny roll cloud, about six feet long. I watch it stunned for about fifteen seconds, and then it dispersed.
[1] I'm pretty sure it was a hot day, what I remember clearly was that it was an unusual temperature. I surmise the air was very warm and so the steam was denser than the air. But it may have been a cold day and the steam cooled and then sank, unfortunately I can't say for sure because I didn't write it down.
One time walking past union square I saw smoke and flames coming out of the cable car slot. There was just a cop watching it and waving people around. Pretty sure just waiting on the repair crew. Totes normal.
Would be way more efficient if that was an power plant (electricity generation), that just made use of its waste heat. There were plenty of those in USSR, but I guess not everyone likes a power plant in the neighborhood.
Answer: Old one way heating infrastructure where the steam gets generated, distributed, used, and then the condensed hot(warm) water gets dumped into the sewer.
This can also just dump steam directly into the sewer. Get a real steam guy to repair and optimize your steam heating system!
>Critics of the system point out that the system produces heat, but also wastes nearly 250,000 gallons of water per day, according to a 2015 story by CBS Bay Area.
Google's datacenter in Hamina, Finland uses salt water for one of the cooling loops. aiui it was not trivial to incorporate the salt water loop (corrosion was an issue) but they've made it work.
Water in a datacenter cooling loop is almost certainly not heated to the same temperatures as water in a (steam) heating loop. Corrosion is temperature dependent.
And on top of that, the Google datacenter in Hamina doesn't use ocean water with 3.5% salinity, but water from the Baltic sea, which in that part of the Gulf of Finland only has roughly 0.3% salinity – a tenth of ocean water.
In my city the boilers run at 600psi.(Not near any salt water, however if we decided to use it if we could, removing all the impurities from the feed-water would be to expensive. At our psi the feed-water must be clean and deaerated to protect the boiler tubes.)
I'm a plant operator so I don't fix leaks in the field, these steam leaks are just that, small leaks that develop in the steam supply piping or the condensate return piping. (True, some lines aren't insulated properly in the maintenance boxes, so you do get some pulverized condensate.)
The steam generated from the main plant is used for all kinds of applications. Heating of course, whether live steam or heating water using a heat exchanger. Also it is used to power steam turbine chillers to create chill water, which cools a significant amount of office buildings and manufacturing plants. (These chillers use refrigerant, usually 134a, to cool down the water being pumped through them, which is then pumped to where the cooling process is needed. Sometimes these pumps are steam driven, but are usually electric motor driven. Water temp leaving the chiller is usually 38 degrees, but may be around 42 by the time it arrives to where it is used.)
My plant uses natural gas to create steam. Many electrical generating power plants still use coal or nature gas to heat treated water to create the steam to spin the turbines which spin generators to create the electricity. (Sorry, I’m not a very good writer.)
There are many other applications for steam boilers, and no matter what they are, there’s always the threat of leaks. The cleaner the system, whether steam of water, the better the chances of not corroding the piping. This is done by using chemical treatments to destroy the oxygen or rust inhibiters.