In the staff report SDStaff McCaff and SDStaff Manhattan replied to inquiry of steam from manhole covers in U.S.:
"Yup, here in the U.S. we’ve got the Straight Dope, steam rising from the streets, and Starsky and Hutch. All that a truly progressive civilization requires.
As for what people put down there that causes steam to rise … why, they put steam, of course. Large steam plants tended to be more efficient than small ones, and some industries have waste heat, so, where the density is high enough to support it, you may find centralized steam plants selling heating steam to their neighbors, distributing it in underground insulated pipes."
We have distribution of heat and even cold throught Helsinki here in Finland but we don’t have steam rising from manhole covers not even during the coldest months. The reason is that those pipes are so well insulated that the heat stays inside the pipes and is not wasted during the flow.
So I have a question: Why does steam rise from manhole covers in U.S.?
I expect the answer is multi-faceted. In reference to urban steam lines, a lot of those pipes are very old and leaking. Folks who control the maintenance budgets tend to think “if it ain’t broke (or isn’t a massive leak in one place,) don’t fix it.” The column says New York City steam distribution dates back to 1882, and it wouldn’t surprise me if some of the pipes are that old.
Other things run underground, too. Heated subway trains, and the breath of the millions of people they carry, produce warm air that condenses when it gets to the street level vents. Sewers under different manhole covers carry the warm, fermenting waste of a busy city, and you’ll see steam there, too.
Last time we discussed this, SDMB Denver claimed to have the oldest continuously operating district steam system in the world, including, last time they looked bits of original insulation made with hollowed-out logs. And NYC said the same kind of thing:
Steam also rises from manhole covers where waste-water is released from buildings. In my town you wouldn’t see that, because the sewer system is never vented that way, and is not run in a way that exposes sewer pipes to water infiltration, and it doesn’t get that cold anyway, but I understand that in some US cities traditionally some indigent people sleep over building outfalls in winter.
Helsinki’s district heating is a liquid loop and not a high pressure saturated steam based system.
In Seattle and other areas the older networks deliver high pressure, saturated super heated steam.
During cold times of the year *steam *rising from the ground is actually a safety feature to remove condensate from pipes and is a normal part of the operation.
The pipes are not losing energy or poorly insulated, water in in high pressure saturated steam lines can resulting in water-hammering and/or explosions.
Here is an example on just how dangerous this is.
This is part of the reason that Helsinki’s system is never above ~239F/115C and is operated as a liquid loop as it is safer. The normal operating temperature for the Seattle system is ~360F/178C.
I know the losses for Seattle Steam to Swedish Hospital which is one of their most distant high pressure customers was calculated to less than 5%. Unfortunately they just had a change of ownership and a lot of the documentation is no longer online.
I don’t know about the low pressure lines but the high pressure lines have condensate traps about every block of so here. These are in those manhole covers you will see condensation (not really steam) rising from as they are critical for avoiding condensation-induced waterhammer.
These high pressure legacy system systems do not have wood pipes or leaking pipes, in fact even abnormal thinning causes major explosions like this one from last year that took out ~33 cars in Boston.
While useful and efficient these legacy high pressure saturated district steam utilities are an artifact of another time and any new system would be a low pressure liquid system like Helsinki and several cities around the world and the US have installed in modern times.
Here in Arizona we’re doing the exact opposite of delivering steam: Delivering chilled water instead, for air conditioning services. Two of the sources are Chase Field (the Diamondbacks) and the Phoenix Convention Center both of which have a lot of capacity if there’s no game or event scheduled that day.
Clarify that Denver was originally using hollowed-out logs as insulation not as water / steam pipes.
Also, interesting to note that in America, at least some of the high-pressure steam systems were operated partly as /power/ systems. To replace building steam systems, with their inherent risks. Used to power elevators/lifts, or whatever. Chicago and Melbourne had high-pressure water systems instead, so I suspect that Chicago, like Melbourne, never had high-pressure steam distribution.
Steam-powered elevators were an American thing: Hydraulic Water was an English thing. The Eiffel tower was water-powered. I think that steam wasn’t widely used for lifts in Europe, and I’ve seen no indication that steam-powered lifts were ever used in Helsinki, but I’m ready to be educated.
It’s funny that when you make elctricity you can use the leftover heat to heat the city. And then when that system returns the heating water you can use it’s leftover heat to make cold and distribute it to the city.
Sorry, you are collateral damage related to a common but incorrect explanations that this is steam leaking or that heat was escaping. I wasn’t targeted your post and I failed to add context.
To add some clarification.
Under insulated or non-insulated pipes pose a high risk for condensation forming and condensation is not safe in high pressure steam systems.
The visible effects are water vapor and not steam as actual steam would pose a serious safety risk. While in casual use the terms may be used to describe either the implications here are important.
Subcooled condensate is a liquid below the boiling point and this is what is intentionally removed from the steam lines.
The traps used may produce visual water vapor and this water vapor may be warmer than the surrounding air but is not “steam”.
I found a video which which may better show how one form of Hammer happens and demonstrates just how violent this becomes.
I have linked to the most relevant section of the video. They are just using compressed air and water but it will show how energetic the slug is.
Vapor is another complicated topic, but I should note I am talking about situations without criminal negligence.
Emergency situations produce a vapor that looks quite different and note how it is not the typical “wafting” of condensation often seen in movies and on a normal cold wet day.
ConEdision caused this accident vs maintaining their steam system in NYC. When they were driving around looking for “vapor” they were looking for cases like figure 2from the previous link.
