[HN Gopher] Harnessing heat from wastewater
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Harnessing heat from wastewater
Author : cannibalXxx
Score : 67 points
Date : 2024-01-15 17:12 UTC (5 hours ago)
(HTM) web link (www.bbc.co.uk)
(TXT) w3m dump (www.bbc.co.uk)
| the_gastropod wrote:
| That photo of steam coming from the manhole cover in NY is pretty
| goofy. NY has 100s of miles of super-hot steam pipes underground.
| You'll see that same steam come up from manhole covers after a
| good rain in August. I'm pretty sure it's not from wastewater
| pipes.
| notkaiho wrote:
| Some of it is, and the picture editor could be excused for
| sticking with a generic "steam manhole NYC" stock image for
| illustration imo.
| calamari4065 wrote:
| _Most_ cities in the world don 't have steam infrastructure
| like that and still have steaming manholes in the winter from
| hot wastewater.
| Groxx wrote:
| Doesn't even have to be hot, it just has to be _hotter_ than
| the air above ground, and relatively humid (how much depends
| on the temperature difference). You can also see rivers steam
| when it gets very cold, and they 're often only a few degrees
| above freezing at that point.
| wolverine876 wrote:
| Is all the steam from hot wastewater? With all the things
| going on underground in cities, I've assumed there must be
| heat (i.e., from basic thermodynmics), and of course it needs
| a place to escape.
| elric wrote:
| Capturing heat before we flush it down the train is probably
| preferable to extracting it after, given that delta T will be
| higher. There are shower drain heat exchangers which can recover
| some of the heat in the water going down the drain.
| bee_rider wrote:
| I wonder what the breakdown is by usage. I imagine the
| combination of: dish washer, sink, and clothes washer, might
| make it appealing to collect it all at once.
| IggleSniggle wrote:
| Clothes detergents have been able to effectively clean in
| cold water for decades. The only reason people still wash
| using these detergents in hot water is ignorance. It's such a
| huge waste. Please stopping washing clothes with brand name
| detergents using hot or warm water. It costs more money, does
| more environmental damage, and doesn't even make your clothes
| marginally cleaner.
| elric wrote:
| Ignorance? I doubt it. There's a variety of reasons to wash
| at least some items in very hot water. Killing dust mites
| for people with allergies sounds like a good reason.
| Getting rid of faecal contaminants sounds like another good
| reason. It does way more than making clothes "marginally
| cleaner".
| IggleSniggle wrote:
| Modern detergents are capable of doing these jobs in cold
| water.
| bee_rider wrote:
| Not commenting to argue either way, as I have no idea
| what the truth is. But, I'm surprised that there can be
| such strong, confident, and basically contradictory
| opinions on this topic which seems to me like it ought to
| be a simple matter of fact.
| jupp0r wrote:
| My clothes will not get cleaned and still smell bad if I
| wash them in cold water with major brand detergents.
| dzhiurgis wrote:
| My dishwasher uses 1kwh of power per load, thats hardly worth
| capturing
|
| Shower tho... esp if you purchase ready made shower capsule
| that does not require external hot water supply and produces
| it's own from recycled water? That might be the one.
| jahewson wrote:
| Not much time to capture heat in a flowing drain, many small
| heat exchangers will be less efficient and more expensive than
| one large one, very hard to fit in a small space without
| utilising a compressor, plus additional plumbing - the captured
| heat pipe would have run all the way back to the water heater,
| losing heat all the way.
| elric wrote:
| A quick google suggests 50-70% efficiency on shower heat
| recovery. Sounds pretty good to me.
| ak217 wrote:
| I'm amazed at how little district heating is used in northern
| climates like Canada and the northern US. In dense areas,
| district heating using waste heat from power plants should really
| be required by urban planners, or at least it would make a huge
| carbon footprint difference if we invest in it.
|
| On an individual household scale, I've always wondered why nobody
| has come up with basic drain heat exchangers to capture most of
| the heat coming out of shower and washing machine wastewater
| before it leaves the building. (Edit: I guess they do exist -
| https://www.homedepot.com/p/Power-Pipe-4-in-x-48-in-Drain-Wa... -
| but I've never seen one in the wild)
| calamari4065 wrote:
| The problem is adding the infrastructure where it doesn't
| already exist. District heating is great when building a new
| city, but we don't do a lot of that anymore. Just imagine the
| cost of laying new pipes under an entire city. I'm sure someone
| smarter than me can do the math, but I'd suspect it'd take many
| decades to recoup the environmental and economic costs of
| installation.
| quickthrowman wrote:
| > In dense areas, district heating using waste heat from power
| plants should really be required by urban planners
|
| Power plants generally aren't located in dense areas...
|
| > I'm amazed at how little district heating is used in northern
| climates like Canada and the northern US.
|
| District heating and cooling are available in both Mpls and St
| Paul in the downtown core. This is the coldest large metro area
| in the United States.
|
| St. Paul: https://www.districtenergy.com/
|
| Minneapolis: https://cordiaenergy.com/our-networks/minneapolis/
|
| > On an individual household scale, I've always wondered why
| nobody has come up with basic drain heat exchangers to capture
| most of the heat coming out of shower and washing machine
| wastewater before it leaves the building. (Edit: I guess they
| do exist - https://www.homedepot.com/p/Power-Pipe-4-in-x-48-in-
| Drain-Wa... - but I've never seen one in the wild)
|
| $851 just for the heat exchanger, not including piping and
| labor. It will take a lot of showers and laundry to pay that
| back. I'd probably add one to a new house build but would pass
| on retrofitting one into an existing home unless I was doing a
| complete plumbing remodel. Similar to daylight harvesting LED
| lighting, it's possible you'll never see a payback on the
| equipment and labor.
| danjrslp wrote:
| I was going to mention the Minneapolis system, I work across
| the street from this plant.
| kube-system wrote:
| I was just about to post that same link. I suspect the reason
| you don't see them much is because installing one will often
| require more plumbing and more labor. Residential installations
| in the US are particularly sensitive to up-front cost, and
| tradespeople in the US tend to be conservative in choosing
| 'new' technology.
| MattGaiser wrote:
| And also exacerbate an already challenging shortage of
| trades.
| FredPret wrote:
| This would work as a sort of energy storage - you could
| overheat your water reservoir during cheap power times and then
| transfer the extra heat to the entire city the rest of the day.
| yetihehe wrote:
| You would need a lake sized insulated reservoir for that to
| work. Too much water is used already by those systems, they
| don't typically want to add another storage. Typically they
| are gigawatt scale systems burning something because just
| using electricity is too much strain on grid, unless you have
| a power plant nearby (like cogeneration, which uses waste
| heat from electricity generation from fossil fuels).
| FredPret wrote:
| Why? Just overheat the water circulating through the
| district water system when you can. People's thermostats
| will simply turn off sooner, leaving more heat in the
| water.
|
| Then later, you underheat the water, and the city's various
| thermostats turn on a bit longer.
|
| The risk is that you underheat too much, and people
| compensate by plugging in their own heaters during
| underheating. And underheating will occur during expensive
| energy periods, so this will exacerbate periodic energy
| shortages. But overall this could work to store a ton of
| energy - there's a huge volume of water in a district
| heating system's pipes.
| bombcar wrote:
| I remember reading on a plumbing blog (or YouTube or something)
| about someone who installed one of these - high end house,
| massive shower, owner who liked to take _hour long_ hot showers
| or something.
|
| In that case, it paid for itself pretty quickly.
|
| For "normal use cases" the cost savings over time just isn't
| there, when you compare the added complexity. You're better off
| saving heat with on-demand heaters or HVAC recirculators, etc.
|
| Places where it could make sense already use them (I believe
| car washes recycle water and heat in some locations).
| hooverd wrote:
| That someone just needs a sauna.
| euroderf wrote:
| So how does one keep all the showered-off gunk from clogging
| up the works ?
| tempestn wrote:
| There's nothing to clog up. The drain is a normal drain;
| the innovation is that the cold water source pipe winds
| around the drain, transferring some of the heat from the
| outgoing water to the incoming.
| blacksmith_tb wrote:
| The builders of my house (who were angling for, and got,
| PassivHaus+ certification for it), built a heat exchange for
| the drains on the second floor that warms the intake to the hot
| water heater. It works, but it's pretty limited, in practice it
| does pass some of the heat from a bath or shower or dishwasher
| run back, so that's something. Of course the timing matters,
| water drains pretty quickly, even from a bath, the there's no
| coordination to guarantee the water heater runs while that
| happens (other than the good chance that if we just pulled hot
| water out it will be running to replace it, but sometimes that
| isn't immediate).
| thinkcontext wrote:
| The DoE quoted a figure of 30% savings on showers, which is
| pretty impressive. All houses should be built so this is
| standard. It's so much more expensive to retrofit it later
| especially if the layout doesn't have the shower over the
| water heater.
| tvb12 wrote:
| $851?!
|
| Well, at second glance, it's definitely larger than it appeared
| to be in the picture. Home depot says 35 pounds, so ~$100 worth
| of copper.
| elric wrote:
| > I'm amazed at how little district heating is used in northern
| climates like Canada and the northern US.
|
| District heating is very expensive to build and difficult to
| retrofit. Doesn't seem very surprising to me. Any time a piece
| of road has to be dug up, costs skyrocket and people are
| inconvenienced for what seems to be an eternity. As far as I
| can tell, this is universally true among western nations.
| mschuster91 wrote:
| > Any time a piece of road has to be dug up, costs skyrocket
| and people are inconvenienced for what seems to be an
| eternity.
|
| Former trench digger here. The cause are usually two
| problems... first, the "underground line maps"
| ("Leitungskataster" in German) are usually not up to date
| because not everyone bothers to update them. Quite the "fun"
| if you suddenly hit a cable at 50cm when the map says you
| should be clear up to 2m!
|
| The second problem is that Western societies almost always
| choose the cheapest bidder, which means no work on weekends
| or, heaven forbid, 24/7 as that would be too expensive. That
| means everything is slow as molasses.
| Tarball10 wrote:
| Why is it cheaper to have one shift work on a road project
| that takes months, compared to three shifts working around
| the clock making the project take 1/3rd of the time? I've
| always vaguely wondered that when driving through
| construction zones that are seemingly devoid of workers
| most of the time.
|
| I assume the workers are paid hourly, so wouldn't the cost
| be the same? Are second and third shifts more costly?
| sokoloff wrote:
| Overtime is more expensive. Shift differentials (paying
| more for 2nd and 3rd shifts) makes those shifts more
| expensive. There are more workers willing to work in the
| 7A-4P window than in the 9P-5A window.
| mattmaroon wrote:
| Second and third shifts are more costly, yes. Many fewer
| people want to work them, so supply is much lower, so
| prices are higher.
|
| Also in evenings, road crews have extra safety
| precautions (there's a higher chance of running one over
| in the dark) and that's labor too.
| spaniard89277 wrote:
| I guess paying outside normal working hours it's extra
| money that adds up?
| miketery wrote:
| It's a cost thing. Prices for energy have been so cheap that
| investing in recapture capex didn't make sense. With energy
| prices going up, it does make sense.
|
| A funny anecdote (or sad?), after gas prices spiked in much of
| Europe due to the war many manufacturing facilities were
| looking to cut energy use, they found a lot of waste. Many
| places were able to reduce their gas usage by as much as ~33%
| if I recall correctly.
|
| I can't find the original source, but here's [1] one that
| claims 23% lower consumption across Germany in 2022 adjusted
| for temperature.
|
| 1 - https://www.nature.com/articles/s41560-023-01260-5
| philwelch wrote:
| [delayed]
| joeyo wrote:
| David MacKay discusses this in _Sustainable Energy Without the
| Hot Air_. He concludes that, while it 's on first glance
| appealing to want to use waste heat from power generation, heat
| pumps are strictly superior to combined heat and power except
| for in a few specialized circumstances (e.g. industrial uses
| that require high temperatures). The book is fifteen years old
| now, so I suspect the math even more strongly favors heat pumps
| than when it was published.
|
| See the section, "Heat pumps, compared with combined heat and
| power": https://www.withouthotair.com/c21/page_147.shtml
| renhanxue wrote:
| But district heating is a _distribution_ mechanism, not a
| heat generation mechanism. Cogeneration plants are one way to
| power it, but you can also use waste heat from industrial
| processes, very large scale heat pumps, or burning household
| waste. All of these are in common use in places where
| district heating is common. The public district heating
| utility in Stockholm claims to have the world 's largest heat
| pump installation, which has the capacity to extract 225 MW
| of heat from treated sewage, in the process generating both
| heat that's sent into the district heating network, cooling
| that's sent into the district cooling network, and finally a
| small amount of electric power by releasing the treated water
| into a lake via a turbine. This facility opened in 1986. The
| utility also has various other facilities, both cogeneration
| plants that burn biofuel (mostly byproducts from the lumber
| industry) or household waste, as well as other heat pumps
| that extract energy from seawater.
|
| District heating/district cooling has three advantages: you
| can change the heat source centrally without having to refit
| every single dwelling, there are economies of scale in the
| heat generation, and you can take advantage of heat _or_
| cooling that 's just in the wrong place and transport it to
| where it's needed.
| tadfisher wrote:
| Seems to me like the electric power grid is an already
| existing, efficient energy distribution mechanism.
| Converting waste heat to electricity is probably a lot
| cheaper to retrofit than adding a new distribution network
| to places that don't already have one.
| ZeroGravitas wrote:
| 5th generation district heat systems can transport water at
| roughly the same temp as the underground and use
| distributed heat pumps to bring them up to the required
| temperature at point of use. This prevents heat losses
| along the way.
|
| https://5gdhc.eu/5gdhc-in-short/
| jupp0r wrote:
| Arguably, decentralized approaches have other advantages
| when it comes to redundancy, gradual upgradability and
| expandability.
| lucumo wrote:
| > On an individual household scale, I've always wondered why
| nobody has come up with basic drain heat exchangers to capture
| most of the heat coming out of shower and washing machine
| wastewater before it leaves the building.
|
| I have had one of those installed in my home recently. A QB1-16
| from Q-Blue https://www.q-blue.nl/en/products/q-blue-
| showersave/ Supposedly it saves about 50% of the loss heat.
| Since I dislike hasty showers, I figured that would save me
| plenty.
|
| > I'm amazed at how little district heating is used in northern
| climates
|
| In my country we can pick our own electricity and gas provider,
| but for district heating you're tied to the provider for your
| area. Consequently, people with district heating get fleeced.
| When buying a house, I gave preference to the ones without
| district heating.
| wenc wrote:
| > I'm amazed at how little district heating is used in northern
| climates like Canada and the northern US.
|
| It is used on most if not all Canadian university campuses.
| Canadian university buildings are also far less sprawling
| because they're all connected to a steam generation plant.
|
| Toronto has district heating.
|
| https://www.toronto.ca/services-payments/water-environment/e...
|
| In the reverse direction, Lake Ontario is part of a cooling
| system as well.
|
| https://en.wikipedia.org/wiki/Deep_Lake_Water_Cooling_System
| chefandy wrote:
| Similarly, I know Harvard and MIT, and also parts of Boston
| have centralized steam heat systems. Harvard uses theirs
| extensively still, at least in the old buildings, but I'm not
| sure about MIT. Boston's is fed by an old commercial steam
| plant on the outskirts of Chinatown. I think it covers a
| pretty limited area though. I never lived anywhere with it.
| jstsch wrote:
| When I renovated my house, I installed such a heat exchanging
| pipe. It reduces hot water usage (=fossil gas) by about 40% and
| with my usage payed itself back in about two years. It's not a
| drop-in replacement, since you should use it only for the
| shower drain.
| raincom wrote:
| How to deal with bad odors from sewage heat?
| crest wrote:
| Heat exchangers.
| quickthrowman wrote:
| Heat exchangers, the sewage and working fluid never mix with
| each other.
|
| https://en.m.wikipedia.org/wiki/Heat_exchanger
| netsharc wrote:
| Heat exchanger, the same technology that doesn't spray you with
| coolant when you turn on the air conditioning in your car...
| pacbard wrote:
| The idea is to coil the sewage pipe with the cold water pipe
| before it goes into the water heater. That way the cold water
| will pick up some of the excess heat from the sewage pipe from
| the shower and it will cost less to heat overall.
| shagie wrote:
| https://www.energy.gov/energysaver/drain-water-heat-recovery
|
| > Drain-water heat recovery technology works well with all types
| of water heaters, especially with demand and solar water heaters.
| Drain-water heat exchangers can recover heat from the hot water
| used in showers, bathtubs, sinks, dishwashers, and clothes
| washers. They generally have the ability to store recovered heat
| for later use. You'll need a unit with storage capacity for use
| with a dishwasher or clothes washer. Without storage capacity,
| you'll only have useful energy during the simultaneous flow of
| cold water and heated drain water, like showering.
|
| > ...
|
| > Purchase prices for drain-water heat recovery systems range
| from $300 to $500. You'll need a qualified plumbing and heating
| contractor to install the system. Installation will usually be
| less expensive in new home construction. Paybacks range from 2.5
| to 7 years, depending on how often the system is used, and the
| temperature of the incoming water, which is dependent on ground
| temperatures.
| RicoElectrico wrote:
| I thought about the exact same thing, inspired by my admittedly
| too long showers. Although I pondered whether too cold sewage
| could lead to more blockages.
| mdf wrote:
| There's a nice heat pump in Helsinki, Finland, as well, producing
| district heating from waste water.[1]
|
| [1] https://www.helen.fi/en/news/2023/waste-heat-plays-a-
| signifi...
| CrazyStat wrote:
| Dynomight suggested [1] recovering the heat from hot showers by
| showering with the drain stopped and letting the water cool to
| room temperature before draining it.
|
| I remember thinking it was interesting at the time, but I have
| not tried it (my shower has a low lip so it couldn't hold very
| much water).
|
| [1] https://dynomight.net/hot-water/
| fbdab103 wrote:
| Being a cheapskate, I did this when I lived in Chicago winters.
| My concern was sometimes I would forget to drain the water. I
| was creating a big thermal mass which my heater would have to
| work to maintain at equilibrium.
|
| This also has the benefit of potentially raising the indoor
| humidity, which is otherwise going to be quite dry.
| mcbishop wrote:
| But in some areas / seasons, the added humidity is a
| negative.
| wolpoli wrote:
| Added humidity is definitely a concern. Perhaps we could
| fix that by covering the water with plastic to prevent
| evaporation, but I never look into it.
| krisoft wrote:
| > My concern was sometimes I would forget to drain the water.
| I was creating a big thermal mass which my heater would have
| to work to maintain at equilibrium.
|
| Is that a bad thing? I honestly ask. I'm twisting and turning
| the idea in my head and can argue in both direction.
|
| I guess it can be a bad thing if you live by letting the
| interior go to cold frequently and then try to heat it back
| to room temp. For example if you would turn off the heating
| for the day, and then try to heat it back up from near
| freezing to room temp. That would be bad in itself, and the
| the extra mass would make it worse.
|
| But if it is just maintained near the room temperature point
| then it is not that clear to me if it is bad. Would be happy
| to hear either way.
| onetimeuse92304 wrote:
| Don't forget, the heat is also keeping the pipes unclogged. If
| you remove the heat a lot of the fats turn into hard mass that is
| extremely difficult to get rid of.
|
| This is what happens when sewage is given time to cool:
| https://www.youtube.com/watch?v=3i_axpk0a7Q
|
| Reminds me of the story of what happened when traffic lights got
| "upgraded" to LED to save on energy. First winter all traffic
| lights got completely covered in snow and traffic ground to a
| halt. The "waste" heat as was not such a complete waste after
| all, it was continuously melting snow off the lights.
| dvfjsdhgfv wrote:
| It can get much worse than that:
|
| https://eng.obozrevatel.com/section-news/news-karelia-is-fre...
| RadiozRadioz wrote:
| Examples of the danger of "but sometimes!"
| https://www.youtube.com/watch?v=GiYO1TObNz8
| iknowstuff wrote:
| Incandescent lights still waste heat 90% of the time when
| there's no snow. Adding some resistive heating to run when
| needed on LED lights is much preferable.
| chongli wrote:
| Yeah really. It's not a story about waste heat at all, it's a
| story about revision 1.0 not being tested in all weather
| conditions.
| akira2501 wrote:
| It's a story about carefully examining the differences when
| changing technologies and avoiding imprecise or dual use
| terms like "waste." This is something that should come
| naturally to a hackers forum, but a bit of marketing does
| get mixed in here from time to time, and people can't seem
| to help themselves from embellishing interesting new
| technologies into universally improved solutions.
|
| So.. you get this back and forth between the two camps as
| they rush to take victory laps around each other.
| schneems wrote:
| > avoiding imprecise or dual use terms like "waste."
|
| Reminds me of the Texas power grid failure due to being
| an energy market designed by ENRON (still is too!). Turns
| out the opposite of "efficiency" isn't "waste" it's
| "redundancy" which their design is very efficient at
| getting rid of.
| snewman wrote:
| Well, moving away from "efficiency" can take you toward
| redundancy, but it doesn't have to. Some waste is just
| wasteful. It's important not to oversimplify, otherwise
| you wind up with counterproductive memes like "that
| project is justified because it will create jobs" or "the
| free market is the best solution for every problem" (it's
| a great solution for _some_ problems, but ignores
| externalities).
| throwbadubadu wrote:
| > This is what happens when sewage is given time to cool:
| https://www.youtube.com/watch?v=3i_axpk0a7Q
|
| First thought when scrolling quickly to the fatberg: How can
| those guys operate there without any "smell protection", could
| never do.
|
| Next scene: See the guy repeatedly choking and puking.
|
| Thanks, now need to get rid of pictures in head (:
| grecy wrote:
| Not just fat either. The cold snap has me dealing with frozen
| pipes in our house right now...
| schneems wrote:
| > Tucked under a Vancouver bridge, an energy centre sits on top
| of the existing sewage pumping station so heat can be captured
| before sewage reaches the treatment plant
|
| Seems like if they're doing this right before a treatment plant
| that they'll be able to localize the problem and hopefully
| handle it effectively. Though it would be more assuring if they
| also talked about some of possible problems.
| kkfx wrote:
| Honestly? It's simply not worth the effort. Yes, we can put a
| grey water reservoir who receive water from washing machines,
| dishwasher, showers, sinks and so on, with a simple three way
| thermostatic valve who divert just hot water to the reservoir and
| than a heat pump suck heat for it to push in a room, but the
| quantity of heat we can recover is simply too little except maybe
| for some industrial activity that produce hot water as a result
| of some process (like an industrial laundry).
|
| It's simply too costly creating such system than the energy we
| can recover.
| szundi wrote:
| Haha my girlfrient thought I am crazy when I asked her not to let
| it down for 30 minutes to extract the heat, LOL
| WalterBright wrote:
| In the winter, I'll let heated water cool to room temperature
| before draining it, releasing all its extra heat into the house.
| nick222226 wrote:
| And humidifying in the process
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