12 ms·
Harnessing heat from wastewater
- deleted 3y ago[deleted]
- the_gastropod 3y agoThat 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 3y agoSome of it is, and the picture editor could be excused for sticking with a generic "steam manhole NYC" stock image for illustration imo.
- calamari4065 3y agoMost cities in the world don't have steam infrastructure like that and still have steaming manholes in the winter from hot wastewater.
- Groxx 3y agoDoesn'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 3y agoIs 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 3y agoCapturing 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 3y agoI 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 3y agoClothes 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 3y agoIgnorance? 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 3y agoModern detergents are capable of doing these jobs in cold water.
- bee_rider 3y agoNot 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.
- deleted 3y ago[deleted]
- ak217 3y agoI'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-Water-Heat-Recovery-Unit-R4-48/203456049 https://www.homedepot.com/p/Power-Pipe-4-in-x-48-in-Drain-Wa... - but I've never seen one in the wild)
- calamari4065 3y agoThe 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 3y ago> 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/ https://www.districtenergy.com/ Minneapolis: https://cordiaenergy.com/our-networks/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 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.
- raincom 3y agoHow to deal with bad odors from sewage heat?
- crest 3y agoHeat exchangers.
- quickthrowman 3y agoHeat exchangers, the sewage and working fluid never mix with each other. https://en.m.wikipedia.org/wiki/Heat_exchanger https://en.m.wikipedia.org/wiki/Heat_exchanger
- netsharc 3y agoHeat exchanger, the same technology that doesn't spray you with coolant when you turn on the air conditioning in your car...
- pacbard 3y agoThe 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 3y agohttps://www.energy.gov/energysaver/drain-water-heat-recovery 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.
- zbrozek 3y agoHow do you actually implement this? Waste pipes are huge compared to supply pipes, and rarely take even remotely similar paths. In my home, which I'm repairing right now, I have one water heater but three different waste egresses from the house.
- shagie 3y agohttps://www.kitchenandbathclassics.com/eco-friendly/advanced-plumbing/drain-water-recovery/ https://www.kitchenandbathclassics.com/eco-friendly/advanced... > A DWHR unit consists of copper pipe tightly wound around a vertical section of copper drainpipe. As water flows down the drainpipe, it clings to the inside surface of the drainpipe. The heat from the drain water is transferred through the copper drainpipe to fresh cold water flowing in the outer copper coil. > The warmed water is then sent either to the hot water tank or other permitted end-use. In either case, the amount of energy needed to provide hot water is reduced. DWHR systems provide greater potential for energy savings as the number of simultaneous flows increases. The Home Depot version: https://www.homedepot.com/p/Power-Pipe-3-in-x-48-in-Drain-Water-Heat-Recovery-Unit-R3-48/203456041 https://www.homedepot.com/p/Power-Pipe-3-in-x-48-in-Drain-Wa... You wouldn't necessarily need this on every waste water egress. In my house, I've got one shower egress route that it would make sense on. The kitchen (I don't have a dish washer) doesn't run hot water for long enough for it to be reasonable - nor the 2nd floor bathroom with just a toilet and sink. (edit) There are spots where (in my house for example), this could be more useful. For example, that 2nd floor bathroom I've looked at a tankless water heater for the sink (so that I don't have to pull hot water from far away and then could simplify to only need to run cold water). Capturing the hot water there and returning the heat there there may make some sense... though for just a sink that would be a long ROI time.
- RicoElectrico 3y agoI 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 3y agoThere'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-significant-role-in-a-sustainable-energy-system https://www.helen.fi/en/news/2023/waste-heat-plays-a-signifi...
- CrazyStat 3y agoDynomight 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/ https://dynomight.net/hot-water/
- fbdab103 3y agoBeing 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 3y agoBut in some areas / seasons, the added humidity is a negative.
- wolpoli 3y agoAdded 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.
- hinkley 3y agoProbably not in Chicago in the winter though.
- whereistherub 3y agoWater is a necessary evil regarding buildings, in general.
- mcbishop 3y agoBut it can be managed, to mitigate mold and decay.
- onetimeuse92304 3y agoDon'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 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 3y agoIt can get much worse than that: https://eng.obozrevatel.com/section-news/news-karelia-is-freezing-due-to-shoigus-department-unexpected-data-on-problems-in-russia-12-01-2024.html https://eng.obozrevatel.com/section-news/news-karelia-is-fre...
- RadiozRadioz 3y agoExamples of the danger of "but sometimes!" https://www.youtube.com/watch?v=GiYO1TObNz8 https://www.youtube.com/watch?v=GiYO1TObNz8
- iknowstuff 3y agoIncandescent 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 3y agoYeah 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 3y agoIt'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.
- kkfx 3y agoHonestly? 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 3y agoHaha my girlfrient thought I am crazy when I asked her not to let it down for 30 minutes to extract the heat, LOL
- WalterBright 3y agoIn the winter, I'll let heated water cool to room temperature before draining it, releasing all its extra heat into the house.
- nick222226 3y agoAnd humidifying in the process
- hinkley 3y agoLate season canning I have a giant vat of hot water on the stove. I let it cool if nobody needs the space. In the fall I pour it on weeds. Heat is a great herbicide.
- wolverine876 3y agoIn some places, India for example, hot water is sometimes supplied by a smallish reservoir at the showerhead. The reservoir's normal state is full of tap-temperature water. For a hot shower, you turn on the reservoir's electric heater; it warms up (pretty quickly - think of electric kettles, and I don't want to shower in 100 deg C water) and you turn on the shower. I've always wanted something like it at home; it seems much more efficient than a central hot water heater that's always warming the water. (I've also read about at-the-spigot devices that heat water like a coffee maker, with water running past something hot.) I wonder how the heat capture of wastewater could work with it. It becomes a sort of closed loop hot water device, with heat exchanged with showering humans, the capture device, and the electrical device to top it off.
- soperj 3y agoWould work the same, since you're still supplying hot water to the sewers.
- wolverine876 3y agoI'm saying the sewer-bound water's heat could be captured and used for the reservoir.
- hinkley 3y agoI don’t know what current wisdom is, but when these were new they (eg This Old House) would suggest putting one at the master bath and maybe the common bath, then run one for the rest of the house. Effectively daisy chaining two of them for piping hot showers, but still warm enough for the washer and dishwasher. Pretty sure the deal was that none of them could really pull a couple gallons a minute at full temperature at the time.
- wolverine876 3y ago> Pretty sure the deal was that none of them could really pull a couple gallons a minute Why not just run them in parallel? If you need more flow, just hook up two or three or N in parallel, feeding the same pipe?
- papertokyo 3y agoI live in a building connected to the False Creek system. Some details that may be interesting: - Most of the apartment blocks currently served are located in a former industrial area that was redeveloped for the 2010 Winter Olympics and gradually built up since then. - All new buildings in the utility's service area are required to be connected to the system for space heating and domestic hot water. The city charges a connection fee and the building must be designed with the requisite plumbing to integrate with the system, but some space is saved by not needing a large central heating plant. - The metering and billing is done with https://www.wysemeter.com/ https://www.wysemeter.com/ (at least in my building). - The hot water is indeed very hot, and reliably so. I wouldn't be able to tell the heat source is sewage if the owner didn't mention it. - In Winter, it's easy to identify which buildings which are connected to the utility, since they don't have have large steam clouds coming out the top. City council info page: https://vancouver.ca/home-property-development/southeast-false-creek-neighbourhood-energy-utility.aspx https://vancouver.ca/home-property-development/southeast-fal...
- lemper 3y agobro, that's really cool (or hot)! why didn't smart people harness this back then?
- elmolino89 3y agoClean water flowing in the pipes to a house will often be warmer than outside air during winter and have a higher heat capacity than air used in heat pumps. No idea if using another heat pump and lowering the temperature from say 10C (ignoring any water heating in the house) to 6C of the gray water flowing out of the house makes sense.
- timthorn 3y agoThere's an installation near Cambridge that uses the heat to warm industrial greenhouses. It has a methane powered generator which runs the heat pumps and releases its exhaust CO2 into the greenhouse to promote growth. https://www.cibsejournal.com/case-studies/growing-interest-using-wastewater-to-heat-britains-giant-greenhouses/ https://www.cibsejournal.com/case-studies/growing-interest-u...