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I'm kind of a novice on this, but what happens to the heated up water? I assume returning it to the bottom of the lake could have effects on local wildlife, so
by Cieric 3y ago
I'm kind of a novice on this, but what happens to the heated up water? I assume returning it to the bottom of the lake could have effects on local wildlife, so is it returned to the top? That seems like it'd have the same effect but take longer since the hot water will remain toward the top. Or is it assumed to be fine since when winter rolls around the heat will be dissipated then.
I'm mainly curious about the result to the native wildlife since practice engineering's videos on the dams and how fish are handled.
- timr 3y agoThe article says that the water is returned to the lake at about the same temperature that it leaves...though I'm unclear how that's possible.
- FredFS456 3y agoThe heated up water is consumed as drinking water. Excess water is returned to the lake.
- timr 3y agoThat makes sense, but is a bit misleading (on the part of the article) if true -- you'd have to be pretty lucky to have your water consumption needs exactly match the heat capacity of the system.
- bunabhucan 3y agoIf you presume the return pipe is much smaller, placing it inside the inlet pipe makes a counter flow heat exhanger. https://learnmech.com/types-of-heat-exchanger/ https://learnmech.com/types-of-heat-exchanger/
- timr 3y agoAnd so what do you do with the heat you've exchanged? It has to go somewhere.
- thsksbd 3y agoThe cold, dark sky of the 4K Universe. This is net cooling L. Ontario because Darlington (hence the its cooling loop) doesn't have to run as hard to power all the displaced ACs
- yetihehe 3y agoThat will just make your extracted water hot, making the whole thing a waste of energy? Return pipe is municipal wast treatment, which is probably enough to make that water essentially the same temperature as surface level waters once it returns to the lake.
- deleted 3y ago[deleted]
- TrainedMonkey 3y agoNot sure if that is the solution here, but the easy way is high volume. If you have enough water volume compared to the amount of dumped heat the temperature rise will be tiny.
- Alex3917 3y ago> The article says that the water is returned to the lake at about the same temperature that it leaves...though I'm unclear how that's possible. The most plausible explanation is that the article is wrong, and that the author meant to say that the lake is about the same temperature as it was before. Which is generally true; although the water being returned is slightly warmer, once you get more than a few meters away the difference is negligible. There is a ton of research on this phenomena with respect to the lake source cooling plant in Ithaca, because people obviously had the same concerns about that one before it was built.
- thsksbd 3y agothis system is probably locally cooling the water since the 4C water picks up relatively little heat from the city and is returned to the warmer surface layer. Although L. Ontario's surface can hardly be described as "warm"
- timr 3y agoWell, heat capacity of water is 1 calorie (4.18J) per gram. The interwebs hand-wavily say it takes about 25 BTU/hr to cool 1 square foot in a commercial HVAC system. 1 BTU is about 1kJ, so every 1 square foot of cooling (per hour) could theoretically be offset by 25,000J / 4.18J = ~5980g of water being heated 1 degree C. Density of water is 1g/mL, so it takes approximately 6L per hour per square foot if you assume that you don't raise the temperature of the water more than 1 degree C. They're talking about 50 million square feet with this system, so that's 300 million liters per hour, or about 80 million gallons per hour, or 1.3M gallons per minute. For context, the third water tunnel project in NYC was supposed to deliver 1.3B gallons per day, or about 903,000 GPM assuming constant flow. That's a big pipe. I tried to find actual citations of their flow rate, but haven't found anything yet. Regardless, I am skeptical of the claim that they aren't returning warmer water to the lake. I'm not worried about it (lake Ontario is gigantic), but I don't believe the article. (edit: 1BTU is the energy required to heat 1lb of water by 1 degree F at maximum density, so you could work it out directly from the bizarro-world units of HVAC systems.)
- _3u10 3y agoIt’s likely returned at a different depth. It would be about 120 psi at 85m.
- thsksbd 3y agoIt is. Its returned very shallow
- thsksbd 3y agoIts not that exciting, really. They're just running the pumps fast. The system has the ability to absorb: H2o_heat_capacity*mass flow rate * delta(T) = cooling_power. The first term is know and very large. The last term is determined by the number of users and is estimated with forcast usage models. Ask an Env Eng a desired delta(T) and you get the mass flow rate required.
- timr 3y agoI made another comment down the thread where I estimate this at 1.3 million gallons per minute if you want to have no more than a 1 degree C heating effect. It's a lot of flow.
- ZeroGravitas 3y ago> The water goes through Toronto’s Island filtration plant where it is treated for use as drinking water.
- michaelrpeskin 3y agoBecause water is densest at 4 degrees, the bottom of every (big enough) lake is that temperature. If they pumped warm water in at the bottom, it would rise because it’s less dense. Regardless that lake is so huge, it would have negligible impact on the overall temperature.
- pkulak 3y agoDoesn’t Toronto have far more cold days than warm? So wouldn’t the water mostly be cooled? And if that’s the case, there’s not a lot of headroom above freezing.