Thanks for sharing this. I have a heat exchanger collection for my energy projects hobby.
I’ve considered a heat recovery on a drain but it was pretty low on the priority list. I would consider it if I was going for a zero carbon house design. And if I had extra cash or could make my own even better. Personally I would simply buy a extra solar panel and add it to my renewable energy system and insulate the heck out of my house and water heaters, etc. As I don’t buy much power but harvest sunlight I don’t pay extra for hot water. But if I did buy I might be more motivated.
Those heat exchangers are not very efficient. I like the flattened pipes and countercurrent flow on this one. I would be concerned about scale, slime, dirt reducing the heat transfer in the waste pipe. Also I don’t take lots of showers or long showers and in general use very little water. So it would not pay for itself.
We have been recommending folks simplify and produce more electricity by installing a better solar energy system with more panels. We have stopped building tracking solar panel arrays, solar thermal domestic hot water systems, and heat recovery systems because solar panels have become affordable and are reliable. We had too many problems with the other systems. However I’m considering a heat recovery ventilator on my Motorhome because I cannot figure out a way to insulate it better than I have which is still very poor. So as often is the case the answer is “it depends”. if you like to take hour long showers everyday and buy power then the drain heat recovery might be worth the investment. .
If you want a simplified solar energy system with no batteries there’s a electronic gizmo that diverts the solar energy directly to your water heater whenever it turns on rather than buying from the grid. Off course this wouldn’t work at night.
My short answer would be I think this heat recovery might be more worthwhile in high water usage situations. Generally residential is not that high. A farm kitchen that uses lots of hot water for example.
I do not think it would be bad to install. It recovers waste heat, and there is no real repercussions from it. How long it would take to pay back your initial cost might be lengthy, but recovering some heat, is still heat.
I would think buying a better water heater might be more worthwhile. My boiler that heats my home does not even have a exhaust pipe that even gets hot. Its exhaust pipe is plastic pipe. That means almost all of its heat is going into the water it is heating.
But I realize buying a new water heater is not always something a person can afford, even if it rather makes sense.
I wanted to recover the heat from waste water by letting it cool in a tank in my basement or a connected greenhouse.
Someone here(?) did some math, and convinced me of the folly.
I have since read about a bakery with a greenhouse built on its roof to take advantage of the otherwise wasted hot water.
A laundromat would have a comparable amount of otherwise wasted hot water.
That would be the problem. Waste pipe _always_ carries and builds sediment. There are ways and means but they all require regular actions, like putting enzymes down a warm drain once a day. Rarely done properly enough to stave off major expense shortly down the road.
I saw one of these in SF. It didn't look good and IIRC it was completely disconnected. I think a little math and a few times cleaning a drain will lead people look elsewhere for solutions. Leaving used hot water to pond in an area needing warmth and humidity seems likely to work far better - if one can afford the space needed and don't mind the ecosystem that will develop.
I looked at these years ago and it was then about USD500. I think it relies on the fact that water tends to flow along the walls of pipes and not in the middle of the pipe. It was only recommended for hotels and other high water use areas.
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