5 ms·

I wonder how different it would be to use an off the shelf heat exchanger, e.g. this one? https://www.ebay.co.uk/itm/263272702860 https://www.ebay.co.uk/itm/263

I wonder how different it would be to use an off the shelf heat exchanger, e.g. this one? https://www.ebay.co.uk/itm/263272702860 https://www.ebay.co.uk/itm/263272702860 You'd probably have to filter the shower water before sending it through, but beyond that I wonder how different the principle is. Maybe being easy to clean is a significant factor in drain showers.

shellfishgene 4y ago
There may also be problems with sanitation rules, only a minimum of water should sit in the pipes, and then ideally hot our cold but not luke warm.
- afandian 4y ago
  Got a link (or explanation) for that temperature stipulation?
  - shellfishgene 4y ago
    Yes, as tempestn explained this is to prevent bacterial growth, especially Legionella. Otherwise this can be a problem in areas where tapwater is not chlorinated.
  - tempestn 4y ago
    Temperature window for bacterial growth. Above about 120F harmful bacteria commonly found in water won't proliferate, but will survive. As you get hotter from there, they're killed off increasingly rapidly. Above 135 or 140 or so they don't survive long. In cold water they won't die off but also won't multiply quickly. The dangerous range is in the middle.
twic 4y ago
I think doing adequate filtration of the full waste water flow without losing most of the heat would be a challenge. And remember you're also sending soap suds down the pipe, which will pass the filter and leave deposits inside the exchanger. Also, if you're just using gravity to push the waste water through, what flow rate would you get on one of those units, and how many would you need to handle the full flow? The most persuasive waste water heat exchangers i've seen are based around the a large-diameter pipe, with conical sections connecting it to the input and output, where the waste water flows down the inner wall of the pipe in a thin layer, and the cold water flows up the outside. It's not as space-efficient as a conventional heat exchanger, but it avoids the problem of blockage. That would also be fairly easy to improvise, i think, given that you can buy copper pipe, or even buy copper foil and wrap it into a large, thin-walled cylinder.

shellfishgene 4y ago

There may also be problems with sanitation rules, only a minimum of water should sit in the pipes, and then ideally hot our cold but not luke warm.

afandian 4y ago
Got a link (or explanation) for that temperature stipulation?
- shellfishgene 4y ago
  Yes, as tempestn explained this is to prevent bacterial growth, especially Legionella. Otherwise this can be a problem in areas where tapwater is not chlorinated.
- tempestn 4y ago
  Temperature window for bacterial growth. Above about 120F harmful bacteria commonly found in water won't proliferate, but will survive. As you get hotter from there, they're killed off increasingly rapidly. Above 135 or 140 or so they don't survive long. In cold water they won't die off but also won't multiply quickly. The dangerous range is in the middle.

twic 4y ago

I think doing adequate filtration of the full waste water flow without losing most of the heat would be a challenge. And remember you're also sending soap suds down the pipe, which will pass the filter and leave deposits inside the exchanger. Also, if you're just using gravity to push the waste water through, what flow rate would you get on one of those units, and how many would you need to handle the full flow? The most persuasive waste water heat exchangers i've seen are based around the a large-diameter pipe, with conical sections connecting it to the input and output, where the waste water flows down the inner wall of the pipe in a thin layer, and the cold water flows up the outside. It's not as space-efficient as a conventional heat exchanger, but it avoids the problem of blockage. That would also be fairly easy to improvise, i think, given that you can buy copper pipe, or even buy copper foil and wrap it into a large, thin-walled cylinder.