9 ms·

What I stumbled upon recently is heat recovery for showers (e.g. https://www.meanderhr.com/en/2012/meander-at-vvs-dagene-showing-plumbers-and-energy-consultants

by fho 4y ago

What I stumbled upon recently is heat recovery for showers (e.g. https://www.meanderhr.com/en/2012/meander-at-vvs-dagene-showing-plumbers-and-energy-consultants-shower-heat-recovery/ https://www.meanderhr.com/en/2012/meander-at-vvs-dagene-show...). Seems like a no-brainer once you think about it ... in the worst case of a flow heater you bring up the water to temperature, let it flow over your body and dump it with most of the heat you put into it. Systems like the one liked above improve on that by recovering some of the energy. I don't know what the "official" way of installing this system is, but I would just put it in the cold water path and have a thermostat controlled faucet to "switch" to the now-warmer-water gradually.

joezydeco 4y ago
I looked into these things a long time ago and part of the problem is that the drains will build up a layer of biofilm (bacteria, soap scum, other waste) on the interior, making the heat exchanger lose efficiency over time.
- danw1979 4y ago
  Could a regular dose of caustic soda not flush that out pretty easily ?
stinos 4y ago
Do you even need a switch? In a normal cosed system (so no additional storage etc, but even then it's usually closed I think), cold water is fetched by the boiler to replenish the hot water which goes out when you're taking a shower. Small amount of time later the drain gets warmer, so it starts heating the copper tubes, through which the incoming water is flowing hence that gets warmer. And hence less work to do by the boiler.
- Arelius 4y ago
  I think it depends on the details of the install, if you can install it directly in line of the cold line input and the boiler, I think that works fine. But I think instead often the heat recovery is installed somewhere in-line after the boiler, to make piping easier, but it makes heat management obviously more complicated.
someweirdperson 4y ago
A mixture of hairs and fat going through a heat exchanger doesn't sound like low maintenance. Luke warm water remaining in the exchanger after a shower feels like a great way to cultivate bacteria, though on frequent use that's probably no issue. Tapping the waste water as heat source for a heat pump seems like a better idea.
- Schroedingersat 4y ago
  If the heat is already higher temperature than the target environment, then a heat pump is just a fancy resistor. Plus this doesn't obviate the need for a heat exchanger. Better to just have a filter on the drain similar to a dishwasher.
  - benj111 4y ago
    Is it a fancy resistor? If you have a cop above 1, you're extracting more energy than could be got just using straight heat exchanger. I don't see why that would break just because you go above an arbitrary temperature (arbitrary because the output temp of the heat pump isn't the ambient temperature of the room) Or am I missing something?
    - Schroedingersat 4y ago
      The heat is conserved. If the waste water is hotter than the incoming water it will conduct on its own (and if they're arranged in back flow the equilibrium will be pretty close). Hurrying it up with a heat pump only makes it happen faster and adds the energy you put into the heat pump. You could cool the waste below ambient, but that's no different to cooling anything else outside. For simplicity, if your hot water system was already a heat pump, you could run it past/into the cold side. No real efficiency gain vs exchanging it with the cold water (actually a loss in theory) but might be cheaper.
      - benj111 4y ago
        Ok I've worked it out myself. I was inventing a magic free energy machine. I was thinking a cop of 4 would be able to extract 4 units of energy to the heat exchangers 1. But there's only 1 unit of energy in it to extract, which the heat exchanger is already extracting basically for free.
stavros 4y ago
I'm always amazed at how people in the US/Canada shower, with the water running constantly. It not only seems like a waste of hot water, but how do you even soap yourself up when the water is just washing everything away immediately? Where I'm from, we take Navy showers[1], where you only use water to rinse things off. Basically: 1. Run water on you so you get wet everywhere, turn the faucet off. 2. Apply body wash and shampoo. 3. Turn the faucet on and rinse everything. 4. Done. The actual water-using portion of this is less than a minute. [1] https://en.wikipedia.org/wiki/Navy_shower https://en.wikipedia.org/wiki/Navy_shower
- benj111 4y ago
  The UK shower like that too. Gas boilers with long pipes means you need to wait for the hot water to come through, and if you stop it again you then have a load of cold water just waiting to take you by surprise.
  - stavros 4y ago
    It only takes you by surprise once in your life, after that you just run the water away from you for a second while the warm water comes in. Since we have handheld shower heads (another thing I can't believe the US lacks), it's no problem at all.
    - benj111 4y ago
      Yes but if you're waiting 20 seconds for the hot water everytime it makes it not worth it to switch the shower on and off.
      - lotsofpulp 4y ago
        The water in the hot water pipe will not have gone cold during the short time it takes to clean one’s self.
        benj111 4y ago
iso1631 4y ago
Seems like it costs in the order of £500 to install from a quick search. Wouldn't that money return more via a solar system, or better insulation?
- fho 4y ago
  I guess 500 moneys is nothing compared to what renovating a bath costs.
fy20 4y ago
In vanlife some people have built recirculating showers that use just a few gallons of water running in a loop. They run it through particle and UV filters which supposedly clean the bad stuff out, but I haven't seen any scientific studies done on how effective that is. I imagine it is no worse than a bath, other than you are potentially putting bacteria into the air and hence your lungs. The idea sounds interesting though, as showers (even low flow) use a lot of water and heat, which typically just goes down the drain.

by fho 4y ago

joezydeco 4y ago

I looked into these things a long time ago and part of the problem is that the drains will build up a layer of biofilm (bacteria, soap scum, other waste) on the interior, making the heat exchanger lose efficiency over time.

danw1979 4y ago
Could a regular dose of caustic soda not flush that out pretty easily ?

stinos 4y ago

Do you even need a switch? In a normal cosed system (so no additional storage etc, but even then it's usually closed I think), cold water is fetched by the boiler to replenish the hot water which goes out when you're taking a shower. Small amount of time later the drain gets warmer, so it starts heating the copper tubes, through which the incoming water is flowing hence that gets warmer. And hence less work to do by the boiler.

Arelius 4y ago
I think it depends on the details of the install, if you can install it directly in line of the cold line input and the boiler, I think that works fine. But I think instead often the heat recovery is installed somewhere in-line after the boiler, to make piping easier, but it makes heat management obviously more complicated.

someweirdperson 4y ago

A mixture of hairs and fat going through a heat exchanger doesn't sound like low maintenance. Luke warm water remaining in the exchanger after a shower feels like a great way to cultivate bacteria, though on frequent use that's probably no issue. Tapping the waste water as heat source for a heat pump seems like a better idea.

Schroedingersat 4y ago
If the heat is already higher temperature than the target environment, then a heat pump is just a fancy resistor. Plus this doesn't obviate the need for a heat exchanger. Better to just have a filter on the drain similar to a dishwasher.
- benj111 4y ago
  Is it a fancy resistor? If you have a cop above 1, you're extracting more energy than could be got just using straight heat exchanger. I don't see why that would break just because you go above an arbitrary temperature (arbitrary because the output temp of the heat pump isn't the ambient temperature of the room) Or am I missing something?
  - Schroedingersat 4y ago
    The heat is conserved. If the waste water is hotter than the incoming water it will conduct on its own (and if they're arranged in back flow the equilibrium will be pretty close). Hurrying it up with a heat pump only makes it happen faster and adds the energy you put into the heat pump. You could cool the waste below ambient, but that's no different to cooling anything else outside. For simplicity, if your hot water system was already a heat pump, you could run it past/into the cold side. No real efficiency gain vs exchanging it with the cold water (actually a loss in theory) but might be cheaper.
    - benj111 4y ago
      Ok I've worked it out myself. I was inventing a magic free energy machine. I was thinking a cop of 4 would be able to extract 4 units of energy to the heat exchangers 1. But there's only 1 unit of energy in it to extract, which the heat exchanger is already extracting basically for free.

stavros 4y ago

I'm always amazed at how people in the US/Canada shower, with the water running constantly. It not only seems like a waste of hot water, but how do you even soap yourself up when the water is just washing everything away immediately? Where I'm from, we take Navy showers[1], where you only use water to rinse things off. Basically: 1. Run water on you so you get wet everywhere, turn the faucet off. 2. Apply body wash and shampoo. 3. Turn the faucet on and rinse everything. 4. Done. The actual water-using portion of this is less than a minute. [1] https://en.wikipedia.org/wiki/Navy_shower https://en.wikipedia.org/wiki/Navy_shower

benj111 4y ago
The UK shower like that too. Gas boilers with long pipes means you need to wait for the hot water to come through, and if you stop it again you then have a load of cold water just waiting to take you by surprise.
- stavros 4y ago
  It only takes you by surprise once in your life, after that you just run the water away from you for a second while the warm water comes in. Since we have handheld shower heads (another thing I can't believe the US lacks), it's no problem at all.
  - benj111 4y ago
    Yes but if you're waiting 20 seconds for the hot water everytime it makes it not worth it to switch the shower on and off.
    - lotsofpulp 4y ago
      The water in the hot water pipe will not have gone cold during the short time it takes to clean one’s self.
      - benj111 4y ago

iso1631 4y ago

Seems like it costs in the order of £500 to install from a quick search. Wouldn't that money return more via a solar system, or better insulation?

fho 4y ago
I guess 500 moneys is nothing compared to what renovating a bath costs.

fy20 4y ago

In vanlife some people have built recirculating showers that use just a few gallons of water running in a loop. They run it through particle and UV filters which supposedly clean the bad stuff out, but I haven't seen any scientific studies done on how effective that is. I imagine it is no worse than a bath, other than you are potentially putting bacteria into the air and hence your lungs. The idea sounds interesting though, as showers (even low flow) use a lot of water and heat, which typically just goes down the drain.