Shower wastewater heat recovery

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This is not true. It would be true if by adding cold water you were increasing the total flow rate out of the shower head. But the flow rate out the shower head is basically fixed, so mixing in cold water reduces the amount of hot water being used.
In other words, given a shower flow rate, desired shower temperature and incoming cold water temperature, the power (energy per unit time) that is required (flow rate) * (temperature rise required), for suitable units. It doesn't matter whether you use that power to heat a little bit of your shower water a lot, and then dilute it with cold, or use it to heat all the shower water a little bit.
The one place that lowering your hot water temperature will save energy is if you use a tank-style water heater. This reduces the temperature differential between the hot water in the tank and the environment, so it reduces the rate of heat loss. This savings by reducing the hot water temperature is independent of consumption, however.
Cheers, Wayne
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Wayne Whitney wrote:

Everyone who has raised teenagers knows that by lowering the water heater temperature, you reduce consumption, as they will take shorter showers because the hot water runs out.
Around here, since we have become ecologically aware, the cost of water is higher than the cost of heating it, so reducing consumption can save me quite a bit.
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Wouldn't it be simpler to just take a bath instead?
--

Larry Wasserman Baltimore, Maryland
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I would also recommend a bath instead AND get one of those one demand water heaters.
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Yes, if you let the water cool before draining it.
Nick
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For most places, you're better off pre-heating your water-supply with a solar collector, and ignoring the waste-water heat entirely.
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Yes, I will put in a solar collector at some point. But that's a purely independent issue, it makes sense to do a solar collector and a waste-water heat exchanger.
Cheers, Wayne
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If you really want to recover lost heat;
insulate....Insulate....INSULATE !
then
Figure out a way to recover the heat ( but not the humidity ) from your DRYER ! Now that's a heat loss.
wrote:

<rj>
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The Graywater from just a shower alone is probably not enough to economically justify a heat exchanger.
However, if you run a dishwasher, the wastewater from one complete cycle will usually be hot enough and of sufficient quantity to consider the possiblity of some sort of heat exchanger. This combined with a shower graywater system and you might save some money.
The conventional solution is a large, insulated graywater tank that contains a heat exchanger (copper coils) ahead of your regular hot water heater. The insulation preservers the temperature gradient to keep the hottest water at the top where the largest surface area of the exchange coils are located. The copper supply line must be isolated from the tank water so that there is no leakage (or biological hazard from a backflow). Also, since the tank will contain standing wastewater, some provision of cleaning or flushing the tank when necessary should be provided.
These are the basic physical requirements. I don't think that most US plumbing codes allow graywater systems though.
Beachcomber
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What some codes prohibit is dumping greywater into the ground separate from the black water system.
There's nothing that prevents you from having a grey water system that ultimately goes the same place as your black water. Ie: running grey water into a heat exchanger, and thence into a sanitary sewer (or septic system).
However, there _may_ be some areas that prohibit grey water in sanitary sewers.
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Chris Lewis, Una confibula non set est
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Well, the shower heat exchanger is simpler, as you know there will be hot water demand coincident with the drain water, so you don't need a storage-type heat exhanger.
Also, I would expect that most households have 4-8 times as many showers as dishwasher cycles. A shower also probably uses more hot water than a dishwasher cycle (10-15 minutes @ 1 gpm hot water for a shower, versus 5-10 gallon for a dishwasher cycle).
So I think that shower grey water heat exchange is the best place to focus on.
Cheers, Wayne
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Wayne Whitney wrote:

The device you are looking for is commercially available. Here is one example:
http://gfxtechnology.com /
Ken
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the heated waste water heats up the drain pipes in the basement so most of the heat is recovered keeping your basement warm and dry...
check the temperature of the waste water that leaves your house...it's pretty low...
not much to recover
Mark
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Considering they were almost giving these away a while back, they were worth it. You simply put the coil in-line with the supply line to your water heater and it reduces the load. If you insulate it, it'll do more.
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Can you expand on this? When were they giving these away? A prefabricated exchanger now costs $275-$450.
Cheers, Wayne
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