Shower wastewater heat recovery

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Hello,
I'm interested in the idea of recovering some of the heat from the wastewater of my shower, and I'm wondering about building my own heat exchanger. For simplicity, I'm just thinking of preheating the shower cold water feed with the shower drain water.
My first option would is to use a piece of 1.5" or 2" copper DWV pipe for the drain portion and to attempt to coil 1/2" soft copper type L pipe around the copper DWV pipe. How tight a bend can one make with 1/2" soft copper pipe? Are there any measures I could take to improve the contact and heat exchange between the DWV copper and the soft copper coil?
The other option I know of is to use a 1.5" copper type M pipe inside a 2" copper type L pipe, where the inner pipe is the drain, and space between the pipes is pressurized with cold water. For a given length of heat exchanger, how would this design's performace compare with the coiled design? I'm not sure if this design would fly with my inspector, though.
Cheers, Wayne
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Check this out http://www.toolbase.org/techinv/techDetails.aspx ? technologyID8
I think I remember such a system on This Old House or Bob Vila's Home Again
Brad
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Wayne Whitney wrote:

I get the feeling that you wouldn't even come close to recovering the cost of a heat exchanger system from the microscopic water heating savings.
Secondly, if really feel you must do this, leave the design of heat exchangers to heat exchanger manufacturers. Although, if you tell them what you're doing, they might tell you that you're wasting your money (unless they really want to sell you something).
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snipped-for-privacy@hotmail.com wrote:

P.S. If you want to save money, just reduce the temperature on your water heater. Waste comes in when you combine extremely hot water with cold water to get a tolerable temperature.
Also, you can use low-flow shower heads (shudder), put a shutoff valve near the shower head to maintain the Hot/Cold mix while you soap up, or take shorter showers.
You could also insulate your water heater if you live in a hot climate or if the water heater is in the garage.
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How long do you or other members of your household spend in the shower anyway?
I reckon I have the hot water on for about 20 secs., then turn it off and soap myself, then rinse myself off with cold water; the water is flowing for a total of about 1 min. When I wash my hair, the water may be flowing for as long as 3 min.
Perce
On 10/25/05 06:55 pm Wayne Whitney tossed the following ingredients into the ever-growing pot of cybersoup:

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Percival P. Cassidy wrote:

most of the heat is already recovered into the air in the bath...
check the water going down the drain,,, it is already pretty cool...
if it isn't then i suggest you switch to a shower head with finer drops...
the water evaporates and cools, there is probably little heat to recover in the drain water...
Mark
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No. Altho a better shower enclosure can raise the drain temp.
Nick
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Percival P. Cassidy wrote:

3 minutes? Takes me at least twice as long to wake up in the morning!
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On 10/26/05 01:45 pm Larry Bud tossed the following ingredients into the ever-growing pot of cybersoup:

Me too, but the shower doesn't switch on with the alarm clock.
Perce
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aem sends (dearly missing the 400 gallon water heater and six-inch mains at the apartments, and still getting used to low pressure well water and only 40 gallon heater here is this house I bought a few months ago)....
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On 10/26/05 06:28 pm ameijers tossed the following ingredients into the ever-growing pot of cybersoup:

Never spent any time on a sub., but I did see one once, I think. And, no, it didn't frighten me.
I just don't believe in wasting water. And cold showers are very bracing -- good for the constitution.
Perce
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Trouble is the water's probably not 'warm enough' and you'd have to leave it in contact with the cold water 'too long' to make it practical. Not to mention the hassles of dealing with gray water crud building up inside whatever exchanger might be involved. This alone would make it rather impractical as the amount of build-up would rapidly degrade any expected recovery. By the time you have enough surface area to recover whatever heat is present you've also created a prime location for the various soap, skin, hair and other waste products to build up on it. Then you've got a real mess on your hands which will undoubtedly take either MORE hot water or harsh chemicals to clean.
Better to turn back the hot water heater temp and avoid wasting the hot water by having to crank up the cold to find a comfortable bathing level.
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Explain please. If you want say, 100 degree water to shower in, you can get it by heating to 100 degrees, or mixing different portions of hotter and colder water to get to 100 degrees. The Btu needed to heat the water is the same.
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Edwin Pawlowski wrote:

No. Energy is wasted. As an anology, imagine that you need 25 psi air, but instead of running the compressor until it gets to 25 psi, you run it until it gets to 100 psi, and then vent the tank until it gets back down to 25 psi. A lot of energy is wasted. In fact, you could have run a pneumatic motor during the venting process.
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Bad analogy.
Dumping air from a tank until you hit 25PSI is an open system - you're dumping energy into the external environment.
Mixing hot/cold is a closed environment, you're not dumping energy anywhere except into the shower. Ignoring 2nd order effects, mixing 190F water (produced by heating 40F cold) with 40F cold to accomplish 100F, uses precisely the same amount of energy as directly heating the same (total) amount of water from 40F to 100F.
[The 2nd order effect is the fact that hotter water radiates more BTUs per hour from the pipes than colder water - it's essentially linear based on the temperature above ambient. The better you insulate the pipes, the less this matters.]
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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If you heat up a hot water tank to 190F and only use a tiny bit of hot water to mix with cold water to get a warm shower, the energy from the rest of the 190F water tank will exit the tank, and moreso the longer it's left sitting, and at a much faster rate because of the higher temperature difference. In addition, copper water pipes transmit heat great and aren't typically insulated.
You've wasted energy running the tank up to 190F. Those "2nd order" effects dump energy into an external environment.
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It will? You dump a full tank of water every time you turn on the tap? No matter how little you turn on the tap?
Where is the rest of the water going?

Somewhat faster. Not "much". Further, in most cases, the heat is staying inside the house, which for at least most of the year here means you're wasting very little of it.

If you care about energy costs (which is the context of this thread), they would be.

Yes, I agree, you've wasted energy running the tank to 190F. It's illegal anyhow. That was just for purposes of the example. The same principle applies even if you set the tank to 140F (or in 120F). Setting the tank to the desired shower temperature (ie: 105F as opposed to 120F or 140F) saves very little money if any, and doesn't take into account things that need the higher temperature, like a dish washer. And means that you likely run out of hot water faster.
--
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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Most dishwashers will bring water up in temperature if need be. Depends on what wastes more energy, overheating a big tank or warming up a small amount to do dishes.
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If your hot water is too hot and you have to add too much cold to it to get the shower to a comfortable level then you're wasting energy. Better to drop the heat of the hot water down a few degrees instead. Think about it. Why take water that's already been heated and waste it?
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wkearney99 wrote:

I did think about it.
If the water is heated to 160 degrees, you use much less of it than if it was heated to 110 degrees. Same energy is expended. Where does the waste come in? If you take a shower with a 2.5 gpm flow, and you shower for 10 minutes, you use a total of 25 gallons. What is the difference in cost if I use 25 gallons of water heated to 110 degrees or if I use 8 gallons of water heated to 160 and 13 gallons of cold water to temper it for a total of 25 gallons?
--
Ed
http://pages.cthome.net/edhome/




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