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Old 11-25-08, 09:20 AM   #11
Daox
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Well, you could install it right under the shower and have it preheat your cold water going to the shower. That would work perfectly. I highly doubt you can take a shower before a drop of hot water goes down the drain.

I wish they had efficiencies listed though. Almost all the other sites require the unit to be installed vertically to create a thin film around the outside of the drain pipe and thus more surface area to transfer heat from. I'm curious as to how they get around this on the horizontal design, or if its just less efficient.

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Old 10-06-09, 08:09 PM   #12
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Originally Posted by Daox View Post
Well, you could install it right under the shower and have it preheat your cold water going to the shower. That would work perfectly. I highly doubt you can take a shower before a drop of hot water goes down the drain.

I wish they had efficiencies listed though. Almost all the other sites require the unit to be installed vertically to create a thin film around the outside of the drain pipe and thus more surface area to transfer heat from. I'm curious as to how they get around this on the horizontal design, or if its just less efficient.

These systems are doing ok, but the efficiency is below 40% at best. They are placed vertically, because of such rules for sewage drains setting up - either vertically or horizontally under a slope of 1.5 degree.

I think that is placed vertically to be able to avoid blockage
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Old 10-06-09, 09:33 PM   #13
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They're placed vertically to maximize efficiency. The water clings to the walls of the pipe giving you the most surface area. IMO, 40% efficiency is pretty darn good. However, a few of the places posted claim up to ~70%.
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Old 10-08-09, 09:50 PM   #14
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They're placed vertically to maximize efficiency. The water clings to the walls of the pipe giving you the most surface area. IMO, 40% efficiency is pretty darn good. However, a few of the places posted claim up to ~70%.
I was thinking about something like this after seeing it in use on Planet Green (I think it was that channel). My first and only thought was to use an actual heat exchanger, water-water style. In essence, my idea was to box in a heater core from a car, flow my cold water through the fins, and flow my wasted warm water through the normal fluid passages.

My only problem with this whole idea is where do the savings come from? Sure, you're heating up some cold water. If your water heater is set efficiently, you don't need the cold water on anyway, do you?

Ok, so the best two uses I could think of after that are heating the home, by running the drain water through a heater core, and placing it somewhere in the HVAC ducting, easily removable. Great, but that only extracts heat when the HVAC system is working, right?

Awesome! Well, last idea, then I'm ditching it if this one won't work out...

Let's do the water/water heat exchanger thing again, but run the water heater's inlet through it, pre-heating the cold water that would normally go in bone cold. THAT'S IT! This way, I"m using less (insert fuel source) to heat my water...

Maybe that was the original intention?

Oh, damn. I planned on solar thermal water heating. I guess I'm still wasting fuel, but it's a potentially infinite fuel that I can't control whether or not it will run out, nor does it really make a difference how much I use for what...

Back to the drawing boards...

(The HVAC idea is actually sticking in my side... I might have to do that one anyway, if it's feasible for me.)
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Old 10-10-09, 12:43 PM   #15
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Hey Mopo3,

Could you edit the open office 'description' link to contain a *.rtf, or a *.pdf, or a *.txt?

Regards,

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Old 10-10-09, 01:44 PM   #16
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Default Domestic Water Heat Recovery...

I saw an interesting and stunningly simple shower heat recovery unit...

It used a coil of copper tubing which lay flat on the bottom of the shower, under a wooden grate.

Incoming cold water would run into the copper tube, get warmed by the shower water, then out to be mixed with hot water and on to the shower head.

I expect that there would be a brief period of temperature adjustment, until things stabilized, but, no massive drain replumbing, no serious problem with the heat recovery unit being fouled with shower mung. Just lift the grate and brush it off from time to time.

Using direct heat exchange has its limits because heat can only flow down hill, and the less the slope of the hill, the lower the rate of heat transfer. Things can be improved by using a vapor-compression device to, in effect, change the slope of the hill.

So, another direction for this discussion might be the use of a small re-purposed vapor-compression unit, such as those found in air conditioners, de-humidifiers, tiny refrigerators, etc, to extract heat from the drain water (COP > 4) and store it in an auxilliary water pre-heat tank, or a large super-insulated water tank, which would be a "thermal battery", or to send the heat into the ground via a polyethylene loop field, where it would, over time also act as a thermal battery.

There are companies in the USA making super-insulated water tanks, but their performance is well behind that of some of the European countries, where energy is 2x what it is here, and the expense of perpetual war is not draining the national economy.

I did some hasty calcs regarding how much water would be required in a water type thermal battery, to make a difference toward helping the heating of my small home (< 900 sq. ft.) and I figured it should be in the 500 to 1000 gallon size.

Once built, a thermal battery could store waste heat from a refrigerator/freezer, solar heat collector, recycled heat from domestic hot water, etc.

There was some work done on thermal water storage tanks at build it solar at this link and also at this link. And of course, there has been work done on building your own in-ground loop field for heat extraction and injection at this link.

Best Regards,

-AC_Hacker

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Old 10-11-09, 05:32 PM   #17
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Hi,
There are some other designs for grey water heat recovery as well -- this is a grey water heater exchanger in a barrel idea of Nick Pine's:
Grey Water Heat Exchanger

We kind of lost steam on the prototype project, but I think the idea has merit, and while the GFX style exchangers are only good for things like showers where there is draining hot water at the same time hot water is being used, Nick's idea can recover energy from any draining hot water.

Here is a Canada study on a somewhat similar design:
http://www.builditsolar.com/Experime...verySystem.pdf

I've often thought that in places like where I live with a 6+ month heating season that just recovering the heat for space heating would be good. We have a well insulated conditioned crawl space that our drain pipes go through -- If I could just figure out a way to retain the draining water in the crawl space or basement long enough for it to lose its heat, it would go into space heating the house. Any ideas?
Since we solar heat the water in the first place, this would be a sort of double gainer.

It just seems so dumb to spend a ton of energy heating water from 50F up to 110F, let it run over your body once, and then right down the drain taking 90+% of the heat you just added right with it -- has to be a better way.

Gary

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