Heat from the Shower Drain

[ghurd]

It has been a long time.  Some of the new guys may like this idea.

Pretty much just replace 4 or 6 feet of the shower drain with perfectly vertical copper, then wrap and solder copper tubing coils around it.

"Perfectly Vertical" means the water spreads evenly all around the inside of the drain making heat exchange more efficient.

Most people ran it into the water heater.

One member ran it straight to the cold side of the shower faucet.

A few links,

Sadly, missing a nice photo,

http://www.fieldlines.com/story/2003/12/26/17724/816

GFX is a brand but gave me the best results, some nice photos too,

http://www.google.com/search?hl=en&q=gfx+heat+hot+water

Best for last,

http://www.eere.energy.gov/buildings/emergingtech/pdfs/gfx_prefindings.pdf

I would have done it except my shower is over a 100% inaccessible crawl space, draining into 4" cast iron with about 1' accessible at the basement floor.  

With a wife and daughter, it would have been worth it.

Not sure what is cheaper anymore... Copper, Gas, or Electric.

G-

Under 'heat' because it's not about pumping water.

[DamonHD]

Yes, I'm hoping to do this (or something similar) eventually to recover as much as 50% of DHW energy each day.  But that's someway off yet...

Rgds

Damon

[TomW]

g-;

I wonder, did you mean "horizontal"?

Maybe I missed something here?

Seems like vertical would let the water just drop thru unimpeded?

Recapturing the heat from just used hot water makes great sense for sure.

I just don't understand that vertical bit,however.

If ours ran horizontal it would trap enough hair to make a wig weekly I think.

All in good fun.

Cheers.

TomW

[ghurd]

The vertical thing is important!

The water sticks to the side of the pipe.

The more perfectly vertical, the more evenly it is spread.  The thinner the layer of water, the more surface area it has per volume to transfer the heat to the pipe.

And IIRC, the thinner the layer the slower the flow, allowing more time for heat exchange.

There is a word for all that, but dang I don't remember what it is.

"anti-laminar flow"?  :-)

I shed more than a Shetland pony...

G-

[zeusmorg]

  I'm actually in the process of building one, and I plan to document and record as much information as i can. From my research, vertical is the best system, because water spins down a vertical pipe and clings to the sides, partially due to the well known whirlpool effect (for you aussies that's counter-clockwise), and also due to adhesion, and surface tension properties of water. In a horizontal run this effect is cancelled, and the water runs along the bottom only of the pipe, reducing heat transfer due to less of the pipe having contact with the waste water, so in a horizontal run, your heat exchanger would have to be longer/bigger.

 Hopefully I can exceed 50% recovery of the waste heat within the drain pipe itself, most studies I've seen the low recovery rates are 20-30%. Even that within a few short months would pay back the cost of building the heat exchanger, if you have high shower usage. Who wouldn't like saving over 25% of their cost to heat water? Especially if you're off grid, and have to pay high rates for your energy to heat it?

[asheets]

You might want to look up the term "Grey Water Heat Reclamation".

[Bobbyb]

I was wondering about a system like that (usually while taken a shower ) The coil around de drain seems a waste of copper? The system I was thinking about had the drain inside a bigger copper tube that supplied the cold water.

It seems a lot simpler and les labor intensive to me (if u can find the tubing)?

Sadly I can't use the system. I'm surprised by the 30% recovery that's a lot of heat. Unfortunately still most of it is going down the drain.

[TomW]

Ok, folks. I get the vertical bit now. Talk about not seeing the forrest for those damned trees.

Thanks, all for clearing that up.

Cheers.

TomW

[zeusmorg]

 What you suggest does have merit, however first off you're putting your drain inside a supply line, and if the drain pipe developed a leak, you may never know it, until you got your water bill! Also there's the risk of contamination. With coiled supply lines around the drain pipe, leaks in either would become apparent. Also there's the cost, ever price large copper pipe and fittings? It becomes readily apparent that it's cheaper with smaller copper lines even though you are taking about more length. By the time you added up all the fittings, and reducers your pocketbook would take quite a hit.

[TAH]

These would probably recover most of the heat by just keeping it in the house and recycle the water too.  http://www.bracsystems.com/home.html

[GaryGary]

Hi,

There is a good paper on a different style of grey water heat exchanger that was built and tested in Canada.  The GFX style exchanger can only recover heat from something like a shower where the hot water is going down the drain at the same time water is being used by the shower.  The drum style one in the paper can recover heat for situation where the hot water demand does not coincide with the hot water drain (like a bathtub).  On the other hand, the drum style exchanger has some challenges of its own:

http://www.builditsolar.com/Experimental/experimental.htm#GreyWater

Also some incomplete work on a version that Nick Pine and I worked on.  Its still sitting in a lonely corner of my garage -- any advice on this version would be appreciated.

Gary

[zeusmorg]

 I have thought about systems such as you describe, but unless you have some usage for the greywater itself, which i don't (water in this area is almost cheaper than the electricity it would cost to pump it) then the gains you would get from such a system, to me outweighs the costs, area that the equipment would take up, and the hassle of periodic cleaning any storage type system would entail.. I think it would be more efficient to use solar DHW in that case. If used in conjunction with a greywater reclamation system, i could see the economic benefits of it. Showers can use up in the average home 30% of your hot water, so just reclaiming 50% of that would realize you a net gain of 15% of your energy on DHW. The other sources of hot water usage are generally lower when they go down the drain anyway having already given up some of their heat to the surrounding area.

[GaryGary]

Hi,

The system I described does not attempt to reuse the greywater, its strictly a heat recovery system.  I suppose you could add a conventional grey water reuse system after the heat recovery.  On a dollar basis, for most people, the cost of heating water is a lot more than the cost of the water itself.

If I remember right, the Canada system recovered around 50% of the total water heating energy (not just showers).  Solar water heaters don't typically do much better than 70%, so they are really not so far apart, and I think that better design could bring them closer.   If this kind of heat recovery system can be built for substantially less money than a solar system, then it might make a lot of sense.  While there are some problems to solve, I think that these kinds of systems show a lot of promise.  These systems also work for people who don't have a good solar exposure.

Gary

[fcfcfc]

Hi: I have thought about this a million times but have never done it. My guess is that today if you want to make it as cost effective as possible (sky high price of copper), off the top of my head I would replace a section of the down (vert) iron or PVC main drain pipe with a stainless steel 4" thin wall (cheaper than copper) and then weld a larger stainless steel pipe, say 8" (maybe sched 10 or 20) with a top and bottom ring to create a small (say 5 gallons) tank around the 4" down pipe that the cold DHW in feeds into. This would accomplish several things: Cheaper than copper, never corrode, it would give you a hybrid solution taking advantage of heating while you load and to a certain degree store heat and load later. I know when I visit my plumbing wholesaler these days, stainless fittings are allot cheaper than copper which is why the market has shifted as long as you don't have to solider it. Weld this up once and you are done forever, no matter how you clean your drains. The heat transfer cof. of stainless really won't hurt that much in this sit..

[spinningmagnets]

Hey Gary, I just checked out the GW heat recovery links, I always like the clever ideas on your site. Each one is appropriate for somebody, somewhere.

This month is when I've switched to a hot bath instead of a shower because of the cold air, must be near 55 gallons of 130F. If somebody can save a couple bucks using near-free junk to capture some of this...

I've always read that crossflow heat-exchangers transfer more total heat than a similar sized uni-directional flow (don't know why...) so here's my idea.

Raise the water heater, set 55-gal drum on floor next to it after wrapping with insulation. Get a 30-gal drum, flip it over, wrap with insulation, bolt bottom of the 30-gal drum to the inside of the 55-gal lid.

The hot drain water flows down into the center section, hits bottom and makes a U-turn and flows up around the circumference where it exits the lid near the edge. The outlet turns, goes through an "S" trap then flows to drain.

To make it cross-flow, cold water that is headed to the water heater is detoured to go into the lid near the edge and coils down the outer chamber and then makes a "U-turn". Then it continues on, coiling up the inner chamber where it exits near the center of the lid, and the short insulated exit pipe immediately feeds the water heater.

The outer chamber is only warm because it has been cooled slightly from the incoming cold tube, and the then-warmed incoming tube-water is further heated by the hotter inner chamber. The warm outer chamber also acts as an insulating jacket around the inner hotter chamber. This would further be helped by the heat in the inner hotter chamber wanting to rise instead of mix with the outer chamber.

My shop gets grease in 30-gal drums (18-wheelers) and we throw them away all the time, although I would prefer the outer 55-gal drum to be one of those one-piece plastic types I get from the horse ranchers.

"I think there is a world market for maybe five computers." - Thomas Watson, chairman of IBM, 1943

[Drawbar]

I don't think the stainless steel idea would work. Stainless steel is very poor when it comes to heat transfer. Maybe I am out of line on this, but my experience as a machinist and fabricator, I know stainless does not transfer heat very well. That is why it is so hard to machine, and why it warps so badly when its welded. It just does not conduct heat. Perhaps with this little amount of heat though, and from the way the water is sitting there, it would work, so I could be wrong.

[desertcoyote]

I am not buying the vertical pipe method of heat transfer. And 50% recovery in this type of mode is not realistic, not at all. Maybe with capillary tubes in a laboratory under ideal conditions. Drains get coated with scum, hair soap... that alone would kill the thermal impedance and the idealized notion of the water spinning on the outside. It would be a fun physics problem to come up to a steady state solution assuming that the incoming water is getting heated by a percentage of the heat going down the drain. The most practical is the bath tube, let the water stand and cool down to the ambient. Otherwise letting the water flow into a plastic 55 gallon drum thereby heating the crawl space or basement could be workable. Entropy happens, .... use less hot water, take shorter showers!

[ghurd]

The PDF says 25 to 31% over 1 year in a real life test.

"Make", not buy.

[GaryGary]

Hi,

Some interesting ideas.

One thought is that if you live in a cold climate it might be easier to recover the heat from the showers and other hot water use for space heating rather than warming the incoming cold water.

Something like an extended drain pipe or holding tank that keeps the water inside the house long enough to get the heat out of it?

This might also be part of a grey water recycling system?  That is, hold the water in a tank long enough to lose it heat, then let it flow or pump it out for plant watering.

You would want a way to bypass this in the summer when you don't want the heat.

If you had solar water heating, you would essentially be getting three  uses out of the  solar heated water -- shower heat + house heat + grey water for plants?

Gary

[DamonHD]

Hi Gary,

One of the best suggestions that I've so far heard is to let the greywater sit in a big tank long enough (eg overnight) to warm the ground that a normal heat-pump is extracting from (or have heat-pump pipes in the tank walls).  Thus you get extra value from your existing (GS)HP system.

Rgds

Damon

[ruddycrazy]

Hiya guy's an gal's,

                     Below is a link to a pdf file where a bloke did the waste water experiment back in 2004.

http://www.voltscommissar.net/countercurrent/countercurrent2.pdf

The home of this website is also the place where the mini maximiser circuit is.

Cheers Bryan

[GaryGary]

Hi Bryan,

Thanks for the link -- very interesting test.

Gary

[BigBreaker]

I agree that copper is overkill.  It is most critical when the difference in temperature is low.  Pre-heating your hot water with the warm gray shower runoff is a high "delta T" application.  No reason to use copper.

[joedupont]

you might be better off going to a batch system .. maybe two or three.

that is you dump your cloths washer, dish washer and shower into three different drums with copper coils in them.  they are insulated and you draw water through copper coils in them in parallel. every degree rise per pound is one btu.  the hotter the tank the greater the btu  transfer to the water going through. but you will extra some btus out of each tank . once the tanks reach close to ground temp. you dump them and wait for more water.