Author Topic: Claim back 60% of energy lost from hot water ???  (Read 6594 times)

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WindyOne

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Claim back 60% of energy lost from hot water ???
« on: February 28, 2013, 08:03:19 AM »
  A "Grey Water" Heat Recovery System can reclaim up to 60% of heat lost from grey water that would normally head down the drain with the water after a shower, dishwasher use or washing machine cycle. In a modern family home, up to 90% of hot water consumption is because of showering and most of that heat disappears down the drain.  A "Grey Water" Heat Recovery System is very simple. Waste water runs through a heat exchanger on its way to the drain. Heat is transferred from the water and the waste water never comes into contact with the fresh water. The heat recovery system is suitable for residential and commercial uses. In Europe it has proved effective in gyms, stadiums, restaurants and hotels. An initial lost cost will result in a very quick payback, relative to other technologies. Average annual savings are equivalent to a small solar water heating system, but at a fraction of the cost.

(see attached photo)

Bruce S

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Re: Claim back 60% of energy lost from hot water ???
« Reply #1 on: February 28, 2013, 09:45:32 AM »
On the funny side, none of the hot water heat makes it down to my drain, my body absorbs ALL of it. ::).
However, I can see this would be easy to setup as well. It could be similar to the dual line heating setup used by many Bio-Diesel users on older diesel cars.
I built one for my old MB300 TD was fairly easy doing copper inside copper pipes.
Those who have older Tile drains could even wrap those with a larger PVC pipe first split in two and "T"s.


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WindyOne

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Re: Claim back 60% of energy lost from hot water ???
« Reply #2 on: February 28, 2013, 11:43:37 AM »
I think the heat recovery from a Shower will work well since warmer water is flowing down the drain and into the heat exchanger as the colder water is flowing up into the heat exchanger providing warmer water in the cold water pipe.  But in a washing machine, a tub or a sink for dishes the warm water is used and then at a much later time the cooler grey water is drained out. Not as effective as a shower.

 Also, now you have to plumb your house with ...
 a) Cold water pipes - toilets & garden hose
 b) Warm water pipes - shower
 c) Hot water pipes - normal

 and split the waste pipes into two different paths = extra costs.

 There is no savings by wasting "pre-warmed" cold water that will go to the toilet or garden hose water.
 

DamonHD

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Re: Claim back 60% of energy lost from hot water ???
« Reply #3 on: February 28, 2013, 11:55:09 AM »
All the evidence that I know of says that this can indeed work well with a shower, and not terribly well with anything else for a variety of reasons.  If you start keeping tanks of grey water around to warm incoming water you have all sorts of blockage, bacterial (etc) growth and potential contamination issues...

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Damon

MaryAlana

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Re: Claim back 60% of energy lost from hot water ???
« Reply #4 on: February 28, 2013, 01:07:54 PM »
My hot water going down the drain in winter can keep the drain from icing up, my basement isn't heated in any way.

DamonHD

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Re: Claim back 60% of energy lost from hot water ???
« Reply #5 on: February 28, 2013, 01:55:50 PM »
And that's definitely a good use of that 'waste' heat IMHO.

Rgds

Damon

Frank S

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Re: Claim back 60% of energy lost from hot water ???
« Reply #6 on: February 28, 2013, 04:27:19 PM »
Such are the woes of geography, I know everything will be Topsy tervy after we return to TX but over here from mid April to mid Nov we turn off the water heater. It then becomes the cooler water side of the house no such thing as cold water in the summer over here. the water in the roof top storage tank can reach temps high enough to make coffee with directly from the cold tap. If the boiler runs out of cooler water while showering then you will get scalded. when we first moved over here my wife accidentally turned on the cold side while in the shower and had to spend 2 weeks in the hospital treated for 2nd degree burns. after that she would draw up a tub of water and let it sit for an hour to cool down. Me I just wait until way after midnight to take my shower     
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DamonHD

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Re: Claim back 60% of energy lost from hot water ???
« Reply #7 on: March 01, 2013, 12:50:51 AM »
Yes, I experienced a similar (though less dramatic) version of that while working in Malta!

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Damon

Frank S

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Re: Claim back 60% of energy lost from hot water ???
« Reply #8 on: March 01, 2013, 02:04:28 AM »
Yes, I experienced a similar (though less dramatic) version of that while working in Malta!

Rgds

Damon
A couple years back the storage tanks were low but not enough to call the water buffalo one particularly hot day about 55c  I noticed vapor coming out of the cold tap while running the water so I stuck a candy thermometer in the stream it hit 90c  about 194f
 People don't realize just how much solar radiation can be absorbed until they witness it.
 as far as grey water heat recovery goes if a well designed ex-changer was placed just before the hot water tank inlet and then allowed to freely flow to the drain there is no reason why there wouldn't be at least some rise in temp. there would be no need for storage and blockage or bacteria growth should be minimal. the problem lies in the detergents and other contaminants. Reduction on flow or obstructions within the system could lead to these contaminants falling out of suspension. This would be why careful designing and attention to angular flow velocities, surface roughness or even the possibility of air injection would need to be considered.   
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XeonPony

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Re: Claim back 60% of energy lost from hot water ???
« Reply #9 on: March 02, 2013, 12:15:55 AM »
I built an Hx like that for my on demand unit, here in the north it is criticle, unles you like cold showers!
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WindyOne

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Re: Claim back 60% of energy lost from hot water ???
« Reply #10 on: March 03, 2013, 09:08:12 AM »
If you start keeping tanks of grey water around to warm incoming water you have all sorts of blockage, bacterial (etc) growth and potential contamination issues...

Damon

Agreed, you do not want to store "grey water" to recover the heat. The drawing shows a FLOW-THROUGH ( ie no storage ) type of Heat Exchanger. The flow-thru design works best when the warmer grey water flows in one end at the exact same time the cold water is flowing in the other end of the Heat Exchanger. Perfect for a Shower and less effective for most other water usage.

 So, instead of storing the grey water from non-shower sources, like the hot water from the laundry machine or dish washer, is there an efficient way to extract the heat and store the heat until needed later?

 1)  Increase the mass of the Heat Exchanger?
 2) Can a small heat pump efficiently transfer waste heat to a warm water storage tank?
 






XeonPony

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Re: Claim back 60% of energy lost from hot water ???
« Reply #11 on: March 03, 2013, 10:11:39 AM »
Heat pump you will freeze the water in unpredictable times possible a heat pipe system till it reached equilibrium but the cost and added mass may not be worth the small returns.

Simple co-axial heat exchanger in a counter flow arrangement will do all it will do, using flattened riffled copper on the inner track will ensure max heat collection but all so increase fouling risk.

So it is a care full balancing act.  I used 2 runs of 3/8 that I compressed down to a fairly flat spiral oval, that was jacketed in a run of insulated 4" pvc with an inside tube of 2" this ensured contact with all the copper yet left the least for material to really cling to due to no sharp edges on the inside of the Hx, on the out side I brazed the  2 ends of the 3/8 to a 1/2 manifold with brass male pipe thread ends and 3" ends on the PVC to make it easily couple to the shower drain.
Ignorance is not bliss, You may not know there is a semie behind you but you'll still be a hood ornimant!

Nothing fails like prayer, Two hands clasped in work will achieve more in a minute then a billion will in a melenia in prayer. In other words go out and do some real good by helping!

ghurd

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Re: Claim back 60% of energy lost from hot water ???
« Reply #12 on: April 07, 2013, 08:16:41 AM »
That is one of my favorites.

There was a test of that several years ago (in a duplex, maybe in Detroit?).
The supply to the water heater went around the drain, so it was not heating water for the toilet.   ;)

The water heater was electric with the typical 2 elements, 1 high power, 1 low power.
The high power element never turned on during the testing and logging duration.
The drain and coils were copper.  Seems like the drain was 4"x4', and the coils were 3/4"?
Coil was just wrapped the drain, and not even insulated!  Seems to me like it would have been more efficient if the coil was soldered to the drain, and the whole thing insulated!

The drain must be as vertical as possible so the warm grey water spreads out over the max surface area of the inside of the copper drain.  It helps the heat transfer and slows the rate of fall, making it more efficient.

Trust me, if my shower was not over a crawl space, I would have made one of those as soon as I saw the reports.
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