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Old 03-14-2008, 07:37 AM   #1
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Drain Water Heat Recovery Devices - Thoughts?


We had an energy audit performed on our home a couple of months back and one of the energy conservation recommendations was for a drain water heat recovery device, or DWHR. Home Depot sells these on the web as the Power-Pipe.

The idea is that the hot water leaving the shower would help to warm the fresh cold water before it goes into the hot water tank, thus taking less energy to heat the fresh water up to the temperature of the water in the hot water tank.

I was wondering if anyone had used these before and if so, what your experiences were? What payback did you experience, i.e. how many hears did it take before the savings on heating the incoming fresh water equalled the cost of the device and installation?

From what I have read, the early versions had water pressure issues which the newer models are supposed to have overcome.

We just don't want to have one installed (apparently Sears in Canada has started to do this now) only to find out the savings are not there.

Thanks very much in advance,
Dan


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Old 03-14-2008, 07:59 AM   #2
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Drain Water Heat Recovery Devices - Thoughts?


I have no experience with this it does sound interesting though. One thing that would seem to limit it's application would be the placement of the WH, water source and the drain. It would seem that there could be issues if these are on opposite corners of the house.

Also, if one were to maximize the energy recovery, I would think that the typical PVC pipe would not be an efficient energy transfer agent, and one could get better results with something like copper...but OMG the $. The payback time would lengthen dramatically.

Interesting nevertheless.

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Old 03-14-2008, 01:19 PM   #3
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Drain Water Heat Recovery Devices - Thoughts?


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Originally Posted by RippySkippy View Post
I have no experience with this it does sound interesting though. One thing that would seem to limit it's application would be the placement of the WH, water source and the drain. It would seem that there could be issues if these are on opposite corners of the house.

Also, if one were to maximize the energy recovery, I would think that the typical PVC pipe would not be an efficient energy transfer agent, and one could get better results with something like copper...but OMG the $. The payback time would lengthen dramatically.

Interesting nevertheless.
That is exactly what the different DWHR device products that I have looked at are made out of, copper. I don't know the exact term, but yes, the hot water from the shower warms up the copper on the way out as the fresh cold water passes on the other side of the copper pipe to be come warmed.

Prices seem to vary by length as does the benefit...the longer the DWHR device the warmer the incoming water can become that is to be directed to the hot water tank.

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Old 03-14-2008, 02:33 PM   #4
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Drain Water Heat Recovery Devices - Thoughts?


What do these inventions sell for??
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Old 03-14-2008, 03:16 PM   #5
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Drain Water Heat Recovery Devices - Thoughts?


Sounds like a crock of $hit to me. Payback, should there ever be a problem requiring any servicing... never.

Better off with a 300' coil of poly on the roof, collecting sunlight in the spring, summer and fall, pre-heating the water heater. Even on warm nights the incoming water would warm up a few degrees.
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Old 03-15-2008, 06:24 AM   #6
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Drain Water Heat Recovery Devices - Thoughts?


You will never recover the cost of the device much less the cost of installation. When fuel oil hits $10 a gallon though it may be a different story.
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Old 03-15-2008, 06:55 AM   #7
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Drain Water Heat Recovery Devices - Thoughts?


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What do these inventions sell for??
Hi justdon,

I found on Home Depot's (Canada) web site that they sell a brand called Power-Pipe for anywhere from $587 for a 36 inch long pipe to $795 for a 60 inch long pipe; both are for a 3 inch diameter. The details state that it can save up to 30% on water heating with return on investment of 15 to 50% (likley the latter would be for a house full of people of all ages who like to take long hot showers ever day).

I also found a web site for the Power-Pipe brand, but there are other manufacturers.

I'm going to keep looking. Just because an idea is new, it doesn't mean that one should immediately dismiss it as a 'crock of' you know what without doing research and finding the facts involved. At least that's my take on things.

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Old 03-15-2008, 08:27 AM   #8
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Drain Water Heat Recovery Devices - Thoughts?


Quote:
one of the energy conservation recommendations was for a drain water heat recovery device, or DWHR.
Ayuh,..... I've been using a DWHR for Years.....

Difference is,... I put the excess Heat into the Air, rather than trying to preheat water.......
It consists of a 2" copper pipe that runs from 1 end of the house, where the shower is, to the other end, where the sewer pipe leaves the building...

Quote:
Sounds like a crock of $hit to me.
Ayuh,.....
At $800.00,...... I Agree.....

Just imagine the Hairballs that'll be clogging the thing up................
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Old 03-15-2008, 08:36 AM   #9
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Just imagine the Hairballs that'll be clogging the thing up................
Hi Bondo,

What 'Hairballs"? I don't understand? From what I can tell the DWHR pipe is the same diameter (3 or 4 inches) as the regular drain pipe.

Thanks for your clarity.

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Old 03-15-2008, 09:36 AM   #10
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Drain Water Heat Recovery Devices - Thoughts?


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Hi Bondo,

What 'Hairballs"? I don't understand? From what I can tell the DWHR pipe is the same diameter (3 or 4 inches) as the regular drain pipe.

Thanks for your clarity.
For this thing to be any kind of effective it needs to have a coils inside of it. If it's just one pipe inside another it's not going to exchange heat well.
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Old 03-15-2008, 09:53 AM   #11
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For this thing to be any kind of effective it needs to have a coils inside of it. If it's just one pipe inside another it's not going to exchange heat well.
Ah, I see.

You know, I haven't come across that model, i.e. one with the coils on the inside. The only models I have seen and are investigating for our possible use have the coils on the outside of the copper drain pipe.

Please do let me know if you know of one with the coils on the inside so I can take a peak (not that I would want that type, but good to be informed about all alternatives).

Thanks!

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Old 03-15-2008, 10:56 AM   #12
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Drain Water Heat Recovery Devices - Thoughts?


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Ah, I see.

You know, I haven't come across that model, i.e. one with the coils on the inside. The only models I have seen and are investigating for our possible use have the coils on the outside of the copper drain pipe.

Please do let me know if you know of one with the coils on the inside so I can take a peak (not that I would want that type, but good to be informed about all alternatives).

Thanks!
I haven't seen one with coils on the inside or any of these for that matter. Having coils on the outside though is going to be much less effective then having them inside.
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Old 03-15-2008, 01:33 PM   #13
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Drain Water Heat Recovery Devices - Thoughts?


Sounds like something somebody dreamed up on paper and thought this will really work. Example of too MUCH book learnin and not enough real world experience. I agree with the solar collector working MUCH more efficiently for MOST of the year!!
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Old 03-15-2008, 03:25 PM   #14
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Drain Water Heat Recovery Devices - Thoughts?


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Sounds like something somebody dreamed up on paper and thought this will really work. Example of too MUCH book learnin and not enough real world experience. I agree with the solar collector working MUCH more efficiently for MOST of the year!!
Actually, I received an email from the actual inventor of the device which included links to, among other things, this video out on Google. It's about 9 minutes including part of a Bob Villa episode from 1999 examing the device.

It's pretty cool (just to receive the email from the inventor guess he liked some of the articles on our blog about what we have learned about theDWHR devices, even though we did not write about his particular model) and helps to understand the device, etc.

Hope this helps everyone. I certainly learned a few things about it and will be writing more in our blog in that regard.
Dan

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Old 04-09-2008, 10:47 AM   #15
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Drain Water Heat Recovery Devices - Thoughts?


Wow, I'm surprised how much resistance I'm seeing! Here's a government study

http://www.eere.energy.gov/buildings...refindings.pdf

of a GFX unit (it's cheaper than Home Depots). It's installed in a multi-unit building, but their findings showed however that savings were constant in both high and low use months meaning, multi-dwelling or single residence one should expect the same savings of 25-30% for the 60 inch unit. Also, savings in winter are higher when inlet temperatures are lower which fortunately corresponds well to how people use it. People want to take hotter showers in winter when inlet temps are at their lowest so in winter you should get more savings. I'm doing the research, since I currently spend $1000 a year (USA dollars) on hot water, and it doesn't look like it's getting cheaper combined with anything that pays for itself within 5 years is deemed a wise investment I'm almost certain I'm going to spring for it.

I have to mention, they're best to use with showers that have two seperate knobs for hot & cold water instead of combined. Todays cheaper shower valves depend on water pressure and ALWAYS mix cold water in to the shower even with the shower on hot only and set screw turned as far as possible. They're designed with the assumption the hot & cold water pressure is equal and will work fine in those cases. However, it's common for your hot water to be less PSI than cold. If you have a situation the cold goes direct to a shower at full PSI and the hot goes through a tankless coil, a few valves, and a mxing valve your hot's PSI will be reduced and you then get into a situation your shower valve designed to work correclty with equal pressure between hot & cold, is getting noticeably more pressure on the cold side and puts in more cold than it should. You shouldn't have that problem with fixtures having seperate hot & cold knobs.

That's what happened at my house, after replacing the shower valve with a new one, my hot going through a tankless coil, few valves, and a mixing valve the pressure is reduced and when it meets at the shower valve I'm not getting enough hot water. I don't even have the set screw stopper in place and can't turn my shower up enough. In desperation I turned the mixing valve up to 160F, even so I can't get more than 90F water out of the shower it's designed for equal pressure between hot & cold. I'm in the process of installing a ball valve that I'm going to partially close on the cold side to reduce water pressure at the shower to help balance things out. Since heat recovering units usually significantly reduce water pressure on the hot side if you have a newer shower valve that depends on equal pressures you'll likely have it working improperly afterward and throwing too much cold into the mix. You too may need to reduce the pressure of the cold to balance things out, or get a high quality shower valve (I got mine at Home Depot, known for poor quality).


Last edited by Piedmont; 04-09-2008 at 01:31 PM.
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