Replies

1. 
   Deets | Jan 15, 1999 03:36am | #4

   *
   Hello,
   %^%$#@#%^^&

1. 
   gstringe_ | Jan 15, 1999 09:19am | #5

   *I played with this idea a number of years ago and built a crude version for tests and I came up with a savings of about 25% on the water heating costs while you are using it, ie;shower. Other uses of hot water don't reap benefits. When I first saw the ads for this product I thought well another oportunity that should have been persued but I am not convinced that the payback is all that quick considering that the shower is the only practical place to save. Actually I looked up my records as I am writing this and it was 1978 that I did this and here are my figures. I did not write down savings % but the 25% is what I remember so maybe some of the whizes out there will compute it for us.My tests were done in december here in colorado and our water is COLD is the winter which makes for better effeciency.water input temp to exchanger at start 54 deg--output temp 65 deg after 1 minute. At 2 minutes, input 52 deg-output 65 deg. at 3 minutes input 50 deg--output 64 deg. At finish, input 50 deg--output 63 deg. This is with shower head discharge temp(no person in shower) of 102 deg. Drain discharge of tub of 90 deg and exchanger discharge of 73 deg. All this with 1.85 gpm flow of hot and cold and 1.26 gpm of the hot only. With a person in the shower the figures would not be quite as good as some of the heat would be absorbed by occupant. Whew! anyway that is the scoop as I know it.

2. 
   Guest_ | Jan 15, 1999 12:54pm | #6

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   Thanks for saving all that data. I calculate 133 BTU/min recovered (12.75F average temp rise x 1.26 gpm x 8.3 lb/gallon x 1 BTU/lb-F - the heat capacity of water) from the potential 583 BTU/min (38F available(90F-52F) x 1.85 gpm x 8.3 lb/gallon X 1 BTU/lb-F) for an efficiency of 133/583 = 22%.

   This approach defintely can work, but getting above 25-30% heat recovery would be very hard because: 1) You've got to have fairly unrestricted flow in a drain pipe which carries hair and chunks, 2) hot water is diluted with cold at the fixture as in your example, and 3) water left in the device, at the end of a hot water flow, goes to waste because it cools off before the next use brings it to the hot water heater. And although the HX device may be 25% efficient, I suspect, as a system, 10-15% is typical. So your savings could range from $10 to $100/year (cheap N.G. to expensive electricity).

   The more your energy costs, the faster the payback. Also, the closer the drain pipe is to the water heater, the more insulation you put on the pipes, the colder your incoming water, and the lower the water heater thermostat is set, the better the investment. -David

3. 
   gstringe_ | Jan 18, 1999 09:30am | #7

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   Dave-thanks for the calculations-my remembers wern't far off. And while my experiment was crude I think it was reasonably efficient as I had 800 inches of 1/2 copper pipe in an insulated 5 gal bucket with drain water entering at bottom and exiting at top.

   I did visit the web sites and while I certainly won't dispute the math, there are some curious figures. Efficiency numbers are thrown about pretty recklessly and you have to read real close because there are so many varibles to the hookup and use schemes that efficiencies can vary all over the place. I think the efficiencies are stated at 30 to 70% and I suspect 30% would be max typical. One curious figure is in their model number spec sheet showing a 6o inch x 3 inch dia model at 60% efficiency and a 67 inch by 2 inch dia model at 70%. Well the 2 inch model is 10% longer but has 25% less exchanger pipe area wrapped around it, and a smaller dia pipe would have faster/thicker water film flowing thru it equating to less heat transfere I would guess.

   Oh well,anyway, I am not being sour grapes and saying these are not worth it cause I obviously thought it was a great idea when I did it but I was not impressed by the savings and a typical user will never know how efficient his installation is.

   Matter o fact I'm looking at my public service bill for last month with three adults in household and my gas cost was $86. I have natural gas heat and water heater and gas fireplace which is hardly used and a outside gas heated hot tub.

   If I assigned 25% to the hot water heater, thats $22 and if 1/3 of that went to the washing machine and other sink uses you are left with $15. Well no matter how efficient the recovery unit is the payout is not that great-especially if you were to use the 2 inch $600 model!

   If we were to save these billions of btu going down the sewer, what happens to the efficiency of the municipal treatment plants? Does heat have any consequence there?

   Besides, my crawl space doesn,t have room for a five foot pipe, only a five gallon bucket hung from the floor joists.

   Now on to greater challenges.

1. 
   mfh | Jan 18, 1999 11:38am | #8

   *Any reason you couldn't make your own with copper tubing and pipe? They don't appear to consist of anything else. Seems like you could save a couple hundred $$. --thoughts?Interested.

4. 
   Guest_ | Jan 18, 1999 07:44pm | #9

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   I have the same situation: gas heat, water heater,
   fireplace. I keep all my receipts, and, in the
   summer, my gas runs an average of $8 a month, @ .513
   per therm. Two adults, 1 shower each per day,
   occasional warm water washer load (usually run w/
   cold). VERY old hot water heater that's been rumbling
   with bottom sediment since we bought the house 5
   years ago.

   If I had an extra coupla hundred dollars I wanted to
   spend, I think I'd be much better off with a new,
   more efficient water heater. The grey water recovery
   system sounds like a good idea that doesn't live up
   to

5. 
   gstringe_ | Jan 19, 1999 01:24am | #10

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   certainly you could build one. Look at the web sites and get ideas-it looks like they insulate the whole unit. If you wrap copper tube around a, lets say 3" copper drain pipe, you need to have good heat transfere from the drain to the tube and a wrapped tube only contacts the pipe at a small area so I assume the manufactured model has some sort of goop on the drain to get the most heat transfere, or they use a soft tube and squish it in the wrap process to get more contact area etc. you get the idea. The drain does need to be vertical as the flow will cling to the sides all way around as it goes down. Too fast a flow and you would lose efficiency if the flow breaks away from the sides. My test model was just coiled tube imersed completely in bucket but this way you only have one seperation between good water and bad water-wouldn't be approved by any recognised agency-but go for it and do some measurements. Go to Radio Shack and get digital thermometer and use stop watch and known bucket for flow calibration and let us all know how it works.

1. 
   gstringe_ | Jan 19, 1999 01:32am | #11

   *I kinda lean that way too but of course there are things we should do environmentaly even though the financial payback does't justify it. Maybe this is one of them but from a purely technical standpoint, ther are so many varibles that each situation is different. Such as: short shower? what kind of tub you have? cast iron? well the tub will suck up a lot of heat from the water before it gets down the drain but then again the heat in the tub would be released into the room over a period of time, sort of like extra insulation on your water heater, what does excape goes into the house and reduces the furnace load. small but still there and also adds to the cooling load in the summer, wow see it just goes on and on.

6. 
   Guest_ | Jan 19, 1999 02:36am | #12

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   I am considering installing a Greywater Heat Recovery device to recover some of the heat from my shower and other waste water. I am wondering if anyone has any first hand experience on their value. I have a natural gas water heater and fairly high hot water usage. This appears to me to be a great device. It is reasonably priced ($200-300), easy to install, no maintenence, and should have a fairly short pay back time (assuming the reported 40-60% heat recovery rates). My primary sources of information are the following web sites (www.oikos.com/gfx/index.html & http://www.vaughncorp.com). I would appreciate your advice. Thanks.

1. 
   Guest_ | Jan 14, 1999 08:31pm | #1

   *Is this the piece of copper 3 or 4" dwv pipe with the small copper pipe coiled around it?

1. 
   Guest_ | Jan 14, 1999 09:00pm | #2

   *Yes, it is a 3-4" copper pipe usually 5 ft long surrounded by a long coil of 1/2 -3/4 " copper tubing. The 3-4" large center copper pipe is spliced into the septic pipe (usually in the basement) and the incoming house water pipe is spliced into the outer coil copper tubing. When the shower or other hot water source is being used the warm water drainage transfers heat to the incoming house water. It claims to preheat the cold water by 20-30 degrees (only when warm waste water is being discharged). There is a good picture at http://www.oikos.com/esb/49/gfx.html.

1. 
   Tr_Anderson | Jan 15, 1999 03:15am | #3

   *I don't have any first hand experience but I have heard second hand reports of these devices being quite effective at boosting the hot water supply and reducing the recovery time of a water heater. I don't know why they are not used more. It is a simple and logical device.

7. 
   Guest_ | Jan 19, 1999 02:36am | #13

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   I have a follow-up question. One of the claimed benefits of these devices is that they increase the first hour rating of a water heater. Do you think they would allow a person to downsize the water heater size somewhat? I calculate my peak hourly hot water needs at 80-90 gallons. I am wondering if I could use a 50 gallon hot water heater (First hour rating of 70-75 gallons) with a GFX device and have enough hot water?