Drain Water Heat Recovery: Anybody?

[btuser]

I've got a real lemon of a location when it comes to solar DHW. I started looking into the GX exchange heat recovery thingies and figured at best I'd be looking at 4 yrs payback and at worst 10 years. I put it on the back burner as possible, but I'm wondering if anyone else has tried/installed a unit.

Any problems with pressure loss? Any data other than sales brochures?

 

[Seasoned Oak]

Probably depends what your paying for hot water to begin with, could be it may be more trouble than its worth.
if you use a LOT of hot water you will save more. I do like Solar when possible.

 

[begreen]

Could you post a link to the product? I would think it would only be valuable if there was a lot of hot water being consumed and that the drains for these hot water users could be routed to a common output through the exchanger. They would have to be separate from toilet drains.

In 1984 I designed and installed a large hot-water recovery system for a major photolab in Seattle. It was a very progressive design at the time. The lab's gas bills were huge and with expansion plans, they were about to go through the roof. My estimates for the system showed a minimum 3.5 yr payback, but the lab expanded very rapidly and the system ended up paying for itself in less than half that time. One of the reasons it worked so well was that their water heating need was almost continuous. By preheating the incoming city water with the outgoing waste water we were able to preheat it almost 30 degrees. That led to a very competitive savings for the lab. It worked so well that they went from 3 gas boilers to one.

 

[btuser]

This is one of the products I'm thinking about.

http://www.gfxtechnology.com/

There's a pissing match going on right now between who's the best, but I'm guessing there all close to the same. The pressure drop is something to consider. I'm thinking I could work a whole house drain because my water heater is about 15' from my vertical drain. I spend about 300 gallons of heating oil per year on hot water which I round up to about $1000. At $800 including shipping, if I could get 30% my payback would be 3 years. Some of the efficiencys are stated at over 41%, but I'm guessing real world/my house would be closer to 30%.

 

[Seasoned Oak]

I read an article where the idea was to get heat from the public sewer system not just you own private drains.
But it has merit you could at least equilize the ttemps in the middle,say incoming water at 40 dEG OUTGOING AT 100 SHOULD GET YOU UP TO AT LEAST 60-70 DEGREES

 

[btuser]

The outgoing drainwater is about 90 degrees and the incomming cold water is about 45 degrees. With a transfer of 40% I should be in the 60-70 degree area. I'm also starting to think about overall gains in system efficiencies. By having a higher incomming temperature my indirect water heater could be held at a lower temperature. Right now I boost it to 140 and then mix it to 120 in order to have a larger volume, but with a higher incomming temp I could maybe reduce that a bit and avoid the higher standby losses. Also, more hot water would mean fewer cycles in the Summer for the Boiler, which again would reduce the standby loss.

One more point is a 40%(already I'm starting to shade the numbers up) reduction in energy for hot water is like a 40% reduction in hot water, which would make my original desire for solar a possibility. Solar in the Summer and Oil backup in the Winter, when standby losses would be negated.

 

[begreen]

Have to admit that I am skeptical about the recovery figures provided by GX with just a coil around a pipe, especially on a vertical run. The type of unit we used was a much more efficient plate exchanger, but it only had water running through it, no waste or grey water. And it was a steady volume, not the on/off cycles seen in a home plumbing during which the pipes can cool down in between cycles.

 

[btuser]

They state a higher efficiency during a steady gpm flow. The higher the gpm the lower the %. I guess its important that the pipe be vertical, because of the film effect of the water coating the inside of the pipe, whereas a horizontal pipe only enjoys about 10-2% contact with the water. A lot of these figures are independantly verified, I just don't know how it really translates into real world savings.

My mind is made up- I'm a gonna try it as soon as I can come up with about $800 for some fun. This weekend I'm putting an hour meter on the new boiler, so maybe it won't be worth it when I figure out the new system's efficiency.

 

[solarstar]

Hi Guys : I'm still kinda new here in the group. Energy is my hobby big time and has been for 20 year. Re the DWHR -Drainwater Heat Recovery. I bought a GFX in 1999 finally took the wall apart a year later i think to install it. I love it. and yes it still works great. Mine is the G3-60" Not 1 problem. I Did install a cleanout at the top as I can mechanicaly brush it with a 3" pellet vent brush to ensure it does in fact stay clean and performance stay good, probably one of my Better energy devices in the House ... Paul

 

[begreen]

Nice info Paul. Thanks for posting. The recovery rate is decent. Is this product most efficient with cast iron pipe?

 

[solarstar]

The GFX ( Yes there are several other brands out therenow!!) replaces the 60" of my 3" drain pipe. Its in the main drain from my second floor . Therefore catching all Heat from my showers or whatever is draining at that time. Slow flow IS the secret ,thats why its needed in the shower drain more so than from other stuff.thats draining. My unit had tested out at about 80% with real cold incoming well water and an ULTRA low flow shower head, therefore giving lots of time across the exchanger to extract the BTU's. I've since switched to a much higher flow showhead so my Eff. are surely back to close to advertised( I think 55-60 %). Heres what I also Like and know that its working good . I cannot get COLD water from an upstairs faucet/tap when someones showering as the water is being Preheated, so the GFX is doing its Job. Paul

 

[btuser]

thanks for the tip about the clean-out. Do you find a lot of gunk in the pipe? My set-up is going to have to be on my main drain downstairs in the basement, and I'm not going to be able to pre-heat my cold; it will only be a cold water preheater to the indirect hot water tank. Nov. 1st

 

[GaryGary]

Hi,
Some stuff on grey water heat exchangers here:
http://www.builditsolar.com/Projects/Conservation/conservation.htm#GWHX
including a Canadian test and evaluation of some of the units.
Also a calculator for estimating savings that can be achieved based on your ground water temp.

I've also heard from one person who has one and likes it quite a bit. He mentioned that he had teenagers who liked long showers.

There are some other ideas on recovering heat from grey water and energy efficient showers here:
http://www.builditsolar.com/Experimental/experimental.htm
Search down the page for "grey water".
These ideas may be a bit far out there for most people.
The Canada paper on a prototype and test of a grey water heat exchanger for a whole house is pretty interesting.

Gary

 

[jebatty]

I gave this some thought and decided against it, not because it couldn't work but because we have a septic system and very cold winters, and we actually need the hot drain water to help keep the septic system from freezing. Cooling hot drain water through recovery would make septic freezing more likely.

 

[oldspark]

I gave this some thought and decided against it, not because it couldn't work but because we have a septic system and very cold winters, and we actually need the hot drain water to help keep the septic system from freezing. Cooling hot drain water through recovery would make septic freezing more likely.

Septic freezing? I have never heard of that being a problem if installed correctly, what would freeze and how deep is the pipes and tank, sorry for the side tracked post.

 

[jebatty]

State PCA requirements do not allow deep tanks or deep drain fields. Effluent liquid is to be absorbed by plants growing above the drain field, not drain down into the water table. Plus, we have -30 to -40F winters, and if we get light snow cover, systems do freeze up. All dependent on length of cold spells and amount of snow cover. Frost can easily reach depth of five feet in non-protected areas.

 

[oldspark]

State PCA requirements do not allow deep tanks or deep drain fields. Effluent liquid is to be absorbed by plants growing above the drain field, not drain down into the water table. Plus, we have -30 to -40F winters, and if we get light snow cover, systems do freeze up. All dependent on length of cold spells and amount of snow cover. Frost can easily reach depth of five feet in non-protected areas.

I heard MN had some strick rules with the septic tanks, here in Iowa it is not that big a deal.

 

[btuser]

We've got a 48" frost line here. I've never heard of a septic freezing unless it was installed incorrectly. Not to say it couldn't or wouldn't happen in a tough situation but I'm looking at about 100k btu for hot water daily. If I get 40% efficiency that would remove 40k btu. 100,000k btu/day isn't enough to thaw the ground. Maybe make the difference in a very narrow band but I think the majority of the heat in the system is coming from the bacteria in the septic tank. I am curious however. Do people usually pump in the Spring, Summer or Fall? If there's no deep tanks, how do they keep the leech field from fouling?

 

[stacyalmando]

Most people still haven't heard about drain water heat recovery units, but the reality is that this eco-friendly technology is lowering energy bills in thousands of homes and businesses every day. In fact, it's one of the easiest ways to improve energy efficiency. The less energy you waste, the less energy you need to buy. Making the world greener and lowering energy bills is just that easy.