Grey water heat recovery system

Bob Gagnon plumbing and heating

is to store the grey water, to hopefully provide all of my toilet flushing needs. The big submerged tankless coil should be partially submerged in the tank water and when you take a shower, I hope to pipe it so the shower water pours over the coil as cold water is going through it. I'm hoping to bump the incoming water up to 66 degrees for 1/3 of my domestic load. Do you think thats possible? The real savings may be in the grey water, because I spend $400- $500 a year on water. I've read that toilets account for 40%-60% of the water usage. Thanks, Bob Gagnon

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Bob Gagnon plumbing and heating

Grey water heat recovery system

Do you guys think this system will work? My incoming cold water in the winter gets as low as 36 degrees, I'm hoping to raise it to about 60 degrees. Thats about 25% to 30% of my domestic load. Therma-flow is going to make me a honking big submersible tankless coil. If I figure 50% of my water bill for flushing my toilets, I'll save $250 per year. Thats about 6 years to payback the materials, not even counting the domestic pre-heat savings. I'm going to run a backwash on the filter, but does anyone see any other way I can improve this system? Does anyone see any problems? Thanks for your help, Bob Gagnon

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Solarstar

In concept of course it has to work..great idea!! I would be somewhat concerned about scum/crud/soap and bacteria that could potentially come back to flush toilets. I love my 7 year old GFX that is out of sight and mind...and I know its working since I cannot get a cold glass of water in an upstairs tap with the shower running since all cold water is being preheated. Paul

LarryC

tank venting and cleanouts

I am assuming that the tank is covered and vented to the sewer vent system. Any concerns about methane gas production? How often will you have to have it cleaned out? Any concerns about corrosion of the potable water line and cross contamination?

hr

I think

the preheat would work ok. You may need to filter and UV or somehow treat the grey water to the toilet? I think most grey water for inside use is multi filtered and treated for potential bacteria.

Rumor tells me one of the major radiant/ pex menufactures may be working on a plug and play grey water package. Pump, filters, tank, etc.

hot rod

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Unknown

You need to use some bacteria in that kind of a tank system to control the nastiness. "Bio Lift" was a product I used to see used with this type of reclaimer.

I would personally just go with the GFX unit. These batch reclaimers can get pretty nasty and require maintenance. But, they are probably more effective as well.

Ed_26

grey water holding tank

I would plumb in some kind of wash-out system to clean the bottom & sides & flush the drain line, perhaps a sump on the drain to collect the suds/grease etc.(or in the tank).
You may have to use a pressure washer on the coil if build-up slows the heat transfer. (I think it will).

Cliff Brady

Take a look at the BRAC System

I admire your attempt at Grey Water and Grey Water Heat recovery. BRAC System's make's a turn-key Grey Water recycling system that you may want to consider or at least take a look at the firly extensive documention an their website for some ideas to use on your own system . You could possibly mod their tank some how to provide heat recovery as well.

A GFX on the floor above the Grey Water system would take care of a lot the heat recovery. At minimum, a GFX for preheating cold side shower water only could be used as well. A GFX with a sump pump below to feed the Grey Wter tank is another possibility.

Brac reccomends a tri-chlor based tablet, such as the Lysol Brand
Continuous Action Toilet Bowl Cleaner tablet for sanitation.

SVDW

Looks like a great idea! I would suggest a hair/lint interceptor such as a JR Smith 8750 or Zurn 1175 in the shower waste line? I'm thinking your pump impeller might resemble something my wife's cat would cough up otherwise. Good luck with this & I hope you update in a couple months about the cost savings.

jp_2

hot rod's other idea!

I like an idea hot rod had on a different post.

make the 120gal tank a rain water collector, add an inexpensive hot tub solar collector to that. when it rains a lot you have free toilet water, when it doesn't you have a pre heater. whos going to change those gray water filters

how many showers a week compared to toilet flushes?

also:what do you figure the degrees/hour the tank will loose? are you going to end up with 100gal at room temp?

Bob Gagnon plumbing and heating

answers and questions

I'm going to pipe it so I can back-wash the filter and I'll insulate the tank. I'm also going to install a .5 gallon flush toilet and I hope to flush with 100% grey water. If I don't have enough, I'll pipe in my washing machine drain water.
Room temperature will be 35 degrees higher than the water temp. but shower water will be pouring over the coil as the cold water goes through it.
SPV was right , I'll change the location of the pump and place it after the filter, and thanks too Cliff for the advice on the tri-chlor tablets, I didn't know how I was going to do that.
I considered GFX but I didn't have the headroom, and my gut feeling is that I'll recover more heat with a submerged heat exchanger. What do you guys think?
The fact theat this system may cover 1/2 of my water bill could make this project a slam dunk.
I have a couple of questions. What kind of pump should I use? Is a fiberglass tank from A.K. Industries O.K. to use? And do you think I have to vent the tank? I was thinking of using an auto-vent on the shower drain to prevent the heat from rising out of the tank through the vent like a chimney. Thanks for all your help, Bob Gagnon

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LarryC

Venting tank

Bob, you need an air gap between the shower drain trap and the suction to the pump or you _could_ suck the water out of your shower trap. I assume that the HX will be about a foot above the bottom of the tank to minimize build up on it. Does the sewer go to a public or septic system? If septic, would draining the tank overwhelm the septic?

Larry

[Deleted User]

As an experienced waste heat recovery recipient, let me tell you

what you can expect.

Remember this, opinions are like butt holes... Every one has one, and they usually stink, and they ALL get washed in the shower/bath tub.

Now, where do you suppose that minor bit of fecal matter ends up going to?

You got it, your waste heat recovery tank. And guess what it does if allowed to sit at room temperatures... It goes septic. And guess what those little bacterium like to do.. You got it, eat and fart. The eating parts not too bad, but the farting part gets pretty darned funky. I used to have to shock my system with clorox about every two weeks, more often during the summer months. I could smell when it was time to dose the tank as soon as I walked into the house... Bacteria farts.

Now, as far as waste heat recovery is concerned, as you will remember, I had the GFX heat exchanger and a sewage ejection pump tied together. My thought was that just getting a single swipe at the outgoing heat seem like a major missed opportunity. It was my intent to recover as much heat as possible from the outgoing heated effluent as I possibly could. In the end run, after all the messing around with tanks, float configurations, bypass piping, overflow piping, delta T controllers and the major parasitic cost to operate the sewage lift pump, I determined that the efficiency of the system as a whole was only 10% better than what I could have gotten from the GFX if applied in a single pass application. I have since riped the whole shebang out of my home in lieu of space needed for my solar DHW preheat system. The GFX will be an integral part of that because I connected it to the exhause pipe of my T50 Munchkin (do NOT try this at home. This stunt is being professionally monitored under extremely controlled circumstances and is NOT endorsed by the appliance manufacturers, either of them). It is essentialy doing the same function it would be doing as a drain stack mounted heat recovery unit, except that it has a much higher operating temperature inside than it would if it were connected to the drain.

Rumor has it that one of my favorite mini mod con boiler manufacturers will soon be coming out with a stack on heat recovery system designed just for that application. I could tell you who it is, but then I'd have to kill you...

Any way, I too admire your willingness to experiment and think outside of the box, however, based on my past experience, I would stick with a tried and proven system, manufactured by professionals.

In a nut shell, waste heat and waste water recovery systems generally end up a stinking mess. They are also quite maintenance/labor intensive.

Personally, I'm thinking that water and energy conservation first and foremost will show you the greatest bang for your buck, and leave a lot of space to boot!

Good luck in your endeavors Bob.

ME

hr

That's two nah's

based on the smell issue alone. Mine developed that same septic odor even filled with well water, no waste products.

Adding chemicals on a regular basis gets expensive and super chlorinanation will start to go after your copper coils.

I like the thought process and I too like to chase that last elusive efficiency point.

But in this case I'm going with a thumbs down

hot rod

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Solarstar

Can you not find an adequate location for one or more of the shorter GFX's... Paul

Bob Gagnon plumbing and heating

tank smell

is that the only objection? I'm going to buy a fiberglass tank with a 1/2' fiberglass cover, that I assume will be gas and water tight. I hate those cheesy plastic sewage ejector tanks, because the covers leak. I went to the Brac web site that Cliff mentioned, and they say 1 chlorine tablet every 8 weeks will keep the tank clean. My neighbor says one will keep his whole pool clean for about a week. He said it is about 50 cents a tablet, that seems like a small price to pay for free water. I'm curious about the chlorine attacking the tankless heat exchanger, the copper is so thin, will 1 tablet in a 120 gallon tank harm the copper? Thanks again for all your help, Bob Gagnon

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jp_2

don't go by your gut,

I'd like to see some est numbers before I went ahead with all this, sounds like mark E gut instinct was well meant too but his experience told him different.

I agree about the water saving though, ever think of just peeing in the bushes at night? my dogs do it all the time.

I use about 1.5 gallons of water a day, i have a lot of bushes.

Bob Gagnon plumbing and heating

estimate

I hope to raise the incoming cold water in the winter from 36 degrees to about 66 degrees before it enters my solar tank. Thats about 30% of the domestic load. It seems like a pretty impressive amount, worth going after. Unlike solar this won't run out, if you take 50 showers you will still get back a percentage back. Do you think I can get this much of a temperature rise out of a 3' submerged tankless coil? Thanks, Bob Gagnon

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hr

The unknown

is how often the hot drain water is replenished. How much, how often, and the standby loss of the tank.

Check into HDPE tanks. I'll bet much cheaper than fiberglass, plenty of shapes and capacities, and sealed lids. Very light weight, rated to 150F.

Farm stores sell them or do a websearch.

hot rod

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Dave Yates (GrandPAH)_1

a customer

has a 500-gallon HDPE tank in their basement to collect gray water from their shower and the kids bath too. It's vented to atmosphere, but the stench in the basement darn near overwhelms the senses! They utilize their gray water for irrigation and incorporated an overflow to the septic tank that's trapped.

At ISH in Germany, there were several turn-key vendors for capturing rainwater and one gray water vendor whose turn-key system captured my interest. Both systems were approved for flushing water closets, washing clothes and hose bibs. The gray-water recycling system was about 10K (US dollars).

Given that our sewer bills are largely based on actual water usage here in the US, the use of recycling systems that would skew those numbers will be fought tooth & nail. Most plumbing codes have yet to get a handle on these systems and very few allow the use of gray-water recycling. During the Solar World Congress in Florida, I sat in on a water shortage seminar where a portion of the topic was devoted to a community in Arizona that has set guidelines in place and the majority of their residents were said to be using gray-water recycling systems.

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Dave Yates (GrandPAH)_1

a link

http://www.contractormag.com/articles/newsarticle.cfm?newsid=673

Follow the article's links for some great info.

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Bob Gagnon plumbing and heating

Thanks, Dave

That link has a lot of good info. Going by the articles you have written, you are pro grey water. I'm going to go ahead with the install, do you think I will get any pre heat out of the submerged domestic coil? Thanks again, Bob Gagnon

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ALH_4

???

How many btu's will it take to pr-heat your domestic water for one day from 36-66F? How many btu's can you capture from the drain water? What will the temperature of the water in that tank be before you pull any heat from it? Keep in mind it wont be constant as you will be pulling heat from the tank and tightening the dT as it does. Make your storage tank the control volume and do an energy balance for an average day. This will tell you what the system will do. Recycling the gray water is a good idea, though the practical issues cannot be ignored. Some quick back-of-the-envelope calculations tell me, best case scenario, you might save around 10 cents a day. That does add up, but it only adds up to something like 36 buck a year. Am I completely missing something here? Do the hydraulics even work out? Is the idea to empty the tank all day with the toilet and then fill it again the next morning? Otherwise you're diluting your warm drain water with yesterday's cooled water.

-Andrew

Dave Yates (PAH)

with a few reservations, yes

I am a believer in using water twice, yet I'm a bit embarrased to say we're not recycling water just yet in my own home. I've toyed with various designs of my own (on paper), but haven't carved out the spare time to tinker. The product displays at ISH in Germany definately left an indellible impression.

They are much more proactive that are we in this area and their plumbing codes recognize and regulate rain water and gray water instead od fighting them as do most of our codes. But then, they treat bacterial amplification with a great deal of respect and open dialog too.

My one concern with your approach, is the potential for contamination with a directly immersed potable water coil. I believe the potential is there to reclaim heat by tempering the incoming cold water and the tank itself will give off waste heat to the surrounding space. It bugs me (too) that I'm heating water and sending it under an insulated slab to the sewer. I haven't measured the actual outgoing water temp from the shower, but 105F is stretching it if 106F is the human threshold for pain.

The pending water shortages in many areas of the US will force us to change and our plumbing codes will have to play catch-up at their present rate of change, which is bogged down by lobbiest and special interest groups.

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[Deleted User]

I too share these health concerns...

as I am sure you AHJ and your water supplier would too.. It just the nature of us master plumbers donchaknow...

Now, if you are willing to spend some money (obviously you are) and are willing to give up some energy in order to recover a WHOLE bunch of energy, let's talk water source heat pump.

It allows you to recover ALL of the energy available in the grey water tank (including some free energy), gives the isolation necessary to protect the health of the inhabitants, and should be relatively low in maintenance (NOTHING is "maintenance free").

Done correctly, it will also serve as a dehumidifier for your basement:-)

Simply stated, using the copper heat exchanger of your choice (immersed copper or tube within a tube type heat exchanger) You use a differential temperature controller, and compare the temperature of the pressureized preheat storage tank (necessary) and the grey water tank. When the GWT is at least 20 degrees F hotter than the PHS tank, but less than say 120 degrees F, the water to water heat pump is started, and begins extracting the heat out of the GWS tank and transfers it to the PHS tank, at efficiencies approaching 300 to 400 percent (COP's of 3 or 4 to 1).
Max temperatue of the PHS tank would never exceed 140 degrees F or below depending upon the refirgerant used, approach temperatures etc.

By chilling the GWS tank down below dew point, the moisture in the air of the basement condenses out of the air, thereby producing "free" water for use in your garden OR your terlet, and the basement air is dehumidified.

The technology is readily available off shelf to perform this feat. Just about every heat pump manufacturer worth their salt has a small unit capable of transfering around 2 ton (24K btuH) that runs on 120 volts and can be easily adapted to this technology. I'm certain that Professor Silberstein could probably come up with DIRECT heat exchange process, therby increasing the efficiency of the system over all.

All I ask, is that you remember me in your will...:-)

Whadya all think?

ME

Bob Gagnon plumbing and heating

health concerns

this submerged tankless wouldn't be much different than a tankless coil in a boiler, except that if it does leak you won't know it because it won't blow a relief valve, the excess water will just go down the drain because the pressure is greater in the coil than the tank. I'm planning on isolating the heat exchanger and a pressure guage with 2 ball valves. The heat exchanger could easily be tested by shutting off the ball valves and watching for a pressure drop. I plan on testing it every time I hose off the heat exchanger and tank, maybe every three months. One of my old high school teachers had a good idea, he recommended a vacuume relief on the heat exchanger coil which will open and protect the coil from incoming bath water, if the city shuts off my water and opens a hydrant lower than my house, creating syphon conditions while I happen to have a pin hole leak in my coil. It sounds like a lot of what ifs. The heat pump idea sound good but I have my hands in way too many things now. I'll let you guys figure out the heat pumps. Thank for your help Mark, I appreciate your input. Bob Gagnon

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LarryC

Instead of a Vacuum breaker

I'm not a plumber, nor a heating guy, but why don't you use a back flow preventer for the potable water feed to the HW system? Or even the whole house? I am guessing that they are alot more common than a vacuum breaker.

But what do I know? I'm just an EE.

Larry C

LarryC

Instead of a Vacuum breaker

But what do I know? I'm just an EE. Who doesn't know when to stop hitting the Return key.

Larry C

realolman

I don't think I would go for this. It seems unsanitary.
If you want to save water, how about a urinal ( or outside - my preference ).

Seems the incoming cold water would condense a layer of God knows what on the heat exchanger, and it wouldn't work too well.

I can't help but think you're gonna end up with a mess. Add me to the "nah" list.

attaboy for your conservation concerns, though.:)

Bob Gagnon plumbing and heating

a vacuume relief valve

lets air into a water heater if the incoming water is shutoff and the tank is drained. I think he feels the vacuume relief will let air in under siphon conditions instead of bath water entering a pin hole leak in the submerged heat exchanger. Urinating in my yard is not an option because I live in the city, although it has been suggested twice now. I'm hoping the small temperature rise will slow buildup on the coil, but I will make provisions to hose it off periodically. I'm suprised so many of you guys are afraid of bath water. Bob Gagnon

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[Deleted User]

Remember my opinion analogy??

It's not the BATH water I'm afraid of, it's what gets washed off IN the bath water that concerns me, and like health technicians.

As a matter of fact, one of the questions asked in the back flow prevention certification programs has to do with bath tub water being back siphoned into a city water main and the resultant cross contamination that occurred killed many people and made many people very ill. (Chicago, late 1800's IMMSMC).

If the chances are 1 in a million, we as health technicans MUST cover that potential.

The only way the city would allow you to perform this installation would probably be requiring the use of a RPPBFP on the incoming water service to the home, or an air gap, which is not feasible.

Some AHJ's might allow the use of a double walled positive leak detecion heat exchanger, which would KILL the heat recovery potentials.

ME

hr

Double walled HXers

are fairly common in the refrigersation industry for heat reclaim. These copper shell HXwer were used on a bunch of solar systems I removed. The finned tube is actually a double walled tube. I believe this is available from Wolverine.

Another simple HX that passed the double walled requirement is (was) the coil Bradford white installed in the Combi and PowerCors. The inner tube had a monofiliment looking string wound around it then plastic coated.

If a leak developed in the inner tube the fluid would track along the line to outside the tank. Clever and from my experience, reliable.

Think if I were to build a homemade HX I would remove the jacket from dsome CSST tube, coil it and drop it in. I thing the design of that tube shape would be more condusive to transfer than plain copper. probably cheaper right now.

A clever fellow might slip the CSST into a copper pipe for a double walled devise.

Although I still think you are barking up the wrong tree

hot rod

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hr

a few double wall

options. The refrigeration industry uses doubled walled HXers for reclain system. I believe Wolverine manufactures this double walled tube, seen here in an old solar HX.

The coil in the Bradford White Combi and Powercor was a clever double walled gizmo. A plastic line was wound around the HX tube then plastic coated to provide a fluid path. Simple, but I have seen many work

Think if I were to build a tube HX, I consider naked CSST. A better shape probably cheaper than copper right now. A guy might jam some inside a copper tube for a double walled home brewed.

Although I still think you are barking up the wrong tree
with your idea

hot rod

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realolman

Peeing in the yard was just a feeble attempt at a little humor... sorry... it won't happen again.

Using a urinal would cut back on your water usage.

Running bath water back into your toilet tank seems unsanitary to me. You can flush your toilet into your refrigerator for all I care.

Larry Weingarten

Feeble attempts...

... at humor are all I'm good for. Keep 'em coming!

An important premise to me is "Keep it Simple". Another one I aim for is "Elegant Simplicity".

Yours, Larry

Cliff Brady

Thinking outsde the tank

Mark I like your idea and I have one of my own. Why not wrap the exterior of the tank in the highest heat transfer pex you can find and run your cold water through the pex for preheat. You could gang pex runs together like some GFXs to reduce head losses or use a pump on a differential control to transfer the heat to the coil in an indirect or just to the taps on a regular water heater. Perhaps a primary secondary pump arrangement that runs when a sensor detects cold water flowing to the water heater or cold side shower.

Some thermal paste on the pex-tank interface and insulation on the exterior would help with heat transfer and you would have a nice insulated double wall heat exchanger that you wouldn't have to clean.