Home Waste Heat Recycling

[Joe Blake]

http://www.gizmag.com.au/go/7142/

Looks interesting, except I don't use any artificial heating (or cooling).

But being able to recycle heat. I like that.

Joe

[Paul Bailey]

Hi Joe : Thanks for the quizmag links , lots of interesting energy news. On the homefront I have been using the GFX to extract heat from wastewater for 7 years now without any problems. Paul:)

[George Craft]

I'm glad to see that this works well. My brother was telling me about this idea and I actually inspected my home system to see how easy that it can be done. After seeing this photo, I think that I am inspired to do the same.

PS: A co-worker has a new furnace that expels its exhaust thru the side of the house instead of the roof. The incoming air for the furnace is drawn over the exhaust flue going out. This is the same concept. I wonder if it would be easy to implement this idea into an existing home gas furnace installation? I think that the system would require a forced air feed to ensure a proper draft.

At the moment, I've been researching used oil burning furnaces. Unfortunately, they are not ULC or CSA approved, so they would have to be run remotely away from any living spaces. My idea is to plumb a coolant jacket around the heater and pipe it thru my existing water circulating heating system in my basement. I can use the evacuated solar tube system to supplement it during the daylight hours.
Reference: http://journeytoforever.org/biofuel_library/ethanol_motherearth/me11.html

[Paul Bailey]

Another updated link to the GFX heat recovery unit..Lots of info in here. Again no I don't work for these guys just impressed with heat recovery performance and potential in this day and age..Paul:)

[Admin: Link removed, until we have a new one that works]

[Dave Turpin]

Warning: the above link redirects to a non-child approved website. Do not click.

[Brian McGowan]

For what it is worth I also have a GFX unit and I am also impressed with it. As far as I can tell it actually does what it says.

http://home.comcast.net/~bigvid/mydhe.html

This unit works.

[Dave Schwartz]

I kinda don't get how these would work for most cases in a residence.

Correct me if I'm wrong but these devices seem to work on the same principle as the HRV... the incoming substance is cooler than the outgoing substance, whether water or air, and as they pass each other (separated to the minimum degree possible) some heat transfer occurs. It would stand to reason that the flows would need to be fairly equally balanced... at the very least occurring at the same time.

Now I can understand that in a multi-residence installation such as an apartment this will, on average, be true. However most situations I can think of in a residence 'fill' and 'drain' do not occur at the same time. Showering is the only one I can think of - and I already have a flow-restricted shower head and take RV-style showers so the recovery will be minuscule and thus take virtually forever to recoup the capital expense. The big users: bathtubs, clothes washers, dish washers and even dish sinks generally do not fill with hot (causing the water heater to fill via the heat exchanger) at the same time as waste heated water is being drained.

What am I missing? Is exchanging the heat to the incoming water sitting statically in the recovery unit supposed to be of any great benefit?

[Dale Sheler]

As far as I can see you're not missing anything, these things can only work when there is waste heated water draining through them and incoming cold water flowing around the inner pipe, the claim of a 40 degree temperature rise in the length of the pictured exchanger is absolutely preposterous, the claim of reclaiming 56% of the heat from the waste water is equally preposterous.
In a normal residence there would never be anything but an almost unmeasurable amount of heat reclamation, the simple fact that there is a longer length of 1/2" copper tube wrapped around the 4" drain pipe and exposed to the warm air in the basement will make a larger difference than the heat reclaimed from waste water ever would.

[Dave Turpin]

It seems to me that this technology only has ONE application. That is, in the drain of a shower, to preheat the water going into an on-demand tankless water heater. It is then a regenerative heat exchanger which might save, conservatively, 15% of the cost of heating the water for the shower. It might also have some use in a dishwasher. But if you have a dishwasher, are you really dedicated enough to conservation to install one?

If you have a tank water heater, it doesn't seem like it would do anything (especially because of the long run of copper pipe you will need to install) and of course it has no benefit in a washing machine or a sink.

And furthermore, it would not be hard to make yourself if you really wanted one.

[Ben Colla]

Heating water is easy. Solar heat collectors for hot water are extremely common in Australia, and even in the cold wet cloudy parts of southern Victoria, enourmously effective. My father in law lives in Portland Victoria, and he turns the power OFF completely, to his system, for 6 months of the year.

Why spend money to relaim a small percentage of free heat. It's just silly.

[Dale Sheler]

I've built and used a lot of heat exchangers over the years, many similar to that and that thing will absolutely NOT produce a 40 degree temperature rise, unless it was solid full of circulating 200 degree water.

[Dave Schwartz]

Mostly snake-oil then.

I think I'll just stick to the desuperheater on my geothermal heat pump... it'll heat a 40 gallon tank ahead of the gas heater from 10C to 35C in a day or two, depending on run-time (and then my wife drains most of it when she fills the soaker tub). Propane usage actually goes DOWN in the winter because of it.

[Dale Sheler]

I guess I'd call it wishfull thinking:) Something like that could work to an extent in a residential situation if you had a the incoming coil inside a tank that waste heated water drained into, the incoming coil would need to be as long as physically possible to give the incoming water the longest possible residence time in "contact" with the outgoing waste heated water.

[Paul Bailey]

Well the GFX simply works....It"s not snake oil, or wishful thinking, having run it for 10 years now I love it . As with solar, a heat recovery device of ANY sort may not be for everyone as payback times could vary greatly. It works behind the scenes extracting heat from shower water . Lots of kids = Lots of showers. I left my GFX uninsulated for about a week after install in the wall to show some people , its heat extraction potential is amazing . Most new Leed certified and advanced homes in this day and age all include GFX exchangers in the build. Dale its time to do your homework!!:cool: Walked past a GFX demo unit at a trade show in Toronto 3 weeks ago ( a local utility company was selling them I think) most people walked away shaking there heads in disbelief after touching the unit and analyzing the temps. Paul

[Paul Bailey]

Heat recovery in reveiw : See the attached PDF file , As stated above, DO your homework, as there is lots drainwater heat recovery units out there doing the same job the same way. Paul

[Dave Turpin]

Well, yes, this system would work good in a commercial application. There is always hot water going down the drain. In a home, it is basically for a shower, and probably only in the US.

The Aussie's aren't going to use it, because they are more worried about conserving water than heating it.

Canadians might use it... But they are generally a level of frugality somewhere between gluttonous Americans and thrifty Aussies.

[Rob Beckers]

I would put one in in a heart beat, if I had a vertical section in the sewer stack long enough to put it...

Like Paul, I had looked at the performance data. I'm a believer. At the time the EcoEnergy rebates would have netted me some money back as well. Unfortunately my sewer stack is 3" from the ceiling in the only place of the basement where I have access to it. From there it goes out to the septic system. Just no vertical drop to work with (no, I'm not putting in a lift pump). These things rely on being close to vertical, to get the filming of waste water on the pipe wall to happen.

-RoB-

[Brian McGowan]

Here is a description of my situation, installation and results.
I got this device because I was trying to drop the amount of power my house uses and because I couldn’t see throwing perfectly good energy directly down the drain when a simple device that has no moving parts to fail and requires no maintenance could recover that energy or even a fair part of that energy.
I never count on getting everything a product promises and I have never been let down. I calculate what I think I can actually get and base the decision to buy on that best guess.
There are only 2 of us here using hot water. We do not use hot water for the clothes washer. We do not fill and drain very much. Basically it is just me when I shave otherwise we use the showers. I fill the sink the minimum required to rinse my razor maybe ½ gallon. I shave 3-4 times a week. My shower has a low flow head that is rated at 2.5GPM and I run it at the lowest rate I can and still get water to come out of all the holes. Wife’s shower has one of those misting shower heads also rated at 2.5GPM and I am pretty sure she does not run that at full blast either.

The two bathrooms are back to back over the drainpipe with the exchanger in it and the 40 gallon tank water heater is right next to it directly underneath the bathrooms. This used to be a 50 gallon tank but when it failed I put in a 40 in hopes of reducing the standby loss a little. The combination of smaller tank and it being newer and better insulated has made a difference. Since it is getting warmer water from the exchanger I figured I could get away with that and it has been fine so far. We have taken 4 showers pretty much back to back when we had overnight guests and there has not been any problem with keeping up with demand. None of the drain lines are insulated….yet.

The kitchen is at the other end of the house and does not tie in with the heat exchanger so all hot water used there is lost. We run the dishwasher about once a week to 10 days. I think it uses about 10 gallons total per run.

The water heater and the clothes dryer are on a separate “off peak” meter by themselves. Cost for this electricity is 6.5 cents/kWh. For this cheap price they are allowed to turn this meter off whenever they want hence the tank heater. The meter they are not allowed to shut off costs 15 cents/kWh. It will be interesting to see what happens to the price when the rate caps expire at the end of the month and the electricity companies can charge what they want. Rate caps ran out in one county about 4 years ago and prices increased by an average of 80% overnight. They are predicting a more moderate 30% rise here and have been offering “savings accounts” you could contribute a little extra to each month to make the increase more gradual. My gut says they will raise it to 20 cents/kWh. I am not willing to speculate on the off peak meter pricing.
We run 3 loads of wash a week. The dryer runs for 4 hours a week. It consumes 11 amps at 220VAC for a total of 2420W or 39kWh/month or I average by the day so rounding up is 1.4kWh/day. The remainder on the off peak meter is all water heater.
I keep a detailed spreadsheet of power usage and was able to notice a significant drop in power measured by what I thought was the wrong meter. I later figured out the power company had my meter numbers mixed up and was charging the peak rate for the off peak meter and vice versa. After much arguing they realized their error and corrected the mixup. I noticed an average 2kWh/day drop in the off peak meter the month after I hooked up the heat exchanger and that was also realized in subsequent months. At the current rate that is 13 cents per day. This amounts to a tiny bit over 30% drop in the power used by the water heater. My exchanger cost me $330 so payoff at this rate would be about 7 years. Copper has gone up substantially since I got mine and the new price is $655 so payoff for me at the current rate and price would be just shy of 14 years. Of course, if your electricity costs more than mine, or you have a larger family with 4 daughters like my wife’s family, your payoff would be much quicker.
I put some temperature probes on the system after I installed it and found that incoming water temperature was 55 degrees. Output temp of the exchanger was 73 degrees. Final output of the water heater is 110 degrees. Since I mix some cold water in the shower the temperature 99.7 degrees. I am sure it hits the drain at a lower temp than that. About ¼-1/3 of the way up from the bottom of the exchanger the temperature is still 55 degrees so I probably could have gone with the 30” unit instead of the 40” one I got. That would have reduced the payoff even more. I had a temperature probe on the copper drain pipe at the bottom and it read 55 degrees all the time so I think drain water is leaving the exchanger at the same temperature as the incoming water so I don’t think there is very much more energy to be recovered. I cannot be sure though. If I had colder incoming water or took hotter showers I would probably get a greater rise in temperature. Basement temp is about 56 degrees so no help there. My last house had both bathrooms and the kitchen all running to a single drain pipe which was, conveniently enough, 3 feet from the water heater so that would even have been better.
I have dropped the power this house uses from 26-28kWh/day to about 13-14kWh/day or basically in half since I moved here about 8 years ago. I haven’t been able to get it down much lower than that in the last 2 years so I figure I am at the bottom for my situation. My thought is to put up a 4kW grid tied PV system to cover this. If I had to cover that 2kWh/day that the exchanger saves me, which I freely admit is the worst use of PV power, it would require another 500W of panels minimum providing every day was totally sunny. As an example, Ebay has Sanyo 220W panels for $732.60 each. Two would not be enough power but would still cost $1465.20. If we divide that number by the 13 cents a day I save with the exchanger it would take almost 31 years to pay them off. This does not include mounting, wiring or additional inverter capacity. At $3.33/Watt the actual amount of panel I would need would be $1665.00 and that divided by 13 cents is a 35 year payoff. I am interested in solar water heating but I have other things on my plate at this moment and I have no direct capacity or pricing information. Perhaps someone more knowledgeable can chime in about this for some comparison. My guess is if I am saving 30% with my exchanger I could use a 30% smaller system. I would like to know the price difference between a full system and one that is 30% smaller.
Anyway, the bottom line is that this device is simple with no moving parts and no maintenance required and the payoff is better than anything else for this purpose that I can find. These numbers work for me. They may not work for you.

[Ralph Day]

Wonderful analysis Brian.

If you can, solar domestic hot water is supposed to be the fastest payback for renewable energy investment. I have a 4x8 panel and exchanger with a 60 gal holding tank which is pre-heat for a Takagi demand propane heater. From March to October we only fire the propane if there's been cloud/rain for 2 or more days. Even 3 sunny days in January and the propane can be shut off in favor of 110F solar heated water.

I had our consumption down to 13kwhr per day by conservation measures, lightbulb changes, power bar installations. The final drop to 6.5kwhr/day came when the electric water heater function was replaced with the Enerworks and Takagai unit. The electric heater even had a timer on it allowing it to run only 2 hrs morning and 2 hrs night. SDHW is really the way to go!

Ralph

[Brian McGowan]

I have decided to avoid burning anything for hot water if I can avoid it. We do not have natural gas here so I would need propane delivered. I have oil heat but I am doing what I can to minimize that usage and it doesn't run for 6 months of the year so using it for hot water would mean leaving it on all summer.
I am interested in how that timer worked for you. I have been thinking about installing one of them to see if I could cut a little more.
Solar water heating is an option I want to consider but as you said, even that is hard pressed to work in the winter months so a backup of some kind is needed.

[Alan White]

Hi just doing research regarding my final year project and came across this site, im designing a heat exchanger (shell and tube) to recover heat wasted when you have a shower. If anyone has any usefull reading material then could you get in touch thanks, :cool:

[Paul Bailey]

Hi Alan : Welcome to Green power talk, A standard shell and tube would normally consist of multiple tubes ( small ones) within a larger tube, for the heat exchange. In a small system for household application a Shell in Tube would plug up with crud/soap and Hair in no time and would surely fail in no time . There are lots of net links on drainwater heat recovery and heat exchangers ,none of these are shell N Tube for drainwater.!!! Did you have a differant idea??? Paul:cool: .

[Paul Bailey]

Well..... where has the time gone !!! Not meaning to start another Fury over believers Vs non believers or that drainwater heat recovery works or not ,or that there is payback in it for you. So Im into Year 14 for the Gfx. Still working great , I haven't done the math on this lately but it has saved me thousands of dollars in lost energy dollars down the drain. I do brush the center section out every now and then to maintain the higher Efficiency levels as specified . This has been one of my better energy saving investments. Paul:rolleyes:

[Brian McGowan]

Mine is doing great too. Also, in the process of renovating my bathroom I replaced all of the cast iron drainage system leading to the exchanger with PVC. I am now getting a 24 degree rise in water temperature where previously I was only getting 16.5 degrees.
Brian

[Paul Bailey]

Well fellow Greenpower enthusiests: I am being reminded that Ontario ( Canada) New home building codes , starting in the new year will mandate a greywater heat exchanger of some sort. If in fact true, it has been rumoured for close to 10 years now and nobody has budged as of yet. I have no idea what these are selling for now , but they can't be cheap and I think the naysayers are still there. But the train is starting to come into the station here in Ontario with HIGH energy rates !!!

[Brian McGowan]

There are similar building codes being enacted here on a state by state basis also. It is still slow on the uptake.
For your amusement I offer this live feed from a heat exchanger. Give it a minute to load.
http://96.88.64.6/

[Alton Root]

hey..Joe
really nice article....keep posting