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Thread: Holy Cow! Now that Prices have changed, Which Way Should I Proceed?

  1. #31
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by master plumber mark View Post
    Here is a digital thermometer that you could use to test your flow.... just be sure to clean it off before sticking it in the Thanks Giving turkey



    That looks painful not digital.

    lol
    Theory only works perfect in a vacuum.

    Cyber Security Protection for Windows C:\ > WWW.WinForce.Net

  2. #32
    In the trades Dana's Avatar
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    Mark- in-re DIY drainwater heat exchangers using soft-copper:

    Key to getting the heat transfer efficiency is contact area between the potable and the drain. The very original prototype designs in the early 1980s did round 1/2" soft-copper wrap and dipped them in solder but those were expensive to make, and not as efficient as 2nd & 3rd generation units that used flattened potable wraps tempered for some springiness, pre-formed to suitable flatness, then and heat-expande to be able to slip it over the copper drain. It has to be a sufficiently controlled process that a gas-tight contact was made between the flat-formed potable and the copper drain to minimize degradation of the thermal transfer efficiency over time from oxidation crystals pushing the potable away from the drain pipe as slightly insulative oxidation layer grows.

    Up for self-engineering all that?



    Of the newer designs Renewability does multiple rectangular cross section parallel potable wraps brazed on to manifolds at the connections to the distribution plumbing. All others use either square-ish cross section potable wraps or D-section wrap with the flat side up against the copper drain. Both work pretty well at single shower flow rates, and 4' or shorter units. With higher flow rates & longer units Renewability units have a slight edge from having less of a pressure drop and less thermal mass and higher turbulence in the potable wrap from the multi-path ribbon-pipe.

    These things are dumber than a box o' rocks (even the Canuckistanis can manage 'em! ;-) ), and in no way comparable to the short-cycling smoke with mirrors represented by overwrought tankless HW heater efficiency claims. They're zero maintenance, and really DO work as-advertised in the real world if you mount them reasonably plumb. (At least within the measuring accuracy I get on the limited number of field-unit's I've measured with IR thermometers. I'm on year 5 with the the example in my basement.)

    The inability to measure the return from a tepid toilet flush doesn't mean they considered it a joke. They are subsidizing it to the amount of net lowered cost achieved by the other ratepayers/taxpayers all over the country to where it's revenue neutral, based on the econometric models of the lifecycle reduction in demand these things achieve, much as other efficiency subsidies are done. If they had been able to measure tepid-water heat recovery that would have gone into the subsidy analysis, but since they couldn't, they stuck to the performance that they can actually measure. And since 2.5 gpm is actually a bit higher than the average real-world shower flows, the real world efficiency is slightly ahead of the NRCAN test numbers.

    I don't put any stock in vendor hype about payback & performance, but I DO have some faith in the certified test numbers listed on the NRCAN site. How you use the thing and your actual hot water heating efficiency & fuel cost determines the true payback, but the NRCAN numbers are good enough to design systems for minimum burner size & storage volumes required meet showering loads.

  3. #33
    Master Plumber master plumber mark's Avatar
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    Default my mistake....

    Quote Originally Posted by DonL View Post
    That looks painful not digital.

    lol


    DonL.... Now that does look painflul when you think about it....

    I dont think I would attempt to get that good a reading
    on my flow, . it would take all the fun out of the experiment




  4. #34
    Master Plumber master plumber mark's Avatar
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    I don't put any stock in vendor hype about payback & performance, but I DO have some faith in the certified test numbers listed on the NRCAN site. How you use the thing and your actual hot water heating efficiency & fuel cost determines the true payback, but the NRCAN numbers are good enough to design systems for minimum burner size & storage volumes required meet showering loads.


    it looks like a good idea, just too expensive for me to swallow....

    of course there is something else that is not factored into the whole
    thing.... there is some heat comming out of the sewer line going out the roof
    too... wether you be on a sewer or septic it would be nominal but I suppose it would
    keep the tubes at a minimum of 55degrees all the time


    if you really have one in your basement, it would be interesting to see
    what or how much difference it would be to install one of those things on the out-going flu pipe


    did you try that turkey thermometer on yourself yet??

  5. #35
    In the trades Dana's Avatar
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    The acidity of natural gas exhaust isn't materially compatible copper drain, and the laminar flows on the flue gas side won't make for very effective heat exchange, as previously mentioned.

    There's very little prospect of dropping the drain stack temp below 55F with one of these things, even with extended draws with 35F incoming water temps. I you're really curious, I'll take IR thermometer temp readings at the incoming water pipe at the base of the heat exchanger, and the section of drain a few inches below it, which would give some indication of where the mid-winter minimum would lie. (If it was actually possible to create a low stack-temp problem it would probably have shown up first in Canada, eh?) The average temp in the drain stack would probably be the temperature in the basement & stack chase, which runs primarily through conditioned space. Any cooling by the heat exchanger would be temporary in any case.

  6. #36
    Master Plumber master plumber mark's Avatar
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    I honestly would not waste the time to do it...
    you have to remember that your room temp wil lbe higher
    than the temps inside the pipe......so its basically a total circle....

    I would be interested in seeing what one would do on the flu pipe...
    go ahead and wrap the chimmney with aluminum foil to protect the copper
    from the flu pipe if you must..... that would be a better experiment because of the
    higher heats....

  7. #37
    In the trades Dana's Avatar
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    Quote Originally Posted by master plumber mark View Post
    I honestly would not waste the time to do it...
    you have to remember that your room temp wil lbe higher
    than the temps inside the pipe
    ......so its basically a total circle ....

    I would be interested in seeing what one would do on the flu pipe...
    go ahead and wrap the chimmney with aluminum foil to protect the copper
    from the flu pipe if you must..... that would be a better experiment because of the
    higher heats....
    That's not necessarily going to be the case. With only a 50% heat exchange with 100F water going down the drain and 40F water coming in, the air in drain near the bottom will be the same temp as the ~70F water clinging to the inside of the drain at that point. (The air in the drain nearest the top of the HX would be about 100F.) In a 65F basement that's a higher temp than room temp, not lower. If the HX is performing at 70% (a really tall one), you might bring the stack temp below room temp with the heat exchanger, but maybe not. I'm really not sweating this one.

    Higher temperature of flues doesn't make up for the much lower thermal conductivity and thermal mass of gases vs. liquid water- the heat transfer rate is still pretty lousy. If it were that easy to extract heat from flue gases, condensing boilers & water heaters would be dirt-cheap, and you wouldn't need complex forms on cast-iron boilers to get the combustion efficiency into the 80s. Knock yerself out, take good measurements, but the exhaust gas heat extraction road is a well-trodden path in the industrial boiler applications, and they're neither simple nor cheap. (Were they simple and scalable it would have long since found it's way in to domestic hot water applications.)
    Last edited by Terry; 11-09-2013 at 09:08 AM.

  8. #38
    Master Plumber master plumber mark's Avatar
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    Quote Originally Posted by Dana View Post

    Knock yerself out, take good measurements, but the exhaust gas heat extraction road is a well-trodden path in the industrial boiler applications, and they're neither simple nor cheap. (Were they simple and scalable it would have long since found it's way in to domestic hot water applications.)

    what I do remember from my solar days would probably hold true with
    what you are saying.... when the heater came on there would probably
    have to be a sensor installed on the pipe which would kick on a low flow pump to keep
    the water in the fins touching the flu pipe from overheating.....

    something like on the solar panels but with much less return

    its basically all just a huge waste of time....

  9. #39
    In the trades Dana's Avatar
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    Yep- a stack economizer on a 40 KBTU/hr hot water heater burner is only sipping from the 8 KBTU/hr streaming up the flue. It would reap at best 3/4 of that (in your dreams!) for a net 6 KBTU/hr, worth maybe 10% of the heat going down the drain a shower flow. How much time are you going to spend to save that intermittent 6 KBTU/hr, which has no consequential effect on apparent capacity?

    The drainwater heat recovery for showers delivers a much higher heat rate, applied immediately, extending showering capacity. In some instances the extra capacity and not having to upsize the burner or the tank will pay for most/all of the drainwater heat recovery unit in reduced hot water heater sizing. In other situations it won't. If the water heating fuels are expensive, there is still a pretty good IRR on drainwater heat recovery on fuel savings for homes where the shower gets a half-hour of use per day. Where the fuels are cheap or the shower only runs 10 minutes/day it gets harder to make any financial case.

    The one in my house was installed for capacity reasons, but it'll be more than a decade before the fuel savings will add up to the installed cost, when the fuel savings are looked at in isolation. But it was cheaper (and takes less space) than adding an indirect HW heater as a separate zone, which would have been necessary to hit similar HW performance without having to raise the heating system water temps. As currently configured, the water in the radiation heating system never breaks 130F, the return water to the boiler never breaks 125F, yet I never have to wait between showers for the buffer to recover, and it all just works. Without the drainwater heat recovery it wouldn't. Clearly YMMV.

  10. #40
    DIY Junior Member Skeptical_thinker's Avatar
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    Newbie late to the party here but this laundry is near where I grew up.

    <http://www.gfxtechnology.com/Coin-Op.pdf>

    It gets wicked cold there.

    Take from that what you will

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