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Thread: Calculating Propane Usage and BTUs for Tankless Hot Water System

  1. #31
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by Diavolicchio View Post
    I've found a great woodburning boiler stove for the living room
    1 therm = 14# of wood at 100% efficiency.

  2. #32
    DIY Junior Member Diavolicchio's Avatar
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    I've had to re-design this system today, mostly because of one factor I hadn't taken into account: the potential for Legionnaire's disease.

    My original plan was to have a 119 gallon indirect-heated water tank heated to around 110F by a boiler loop from the wood stove. This however is also within the ideal temperature range that promotes the growth of the bacteria that causes Legionnaire's disease. The water tank would only be heated to that temperature if I were home with a fire going in the boiler stove, nevertheless there could be circumstances when that water could be sitting in the holding tank for a couple of days at 110F not being used. The tank I'd planned on using really should only be used when it's connected to an energy source capable of getting the water up to 140F.

    I also learned today that the GFX system I'd planned on using was about 50% more expensive than I was anticipating, so I've chosen a smaller (and less robust) model. I'm no longer going to be using a water tank that is preheated with a boiler loop, but am simplifying to a 119 gallon uninsulated pressurized well water tank. I will be keeping the two original Noritz tankless water heaters, but scaling back from taking two 30 minutes showers daily, to two 20 minutes ones.

    One aspect of the original design I have decided to keep is the ESSE Ironheart stove with the 16,000 BTU/hr boiler loop. It's a pretty weak boiler for preheating a tank of water, but it's sufficient to accomplish three things for me six months out of every year:

    It'll provide the BTUs necessary for three hydronic radiators: 1) in the home office (7,440 BTUs); 2) in the basement mechanicals room (2,860 BTUs); and 3) on the enclosed back porch (5,430 BTUs.)

    If I'm able to keep the ambient temperature in the mechanicals room at 75F, I'm betting both the uninsulated well water tank and the copper GFX coil (when not in use) should stay around 75F, increasing their effectiveness. I can't help but think that all of that copper in a 55F room is going to take a bit longer to preheat the water going through it than the same copper would in a 75F room. The new GFX system will be comprised of two identical 80" columns exactly like this, connected at the top by a copper manifold. It will supposedly have the capacity to increase the water temperature 17 degrees (rather than the 24 degrees of the previous GFX) before it enters the pair of tankless water heaters, requiring an average annual rise in water temperature of 42 degrees (from 68F to 110F.)

    How do these changes affect the final numbers? The components of the shower/hot water system are less expensive by about $3,500, but the cost per shower goes up accordingly. My two 20 minute showers/day (300 gallons each) will now require a total of 2.4 gallons of propane/day at a cost of around $2.80/each (as opposed to the original $2.40/each for 30 minute showers.)


    * * * * *

    Does anyone see a danger in having a mechanicals room heated to 75F by a hydronic radiator?


    John
    Last edited by Diavolicchio; 12-14-2009 at 10:35 PM.

    Lamb Abbey Orchards
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  3. #33
    DIY Senior Member Runs with bison's Avatar
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    What about the GFX pricing changed so much? Install or the units themselves? The payout for me just isn't there because my flows and durations are a tiny fraction of yours. I've used your links to examine the heat transfer coefficients vs. my flows and the cheapest unit still exceeds 10 years payoff for me.

    Legionaire's is a reasonable consideration. I would not consider an under 120 preheater as an all day control point. At 120+ a fired unit will easily prevent legionaire's proliferation. From what I've gathered from technical reports, electric tanks get into trouble at ~120 F setpoint (versus gas at the same setpoint) because they often scale and have sections well below 120 F. A natural gas heater is better configured to retard/prevent legionaire's growth at 120 F.

    A colder GFX coil will transer heat more easily from the drain. Don't waste heat on the utility space. I've been trying to minimize my losses there by sealing duct gap air losses and insulating ducts. I've cut them in half, putting heat/cooling where it is needed, not in the utility room. It was a waste having utility space running cold in summer, hot in winter.

    Honestly, I always considered the 1 hour shower at 15 gpm and 110 F to be very extreme and well past what I figured you would actually find comfortable. 15-20 years ago I considered a multihead shower to be ideal...and arranged showerheads to do this in college which is where I got the idea...so I know what you are getting at...I've experienced it. It was awesome. But I think the same effect could be acheived at less than 40% of the flowrate today. Efficient distrubtion can give you more bang for the buck.

    What sort of flow and design shower temp are you targeting?

  4. #34
    DIY Junior Member Diavolicchio's Avatar
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    Quote Originally Posted by Runs with bison View Post
    What about the GFX pricing changed so much? Install or the units themselves? The payout for me just isn't there because my flows and durations are a tiny fraction of yours. I've used your links to examine the heat transfer coefficients vs. my flows and the cheapest unit still exceeds 10 years payoff for me.
    The folks behind the GFX units I'm considering (www.gfxtechnology.com) don't publish a price list for the more customized units they make. I knew the pricing of their basic off-the-rack models from their website and made a rough guess as to what the more elaborate models might run. I was off. Plus, with the volatile price of copper, the cost for these units probably changes on a quarterly basis.

    Quote Originally Posted by Runs with bison View Post
    Honestly, I always considered the 1 hour shower at 15 gpm and 110 F to be very extreme and well past what I figured you would actually find comfortable.
    I'd never planned to take a 1 hour shower. It's always been two 30 minute showers, one in the morning and one in the evening.

    I've designed this system on the basis of using it to the extreme, just to cover my bases. The 6-head shower I'll be installing will have a digital thermostatic valve and digital interface so each shower can be 'designed' and pre-programmed, on the basis of which, when and how many shower heads it uses, as well the flow rate through each and how long a shower lasts. Anyone using the shower can customize and pre-program their own.

    It defeats the purpose of having a programmable system like this and ignoring it by only showering at full bore. Most likely I'll still end up taking 30 minute showers, but programmed in such a way that I'll end up using an amount of hot water comparable to a 20 minute shower running at capacity through all six heads.

    For the record, this isn't about getting clean; that's just a side benefit. It's about having a killer water massage twice a day. Pure hedonism.


    John
    Last edited by Diavolicchio; 12-15-2009 at 01:06 PM.

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  5. #35
    In the trades Dana's Avatar
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    Quote Originally Posted by Terry View Post
    I don't know how efficient some of the exchangers are for reclaiming energy,
    I did install a few in the 70's, some would reclaim from commercial washers to preheat the incoming.
    A lot of it was done from sketches on paper by hand and was left to me to figure out how to do it.

    That was a long time ago though.

    I've always liked the idea of air heat exchangers.
    Natural Resources Canada has spent quite a bit of money chasing the answer to that question. They developed a standardized test based on 2.5gpm flows and maintain an apples-to-apples comparison of some vendors' models here:

    http://oee.nrcan.gc.ca/residential/personal/retrofit-homes/questions-answers.cfm#q44


    Percentage recovery will be higher with lower drain flow, but total recovery rate in BTUs/hr increases with increases in either drain & potable-side flows.

    Heat transfer efficiency increases with surface area, so taller fatter (and to some extent, squarer cross section on the potable wrap) is more effective than smaller bore drain & shorter length.

    More detail than you ever wanted to know about their early test methods can be found here:


    http://gfxtechnology.com/NRCAN-6_29_07.pdf


    There's more elsewhere if you want. Basically, at 2.5gpm a 4" x 48" or a 3" x 60" yields about a 50% energy return at shower drain temps. If you have the space, 70% is possible with the tallest fattest PowerPipe.

    Most of the manufacturers will give you the raw data at other flow rates & temperatures, if you beg hard enough.

  6. #36
    DIY Junior Member Diavolicchio's Avatar
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    I've been speaking with the folks at Power Pipe too, in the hopes of getting a system from them just as effective for a little less money (or more effective for the same money.)

    I'll post how things price out once I've gotten my quote back from them.


    John

    Lamb Abbey Orchards
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  7. #37
    In the trades Dana's Avatar
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    Quote Originally Posted by Diavolicchio View Post
    I've been speaking with the folks at Power Pipe too, in the hopes of getting a system from them just as effective for a little less money (or more effective for the same money.)

    I'll post how things price out once I've gotten my quote back from them.


    John
    Beyond heat recovery issues, keep flow in mind too. High flow apps, look at how much head the potable side represents too. Some models have quite a pressure drop at 5+ gpm. The PowerPipe design seems inherently higher flow than some of it's predecessors, but development has not stopped. Ecoinnovation, vendor of the Eco-GFX line (not to be confused with GFX Technology) claims to have a lower cost high efficiency solution (as yet untested by 3rd parties. The preliminary data look pretty good for the money. (Don't be surprised if they start bad-mouthing the competition if you get 'em on the phone though- this industry has a whole lot o' back-biting & patent fighting issues.) See: http://www.ecoinnovation.ca/residential-solutions/

  8. #38
    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by Dana View Post
    Beyond heat recovery issues, keep flow in mind too. High flow apps, look at how much head the potable side represents too. Some models have quite a pressure drop at 5+ gpm. The PowerPipe design seems inherently higher flow than some of it's predecessors, but development has not stopped. Ecoinnovation, vendor of the Eco-GFX line (not to be confused with GFX Technology) claims to have a lower cost high efficiency solution (as yet untested by 3rd parties. The preliminary data look pretty good for the money. (Don't be surprised if they start bad-mouthing the competition if you get 'em on the phone though- this industry has a whole lot o' back-biting & patent fighting issues.) See: http://www.ecoinnovation.ca/residential-solutions/
    That EcoInnovation site is amusing in that some of the pdf's have not been completely translated from Quebecois French ("fonction") and have the euro style comma/decimal inversion.

    On a more substantive note, 3/4" tubing coils vs. 1/2" is a key criteria for whole house flows. One of the things I liked about the S series GFX design was that they took a small recovery performance hit on the longer units by using two coils on the single drain tube to provide parallel flow path for the supply. Powerpipe takes this a step further apparently by doing a 4 parallel tube path...but it looks like those might be 1/2" flat faced tubes.

    The EcoInnovation savings comparison was suspect because of the water heater efficiency used. They should have been using an AFUE, not the efficiency factor which includes storage losses.

  9. #39
    In the trades Dana's Avatar
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    Yeah, I've had "issues" with the president of EcoInnovation's sometimes overzealous marketing (and his screaming about his competitors), which is why I'm awaiting 3rd party test results to show up on the NRCan list.

    Full disclosure: I went with a 4" x 4' PowerPipe in my system. I haven't instrumented it to verify effieciency, but it presents far less head to the DHW flow than a tankless HW heater(!). I'd have gone with a taller one if I had the space.

  10. #40
    DIY Junior Member Diavolicchio's Avatar
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    I'm talking with Joel and Francois specifically at Power-Pipe. They seem to be good guys and eager to help people make this technology work for them.

    The major expense seems to be going with a copper manifold. Yet I can't wrap my head around going with PVC. These beautiful copper columns wedged into a PVC manifold look like gold detailing on a Yugo.

    I'm having them work up a quote for a three-column system using 80" columns and sticking with the copper manifold. I'll post details once I've got them.


    John

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  11. #41
    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by Dana View Post
    Yeah, I've had "issues" with the president of EcoInnovation's sometimes overzealous marketing (and his screaming about his competitors), which is why I'm awaiting 3rd party test results to show up on the NRCan list.
    This seems to be pretty common with small vendors. I'm of the opinion that it is best not to oversell something. It is better to over deliver than under deliver. It doesn't do anyone any good to sell somebody something that doesn't fit their application. My personal numbers might come out wrong at times because I missed something, but it isn't intentional or an attempt to misrepresent.

    Full disclosure: I went with a 4" x 4' PowerPipe in my system. I haven't instrumented it to verify effieciency, but it presents far less head to the DHW flow than a tankless HW heater(!). I'd have gone with a taller one if I had the space.
    I used the GFX data to work up heat transfer coefficients and create estimates of the maximum I might expect to recover from the two showers it could be connected to. With my low flows and short showers it works out to only about 30 ccf/year with a 60" G3 GFX in the 3" drain size. It wouldn't surprise me if it was 5 ccf/year less due to dead volume/lag effects--this is a large relative effect for our short duration shower habits. The 60" S3 would yield about 28 ccf/year but would allow for three simultaneous shower operation.

    The 60" would be a bit tight, but should fit my application. Failing that I would drop down to 40".

    That's a good point about taking less pressure drop than a tankless.

    The typical target market for these is pairing with electric water heaters since the energy cost for heating water that way is about twice as great. I can't support much capital at $25-30 year savings...but at $50-60/year I could make a case for it. If we took 10-15 minute showers and/or 2.5 gpm showers then it would also greatly improve the economics. DWHR makes a fair bit of sense for the colder climates with several months more per year of very cold supply water.

  12. #42
    In the trades Dana's Avatar
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    Quote Originally Posted by Runs with bison View Post
    This seems to be pretty common with small vendors. I'm of the opinion that it is best not to oversell something. It is better to over deliver than under deliver. It doesn't do anyone any good to sell somebody something that doesn't fit their application. My personal numbers might come out wrong at times because I missed something, but it isn't intentional or an attempt to misrepresent.



    I used the GFX data to work up heat transfer coefficients and create estimates of the maximum I might expect to recover from the two showers it could be connected to. With my low flows and short showers it works out to only about 30 ccf/year with a 60" G3 GFX in the 3" drain size. It wouldn't surprise me if it was 5 ccf/year less due to dead volume/lag effects--this is a large relative effect for our short duration shower habits. The 60" S3 would yield about 28 ccf/year but would allow for three simultaneous shower operation.

    The 60" would be a bit tight, but should fit my application. Failing that I would drop down to 40".

    That's a good point about taking less pressure drop than a tankless.

    The typical target market for these is pairing with electric water heaters since the energy cost for heating water that way is about twice as great. I can't support much capital at $25-30 year savings...but at $50-60/year I could make a case for it. If we took 10-15 minute showers and/or 2.5 gpm showers then it would also greatly improve the economics. DWHR makes a fair bit of sense for the colder climates with several months more per year of very cold supply water.
    Be sure not to confuse GFX Technology with Eco-GFX. There has been some (intentional, IMHO) obfuscation using similar model names, which helps to confuse the sitution. In NRCan documentation GFX usually refers to Eco-GFX. GFX-Technology is apparently currently reselling WaterCycles equipment to the US market, and it's at the lower-performance end of the spectrum on the NRCan standardized 2.5gpm tests. ALL will do significantly better percentage-wise at the lower flows you're talking.

    There can be paybacks beyond the annual CCF when designing a system. The dynamic BTU/hr or kilowatt return is real power, and can be used to reduce the size of both the storage and the burner/heater behind it. If you can knock 30K off the boiler size or 20 gallons or 50F off the storage and still meet the peak load, it can mostly pay for itself up front in reduced hardware cost.

    For me it allows me to run the Rube-Goldberg contraption of a combi-system at a much more favorable burn rate for heating efficiency while still guaranteeing I never run out of hot water for showering. And by avoiding a situation where mi esposa might be screamin' at me or the kid from a tepid shower, it's paid for itself already!

    NRCan's models aren't terrible, and will probably model your lower-flow situation reasonably, but with shorter, fewer, lower flow showers you're still only looking at a few tens of CCF, provided your hot water heating system is better than 50% efficient.

    See:

    http://www.regie-energie.qc.ca/audie...2_28sept07.pdf

    There's a lot in there- look at figure 9- while a PowerPipe may be lower head than a tankless, most of the competition isn't. (The Retherm 60 does OK though, but it's heat transfer efficiency is somewhat lower.)

    (My kid probably uses more hot water in showers than your whole family does.)

  13. #43
    DIY Junior Member Diavolicchio's Avatar
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    I've discovered a decent amount of information online regarding the Canadian version of the GFX known as the Power-Pipe (www.renewability.com). If you're considering a drain heat recovery system, please at least consider the following information before making any decisions about the type you end up buying:

    * * * * *

    "The Powerpipe is an illegal copy of the original GFX. The Powerpipe also uses recycled copper that is not recommended for potable water by the US and Canadian copper association due to contamination." … “The posted results on the renewability (POWERPIPE) websites are false. The testing at Natural Resources Canada show that these numbers are far from the truth. Heat recovery from a Powerpipe is 30-35% while the GFX is 40 to 50% as posted on the WWW.GFXSTAR.CA website. BUYER BEWARE OF FALSE CLAIMS MADE BY RENEWABILITY” (from www.househacker.com/permanent/PowerPipe-Drainwater-Heat-Recovery-System)

    “Purchased this and found out the building inspector refused to authorize it. Something to do with the fact the UL certification is not applicable to potable water and since the device does not have ASTMB88 stamped on its copper, it was not considered safe for potable water.” (from www.conservationmart.com/p-714-power-pipe-drain-water-heat-recovery.aspx)

    “Powerpipe is made with recycled copper from China. The company makes false claims. I purchased 4 units from power-pipe and they were recalled due to lead in the braze. Two of the replaced units were leaking at the joint and 2 others were clogged with metal shavings in the fresh water feed. Highly not recommended.…How does ********* EXPLAIN THIS? I looked at one of these at RONA and noticed only a UL label on the pipe. No NSF 61 (toxicity tests for potable water) was written on the pipe. I called Renewability and they said they were UL certified for use with potable water. I did some more research and it looks like they make this same claim on several Powerpipe documentation. When asked if Powerpipe was safe for use with potable water, UL answered..."Searching for file number MH29466, I see that the file is held by the company Renewable Energy Inc. It appears that their Power-Pipe Series heat exchangers are listed as Specialty Heating-Cooling Appliance Accessories under UL Category Code MJAT (USA) and MJAT7 (Canada), but they do not appear to be certified to any drinking water safety standards."… "Powerpipe is made with recycled copper from China. The company makes false claims. I purchased 4 units from power-pipe and they were recalled due to lead in the braze. Two of the replaced units were leaking at the joint and 2 others were clogged with metal shavings in the fresh water feed. Highly not recommended… To set the record straight - Powerpipe is an IMITATION of GFX. “ (from www.treehugger.com/files/2006/06/the_powerpipe_r.php)

    “To set the record straight - Powerpipe is” a toxic-GFX not approved for potable water; advertised by Conservation Mart as “Power-Pipe™ (formerly known as GFX)…” @ www.gfxtechnology.com/C-Mart.pdf.


    * * * * *

    I'm not endorsing any particular model or manufacturer; I simply thought that people considering a GFX should consider this information before making any rash decisions about what to buy and from whom.

    John

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  14. #44
    In the trades Dana's Avatar
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    Diavolicchio, MOST manufacturers of drainwater heat recovery heat exchangers are in Canada, not just Renewability/PowerPipe. (Watercycles, Retherm, Ecoinnovation, etc.)

    Take all that crap you read about licensing & labeling issues with a pound (not a mere grain) of salt. This is an industry that's been in a pissin' match for over a decade. Until/unless there's been a ruling of LAW that a patent has been violated or labeling mis-used or any of the other allegations floating around out there, I prefer to just stay out of the splash and rely on 3rd party testing on performance data. YMMV. The US & Canada are both first-world countries with first-world legal systems- let the players duke it out in court if they think they have a case. Repeating the allegations in a forum posting adds no light, only heat to the subject (and not to the incoming water.)

    Ever since Renewability's number started edging out the competition the grousing has gotten louder. But if they have a case they should present the evidence to a judge. Neither you nor I are in a position to verify the validity of the above claims, no basis on which to accept the veracity of the folks making them.

    Indeed, Beauchemin of Ecoinnovation seems to spend more time bitchin' online about Renewabilty than properly marketing his own stuff. But what's the source of his cred over the other players? As a disinterested party all I see is assertions being made by a company whose goods under-perform those of the company they're bad-mouthing in the NRCan 3rd party testing. I bear him/them no ill will, but I'd prefer it if they'd just put-up or shut-up, take it to court if there's a case to be made. (Get him on the phone and I'm sure you'll get an earful! )

    And since when did "Anonymous user" on some web forum have any cred?

    I'll take NRCan's 3rd party test results over what anybody else has to say, and let the rest of the BS twist in the wind. There's more smokescreen than substance behind it, near as I can tell.

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