Calculating Propane Usage and BTUs for Tankless Hot Water System

[Diavolicchio]

I hope there are some techies following this forum who may be able to help me do some basic calculations regarding anticipated propane usage.

I'm building a new home this coming year and one of the indulgences I'm allowing myself is a luxury shower with 6 shower heads, each using 2.5 gpm (or 15 gpm total) of hot water. I know how incredibly wasteful this sounds, so I'm utilizing some technology to get my costs down on heating the water. It's also water coming from my own well and going back into my own land.

I'm trying to calculate the amount of propane I'll need to use on a daily basis in two different scenarios--summer and winter.

My basic set-up consists of a TriangleTube Smart 120 indirect hot water heater (http://www.triangletube.com/documents/2/SMART%20Literature.pdf) that is preheated by a boiler loop coming from the wood stove heating the house (http://www.esse.com/stoves/multifuel_wood/ironheart.html) in the cold months. A GFX Drain Heat Recovery System (http://www.meticulum.com/GFX.jpg) will also preheat the water going into the on-demand water heaters by means of a copper coil wrapped around the shower drain. The preheated water will then be fed into a pair of Noritz 0841 condensing tankless water heaters (http://www.noritz.com/homeowners/products/view/0841_series_condensing_tankless_water_heater). In addition, I'll be using a Puritec MC-14 whole house well water filter and hard water conditioner (http://www.puritec.com/store/index.cfm?fuseaction=product.display&Product_ID=123) to filter out any impurities.

In the summer months, my well water is around 56F and my goal is to be able to produce 15 gpm indefinitely at 110F. The GFX coil on my drain will be able to preheat the well water from 56F to 80F, leaving a needed rise in the summer of 30 degrees to get to 110F.

In the winter months, my well water is around 45F. I'll have the benefit in the winter of preheating the water twice, once with the boiler loop between the wood stove and indirect hot water heater, and a second time with the GFX coil on the shower drain. The boiler loop should get the water from 45F to 65F, the GFX from 65F to 89F, leaving a needed rise in the winter of 21 degrees to get it to 110F.

I'm anticipating using the shower at full capacity (15 gpm) for a full hour every day. How do I calculate how much propane I'll need to use on a daily basis, both in the summer and in the winter?

By the way, the pair of on-demand water heaters I'm using are 94% efficient, if that needs to be factored in here. They each have a maximum consumption of 199,900 btu/hr, for a total of 400,000 btu/hr for the pair. Note that I'll be setting the on-demand water heaters to the exact water temperature I want because it won't be mixing with any cold water.

I'm at a loss how to calculate the BTUs needed on a daily basis, and the subsequent amount of propane needed.

Anyone willing to help me calculate this? I'd greatly appreciate it!

John

[jadnashua]

22K BTU/pound of propane. 400K/22K=18.18pound per hour/4.23pound/gallon = 4.3 gallons. Throw in some efficiency losses and 5 gallons/day, then add a bit more for routine hot water use, and you may have another gallon (probably less). Now, that's at full output, and that is likely to make the water hotter than you need. So...

If you figure roughly 8#/gallon of water and you have 15gpm*60min*8=7200# of water per hour. So, it will take 7200BTU for each degree you need to raise the water temp. WIth these numbers, you can do the rest of the calculations.

[Diavolicchio]

22K BTU/pound of propane. 400K/22K=18.18pound per hour/4.23pound/gallon = 4.3 gallons. Throw in some efficiency losses and 5 gallons/day, then add a bit more for routine hot water use, and you may have another gallon (probably less). Now, that's at full output, and that is likely to make the water hotter than you need. So...

If you figure roughly 8#/gallon of water and you have 15gpm*60min*8=7200# of water per hour. So, it will take 7200BTU for each degree you need to raise the water temp. WIth these numbers, you can do the rest of the calculations.

Jim:

I'm still a little confused here. You say I'd be using roughly 5 gallons of propane per day if I used this shower for a full hour at full capacity, and allowed for other incidental hot water usage in the house.

Yet when I follow your other numbers of 7200BTU/each degree, I get:

Summer: 7200*30 = 216,000 BTU/hour
Winter: 7200*21 = 151,200 BTU/hour

And dividing these by 91,500 BTU/gallon of propane, I get:

Summer: 216,000/91,500 = 2.36 gallons propane / hour
Winter: 151,200/91,500 = 1.66 gallons propane / hour

Why is there such a disparity between the 4.3 gallons of propane you're estimating for an hour of showers/day and the ~2 gallons of propane I'm estimating when I work backwards from BTUs/gallon of propane?

I hope it's your calculations that are off, because I can't imagine spending $12/day just to take 2 indulgent showers. That's $4,380 a year using significantly preheated water!

John

[Runs with bison]

Man, that is a lot of flow. An hour at 15 gpm is 900 gallons...that is 9 times as much total water as what my family uses in a day. It is good that you will be able to recover some of the heat through a falling film heat exchanger. However, I do wonder about how much area it will have and how much it can really recover. What length of unit, what tubing size, and what pressure drop do they project for 15 gpm?

Back of the envelope, even with heat recovery it looks like your water heating fuel use will equal or exceed what it takes to heat my home.

Since you say you will heat 900 gallons/day by 30 F in summer and 21 F in winter with a 94% tankless heater I believe the calcs work out as follows:
Winter = 15 gal/min * 60 min/day * 8.33 lb/gal * 1 Btu/lb F * 21 F / 0.94 = 167,500 Btu/day
Summer = 15 * 60 * 8.33 * 1 * 30 / 0.94 = 239,000 Btu/day

Propane's heating value is 91,600 Btu/gal. So you would use 1.8 gal/day in winter and 2.6 gal/day in summer if I did the calcs correctly.

Of course if the preheating falls short you will need more than this. Plus I've not included water heating for other uses: handwashing, dishwashing, clothes washing, etc.

[Diavolicchio]

Jim:

I'm still a little confused here. You say I'd be using roughly 5 gallons of propane per day if I used this shower for a full hour at full capacity, and allowed for other incidental hot water usage in the house.

Yet when I follow your other numbers of 7200BTU/each degree, I get:

Summer: 7200*30 = 216,000 BTU/hour
Winter: 7200*21 = 151,200 BTU/hour

And dividing these by 91,500 BTU/gallon of propane, I get:

Summer: 216,000/91,500 = 2.36 gallons propane / hour
Winter: 151,200/91,500 = 1.66 gallons propane / hour

Why is there such a disparity between the 4.3 gallons of propane you're estimating for an hour of showers/day and the ~2 gallons of propane I'm estimating when I work backwards from BTUs/gallon of propane?

I hope it's your calculations that are off, because I can't imagine spending $12/day just to take 2 indulgent showers. That's $4,380 a year using significantly preheated water!

John

Jim:

I forgot to point out one thing. Extrapolating from the chart on the Noritz site (noritz.com/u/flow_chart.gif) (see specifically the 841/842 series column) and factoring in the necessary rise in temperature, 400k BTU/hr for the pair of Noritz would give me 23.5 gallons/min of hot water in the summer (with a 30 degree rise) and 28.0 gallons/min of hot water in the winter (with a 21 degree rise). There would need to be a 50 degree rise for the 400k BTU/hr to provide me with no more than the 15 gallons/min I'm after. Make sense?

Let me know, would you? I may have this totally backwards.


John

[Runs with bison]

I hope it's your calculations that are off, because I can't imagine spending $12/day just to take 2 indulgent showers. That's $4,380 a year using significantly preheated water!

John,

If it was municipal water and sewer like here you could add another ~$4/day for those.

Is your well going to be able to produce this much water each day and will your septic tank and field lines handle it? I would imagine the size of both is effectively doubled compared to what it would be otherwise.

[Diavolicchio]

John,

If it was municipal water and sewer like here you could add another ~$4/day for those.

Is your well going to be able to produce this much water each day and will your septic tank and field lines handle it? I would imagine the size of both is effectively doubled compared to what it would be otherwise.

Thanks for the feedback. I'm glad the numbers look to be closer to 2 gallons/day rather than 5!

I lucked out with my well; it produces 20 gallons/minute. Pressure drop with the GFX I'll be using will be around 2.7 psi. You'll find a schematic of the particular unit here (http://www.meticulum.com/GFX.jpg).


John

[Diavolicchio]

Back of the envelope, even with heat recovery it looks like your water heating fuel use will equal or exceed what it takes to heat my home.


The funny thing about it is that the house into which this system is going will be so super-insulated, that in the dead of winter here in Maine, it'll take around 12,500 BTU/hr to keep the house at 70F when it's -20F outside. And I'll be heating predominantly with wood.

If it weren't for this, I wouldn't be allowing myself the indulgence of such an over-the-top shower.


John

[Diavolicchio]

Here's an illustration of the shower set-up. I'm eliminating the transfer valve so that all six shower heads can work simultaneously, and setting the whole system up so custom showers can be pre-programmed using a digital thermostatic valve and interface:

http://www.meticulum.com/hydromassage.jpg

I think it's a pretty safe bet that when you step out of one of these showers in the morning, you're AWAKE.

* * * * *

Here's a photo of a 4-column GFX similar to the one I'll be using, but this one uses PVC manifolds instead of copper. It gives you a good visual of the set-up though:

http://www.meticulum.com/4ColumnGFXArray.jpg


John

[hj]

IF you take the money you will save by using the GFX system and add about $4.45 to it, you MIGHT be able to buy a $4.50 Starbucks cup of coffee. By the time your "hot water" goes down the drain it will not have enough residual temperature to do much preheating, especially if the water does not gravitate to the pipe walls while flowing down the risers, and if your drain system looks like the one in the picture, you have created a drain nightmare. Especially when it comes to unplugging it, because you will not know it is getting obstructed until ALL four risers are plugged, and then unplugging them all will be somewhat expensive.

[Diavolicchio]

IF you take the money you will save by using the GFX system and add about $4.45 to it, you MIGHT be able to buy a $4.50 Starbucks cup of coffee. By the time your "hot water" goes down the drain it will not have enough residual temperature to do much preheating, especially if the water does not gravitate to the pipe walls while flowing down the risers, and if your drain system looks like the one in the picture, you have created a drain nightmare. Especially when it comes to unplugging it, because you will not know it is getting obstructed until ALL four risers are plugged, and then unplugging them all will be somewhat expensive.

I appreciate your 2-cents. Seriously. I've done my research though and am content with what I've learned and the technology I'll be utilizing. The water in this particular shower should hit the drain at around 95F and have no problems doing its job clinging to the pipe walls.

My drain system will be a bit different from the one in that photo. I just posted that because it was the best example I could find of a 4-column GFX. They do work though if you size them and set them up properly. I know a number of people who have them and are quite happy with the results.

I will say though that I was saddened to learn you'd waste $4.50 on a mediocre cup of designer coffee. Isn't that a little wasteful?

Cheers,


John

[Runs with bison]

IF you take the money you will save by using the GFX system and add about $4.45 to it, you MIGHT be able to buy a $4.50 Starbucks cup of coffee. By the time your "hot water" goes down the drain it will not have enough residual temperature to do much preheating, especially if the water does not gravitate to the pipe walls while flowing down the risers,

Plumbers should stay away from bold statements about economics, it isn't their strong suit. :rolleyes: For the extreme amount of hot water he is using and propane this will easily pay for itself if used as stated.

The blanket assumptions you make don't hold a candle to doing actual calculations and measurments. Economics for my own use in DWHR are marginal because my home uses 1/27th as much hot water for showering as what this fellow is talking about.

I might try one of these systems just out of curiosity. The deal killer in the economics for my home is not so much the cost of the exchanger, it's the additional cost of paying a plumber to install it. That holds true for about anything that requires plumbing or flue changes. And with the serious attitude that plumbers seem to have (not to mention frequent competency problems), it probably makes more sense to cut them out and DIY properly.


I've done my research though and am content with what I've learned and the technology I'll be utilizing. The water in this particular shower should hit the drain at around 95F and have no problems doing its job clinging to the pipe walls.

My drain system will be a bit different from the one in that photo. I just posted that because it was the best example I could find of a 4-column GFX. They do work though if you size them and set them up properly.

If you really shower at about 110 with that high of a flow you shouldn't have any trouble getting 95 F water at the drain. I measured my 1.6 gpm shower temp as 106 F at the head and 97 F at the drain. A much higher flowrate on the same body/space will result in less temperature loss.

Getting even distribution of the water among the drain exchangers could be challenging. The entrances for each need to be very level and uniform with respect to one another to minimize maldistribution. That's why they did the 1 to 2 to 4 split. I've done distillation and scrubber tower distributor design/troubleshooting and subtle differences had large impacts on performance.

With the high flowrates and relatively smaller ratio of soap scum and hair, plugging in the big lines is unlikely.

One concern I have with your earlier numbers is your assumption of winter preheating by a wood stove (at least based on the Btu rate you provided.) It wasn't apparent to me how the stove would provide much preheating after the first 10 minutes of shower. What sort of Btu rate do you see that injecting into the system.

Another thing that had me puzzled about the preheat is wouldn't it make more sense for the boiler preheat to be after the drainwater preheating rather than before? The greater the delta T at the DWHR coils, the greater the total heat flux. I would expect the boiler preheating to be relatively fixed heat flux by comparison. I'm going by what you stated in the initial post about preheating. Process flow diagram wise I believe the arrangement should be reversed for maximum efficiency.

[Thatguy]

50 to 200 gals/person/day, ~100 is avg., but see below

http://www.census.gov/compendia/statab/tables/09s0354.pdf

[Diavolicchio]

Plumbers should stay away from bold statements about economics, it isn't their strong suit. . . And with the serious attitude that plumbers seem to have (not to mention frequent competency problems), it probably makes more sense to cut them out and DIY properly.

Can I get a Hallelujah here?


One concern I have with your earlier numbers is your assumption of winter preheating by a wood stove (at least based on the Btu rate you provided.) It wasn't apparent to me how the stove would provide much preheating after the first 10 minutes of shower. What sort of Btu rate do you see that injecting into the system.

Another thing that had me puzzled about the preheat is wouldn't it make more sense for the boiler preheat to be after the drainwater preheating rather than before? The greater the delta T at the DWHR coils, the greater the total heat flux. I would expect the boiler preheating to be relatively fixed heat flux by comparison. I'm going by what you stated in the initial post about preheating. Process flow diagram wise I believe the arrangement should be reversed for maximum efficiency.

Bison:

I'm glad you're on this list and not only understand what I'm trying to do, and how it all works, but why someone would want to do it. Your feedback is exactly what I was hoping to get.

The preheating by the loop in the wood stove was based on nothing more than feedback from a plumber friend of mine. Your suggestion about reversing the order in which the coils get heated makes perfect sense. This system hasn't yet been fully designed, nor have I broken ground yet for the house, so I'm open to any suggestions you have that may make things more efficient. Do I need a 119 gallon tank? Would two 80 gallon tanks hooked up to the boiler loop make more sense? Would a completely different option make better sense? I simply don't know.

My goal is ultimately being able to somehow preheat the water in the winter that jump starts a shower so that the delta T is around 20 degrees. I know in the Summer when there's no boiler loop to assist that I'm dealing with a delta T of 30 degrees. How would you suggest tapping into the energy of the boiler loop to bump the 45F well water up to 65F relying solely on the free energy produced by the wood stove ? Should I be looking at a different tank than the SuperStor Ultra to harness this?

What I can tell you about the boiler loop is that it's "a 16,000 BTU boiler capable of running a single radiator as well as providing domestic hot water." I plan on harnessing this extra energy in the winter both for the shower water pre-heat as well as for a radiator on the 2nd floor of the house. I'm completely open to your suggestions as to how best to get that 20+ degree pre-heat for the shower system. I'm all ears.

Thanks, Bison.


John

[Doherty Plumbing]

http://www.meticulum.com/4ColumnGFXArray.jpg

I can't believe this "device" is even acceptable in any code jurisdiction.

And Bison us plumbers should maybe stay away from economics but you should stay away from math.

[jadnashua]

IF you needed all of the tankless output to produce the hot water you need, it would be the values indicated, and I also said you probably wouldn't need all of it. So, since one pound of water raised 1 degree is one BTU, and knowing the temperature rise you need and the pounds needed, you ran those numbers. My first calc was using all 400K BTU running full out for an hour. My goal was to give you the info you needed to run the calculations with an example, not do your homework for your!

That's still pretty indulgent, but if you've got it and don't care about your carbon footprint, it's your choice. You'll need a MUCH bigger septic system to accommodate the flow, too. Hopefully, you have enough land, or you'll have a swamp after a bit. Well, maybe not if it is really sandy.

[Diavolicchio]

IF you needed all of the tankless output to produce the hot water you need, it would be the values indicated, and I also said you probably wouldn't need all of it. So, since one pound of water raised 1 degree is one BTU, and knowing the temperature rise you need and the pounds needed, you ran those numbers. My first calc was using all 400K BTU running full out for an hour. My goal was to give you the info you needed to run the calculations with an example, not do your homework for your!

No worries. Bison understood what I needed. I appreciate you responding.


That's still pretty indulgent, but if you've got it and don't care about your carbon footprint, it's your choice.

For the record though, I do care about my net carbon footprint. That's why I'm building a house that only requires 12,500 BTU/hr in the dead of a Maine winter to keep it at 70F. Even with the indulgent shower, I'm guessing that my net carbon footprint is still considerably less than most people. Keep in mind that I'm only using propane for a delta T of 20 to 30 degrees. Everything else is produced by renewable energy (wood) and free recovered energy (GFX on the shower drain). Even the water for the shower is coming from my land and going directly back into it.

Don't be so quick to judge.


John

[Runs with bison]

And Bison us plumbers should maybe stay away from economics but you should stay away from math.

Have you got a basis, or are you just pulling this out of your wazoo the same as you did your declaration that smaller piping produces less pressure drop?

[Runs with bison]

The preheating by the loop in the wood stove was based on nothing more than feedback from a plumber friend of mine. Your suggestion about reversing the order in which the coils get heated makes perfect sense. This system hasn't yet been fully designed, nor have I broken ground yet for the house, so I'm open to any suggestions you have that may make things more efficient. Do I need a 119 gallon tank? Would two 80 gallon tanks hooked up to the boiler loop make more sense? Would a completely different option make better sense? I simply don't know.

I've not ever had a home boiler and radiator set up, so I don't know what sort of arrangement is feasible. (The boilers I've worked with were industrial high pressure in the 1200 psig range.) Others here have had more experience with domestic boilers.


What I can tell you about the boiler loop is that it's "a 16,000 BTU boiler capable of running a single radiator as well as providing domestic hot water." I plan on harnessing this extra energy in the winter both for the shower water pre-heat as well as for a radiator on the 2nd floor of the house. I'm completely open to your suggestions as to how best to get that 20+ degree pre-heat for the shower system.

The problem I see is the 16,000 BTU (Btu/hr?) rate. If I'm interpreting that correctly at 15 gpm that will give a rise of only 16,000 / (15*8.33*60*1) = 2.1 degrees F. By comparison a typical natural gas tank water heater runs ~40,000 Btu/hr input.

I do think you will want a large tank like you were thinking of to get things rolling for showers, but I have no experience with the controls on such a system in the home.

[Diavolicchio]

The problem I see is the 16,000 BTU (Btu/hr?) rate. If I'm interpreting that correctly at 15 gpm that will give a rise of only 16,000 / (15*8.33*60*1) = 2.1 degrees F. By comparison a typical natural gas tank water heater runs ~40,000 Btu/hr input.

I do think you will want a large tank like you were thinking of to get things rolling for showers, but I have no experience with the controls on such a system in the home.

Bison:

Maybe someone else in this Forum will have some constructive suggestions. I'm planning to give a call to the folks at Heat Transfer Products (SuperStor), TriangleTube and ESSE Wood Stoves on Monday to run this by them directly. I like the sounds of TriangleTube's Smart 120 indirect water heater even better than the SuperStor Ultra, but I'll need to have someone calculate just what affect the boiler loop on the ESSE may have in getting a Smart 120 to continuously pre-heat water at least 10 to 12 degrees.

There's got to be a way of making this system work year-round without exceeding a delta T of 30 degrees with the Noritz's and without requiring any additional energy in the winter beyond the boiler loop from the wood stove. I'll post my findings.

Thanks for all of the feedback.


John

[Terry]

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.

[Runs with bison]

The key thing that the GFX hit on was the falling film design. It makes perfect sense for resolving the problems of a gravity drain with venting concerns and the like. This maximizes the heat transfer coefficient on the drainwater side while minimizing the potential for plugging.

I haven't had the opportunity to see one of these units in action. I'm skeptical of manufacturer's claims and would like to see their real world performance, especially since short ultra low flow showers and piping lag and lost volumes would hammer the overall performance.

[Diavolicchio]

The problem I see is the 16,000 BTU (Btu/hr?) rate. If I'm interpreting that correctly at 15 gpm that will give a rise of only 16,000 / (15*8.33*60*1) = 2.1 degrees F. By comparison a typical natural gas tank water heater runs ~40,000 Btu/hr input.


Bison:

I've found a great woodburning boiler stove (http://www.broseleyfires.com/Wood-Burning-Stoves/Hercules-20B_Woodburning-Boiler-Stove.html) for the living room (here's a better photo (http://www.meticulum.com/Broseley_Hercules_20.jpg)) that will easily heat the whole house as well as provide a 50,000 BTU/hr boiler (as opposed to the 16,000 Btu/hr boiler with the ESSE) to pre-heat the water in the storage tank. I'm just not sure what kind of a bump-up in temperature this will give me in the hot water tank if I'm starting with a full tank that's already hot from the boiler loop and bleeding the tank at the rate of 15 gallons/minute for 30 minutes at a time.

I'll talk to the folks at TriangleTube on Monday and have them do some calculations for me. If I'm able to get the cold water that's replenishing that tank at 15 gallons/minute to warm up by at least 10 degrees before leaving the tank, I'm happy with that. A 20 degree increase would be optimal though. I just don't know what 50,000 Btu/hr would be able to do using the technology behind this particular tank. From what the TriangleTube website says, these tank-in-tank systems heat up MUCH faster than the ones with a coil-based heat exchanger. Check out this quick Flash demonstration (http://www.triangletube.com/Flash_TANK.html) for the TriangleTube tank and let me know what you think, would ya? It's an intriguing set-up.

If I'm able in the cold months to get the additional 20 degree increase that I'm after from the boiler, two 30 minute/450 gallon showers in a given day will cost an average of $2.40/each in propane (which is the current cost per gallon for propane in my part of the country.) Personally, I think they'll be worth every damn nickel.

Incidentally, without the GFX and wood boiler pre-heat they'd cost over $7.00/each--nearly 3X as much.


John

[Doherty Plumbing]

Have you got a basis, or are you just pulling this out of your wazoo the same as you did your declaration that smaller piping produces less pressure drop?

Yep. I'm a ticketed gas fitter not just some guy who searches google to come up with answer about a field he knows NOTHING about. Your math was wrong plain and simple. Not by a lot but still wrong none the less.

[Diavolicchio]

Yep. I'm a ticketed gas fitter not just some guy who searches google to come up with answer about a field he knows NOTHING about. Your math was wrong plain and simple. Not by a lot but still wrong none the less.

I'll give it 10 minutes and this guy is going to start pulling someone's hair and calling him a doodyface.


John

[jadnashua]

IF you're going to have multiple heating sources for an indirect (and even just one), it's good to put a tempering valve on the output to limit the temperature of the output so you don't get scalded. The only thing you don't want to do is ensure you don't get the water so hot you could start to get steam..that could be catastrophic.

[Diavolicchio]

IF you're going to have multiple heating sources for an indirect (and even just one), it's good to put a tempering valve on the output to limit the temperature of the output so you don't get scalded. The only thing you don't want to do is ensure you don't get the water so hot you could start to get steam..that could be catastrophic.

Thanks. I really appreciate the advice.


John

[Runs with bison]

Yep. I'm a ticketed gas fitter not just some guy who searches google to come up with answer about a field he knows NOTHING about.
Your lack of even the most basic knowledge on piping losses indicates the exact opposite: you comment on things you know NOTHING about.

You did it again with your assinine comment about that parallel GFX set up arrangement.


Your math was wrong plain and simple. Not by a lot but still wrong none the less.

Excuse me if I'm unimpressed at your attempt at a pissing contest. I'm just a chemical engineer accustomed to operating on a much larger scale, chemical plants and refineries. I've designed, modeled, troubleshot and operated various equipment, reactors, exchangers, distillation vessels. etc. I'm accustomed to using natural gas, propane, ethylene, propylene, ethane, hydrogen, carbon monoxide, O2, etc. as reactor feedstock...as well as for simple combustion.

Now, if you want to point out where my "math was wrong", please go ahead. I don't claim to be perfect. (You might also be taking something out of context...that's my guess...I'll wait and see if there is any substance to what you say.) If I have gotten something substantially incorrect then it should be corrected.

[Runs with bison]

IF you're going to have multiple heating sources for an indirect (and even just one), it's good to put a tempering valve on the output to limit the temperature of the output so you don't get scalded. The only thing you don't want to do is ensure you don't get the water so hot you could start to get steam..that could be catastrophic.

I agree.

Diavolicchio

I looked at the flash presentation of the tank and it still isn't clear how this is going to work into the preheating. You will start with a very hot tank so you would have to do a mix control valve to achieve some specific preheat target I suppose. Otherwise it's hot water would be used first, then the big tankless burners would kick in several minutes later. Residential boiler's are an area I don't have experience with. The tankless folks might have some experience working these in.

Even at 50,000 Btu/hr the steady state rise (once the tank was depleted) would be ~7 deg. F.

The project is far from the beaten path and that makes it interesting.

[Diavolicchio]

Diavolicchio

I looked at the flash presentation of the tank and it still isn't clear how this is going to work into the preheating. You will start with a very hot tank so you would have to do a mix control valve to achieve some specific preheat target I suppose. Otherwise it's hot water would be used first, then the big tankless burners would kick in several minutes later. Residential boiler's are an area I don't have experience with. The tankless folks might have some experience working these in.

Even at 50,000 Btu/hr the steady state rise (once the tank was depleted) would be ~7 deg. F.

The project is far from the beaten path and that makes it interesting.

I was just intrigued with the particular slide (the one entitled "tank-in-tank: the advantages") that showed how the tank-in-tank system preheated the same amount of water as the coil-based cylinder tank but in 1/3 the time because of the exceptionally large heating surface area inside the TriangleTube tank.

If each shower requires 450 gallons of 110F water, and the first 100 gallons/shower are already at the proper temp inside the tank, I'm trying to identify the quickest solution for preheating the remaining 350 gallons still to enter the tank using energy solely from the wood boiler. The GFX should then give it an additional 24 degree boost prior to it hitting the pair of tankless water heaters. I guess I'm hoping that the TriangleTube technology will have some kind of edge over the tanks with the traditional coil heat-exchangers to allow me at least an extra 10 degree of preheating before the water hits the GFX.

I'll run this all by the folks at TriangleTube tomorrow and will let you know what they have to say.


John

[Thatguy]

I've found a great woodburning boiler stove (http://www.broseleyfires.com/Wood-Burning-Stoves/Hercules-20B_Woodburning-Boiler-Stove.html) for the living room
1 therm = 14# of wood at 100% efficiency.

[Diavolicchio]

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 (http://gfxtechnology.com/G4-80-4.PDF), 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

[Runs with bison]

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?

[Diavolicchio]

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 (http://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.


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

[Dana]

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 (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 (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.

[Diavolicchio]

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

[Dana]

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/ (http://www.ecoinnovation.ca/residential-solutions/)

[Runs with bison]

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/ (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.

[Dana]

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.

[Diavolicchio]

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

[Runs with bison]

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.

[Dana]

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/audiences/3637-07_2/DDR3637_2/RepDDR/B-12-GI-23Doc1-2_RepDDRSE-AQLPA_3637-2_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.)

[Diavolicchio]

I've discovered a decent amount of information online regarding the Canadian version of the GFX known as the Power-Pipe (www.renewability.com (http://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 (http://WWW.GFXSTAR.CA) website. BUYER BEWARE OF FALSE CLAIMS MADE BY RENEWABILITY” (from www.househacker.com/permanent/PowerPipe-Drainwater-Heat-Recovery-System (http://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 (http://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 (http://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 (http://www.gfxtechnology.com/C-Mart.pdf)/C-Mart.pdf (http://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

[Dana]

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! :eek: )

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.