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Making hot water without a heat exchanger by routing combustion gas directly through water?

cowdog
cowdog Member Posts: 91


Boiler heat exchanger is a frequent point of failure of hot water hydronic heating systems.

Can we avoid using a combustion-water heat exchanger by routing combustion gas through water, making direct contact with water?

Exhaust could be a little acidic from sulfur in fuel, we should add baking soda into the recirculating water to avoid corrosion to metal.

For efficiency we can also add a small heat pump (about the same cost with a portable AC unit) to condense vapor in the humid combustion gas after passing through water.
mattmia2

Comments

  • retiredguy
    retiredguy Member Posts: 977
    Before I retired there was a company that did just that but the heated water was not for domestic use but was mostly used to heat water for use in a concrete plant. Could this be done for household domestic usage, I am not sure, it would take someone smarter than me to make that determination.
    cowdog
  • ratio
    ratio Member Posts: 3,791
    I'm sure you'd transfer heat to the water. I'm also sure you'd transfer all kinds of yummy chemical compounds to it as well. I wouldn't want to drink that water. Or wash with it. Or touch it. No matter how much filtering you do to it.
    kcoppSTEVEusaPAMikeAmann
  • pecmsg
    pecmsg Member Posts: 5,297
    cowdog said:
    Boiler heat exchanger is a frequent point of failure of hot water hydronic heating systems. Can we avoid using a combustion-water heat exchanger by routing combustion gas through water, making direct contact with water? Exhaust could be a little acidic from sulfur in fuel, we should add baking soda into the recirculating water to avoid corrosion to metal. For efficiency we can also add a small heat pump (about the same cost with a portable AC unit) to condense vapor in the humid combustion gas after passing through water.
    Condensed Vapor is extremely acadic!
  • Jamie Hall
    Jamie Hall Member Posts: 24,859
    Yes you would warm the water. And turn it into dilute nitric acid with a trace of suphuric -- pH probably around 2 or so, and capable of dissolving gold. It would also have any trace metals which were in the fuel (there always are some) or in the combustion air, and probably an interesting assortment of low level concentrations of various interesting organic compounds with scary names, some of which, like dioxins (a normal combustion product) scary properties as well.

    But would it me more efficient?

    Not if you were using a well-designed condensing water heater from the beginning...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    HVACNUTcowdog
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,518
    Joke?  I don't like the idea.  Too easy for Cross Contamination..Mad Dog 🐕 
  • HVACNUT
    HVACNUT Member Posts: 6,332
    edited July 2023
    I can't even picture it in my head. A vertical or horizontal flame(s) going directly through (interacting with) the path of the water to a flue or exhaust? 
    Is the water side under pressure? Actually, I guess there is no water side.
    How would you direct the combustion gases to the exhaust? I imagine a high point, but not directly. That's a lot of mixing. 
    And the combustion itself would need to be like welding under water, and hot enough to heat a vessel to 140° minimum. 
    Even if it could be done, are there any benefits?


  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,518
    Those fishes are gonna sleep 💤 with the fishes...in this environment.   Mad Dog
    JohnNY
  • cowdog
    cowdog Member Posts: 91
    edited July 2023

    Yes you would warm the water. And turn it into dilute nitric acid with a trace of suphuric -- pH probably around 2 or so.

    Saturate the water with baking soda to absorb the acids. Use a device to change water once the pH is lower than 7.
    We don't need clean water for room heating.


    Not if you were using a well-designed condensing water heater from the beginning...

    We need equipment affordable by the poorest Americans.
  • cowdog
    cowdog Member Posts: 91
    HVACNUT said:

    I can't even picture it in my head. A vertical or horizontal flame(s) going directly through (interacting with) the path of the water to a flue or exhaust? 
    Is the water side under pressure? Actually, I guess there is no water side.
    How would you direct the combustion gases to the exhaust? I imagine a high point, but not directly. That's a lot of mixing. 
    And the combustion itself would need to be like welding under water, and hot enough to heat a vessel to 140° minimum. 
    Even if it could be done, are there any benefits?


    1. Water side cannot be under pressure. To heating radiators by circulation pump.
    2. Simplicity is the benefit. Simplicity = affordability + low maintenance. High efficiency water heaters are expensive.
  • Steamhead
    Steamhead Member Posts: 17,387

    Hi @cowdog , The dead guys did this many years ago. I have a water heater from 1895 that does this. Here's a cutaway of a similar one.
    These were called contact heaters, where water and combustion products were mixed directly. They claimed to be 92% efficient. I assumed the acidic water cleaned better. You may note that venting wasn't a concern either :p

    Yours, Larry

    IIRC, Burnham tried this with their "Opus" gas boiler some years ago. Obviously we never see them now.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    cowdogMad Dog_2
  • hot_rod
    hot_rod Member Posts: 23,398
    There are direct fired water heaters out in the world😉

    https://www.maximizersystems.com/direct-fired-water-heaters
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    cowdog
  • cowdog
    cowdog Member Posts: 91
    edited July 2023
    hot_rod said:

    There are direct fired water heaters out in the world😉

    https://www.maximizersystems.com/direct-fired-water-heaters

    Nice! I hope direct-fired oil and wood fuel heaters could reduce cost of these units.
    Natural gas price has increased too much. Residents cannot afford the warmth. Wood chips are very cheap.
  • Jamie Hall
    Jamie Hall Member Posts: 24,859
    "We need equipment affordable by the poorest Americans."

    That is a political question, not an engineering or scientific one. Go talk to the EPA or the Consumer Products Safety people.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Solid_Fuel_Man
  • cowdog
    cowdog Member Posts: 91
    edited July 2023

    IIRC, Burnham tried this with their "Opus" gas boiler some years ago. Obviously we never see them now.
    In this forum thread, looks like the "opus" cannot tolerate hard water. Don't know exactly why. Maybe there needs to be some filtration and flushing system.
  • cowdog
    cowdog Member Posts: 91
    edited July 2023

    "We need equipment affordable by the poorest Americans."

    That is a political question, not an engineering or scientific one. Go talk to the EPA or the Consumer Products Safety people.

    Solution 1: subsidize them (we already do with LIHEAP and some EPA credits/rebates, but apparently not sufficient, many people still cannot afford)
    Solution 2: make simpler and cheaper equipment that need fewer repairs. Personal computers went a long way on this one.
  • STEAM DOCTOR
    STEAM DOCTOR Member Posts: 2,211
    @Erin Holohan Haskell @cowdog. Whether or not the government should subsidize anything, is a discussion for a different forum. Whether or not this particular idea is mechanically or otherwise feasible, is very much a discussion for this forum. 
    cowdog
  • Erin Holohan Haskell
    Erin Holohan Haskell Member, Moderator, Administrator Posts: 2,354

    @Erin Holohan Haskell @cowdog. Whether or not the government should subsidize anything, is a discussion for a different forum. Whether or not this particular idea is mechanically or otherwise feasible, is very much a discussion for this forum. 

    Yes. Thank you @STEAM DOCTOR.

    President
    HeatingHelp.com

  • Steamhead
    Steamhead Member Posts: 17,387
    edited July 2023
    cowdog said:


    Steamhead said: "IIRC, Burnham tried this with their "Opus" gas boiler some years ago. Obviously we never see them now. "

    In your link, looks like the "opus" cannot tolerate hard water. Don't know exactly why. Maybe there needs to be some filtration and flushing system.

    I didn't include a link. The ones I had are long dead.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,599
    Hi, I seem to remember that PVI made modern day contact heaters with a 99% efficiency. It was not clear by looking on their site if they still make these contact heaters. They seem to make bigger, commercial equipment.
    Yours, Larry
    cowdog
  • jumper
    jumper Member Posts: 2,385
    hot_rod said:

    There are direct fired water heaters out in the world😉

    https://www.maximizersystems.com/direct-fired-water-heaters

    One I saw had flame going down from water induced air flow. The was a heat exchanger down in the pan and directly heated water was recirculated. I forget how often recirculated water was changed. It was supposed to be super efficient at producing relatively low temperature (~100°) water.
    cowdog
  • Jamie Hall
    Jamie Hall Member Posts: 24,859
    Have to admit that that the beauty of direct contact approaches lies in having no heat transfer problems in a heat exchanger, plus they are inherently condensing systems, so the efficiency can and indeed sould be very high. The two downsides is making sure you are getting good complete combustion --which has to be done before contact with the water -- and then the water quality which results which is likely to need tweaking.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    cowdog
  • Matt_67
    Matt_67 Member Posts: 301
    One of the concrete batch plants by us has a direct fired aggregate heater. www.vortomech.com It works well but I don’t think it would be scalable for residential use.
    cowdog
  • ethicalpaul
    ethicalpaul Member Posts: 6,669
    If a dead person once did it, it is obviously a good idea. Case closed!

    NJ Steam Homeowner.
    Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
    See my sight glass boiler videos: https://bit.ly/3sZW1el

    Larry WeingartenSTEAM DOCTORSolid_Fuel_Man
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,386
    edited July 2023

    If a dead person once did it, it is obviously a good idea. Case closed!

    Unless of course, the death was caused by the contaminated water!

    This sounds like the beginning of a Marvel Comic story about AquaHulk

    This ordinary man that one day inadvertently bathed in the thermally heated water from an experimental Maximizer water heating system, at the brink of death, suddenly transformed into the words first amphibious super-hero

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    Larry WeingartenMikeAmannGGrossWMno57
  • cowdog
    cowdog Member Posts: 91
    edited July 2023

    Have to admit that that the beauty of direct contact approaches lies in having no heat transfer problems in a heat exchanger, plus they are inherently condensing systems, so the efficiency can and indeed sould be very high. The two downsides is making sure you are getting good complete combustion --which has to be done before contact with the water -- and then the water quality which results which is likely to need tweaking.

    It also lies in water, being a natural cleaner, is able to wash out air pollutants from flue.
    Wood, coal and oil flue have much less pollutants released to air after sufficient contact with water. The resulting dirty water can be periodically discharged as sewage, which is then centrally processed in the city's wastewater treatment plant.
  • Jamie Hall
    Jamie Hall Member Posts: 24,859
    Oh boy. Well, you do have a point. However, I have to mention two things. First, of an overall basis, I'm not at all convinced that moving contamination from one place or medium to another is a very good idea, although humans have been doing it for millenia. Second, a municipal wastewater treatment facility is not set up for, nor does it do a very good job at, managing very low levels of what are basically industrial contaminants (I've designed a number of the years, and run a few myself).

    So, not to put too fine a point on it, that's not, in my view, a very good justification for direct contact...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • cowdog
    cowdog Member Posts: 91

    Oh boy. Well, you do have a point. However, I have to mention two things. First, of an overall basis, I'm not at all convinced that moving contamination from one place or medium to another is a very good idea, although humans have been doing it for millenia. Second, a municipal wastewater treatment facility is not set up for, nor does it do a very good job at, managing very low levels of what are basically industrial contaminants (I've designed a number of the years, and run a few myself).

    So, not to put too fine a point on it, that's not, in my view, a very good justification for direct contact...

    You mean fly ash, soot and creosote cannot be neutralized by anaerobic and aerobic digestion of sludge?

    I think
    • fly ash from wood burning are mostly minerals naturally contained in soil, since wood grows from soil.
    • soot is basically carbon, once it attach to soil to become the "peat" part of soil.
    • Creosote is naturally produced by wildfires, since you don't see a natural forest full of creosote, it can be degraded in natural environment.
  • WMno57
    WMno57 Member Posts: 1,408
    Here are some Polycyclic Aromatic Hydrocarbons that have not broken down or degraded in 65 million years.
    https://en.wikipedia.org/wiki/Polycyclic_aromatic_hydrocarbon#Natural_fires
    "High levels of such PAHs have been detected in the Cretaceous-Tertiary (K-T) boundary, more than 100 times the level in adjacent layers. The spike was attributed to massive fires that consumed about 20% of the terrestrial above-ground biomass in a very short time."
  • Jamie Hall
    Jamie Hall Member Posts: 24,859
    My comment stands.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    There was someone who made a condensing woodstove with this idea. They sprayed the water down a pipe which induced the draught. The naturally heated water was run through a small fan coil to extract latent heat. I'd expect the water to get nasty fast. I think there was a bypass to get the fire going and reach secondary burn temperatures first. Then the condensing mode was started. 

    I'll go through some archives and see if I can find it. I'd like to experiment with that someday in my shop. 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • Big Ed_4
    Big Ed_4 Member Posts: 3,020
    Combustion is acidic , it would kill the fish....

    There was an error rendering this rich post.

  • jumper
    jumper Member Posts: 2,385
    Big Ed_4 said:

    Combustion is acidic , it would kill the fish....

    bah! who tells fish to drink it? Seriously, pollutants have to go somewhere. Down the drain; into the air; or get buried.
    Solid_Fuel_Man
  • jpsr
    jpsr Member Posts: 5
    edited July 11

    Contamination is based on the fuel used and combustion process. If hydrogen was used instead of a carbon-based fuel, this would solve the problem as the byproduct of burning hydrogen is actually water!

  • Jamie Hall
    Jamie Hall Member Posts: 24,859

    And one of the byproducts of burning hydrogen in air is various nitrogen oxides, which are serious air pollutants (why do you think you have a 4 figure cat. converter on your car?) (or DEF for diesels?) which turns into nitric acid when dissolved in water… no one mentions that, do they?

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • jpsr
    jpsr Member Posts: 5
    edited July 11

    not sure if the NOx would simply be an air byproduct or if it would be in solution, but I fear you may be right.

  • Intplm.
    Intplm. Member Posts: 2,197

    Commercially I have seen coils installed on boiler exhaust. Heating water through a coil and returning it to the boiler.

    It was called back then, an economizer.

  • Jamie Hall
    Jamie Hall Member Posts: 24,859

    Or reed water heater. Look at almost any railroad steam engine built since WW I and you will find one on there somewhere.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Intplm.