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Hydronic heat quiz

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Eric Johnson, Feb 12, 2006.

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  1. joshuaviktor

    joshuaviktor New Member

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    Ok, so instead of a coil in the wood boiler, you have a jacket around it to get heat, and then pipes and circulator to circulate jacket to tank. Ok. Got it. return water, hopefully still warm, heats a heat exchanger for a sidearm DHW system. Sidearm - like the amtrol tank off my oil furnace, right?

    How does water get added to tank, if it blows off a PRV, or just gets a little low? Off top of head, toilet float switch of some sort, but there might already be way.

    Your way has much less possibility of BLEVE (Boiling Liquid Expanding Vapor Explosion), cause it has much more liquid in the system to impart cooling properties, and PRV valves in several places.
    The only problem I can think of is that your system might have too much likelihood of the thermosiphon effect causing a cooling of the jacket/tank when the system is idle, (no flame), but you still want it to hold heat (for dhw, a little remaining household heat, etc.)

    Also, with the heat exchanger system, all the heat can be input to the tank, and all the output to the DHW, for summer use. With your system, the thermosiphon effect will move the hot water upstairs to the radiators, and cool it off, but heat the rooms, even without circulator pumps.

    Actually, to be honest, the heat exchanger system might do the same. I'm not sure.

    Something to think about.

    Joshua

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  2. Eric Johnson

    Eric Johnson Mod Emeritus

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    I'm at work now and have to head home before they close the highway due to high winds and weather. I'll read your post again tonight and we can take this a little further.
  3. elkimmeg

    elkimmeg Guest

    you would use a variable fill vavle attached to your domestic hot water system. It is pressure activated. Once
    the pressure inside the loop of the burner fall say below 15 lbs, the valve would open and restore the vollume
    and pressure, once met it automatically shuts off.
  4. Eric Johnson

    Eric Johnson Mod Emeritus

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    That's a good explanation, elk. Most boilers I've seen have those connecting the closed loop system to the domestic water supply. Mine both do. If the boiler(s) overheated and lifted the PRVs, cold water from the domestic water supply rushes in to replace it. In a catastrophic release, the flow of cool water would theoretically help cool things down. Of course, there goes your glycol, but it beats having to replace a burned-out (or exploded) boiler.

    Josh, this sort of thing is just a hobby with me, so I'm really not qualified to design or build these systems, although I would certainly jump at the chance to do it.

    Anyway, I like to keep things simple if possible. To me, the water storage tank would simply be another zone off the wood-fired boiler. Actually, it would be a zone off both the wood boiler and, say, a gas backup.

    I would connect the two boilers and circulate hot water from the wood boiler into the existing gas unit, from which the zones would be served by the existing circulators or zone valves. All the wood-fired boiler is doing is replacing the gas burner as a means of heating the water that is distributed up into the house. I would set the tank up as an auxiliary storage vessel, where hot water could be stored when the boilers would othewise be either idle or working on a light load. Put a zone valve or a circulator in the pipe between the wood/gas boiler and the tank, and allow hot water to flow through the tank when appropriate. What's appropriate? For the sake of simplicity in explaining, let's say there's a circulator that circulates water into the tank when none of the zones in the house are calling for heat. The boiler keeps cranking, it just diverts hot water into the tank. Then when there's a call for heat in a zone, the exchange circulator shuts off and the zone gets the heat it needs from the boiler vessel. This way, over time, you "bank" hot water that can be used later. This also allows the wood boiler to operate at a consistent load, which I suspect would be more efficient. At times when the wood boiler has burned down (like early in the morning), the circulator kicks on and supplies hot water to the system from the tank, resulting in basically uninterrupted home heating even when the wood fire has burned down.

    The DHW thing could be done any number of ways. You could run a coil into the storage tank, or pump water from either of the boilers or the tank to a heat exchanger on the hot water heater, or run a conventional coil through one of the boilers. Whatever you like.

    A sidearm heat exchanger is simply a long piece of large diameter copper tubing with tees on each end and slide-through reducers on each end, through which a smaller piece of copper tubing is attached. In my case, it's a 4-foot piece of 1 1/4-inch copper with a 3/4-inch piece of tubing soldered into the reducers so that it runs right down the middle. You circulate boiler water through the outer jacket (in through the bottom tee and out the top tee). The 3/4-inch inner tube contains domestic water from the water heater. As it heats, it circulates with gravity, creating a constant flow of hot water into the top of the water heater. You can pump it if you need more capacity. Mine works on gravity and provides plenty of hot water.

    I'm going to draw a pice of a sidearm heat exchanger and attach it to this post in a minute so you can see what I'm talking about. EDIT: looking at the drawing, the flow I show is not the most efficient arrangement. Heat exchangers should be piped to counter-flow, so that the boiler water and the domestic water are flowing in the opposite directions--colliding, in a sense. In this case, the supply feed would be on the top and the return would be on the bottom. I think mine is hooked up like in the diagram, though, and it still works great.

    Anyway, my bottom line is that the storage tank is just another (albeit, big) pressurized zone off your boiler system, to be exploited as needed. Most of the magic would be in the controls.

    Attached Files:

  5. elkimmeg

    elkimmeg Guest

    Eric have you factored the heat loss from the water in the tank even an insulated tank looses heat.
    Consider this a 30 gallon gas hotwater system is effecient because it heats the water fast and has a good recovery rate In this case a 30 gallon gas or oil fired system is far more effecient than an 80 gallon electric system.. Dpomestic hot water is set adound 120 fhw heat 180 there is a huge difference in maintaining the 180 level. Have you considered that the huge tank might less the effeciency of the boiler drawing heat away and actually cost more to maintain 250 insulate and reheat it for use than a much smaller tank?
  6. zogboy

    zogboy New Member

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    If you bury the the tank in a pearlite / cement insulation the heat loss is minimual.
  7. Eric Johnson

    Eric Johnson Mod Emeritus

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    I'm not necessarily advocating a tank. Like I said, I've heated with wood-fired boilers for about 15 years, had great results, and never used one. However, the fact that Tarm highly recommends storage tanks with their boilers is interesting. One would think that the boiler ought to stand on its own. But since I'm Joe Schmoe and they're the top-of-the-line wood-fired boiler manufacturer, I suspect they have a good reason for recommending the tank.

    So if we assume that having a tank is a good idea, then my next instinct is to try to figure out a cheaper way to get the job done. I suspect there are plenty of things I haven't considered, but thinking about it and discussing it is an interesting intellectual exercise. I agree, potential heat-loss is an important consideration. My impression is that Tarm boilers are designed to run hot, both for the sake of efficiency and emissions, and that doing that is only practical if you have a place where you can dump the heat and then recover it later. Maybe the efficiency gained by doing that more than compensates for any loss you would have with the tank.

    Just a thought. The Tarm website doesn't make a strong enough case for spending $6-$10,000 on the boiler, plus another $3,000 to $5,000 on a tank (plus installation), IMO.
  8. elkimmeg

    elkimmeg Guest

    I have seen 250 gallon Hot water tanks used in comercial buildings. Then again, I have seen multiple tanks used for high vollume.
    What one would have to factor is the gmp flow , figure out what is needed to complete a cycle and the regeneration factor of the boiler.
    This would take some math and educated guess work. One to size a tank and as to how much benifit that size and additional capacity really saves. Like you, trying to keep it simple, one could start withan 80 gallon electric tank (It only has to hold water not heat it
    find one witha blown element) and test your theory. If it works you could daisy chain another one, double your reserve capacity. Learning all the way without a huge expense. This is no different than the add on boiler mates found today. Either zoned with a zone valve or another cir pump. You also could do it one tank for domestic hot water and one for baseboard. You are right about glycol and using a varible fill valve. Over a period of time the anti freeze does become diluted and has to be recharged or replaced. 3 to 5 years is the norm. I also think if you are using Cast iron radiators you will need to boost your water temp above 140. or you will dissipate too much heat at the start of the zone and have little left at the end run. Either that re zone to smaller runs. Again good pipe insulation will help The best is fiberglass wrapped with the outer white facing with foil facing towards the heated pipe. Home Cheapo
    may sell it. I think I saw it there once. The rubber armor flex is second best and foam styrofoam is useless as it melts at 180. At peak demand 180 is exceeded often even if set for 180
  9. Eric Johnson

    Eric Johnson Mod Emeritus

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    zogboy, how about straight vermiculite or perlite? What's the advantage of mixing it into cement? And how thick should it be?

    I've noticed that when you run a coil in the boiler and circulate it through a 40-gallon water heater it acts as a heat storage device, giving some heat back to the boiler when it needs it. That evens out the burning cycle somewhat and you get a longer burn, plus all the hot water you need. If 40 gallons will do that as an afterthought, imagine what you could do with 80 or 160 or 250.

    My current system works great when the outside temp is zero or above. Anything below zero and it has trouble keeping up. Short periods below zero (like at night) are fine, as long as there's a chance for it to recover later in the day. Day after day of below zero temps, and keeping the house warm with wood becomes a struggle. I'd like to tweak another ten degrees out of it before next winter, just in case. I've done just about everything but heavy-duty pipe insulation, so I guess that's the next step.
  10. joshuaviktor

    joshuaviktor New Member

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    Eric, during the summer, how do you run DHW? You have said in other threads that the gas furnace flue for you is stuffed to keep air from entering, and cooling the flue. Is this something you undo every year, so the gas furnace can run the DHW?

    Also, for the straight vermiculite/pearlite question. I asked about pouring straight perlite in a chimney liner installation, so as to not change my historic chimneys. I think Craig said that he used to do it, bgut that a stove pipe rep told him that the contact of the perlite vs. the spots on the pipe where the perlite DIDN'T touch, created hot spots that screwed up the chimney liner some way.

    PErsonally, I would think it should work around a hot water heater tank. We're talking 200 degrees max, right? Not like a flue. It would require a framework around them to hold the loose perlite in.

    As for mixes check out schundler.org (from memory). They are the biggest perlite people around.


    Ya know, it just struck me. Mixing a heat storage tank with a wood furnace is sort of like creating a giant masonary heater using water, instead of brick. OK, half of you are going, "No s#$t, sherlock". Sorry.

    Joshua
  11. Eric Johnson

    Eric Johnson Mod Emeritus

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    I have a gas hot water heater. In the late spring and early fall I pull the insulation out of the gas boiler exhaust, turn on the gas, light the pilot and run the gas boiler to take the edge off. It's usually a relief to have to quit fooling with the wood after a long winter. But in the summer neither boiler has anything to do with DHW. But I would like to put in a solar water heater some day.

    LOL, no chit, Sherlock. And water has the added advantage of being transportable.
  12. zogboy

    zogboy New Member

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    Eric I do not know the exact insulation value of vermiculite or the mix of cement / pearlite but it should be around a R-30 per foot. You could use an old fuel oil tank for storage, as you won't be consuming that water. Burying it in the ground may not be practical but it sure would get the tank out of the way.
    I was reading about a mixture of paper Mache’, sand, and Portland cement. They called it papercert. I have heard it called fibrous cement also. It would cost less than buying pearlite or vermiculite. I believe it would have a R-30 rating at 12" same as the aircret mixture of vermiculite/cement.
    I used the vermiculite/cement mixture to insulate an electric run between the meter and main panel in my home. The inspector told me it would give a 5-hour rating at 12". I did it to save re-wiring the main panel after I built the mother-in-law apt.

    Gas hot water heater?............ Why would you heat water that is already hot . :)
  13. Eric Johnson

    Eric Johnson Mod Emeritus

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    I turn the water heater down to its lowest setting during the heating season. Therefore the gas never kicks on. It's always a happy day around here in the winter when the gas bill arrives.

    When I built my cinder block boiler room this past summer, I filled the blocks with vermiculite. Seems to work OK for insulation. You can always use more.
  14. zogboy

    zogboy New Member

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    I think I may try to find a used wood fired boiler and install it in a boiler room /out building. I believe it will give me the most bang for my buck. That is unless the price of heating oil drops back to $1.00 a gallon. Even if I have to burn 7 cords of wood a year, I will be saving and I will be able to set the heat at 70. I have water heat fired by oil. I supplement with a coal stove but as hard as I try to keep the dust down it still manages to get everywhere in my home. Not what we are use to after years of water heat.
    So far this year I have used 400 gallons of oil and 1 and 3/4 tons of coal. I paid $220 a ton for the coal and $2.39 a gal for the oil. With another 2 and 1/2 months or so to heat my bill will only go up.
    I spoke with my coal supplier and she said the cost would go up by next winter due to shipping cost. That makes wood an even better value for the home able to store and burn wood.
    I still intend to attend the farm show next week. I hope to gain some more knowledge and pick up a few ideas for the old place.
    I would love a winter without using heating oil.
  15. joshuaviktor

    joshuaviktor New Member

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    Zogboy,

    Bravo, Amen, and damn straight!

    I intend to find a used indoor wood fired boiler. I seriously doubt my town (a suburban, seriously straitlaced township) would let me put one of those outdoor wood boilers in, so I want to find a tarm or such, and install it along with a tank, such as we have been discussing. I want to figure out how to keep my amtrol, as I suspect it is pretty efficient as is, and keep my oil burner as a backup (vacation, run out of wood, ((god forbid)) etc.)

    An OLD tarm was recently sold on Ebay, and oh, BTW, has anyone noticed the extremely recent rise of pellet and wood stoves on ebay. Looks like everyone who draggedd the old monsters out of the basement, or bought one without really knowing how to use it, is trying to get rid of them. hehe.

    Just wait (washing hands in air) Just wait, my pretties.

    And your little dog, too!


    Joshua, The wicked woodlock of the Northeast.
  16. Eric Johnson

    Eric Johnson Mod Emeritus

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    Ebay is a good place to look. Just check it a couple of times a week. There seem to be a few over in Vermont and New Hampshire for sale from time to time. Might be more if people with older boilers are looking to upgrade.

    The problem with a used steel-plate boiler is that you have no idea what condition it is in (and really no way to tell by looking at it), so it's a pig in a poke. But if you buy a pig for $500 and get three heating seasons out of it, that's not a bad deal. And it might last for another 20.

    Also, bear in mind that older boilers (and most new ones, too) produce a lot of smoke at times. If you live in a populated area, draft and wind direction are important considerations. I put an add-on cat on mine and it works pretty well. That and learning how to fire it. In my experience, the learning curve on a new boiler is a couple of years.

    Mine (150,000 btu/hr) is a little on the small size for the house I'm heating. But with three zones, my wife has figured out a sequence for turning on the pumps so that even on very cold days we can spread the heat around enough to keep the place around 70.
  17. joshuaviktor

    joshuaviktor New Member

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    Eric, how big is your house? 3500 sq ft, I seem to misremember. Is that right?

    BTW, I want to thank you for answering so many of my questions.

    Very much appreciate it.

    Joshua
  18. Eric Johnson

    Eric Johnson Mod Emeritus

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    It's about 2,800 square feet. The original section was built around 1865 (old Federal style), but it's had several major additions in recent decades. The additions are well insulated, at least by '70s and '80s standards, while the original house is probably about as good as it's going to get. I've been tearing the vinyl siding off and restoring the wood clapboards, so there goes some of the insulation. About a quarter of the rooms in the house have 10-foot ceilings and another third has 9-footers. Central NYS is a pretty cold climate.

    If my boiler was in the basement it would be no problem at all. Maybe even overkill. I think my main problem is inefficiencies inherrent in getting the hot water from the boiler room out in the barn into the house and up into the radiators. Lots of above-ground pipe and a heat exchanger all take their toll.
  19. joshuaviktor

    joshuaviktor New Member

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    Eric,

    found an illustration of tarm tank. They use the heat exchangers, and the caption for this photo stated a third coil would typically be added for DHW. Just FYI.

    Joshua

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  20. Eric Johnson

    Eric Johnson Mod Emeritus

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    Wow, Josh. That's a lot of copper. I'm thinking it might hard to pressurize a tank that big. Or maybe I should say maybe it would hard to make a tank that big that would hold pressure. Thanks!
  21. joshuaviktor

    joshuaviktor New Member

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    No, the tank in a full heat exchanger system isn't pressurized. The water in the tank never moves. The two copper coils (actually 1 in and 1 out, split into two coils for more surface area, I think), are to bring heat into the tank, or pull it out in lean times. The third coil, for DHW, I guess just pulls the heat out when needed.
  22. elkimmeg

    elkimmeg Guest

    I saw a burham wood coal oil FHW system advertised in my local area I will supply more info tomorrow
  23. Eric Johnson

    Eric Johnson Mod Emeritus

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    That's my point, I guess. If you had a pressurized tank you wouldn't need all that copper tubing. Wouldn't it make more sense to connect the tank directly to the boiler? You can still bypass the tank when the heat is needed somewhere else.
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