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Gravity Convert: Backwards? How tell? Matter?

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Mark,
Thanks for your thoughts. I also appreciated an old History of yours I found on the web, "Past and Future of Hydronic Heating."

Yes, strange things happen when the pump goes off. Heat seems to re-distribute as you suggest, and the system may run backwards? Often, when the system is off, many of the return lines are hotter than the supply. I think hot water may be going from hot radiators on first floor to ones that only get warm on 2nd floor, but with water going backwards. (Since the return lines are warmer than supply.)

Re: telling which way it was done originally by the deadmen. All my pipes are the same size as you suggest, 2" mains going off (and coming back) in main loops, except just above the boiler where there is only one 3" fitting on one set of pipes (now the return but in past who knows??).

Does this 3" fitting tell us anything? I've tried attaching a photo of main split where supply goes left/right and returns come from similar directions. The 3" fitting is the current return.

Re: pitch: most of the pipes, both supply and return, both mains and branches, both sides of main split, look level to the eye. I haven't put a level on them. Should the "pitch" you describe be obvious? The current returns are higher than the current supply, but only by inches and they run basically parallel and level to the eye.

Finally, are you suggesting have the Wilo pump run basically anytime there is heat in the system, even when the thermostat is satisfied? That makes sense to me if the pump is strong enough. I now have a Taco-007 when goes off when the thermostat is satisfied.

I'm thinking I could hot-wire the pump to run full time for a day and se what that did? Is there something magic about Wilo, or will that work w/ the Taco? I'm thinking the 007 might be small, too? The 007 is rated 20gmp at 0-11feet heat.

Any thoughts appreciated, esp. on the question of a) how to tell which way the system ran originally, and b) the question of whether you are suggesting to run the pump more of the time, and c) if it makes sense to try running the Taco full time as an experiment, and d) whether the Wilo is special in way vs. Taco for this purpose.

Thanks very much. Your wisdom and experience are appreciated.

Comments

  • Doug Pearl
    Doug Pearl Member Posts: 7
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    Gravity Convert: Backwards? How tell? Matter?

    I have on old (1911?) gravity system converted 5 yrs ago (by previous owners) to run w/ a Weil gas boiler and a Taco 007 pump. My plumber is telling it me may be plumbed "backwards" but he's not sure, and I'd like to find out before we do other work on the system as he suggests "putting it back the way it was" if it is backwards.

    My question is: How can I tell if it is backwards? And does it matter?

    Any thought or advice would be much appreciated. Some further background is below, and a picture of the initial pipes coming off and returning to the boiler is attached.

    Doug Pearl

    --------------------------------------------------------------------------------------------

    There are a few radiators that don't get hot, even after bleeding, and they have the oddity that when they do get warm (not hot) it is when the system CYCLES OFF and it appears to be through the current RETURN line. I can tell this from the pipes that lead to them from the basement--the "return" line gets warm, but the "feed" stays cooler. I'm wondering if the "gravity" system is working to warm these radiators, but backwards from how the pump runs? Could this explain why the pump doesn't make them hot?

    Other relevant information:
    -The current return lines merge two 2" legs of a Y into one 3" fitting before going back to boiler, while the current outbound does not have any 3" fittings or pipe. This is what makes my plumber think it might be backwards.

    -3 story house; 2900 feet; 9 radiators on 1st floor; 7 on 2nd; 2 on third.

    -System is split left/right or "North/Sourth" and South side has only 1/3 of radiators and North side has 2/3. The cold radiators are on the North side, but they are on second floor, while the THIRD floor radiator on the North (furthest end of the loop) DOES get hot.

    -Most of the radiators have their own pipes--to and from--rather than being in series. The two on the 2nd floor that don't get hot have pipes hidden in walls, so I cannot be sure, but they appear to be branches off the same line, which also goes (or branches to) a third floor radiator, which DOES get hot.

    -In the basement, sometimes some sections of the largest RETURN pipes are HOT when the largest FEED pipes are cool. This usually is after the system cycles off, but may also be after it has run very hard. Does this tell us anthing? Why is this?

    -Currently, some of the radiators have water flow "in" through the valves, while others have the return going through the valves. There are only two radiators in the house that have a "top" and "bottom" inflow/outflow; on these two radiators, with the current plumbing, water is currently running INTO the BOTTOM of the radiator and OUT of the value at the top. I don't know if this is an indicator, one way or the other, or if this is random. I would think you'd want hot to go in the top and cool and go out the bottom, but maybe not. Maybe they wanted hot to go in the bottom and then rise?

    I have attached a digital picture of the initial T branches (into left/right or North/South) of the outlfows and returns at the boiler. You can see that the current return has some 3" fitting, while the current OUTflow does not. Also, there appears to be "throttle" valve of some kind on the current OUTFLOW, and some have suggested to me that this throttle was usually on the return, as another indicator that things might be backwards.

    Any thoughts/suggestions most welcome.
  • Timco
    Timco Member Posts: 3,040
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    Can you trace the pipes? The shut off valve on the rad is the supply side.

    Tim
    Just a guy running some pipes.
  • Steamhead (in transit)
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    Not always, Tim

    I've seen some with the radiator valve on the return- don't know why, but since these were piped with an un-valved supply coming in the top and a valved return coming out of the bottom, it's clear which is which. True, this arrangement is not too common.

    Doug, if any of your radiators are connected with one pipe at the top and the other at the bottom, the top is (or should be) the supply.

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • [Deleted User]
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    Seen it both ways...

    Gozinta and gozouta. Does it matter? Can't say's I've ever seen a gravity system with either the supply OR the return in a smaller pipe, other than near boiler piping, the old gravity systems had big pipes everywhere, with pitch upward on the supply, and the dead men did things like NOT reaming (blasphemy?) the pipes on the upper floors. (non- blasphemy, just extremely smart fitters...)

    They were also known to use restrictive orifi (plural for orifices) in the radiator unions of the higher floor rads to create resistance. I'm guessing that you've done been fiddle faddled by the fickle finger of fate... (a DADism)

    When you add a pump to a truly well balanced gravity system, NOTHING works as it should. THose radaitors that used to flow well no longer do, and those that didn't used to flow well flow like a Banshee. You can do one of two things. Make more of a gravity system, or a pressure system. You'de have to flip flop the orifi from those that do to those that don't and viceaversa.

    When the pump shuts off, gravity takes over and does its thing PLUS heat flowing to cold, and drains the boiler of any residual energy in it. I'm betting your boiler cools off REAL quick.

    If it were me, I'd get one of them varible speed Wilo pumps, and set it for a fixed differential of say 30 degrees F, and let 'er rip. You can also set it manually to anywhere between 1% and 100% of its capacity. You can even hook it up to another Honeywell controller and vary its speed based on system differential pressure or temperature (0-10 vdc input)

    I'd try that as a "gravity enhancer", which if I'm not mistaken is what they called their first electric circulator.

    Smart pump them WILO's...And smart folks who work for them to boot!

    ME
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    If I had to venture a guess...

    I'd say that the pipe with the brass fitting is probably the supply. Looks as if it might have been some sort of temperature regulator. Not that it really matters, unless there are check valves in the system someplace not shown.

    The difference between Wilo and currently available circulators is that the Wilo is intently intelligent. It is an extremely smart, extremely efficient variable speed pump. It's worth the price of admission.

    As far as continuous run pump, it might help, but if you have orifices in the system it won't make a whole lot of difference, but with negligible costs, what the hay.

    Thanks for the kudos. Just here helping out.

    ME

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  • zeke
    zeke Member Posts: 223
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    The way you tell is the pipe leaving the boiler at the highest elevation is the supply, since it is on top of the hot boiler water having lower density.
  • [Deleted User]
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    It's a replacement boiler Zeke...

    He's thinking someone may have done the ol' S-N-R Switcheroo on him...during the replacement boiler plan.

    ME
  • Doug Pearl
    Doug Pearl Member Posts: 7
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    Mark,
    Thanks. That brass valve you see is, I think, to reduce the flow to the "side" that has fewer radiators (7 of 18) and that gets hotter, and force more water to the "side" that has more radiators, some of which only get warm.

    Two specific questions, if you are willing to indulge a novice:

    1) Can you mention a Wilo model or model line to look at, just as an example? I just looked at their web-site and it's not clear to a mere mortal where to begin.

    2) Is there a way to tell if I have orifi on the two radiators that only get warm, which are on 2nd floor and near each other, but have pipes hidden in walls/floors. And if they do have orifi that are in walls/floor am I SOL unless I rip up floor/wall? Would reversing the radiator help?

    Thanks.
    Doug
  • tim smith
    tim smith Member Posts: 2,752
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    Regarding supply & return

    I agree with Mark, I think that brass fitting was an aquastat on the supply at one time or an old Weatherman reset control well. With it not being an overhead feed I would not think the flow direction would be as much of an isue as pipe reduction would be similar on returns and supply's. Just thinkin, Tim
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    Confined to Gravity Conversions

    No circulator can recreate gravity flow in an original gravity system and I would suggest that VS circulators are wasted unless the head loss of the mod-con is included and the rads are equipped with TRVs--only this combination of which can emulate gravity flow.

    VS circulators need to see changing delta-p before they can modulate via delta-t.


  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    In regards to your questions...

    1. I'm thinking that their smallest circulator would be more than adequate fo ryour needs. The Stratos Eco should do the trick. You have very little pressure drop on the system distribution, and the Eco will just be a circulation "enhancer". Ma Nature will do most of the work.

    2. The restrictive orifices are typically incorporated into one of the unions serving the radiator. In my 33 years of boiler room spelunking, I've never seen one mid pipe. The ones I've seen were made of tin, with a 1/2" hole in the middle. You would have to drain the system low enough to disconnect the radiator to confirm or deny their presence.

    Typically, what SHOULD be done, is to move the orifices from the upper radiators to the lower radiators in an effort to balance flow once a circulator has been added. That, or if you have 1/4 turn valves, go through the system and "balance it" which can be done but is hit and miss at best.

    The best option is to install non electric thermostatic radiator valves which will automatically balance out the flows of the system. Look at Danfoss, Oventrop, Honeywell for options in this area. Between them and the variable speed circulator, you will have the utmost comfortable system. Now, all you need to add is a modulating/condensing heat source and in my opinion you will have the ultimate in efficient operating systems. Expect fuel savings of between 30 and 50 %, and SIGNIFICANT increases in human comfort.

    You have the basics (hot water heat, large mass cast iron radiators, big bore pipes) all you need to do is add bells and whistles.



    Are you POSITIVE that you don't have closed/partially closed hand valves on those under heating radiators? Those things have a tendency to have little to no tolerances and get locked up REAL easy from the naturally occurring oxides (rust) in the system.
    .
    Can you take a picture (close up) of the valves for our perusal?

    Get back to us. We WILL find resolution to your dilemma

    ME

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Not necessairily so Mike...

    If the circulator is set to maintain say a 40 degree delta T, and the system is capable of doing a thirty degree delta T without the aid of a circulator, then the circulator would only be on during warm up, and as the heat rises (gravity circulation takes over) then the pump backs out of the equation. Not a waste, more of an enhancement. These pumps are much smarter than you'd imagine.

    We agree that if the system is retrofitted with TRV;s that it should be operated with delta P (constant) and that the boilers pressure drop (Triangle Tube) should also be considered in THAT equation.

    ME

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  • john_181
    john_181 Member Posts: 93
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    my story sounds like yours

    My system looked backwards too. Well after talking with Brad online we determined it was backwards. Even my circulator pump was in backwards. I too had a "Y" joint returning the cold water to the boiler TOP with 3" pipes. I reversed the direction of the pump and I cannot believe the difference in operation. My tenants told me last year (old owner of the building) that their rads were just warm - now they are HOT and even heat throught the building. I have plenty of pictures of my system if you want to compare just email me. I must thank Brad again for his knowledge and help in my situation.
  • bob_46
    bob_46 Member Posts: 813
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    Doug

    This is somewhat educated, speculation. From what little information I can glean from your photo and your text, I would guess that. 1. you probably had an Arco(snowman) boiler. 2. it probably had one supply and two returns. 3. the brass gizmo looks like a union radiator valve. Based on that I would say the 3" tee was the supply. I think a 007 shuld be plenty of pump. Is there any pipe exposed on the second or third floor or in an attic? Is there an old expansion tank hiding somewhere on the third floor or in an attic? Maybe in the top of a closet. Is there an compression tank on the new boiler? Dan has a book, I think it's "How Come" that should help you. bob

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  • Doug Pearl
    Doug Pearl Member Posts: 7
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    Diagram of the Beast

    Thanks. No, I'm not _positive_ the valves are open, but two plumbers have checked them as best as possible until we drain the system. I will send a pic of valves. Some are "quarter turn" says one plumber, but I notice myself that many appear to turn 180. There are also some new valves on some.

    Meanwhile, I've spent a few hours with hands on various pipes at various times and have come up with a hypothesis that is shown and summarized in the attached sketch. In short, I have two loops, one running counterclockwise and the other running clockwise, both pulled by the same pump. But I think one loop is overwhelming the other, and forcing it to run backwards at times. Diagram attached.

    I've also attached another pic of the initial splits that shows a better angle than prior pic.

    Any thoughts on 1) if my hypothesis makes sense, 2) if there are other ways to confirm it and 3) what I should do if it's true.

    This is a frustrating puzzle, but I think I am making (slow) progress, with much help from all of you, which I very much appreciate.
  • Doug Pearl
    Doug Pearl Member Posts: 7
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    I posted diagram of system and new pic

    Thanks very much to everyone who has offerred advice on this issue.

    I have posted a diagram of system and new pic, but I realize the header for the new message w/ the diagram is up in the middle of this thread line. If anyone wants to see the diagram, it's located in a reply to Mark labelled "Diagram of the Beast."
  • Eric_8
    Eric_8 Member Posts: 66
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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Qwestshun on your radiators...

    Are they bottom tapped or bottom/top taped. It DOES make a difference...

    By the way, we have a technical name for that touchy feely test you did. We call it the "OOOooo, AHHHHhhh " test...

    One MUST use it carefully lest they burn their hands. If one is silly enough to stick his hand on a REAL hot pipe, maybe he deserves to be burnt...

    I did it once...

    ME

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  • Doug Pearl
    Doug Pearl Member Posts: 7
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    bottom or top tapped taped

    I think you're asking if the pipes to rads go in/out bottom or top? If not please forgive my ignorance and clarify the question.

    If I got the question right, here is the answer:of 18 radiators, 16 are in/out both at bottom. (Some supply through valve and others return through valve, but that's a different issue.)

    The other two have valves at top and another pipe at bottom. By feeling the heat rise in pipes all the way from basement after a cold start, I have determined that at least the one of these top/bottom rads that I checked is currently supplied at top, through valve, and returns through bottom, with no valve. I have also determined that the pipes switch orientation under the floor to accomplish this task (left/right riser is switched to right/left.)

    Thanks for the technical nomenclature, I'll keep it in mind, along with the subtle caution.

    Any thoughts on the diagram? I have several books coming in mail to help me understand this stuff better (How Come and Pumping Away) but I'll never have the accumulated experience etc that you guys do.

    Doug

    Doug
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    Considering the price Wilo Canada quoted me for a Stratus, they better be smart!

    Am still not seeing how they could possibly create gravity flow in the system after it has been converted. The circulator itself--not to mention the greatly smaller near-boiler piping--likely has far more restriction that allowed for the entire system.

    Are you suggesting use in a converted gravity system with mod-con using primary-secondary (or LLH) piping? Where would you put the temp sensor(s) for the circulator? Is one temp measured internally--e.g. only one temp sensor? If so, is it supply temp as I would expect?

    What happens when 40F delta-T is impossible--e.g. reset target is less than 40F above room air temp? Even my generous reset curve doesn't require 110F supply until the outside temp drops into the lower 20s. Does the circulator keep running slower and slower in attempt to find the required delta-t? If so, there's a good chance you'll only be 2-3 gpm (rather like under gravity) but how can such a low flow rate ever distribute itself evenly in a wide-open gravity-piped system? Do you believe the circulator will stop with gravity flow taking over even though it has to force itself through the circulator?

    Also, what happens when the circulator cannot find any delta-p no matter what speed it runs? Yes, I know you've set it to modulate on delta-t, but something tells me delta-p is still part of any "smart" stand-alone circulator's intelligence. Much of the time, it looks like the circulator will be facing a catch-22: I can't move slowly enough to find the required delta-t and I can't move fast enough to find any delta-p. What do I do? My guess would be "operate flat out until the required delta-t shows itself and then attempt to modulate.

    Too bad because unless you have proportional emitter control, the heat supply and/or circulator are likely to be shut down by the wall thermostat quite rapidly after delta-t is achieved unless the system is operating near design conditions.
  • J_12
    J_12 Member Posts: 4
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    Would love to see photos of your system john

    Hi John,

    I've been conversing with Doug about "backwards" gravity systems, as I too have a ca1929 overhead gravity system that I am convinced was "plumbed backwards" when it was converted to a sealed circulated system in 1991.

    I plan to convert it back to the "correct" direction with a simple primary/secondary loop setup and TRVs(where appropriate) this Spring, and like Doug am collecting various tips and experience.

    You mentioned that you had loads of photos of your system, I assume before and after.

    If so, it would indeed be very helpful if you wanted to send those to me(and I assume Doug as well) for future reference.

    Any other tips or lessons learned are also welcome.

    And yes, as someone mentioned above, my current(backwards) return is now the "higher" pipe as measured from the floor. Along with a lot of other evidence, it seems apparent that this riser was meant to originally be the supply.

    Also, all of my radiators have a top/bottom supply and return piping setup. With the current "backwards" setup, the radiators heat/feed from the bottom connection, instead of cascading down from the overhead riser as originally designed. Incidentally, all of my radiators have the control valve on the bottom(original return) connection, so I guess that valve location can vary.

    Cheers,
    Al
  • J_12
    J_12 Member Posts: 4
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    The Wilo seems like overkill to me...

    But then again, I too am trying to learn and figure all of this out as a DIYer =)

    However, please correct me if I am wrong, but I see two or three issues with using the relatively expensive Wilo in this application:

    1) The pressure differential will likely be negligible since this is a filled closed circulating system, correct?

    2) Won't the supply/return temperature delta be controlled by other devices in the system such as a outdoor temp reset and the aquastat? If so, I can see that a circulator that can still vary its consumption could save energy, but will it really work independently with its own logic in concert with something like an ODR? I perhaps have unfounded concerns this may overcomplicate the solution and make it harder to "tune".

    3) Are the savings as compared to a constant 24/7 running circulator as compared to this variable circulator really enough to justify the cost difference?


    Again, perhaps speaking from a position of ignorance as I too am still learning.... but am curious to hear your thoughts on my suppositions.

    Cheers,
    Al
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    Mark. Just spent a few minutes on the phone with Triangle and they could not recommend use of a VS circulator on a "direct drive" system--no form of primary/secondary--unless the circulator has an input to allow the boiler to give it at least a reasonable estimate of current output. They have not however tested VS circulators with their boilers but are "looking into it". I suspect all mod-con manufacturers will say the same thing.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    Again--Confied to Gravity Conversions

    Exactly the concerns I have Al. Except:

    1) The pressure differential will likely be negligible since this is a filled closed circulating system, correct?

    No. There is almost no pressure differential (head loss) in a non-TRVd gravity system at any rational flow rate not because it's "closed", but because the piping is so large that there's simply no restriction to flow. Head loss in those systems was measured in milinches (thousands of an inch). At 30F delta-t the motive force for gravity circulation is only about 2 1/2 INCHES to a 2nd floor radiator--typically somewhat less than half that for ground floor rads. Any more head loss and you get no circulation...

  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    With the majority bottom tapped, it doesn't matter...

    Where it DOES matter is on the radiators that are diagnally tapped. On a gravity system, the supply must come in at the top, and come out of the bottom in order for things to work. With a forced system it is not as critical, and people typically pipe the supply in to the bottom, and out of top, primarily for ease of air removal, which really has to be bled manually at each radiator anyway. It is virtually impossible to force purge a large upright cast iron radiator, especially if it is double bottom tapped.

    So, in short, I don't think in your case it matters which is supply and which one is the return. I also suspect that your system has been a circulated system from day one due to the lack of pipe pitch to enhance gravity circulation, but I could be wrong on that point.

    As for valve placement, it too is moot unless you are dealing with a non electric thermostatic radiator control valve which IS sensitive to direction of flow, and is typically applied to the outlet of the radiator.

    The piping diagram you supplied is piped in parallel direct return. Water is like my ex-brother in law. Wet, lazy and stupid. Given its own choice, it will find the path of lest resistance, which may not be the path YOU want it to flow in. YOU must show it where you want it to flow. Otherwise, it will short circuit. In other words, if you don't have restrictive orifices in the radiator unions, then you will need to balance out the flows to the radiators. Those that are the furthest away from the pump will have their valves wide open, and those radiators closest to the pump will have their valves mostly closed.

    ME

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Ahead of the curve...

    The folks at Lochinvar understand the potentials and are incorporating its operation into their control logic. I agree with you, and I suspect that al the others will soon follow.

    Based on my personal experience, the SIT controls on most of these modcon boilers are much more intelligent than most boiler manufacturers give them credit for. They would prefer to show the boiler a constant, that constant being the flow across the heat exchanger. I have varied the flow to my Contender, and it handles it just fine. I've also seen the modcons piped like a conventional boiler (instructions, we don't read no stinkin' instructions!} and they too worked quite efficiently, provided that the minimum flow does not drop so low that the heat exchanger starts flashing to steam.

    And your favorite flavor of boiler has a variable speed function to some of their smaller modcon boilers too if I'm not mistaken...

    ME

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  • ll velasquez
    ll velasquez Member Posts: 5
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    My system in Dan Holohan Book \"How Come\"pages 8 &13

    Do you guys think my system is old gravity? Or was it always ciculated with a pump?

    The diagram of an upfeed gravity system on page 8 of Dan Holohan's book "How Come" looks very much like my system. We have the loops out from the furnace, just as he shows, and our expansion tank in attic (now disconnected) has what looks to have been both supply and return as shown on p 13, as well as a water inflow line and a ballcock.

    One difference however. All our risers are pairs that go up in parallel (one supply and one return) and they are smaller pipe--about 1 1/4" (one and one quarter) OUTSIDE diameter. The biggest pipes from the boiler appear to be 2" cast iron (2 7/8 OD) and then they branch to cast iron about 2 1/2 OD and then down to smaller pipes and finally all the risers going up.

    Does this sound like it was originally gravity feed? All the pipes in the basement appear basically level to the eye, but so do the pipes in Dan's book on p 8?

  • Doug Pearl
    Doug Pearl Member Posts: 7
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    was it always gravity or not?

    Mark,
    You suggest maybe my system was circ from the beginning.

    I've posted new message at bottom of threat w/ ref to how my system looks very similar to Upfeed gravity system in Dan Holohan's book "How Come" on p8. They look virtually identical (his pipes are basically level in the basement??) except my risers are all pairs (supply and return to almost each radiator individually)and the risers are smaller pipe (roughly OUTSIDE diameter of 1.25") after step down from branches from the mains which mains start as OD 2 7/8" which I assume is 2" cast iron pipe.

    So does this sound/look like it was gravity or circ from the beginning?
  • ll velasquez
    ll velasquez Member Posts: 5
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    Pics of valves on rads

    Mark asked for pictures of my valves.
    Here are 3 pics of two valves. The top valve is on a rad that gets very hot; it is diagnally piped. The valve turns roughly 1/3 of a turn.

    The second is on a rad that occasionally gets warm, sometimes (not always) through the return line (based on pipe temps in riser in basement.) This valve turns roughly 180.

    Most of my valves are similar to these. I have also a few modern valves.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    Favorite Boiler Flavor

    Yes, it certainly has an integral variable-speed circulator, but unlike the stand-alone VS circulators, it is under the control of the boiler.

    It's taken me quite a while to get a decent idea of how it modulates the circulator in a TRVd, directly driven system (no LLH) when it has only one temp sensor (supply) and no differential pressure sensors.

    With a known volume of water in the heat exchanger and a known amount of fuel input, the boiler [should] be able to estimate both flow and delta-t across the boiler with surprising accuracy. It likely even compensates for a presumed level of heat transfer efficiency at any given combination of supply temp/burner input.

    When the burner is operating constantly and truly modulating, delta-t increases in perfect correspondence to increasing load. While my only way of "measuring" circulator speed is via the little Grundfoss "Indicator for A/C magnetic fields", I'm nearly positive that circulator speed also increases gradually with increasing load. While this might sound contrary to the "move the water slower to get more delta-t" rule, remember that burner and emitter output are also increasing.

    During the lowest load periods when the burner makes a batch of heat by firing at max input for just a few seconds, circulator speed is at or near 100% (if I manually lower the max circulator speed from 100% it will slow down after a few seconds). In my system this corresponds to moving about 6 gpm @ 2F delta-t at the boiler. Supply temp is typically 72F; return typically 70F. I can maintain about 65F air temp in most rooms with 72F supply with outside temp down to the high 30s or low 40s.

    Once load increases somewhat (but is still below minimum burner output) the circulator appears to be operating quite slowly--if I had to guess, I'd say at about 25%.

    While any directly connected TRVd system would probably have similar operation, the actual delta-t target (dare I use that word) likely varies with the nature of the emitters. The greater their volume/mass, the more accurately it seems to be able to both compute and maintain. The logic appears to break down with systems of low volume/mass requiring an accessory wall thermostat-like device.
  • [Deleted User]
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    1/4 turn valves...

    Those valves have a small cylinder inside with a tapered angled cut on them (proportional control). They also have a 1/16" hole drilled in them so that even in their fully closed position, there will still be SOME flow to the radiator (early freeze protection). They are alos VERY easy to lock up in they go unused for long periods of time. About all one can do is attempt to coax them, and keep moving them back and forth until full movement is acheived. It generally involves having to put a pair of channellock vise grips on the stem and work it back and forth. Loghtly tapping on the body of the valve may also dislodge some of the binding agents.

    Worst case scenario, you may have to replace them, and if it goes that far, it would be my recommendation to replace it with a non electric thermostatic radiator valve (TRV).

    ME
  • [Deleted User]
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    Not sure Doug...

    All of the gravity systems I have personally worked on had substantial pitch on their supply and return piping. But, it does not preclude the possibility of this system working without the pitch I reference.

    With the bottom tapped radiators, the hot water would rise up the outter tubes of the radiators, and the cooler water would fall down the middle, and flow back to the boiler. But as I said, ALL of the gravity systems I work on have significant pitch, ensuring flow back to the heat source.

    Maybe someone with more east cost experience will chime and and confirm your findings.

    ME
  • john_181
    john_181 Member Posts: 93
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    I posted the pictures
  • Buzz G.
    Buzz G. Member Posts: 61
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    reverse gravity

    Mark, will Knight boiler be able to do what you describe- where circ shuts off and gravity resumes as before conversion? Any other changes needed for this to happen?
  • Buzz G.
    Buzz G. Member Posts: 61
    Options
    reverse gravity

    Mark, will Knight boiler be able to do what you describe- where circ shuts off and gravity resumes as before conversion? Any other changes needed for this to happen?
  • Buzz G.
    Buzz G. Member Posts: 61
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    Attic Tank

    Have you guys tried using open attic tank as water source (low Pressure) for filling converted gravity system rads? Seems could keep out of picture with valve except when filling all those rads upstairs. Maybe save trips up & down.
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