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Near boiler piping design

rhlrhl Posts: 58Member
edited February 24 in Radiant Heating
im adding more floor heat in my basement, first floor, and some bathrooms. I currently have the whole house on one zone of radiators, and I want to move to two zones, everything home runned to the boiler room.

My near boiler piping doesn’t support all of these extra zones, so I was thinking of repiping. It’s a modulating condensing boiler, so I thought it would make sense to pipe the floor heat and the radiators “in series” at the the boiler, so if the floors and any of the radiators are in simultaneously then we could reuse some heat.

Some notes, i left off the boiler trim in this drawing, expansion tanks, fill valves, spirotherm, on the supply, and the dirt separator on the return. the boiler itself has a circulator on the return pipe.

I drew this and attached it here. Any thoughts ?

Comments

  • neilcneilc Posts: 683Member
    that looks busy,
    are you saying zones as in temperature zones, with thermostat for each? can you add that to your base drawing?
    or are you trying to have 2 different(or more) supply heat temperatures, as the drawing suggests with odd mixing valves?
    guys here will need more information(s)
  • rhlrhl Posts: 58Member
    edited February 24
    Right, so "zone" in this sense is not necessarily temperature zone, the top two zone pumps + manifolds are traditional cast iron radiator zones, piped in parallel.

    Then a floor heat zone which is on the first floor, low mass, so needs a higher temperature, im currently designing this as one temperature zone.

    The next manifold is a zone pump + actuators with small temperature zones for bathrooms (controlled by floor sensors). These will all be poured, with say 1"-2" slabs. Currently only one zone here, but futures for future bathroom remodels.

    The final zone pump + manifold is for the basement slab.

    I could clean up the layout itself for the first two so that it looks more like a traditional header.

    Again, the main thing I'm trying to achieve here is that I want to take advantage of the floor heat needed lower temps than the rads. so if the radiators return 160 degree water, at say, 10+ GPM, and the floor heat zones need lower water temperature, and at lower flow rates, then this piping lets me use the return water from the hotter zones, and return colder water to the mod-con boiler.

    I wanted to draw this cleaner, but, the (free) software i was using is missing some widgets, and a bit complicated to actually draw with. I had some trouble making the pipes that should be straight lines, actually be straight lines. One way to make the layout perhaps look cleaner is to draw the top two zones with a pair of two pipe header pieces.
  • rhlrhl Posts: 58Member
    I redrew the layout to have show that header manifold more explicitly, the topology hasn't changed
  • rhlrhl Posts: 58Member
    Anyone have any issues with this layout? Advice on a better way to do things?
  • IronmanIronman Posts: 5,144Member
    Are you creating any micro zones that have less load than the minimum firing rate of the boiler?
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rodhot_rod Posts: 11,753Member
    not so good! You need a loop thru the boiler to assure flow, without passing thru all the mixing valves

    Can you do it with one mixing valve? What is the hon requirement?

    The mix valves should pipe off closely spaced tees on a primary loop
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • rhlrhl Posts: 58Member
    edited February 28
    @Ironman Let’s assume the answer is “no” for now, when in reality i will have a few bathrooms, whose load will be off by a bit, so a buffer tank would be better for sure.

    @hot_rod the boiler itself has a pump in it, on its return, I don’t understand what your saying, are you saying you want the boiler loop and the primary loop to be different loops with different pumps? Wouldn’t that ensure the mod con wouldn’t get the lowest water temps? Or is your issue that as drawn the mixing valves don’t act as closely spaced tees? I could redraw this to have that..

    I could get away with two mixing valves for high mass and low mass radiant, but, the bottom one is for my basement which is its own temperature zone.
  • hot_rodhot_rod Posts: 11,753Member
    Wha type of boiler? You need to loop out and back to the boiler sized to move the flow the boiler requires, see the manual. The onboard circulator probably has enough additional output to flow the loop.

    Then every connection needs to tee into that loop, including the mix valves, via a couple of closely spaced tees. More like this.

    The mix valves cannot be directly in the loop like I think you have, flow goes into two ports on a 3 way valve and mixes out to the third, typically A&B in, hot and cold, AB as the mix port.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • rhlrhl Posts: 58Member
    edited February 28
    The boiler is unfortunately an aquabalance combi 155 from Weil McLain. (I say unfortunately because i personally don’t like it). It’s minimum turndown is 15k btu input.

    Ok, so your drawing something very similar to my drawing, except using a separate t different from the one used for the mixing valve.

    However by experimentation, I suspect the mixing valve probably can be used to make closely spaced tees.

    For example if you incorrectly put the pump on the return to the boiler, you’ll find that the loop gets little to no flow, but lots of water moves around the primary loop, and the piping around the boiler gets real hot, So water certainly can go through the mixing valve without mixing.

    Anyways what’s two tees and a little more pipe? I’ll do it that way and I’ll also use a 4 way mixing valve like the tamas z-mix
  • hot_rodhot_rod Posts: 11,753Member
    I highly doubt a 3 way thermostatic could substitute for a set of closely spaced tees? There is no path on a thermostatic valve to go directly from A to B, it needs to go either in or out the 3rd port. As one side opens, the opposite side closes the same amount, there is no straight across option.

    Remember a typical 3/4 or 1" thermostatic valve is around a 3 Cv.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • rhlrhl Posts: 58Member
    edited February 28
    I mean. I’ll do it that way, because it’s not big deal, but i think it probably is possible to skip the mix port, consider what happens if you put one of the pumps in your secondary loops in your drawing on the return past the tee that loops back into the mixing valve.

    See the first incorrect example here:

    https://www.pmmag.com/articles/88035-the-do-s-and-don-ts-of-three-way-thermostatic-valves-br-john-siegenthaler-pe
  • hot_rodhot_rod Posts: 11,753Member
    True with most cast iron boilers or tank type boiler, no flow is required when the burner is firing. So a three way valve would allow the system to work and the boiler would be fine. Most cast iron boilers can run with little or zero flow just like a tank style water heater.

    Again if you have say a 150K boiler that required 10- 15 gpm to move full output, that 3 Cv valve will have a very high pressure drop. Here is the pressure drop at 12 gpm. And you show 3 valves in series.

    But your Weil boiler requires flow at anytime it is firing. The manual is pretty clear on how the piping needs to be primary secondary to assure flow, as well as showing additional pump capacity. Failure to follow the manuals piping and boiler flow rate requirements would of course void any warranty.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • rhlrhl Posts: 58Member
    Right, I’ll do it the right way, also with a tamas 4 way zmix
  • hot_rodhot_rod Posts: 11,753Member
    great idea.
    4 way mixers were very common when we did radiant with cast iron boilers as they could provide boiler protection and temperature mixing distribution at the same time. But only when equipped with a motor and control.

    Still pipe it off the boiler loop with closely spaced tees to assure that boiler always has the flow it needs.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • Paul PolletsPaul Pollets Posts: 3,200Member
    I'd be using 5 zone valves instead of pumps. And a Smart pump to power the system side. More efficient and 320 watts/hr of power saved.
  • rhlrhl Posts: 58Member


    Here is the cleaned up version of this.
    The way i'm designing this, the 3 series loops are all floor heat loops, the top one is a staple up loop, the next two are in slabs (middle is for the various bathrooms around the house + garage), the bottom is the remainder of the basement).

    The way I have this setup it seems the boiler delta-t is widest at high temperatures. I figure the water temperatures will vary from 115 degrees to 180 degrees (as the outdoor air varies from ~55 degrees to 0),

    the top two in parallel zones are for radiators on each floor, which operate at: ~5.3k btu ~3.4k btu respectively, with 20 degree delta-t.

    the next floor heat loop is the biggest floor loop with 20k btu ideally at a 10 degree delta-t, the middle loop + bottom loops together amount to about ~10k-ish btu.

    When operating at 180 degree output I see return temperatures just ever so slightly above 130 degrees.

    The delta-t at the boiler is at most 50 (and in that scenario we have a flow rate of 6.3gpm just above the minimum).

    It's a little complicated, but, i think it will actually serve to operate the thing more efficiently.
  • hot_rodhot_rod Posts: 11,753Member
    The boiler has a pump inside? If so, and you need one :), and the pump is flowing into the boiler, move the expansion tank connection to the right of the tees where you show it, pumping away.

    The air purger needs to be on the hot out of the boiler, hottest fluid is the best air removal location.

    3 way mixers would be fine, 4 way are more for boilers that need return temperature protection.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • rhlrhl Posts: 58Member
    Yes, there is a pump on the return side of the boiler. I realized that the tanks now in the wrong spot. The tool I used doesn’t have a dirt separator, but what looks like an air separator there is meant to be the dirt separator.

    Does the nearly 50 degree delta-t matter for anything? Does it improve or hinder efficiency at all?
  • hot_rodhot_rod Posts: 11,753Member
    Do you need 180F, even on design days?
    The lower the operating temperature the more efficient the boiler will operate. The return temperature is key to condensing and the efficiency gain you get from that operation mode.

    Be sure the boiler can operate under wide ∆ operating conditions.

    I'd look at lowering SWT required on design days, adding emitters, upgrading the structure, etc.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • rhlrhl Posts: 58Member
    Sure that all makes sense. I think i need 180 degree water when its zero degrees out, (thats whay i based the above on), which is essentially not very often. More realistically it seems they should operate alright at ~165 degree water on 10 degree days. Then it makes the delta-t of the floor heat more in line.

    I have done a Manual J, and I also have all the edr's for each radiator in each zone.

    I was modelling things by assuming that the flow rates were based on btu-output on design day/(500*delta-t). It seems like this isn't really how all of this works: https://www.pmengineer.com/articles/93344-flow-rate-heat-output-and-delta-t

    Im a bit confused about reality vs. theory here. For example: since heat output is obviously dependent on delta-t to outdoor air, should the flow rates lower as it gets warmer outside? It seems hard to design around both variable flow and variable SWT, what is typical nowadays?

    Also, if i use grundfos alpha-2 pumps everywhere, how does the "smart" pump know the flow rate? this is related to measuring changes in pressure I guess?

    I guess my overall question is, (and im happy to provide you more information @hot_rod), is the idea of series piping the LWT heat emitters after the HWT heat emitters a bad one?

    Its basically a trade off between high delta-t or high flow rate, both ways can put out the same quantity of heat, but, i guess this way would be more efficient since the return temps are lower?
  • rhlrhl Posts: 58Member
    It sounds like, i answered my own questions. The boiler locks out at 40 degree delta-t. So possibly this design isn't the best.
  • hot_rodhot_rod Posts: 11,753Member
    I'm of the opinion it is much easier, more predictable to vary heat output by varying temperature compared to varying flow rates. Temperature control is very linear.
    Changing output by varying flow has a "hockey stick" curve.

    Understanding how het transfers is key to successful hydronic design.
    https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_23.pdf
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
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