Using pumps instead of zone valves with 'full flow' plumbing

Discussion in 'Boiler Forum' started by dwassner, Apr 2, 2019.

  1. dwassner

    dwassner Member

    Joined:
    Jan 31, 2012
    Location:
    Finger Lakes, NY
    My Lochinvar mod con was installed with 'full flow' plumbing (as opposed to a primary/secondary loop). It has been running great for 7 years.

    The setup currently is 2 zones controlled by zone valves and a single pump

    I have noticed 2 things:
    -one of the zones has baseboards that are typically cooler than the other zone
    -the install manual states the importance of making sure flow requirements are met when plumbing with 'full flow'

    My questions:
    -by switching to pumps instead of zone valves, would this fix the issue of the cooler zone not getting its equal distribution of flow/heat?
    -if the boiler has been running this long with no issues, is it safe to say that there is not a flow issue with the current 'full flow' plumbing?
    - if the flow through the boiler was too low due to its current plumbing configuration, what signs would I see? Too large of a delta T? Any other symptoms?

    Thank you,
    Dustin
     
  2. Dana

    Dana In the trades

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    Jan 14, 2009
    Location:
    01609
    Doing it with multiple pumps could over-pump the Lochinvar. If it's been working for 7 years let's not steal defeat from the jaws of victory here.

    Does the zone with the cooler baseboards keep up with the heat load? Does the thermostat eventually get satisfied, or does the room never get up to temp on cold days? What is the delta-T on that loop compared to the other zone?

    If there are isolating ball-valves on the zones, throttling back flow on the "hotter" baseboard zone would force more flow into the cooler zone loop when both are calling for heat. But if the rooms aren't cold it really doesn't matter a whole lot if the baseboards are running cooler.

    A flow that is too low would have an excessive delta-T, or at the extremes you might even hear some sizzle/hiss/bang of "kettling" on the heat exchangers, and a higher stack temperature on the exhaust.

    Most boilers can handle up to a 50F delta, but keeping in the 20-40F range when the boiler is running at the higher temp end of the outdoor reset curve would be about right.

    Swapping the pump for an ECM drive "smart" pump set to constant flow can guarantee (within limits) that the boiler is never over or under-pumped. The output of baseboard doesn't change dramatically between 1 gpm and 4 gpm and anything between those numbers works fine for the 3/4" piped baseboard.

    What is the specified minimum flow rate for the boiler? Does that model report a flow rate to the front panel controls?
     
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  4. dwassner

    dwassner Member

    Joined:
    Jan 31, 2012
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    Finger Lakes, NY
    Thanks, Dana.

    The cooler zone does eventually achieve its setting, but it is ALWAYS after the warmer zone. Per our last discussion from last year, I have the reset curve temps set so that the thermostats are almost always calling for heat. The boiler is often humming along at 20%. The time the cooler zone will often achieve its setting is when the indirect hot water calls for heat, which then boosts the setpoint significantly. Since I only have 1 pump with the 'full flow' plumbing, if the spaceheat zones are still calling for heat while the indirect begins to call, the baseboards then get much hotter water, which is usually how the colder baseboard zone gets satisfied.

    The cooler baseboard zone is definitely noticeable, especially throughout the morning. maybe I will try to slightly close the ball valve.

    My delta T, every time I have glanced at it during both the high and low end of the reset curve, is almost never above 25deg. and this is with the pump on its lowest setting.

    The manual states the following flows: 20 deg rise - 5gpm, 25deg rise - 4gpm, 35deg rise - 3gpm. Below is the link to the specs of my pump. In all honesty, I am unable to make sense of the curves as I am unable to see a spot on the curve where the ft/hd matches the needed flow of the boiler

    https://product-selection.grundfos....tid=GPU&productnumber=59896341&qcid=544049656

    thank you,
    Dustin
     
  5. Dana

    Dana In the trades

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    Just to maker sure, it's the HOT baseboard zone that gets throttled back a bit, to force higher flow in the colder baseboard zone. That will lower the overall combined flow and increase the delta-T on the boiler a bit, but it looks like you have plenty of headroom.

    Throttling back the flow on the hot-baseboard zone increases it's pumping head, lowering the flow on that branch, but if the delta-T on the cold-baseboard is still under 25F even when the hot-baseboard zone's zone valve is off (thermostat satisfied) it's not going to hurt anything.

    Regarding the pump curves, did you even calculate the pumping head on each zone separately, as well as when running in parallel?

    [​IMG]

    The pump curve indicates that on low-speed at 5' of pumping head it delivers about 5 gpm, which would be consistent with a 20F rise at the boiler per your reported notes from the boiler manual. With one or the other zone valves closed the pumping head of just the single zone could rise to 6-7' of head and less than 4gpm, delivering a delta-T north of 25F.

    There are a few dumbed down online pumping head calculators to help figure this out.
     
    Last edited: Apr 3, 2019
  6. dwassner

    dwassner Member

    Joined:
    Jan 31, 2012
    Location:
    Finger Lakes, NY
    Thank you Dana.

    So with all that being said, how would I go about determining if having 4 pumps instead of 4 zone valves (I plan on finishing the basement which will have two zones) will over-pump the boiler? Would I just use the total length of all 4 zones as the length in the calculator to find the total head of the system and set the pump at the speed that provides the flow for my target delta t?

    I don't know if the specs in the manual are max/min/target flow rates, so I am not sure what would be considered over-pumping.

    If over-pumping took place, would the only symptom be a very low delta T and therefore a higher than necessary inlet temp resulting in being outside of condensing mode more often than necessary?

    thanks again,
    Dustin
     
    Last edited: Apr 3, 2019
  7. Dana

    Dana In the trades

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    You'd spend less money and have more easily adjustable results by using zone valves and buying a "smart" ECM drive pump with flexible control feedback options. The pumping head of your new basement zones is probably going to be crazy-low, resulting in near-zero delta-Ts on the zone radiation if using a standard 3-speed circulation pump.

    The heat loads of most basements are miniscule if insulated to current IRC code minimums (highly recommended first step), usually below the minimum fire output of any mod-con boiler- it's already a "micro zone" from a system design perspective. Breaking the basement up into a PAIR of nano-zones, each with their own pump isn't a great idea.

    I have a recently installed micro-zone in my house with only 9' of 10" cast iron baseboard, and even with an AquaMotion Einstein AM55-FVL pump permanently set to "Night Set Back" mode using (industry lowest) 5 watts of power, the delta T on that zone is less than 5F. Even with twice the radiation it would probably still be under 5F. With a standard 3-speed the delta-T on that stub of radiation would be less than 1F. You could run your whole system on the AquaMotion AM55, or a Grundfos Alpha 2 or Taco Veridian VR1816, with 4 zone valves, and be using less power than what you're doing now. If my system hadn't already been built with a pump per zone I'd be using a smart pump and zone valves. Two of the other zones are overpumped with Taco 3-speeds running at the lowest speeds too, but at least with a delta-T greater than 5. I should be swapping the pumps for those two zones out for ECM drive smart pumps later this year (if for nothing else to make those zones quieter), but for the time being I'm throttling them down with ball valves. (That's what I get for explicitly suggesting it but leaving it up to the contractor whether to do it with a single ECM drive pump and zone valves vs. a circulator per zone. If I only knew then what I know now...)

    Four circulation pumps would be insane over-pumping if they all ran at the same time unless you ball-valve or globe-valve throttled them back limit flow. You are arguably over pumped now, just not by enough to matter. Over pumping results in erosion of the tubing inside the boiler, and erosion on the radiation plumbing due to excessive flow velocity. Half inch copper pipe really doesn't want more than 3.2 gpm as its normal operating flow, and 3/4 inch should be limited to 6.5 gpm.
     
  8. dwassner

    dwassner Member

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    Location:
    Finger Lakes, NY
    Thanks, Dana.

    The basement zones are split into two because one area is a workshop that is completely sealed off from what will be the finished side of the basement.

    Per our discussion last year, I did buy 3" recycled roof insulation and lined the entire basement less the shop area. It has made a clearly noticeable difference.

    To find the max head of the system, so that I select a pump capable of the maximum potential load of the system, would I measure the total length of all zones and use a 1.5" dia pipe in the system? (this is the diameter pipe that has the same area as 4 .75" pipes)

    At the high outdoor temp end of my reset curve, the boiler temp climbs even while it is throttled back to its min of 20%, since the baseboards cannot pull enough btu's from the system. I am hesitant to decrease the water temp below 115 at 35deg outdoor temp as I don't want to make the boiler short cycle. Will having the variable control pump allow the outdoor temp to be set lower, as the water should be able to pump slower and have a larger delta T?

    I did increase my offset by 5deg and decreased my offset by 5deg to combat this. My thought was that if the zones are not satisfied but the setpoint p is being met, it causes the boiler to shut off, then why not just increase the offset to keep the boiler on longer? The zones are still calling for heat so its going to turn back on in a few minutes anyways...

    thank you,
    Dustin
     
    Last edited: Apr 3, 2019
  9. Dana

    Dana In the trades

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    The lengths (including "equivalent lengths" of all ells tees & valves ) of the loops are all different, yielding different head numbers, so there is no way to make an equivalence to a larger diameter pipe of some single length.

    The maximum head on the system would be the zone with the longest plumbing length, since that's what it would be pumping against when only that zone would be calling for heat (the others would all be off.) The minimum head on the system is when all zones are calling for head, flowing in parallel.

    Read up on the different control mode options on the different "smart" pump models. It often works well on system with zone valves to use a constant-pressure feedback, so that when more zones open up it speeds up the pump to maintain pressure, and when zone valve close it backs off, keeping the flow to any active zone the same independent of the state of other zones being on or off.

    With very short plumbing runs on the basement zones, if there isn't some sort of flow limiter/balancer they will hog the flow due to the much lower head relative to other zones. If using a ball valve for the flow balancing function it will eventually wear the ball valve out, and it may not fully seal when turned off. Using a globe valve (a very different internal function) to balance flow is the "right" way to do it, but it's more expensive. There are comparatively inexpensive ball-valve type flow balancers (not intended to be isolating valves, like full-handle ball valves on they system would be) that could/should be installed on all zones when you open up the system to install the new zones to allow you to adjust flows accordingly.

    It's fine to open up the differential offsets to get longer burn times, and unless you over-radiate the zones for the basement even that may not be sufficient to suppress short cycling whey they are the only zones calling for heat. (Which boiler was that, again?) It wouldn't be crazy to add a pump and plumb the thing primary/secondary using an (unwired) electric water heater as the hydraulic separator if you can't get enough thermal mass or radiation into the micro-zones to keep cycling well bounded.
     
  10. dwassner

    dwassner Member

    Joined:
    Jan 31, 2012
    Location:
    Finger Lakes, NY
    Thank you, Dana.

    The boiler is a Lochinvar wall mounted 55k btu. I don't remember if it is the whn or something similar.

    I did plan on over-radiating the finished zone in the basement, along with over-radiating the shop area.

    If I put an infinitely variable speed pump in the system, if only 1 basement zone is calling for heat, why wouldn't the pump just drop the flow to absolute min to maintain the correct delta T, and prevent the short cycling?

    When you say that the ball valves will eventually wear out, does this mean they will eventually leak, or just not completely seal?

    I slightly closed the hotter zone yesterday. This morning both zones both came up to temp at almost the same time. I expected this to work, but didn't think I'd get it on the first try... Thanks again for the input.

    Dustin
     
  11. Dana

    Dana In the trades

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    There are no infinitely variable speed pumps out there.
    There are no infinitely variable speed pumps out there, but short cycling is a function of more than just flow- the heat emittance of the radiation and the amount of thermal mass in the loop both matter.

    Since ball valve throttling worked, it's clear that a more appropriate flow limiter will work. When a ball valve sees excessive wear from being partly open it will eventually fail to seal completely in the "off" position. With a purpose specific balancing ball valve that doesn't matter- it's not designed to ever be fully "off", and the internal holes/ports/channels are designed to be able to smoothly fine-tune flow better than a simple quick shut-off ball valve does.

    The KHN/WHN-055 can throttle back to about 8000 BTU/hr at condensing temps, and 35'-40' of baseboard per zone would be enough to keep the cycles reasonably long, even though the heat load of your whole basement (not just each zone) is probably less than 8000 BTU/hr


    A ~48" (x 5" x 20" tall) Sunrad type cast iron radiator would be enough radiation too, and has enough thermal mass in the water volume & cast iron to make a difference even if you come up a bit short. They show up cheap on the used market all the time (keep scanning the local craigslist for cast iron radiators- they're out there.) They're pretty hefty- a 45-50 incher is north of 300lbs, but they're also very rugged compared to fin tube convector housings, something worth considering in a workshop environment. Unless you're running 160F+ water in them they can be cleaned up and painted with standard latex wall paint. Be sure to flush any used radiator well by running 30-50 gallons of water through it with a hose, and have a decent filter on the system in case it sheds chunks of scale/rust when first put back into service.

    [​IMG]
    ^^The original Arco Sunrad^^

    [​IMG]
    ^^ Burnham Radiant, with identical output specs^^
     

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