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Zone pumps and constant circulation

leegej
leegej Member Posts: 30
I’m installing a condensing boiler with ODR on a two temp system. One high temp zone with 4 panel radiators with TRVs through a mixing valve and have a delta p alpha pumping them. Then two low temp zones of radiant heat will be zoned with pumps. I’d like to have constant circulation but having trouble wrapping my head around how to do it. Would a delta T pump be the best way to zone with pumps and achieve constant circulation?

Comments

  • leegej
    leegej Member Posts: 30
    I understand that if the outdoor reset curve is set correctly, the circs just keep pumping away and the boiler does what it needs to. I’m just trying to understand what pump will do this. A delta p pump should never see a pressure difference since I’m zoning with the pump and not zone valves. Is there an application or a benefit from a variable speed pump in constant circulation while using the pump to zone? Or just a simple 3 speed pump?
  • hot_rod
    hot_rod Member Posts: 16,315
    The delta P circulator is ideal with TRVs, it will modulate flow along with the valves.

    You will needed to adjust the boiler max setting for the temperature required on a design day for the high temperature loop. The ODR when dialed in could keep that running near constant circulation.

    Low temperature zones mixed with a 3 way thermostatic valve? The thermostatic valve will target whatever temperature you dial in. You may reach a point where the 3 way thermostatic doesn't see hot enough temperature on the H port when the boiler ramps down on ODR. The hot would like to be about 25 higher than the mixed outlet. Fixed speed circuit is fine with a single zone on the 3 way valve.

    The 3 way will always flow, but temperature regulation gets a bit unstable without enough differential between H and mixed temperature.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Steve Thompson (Taco)
  • leegej
    leegej Member Posts: 30
    I currently have an I series 3 way motorized mixing valve I am going to install, will that handle things better than a thermostatic when the differential gets a bit tight?

    When pumping a single zone, is there any benefit or application for a variable alpha style pump?
  • hot_rod
    hot_rod Member Posts: 16,315
    A 3 way valve with an ODR would give you better control.

    With a multi temperature system, constant circ on all zones is a bit tougher to do.

    The true constant circ systems had the distribution circ run 24/7, then an injection mixing setup to pull in the correct amount of temperature to mix. You need SOME method to pulse heat into the load to match the heat loss. ODR, with indoor feedback, temperature and burner modulation are all part of the tools to help get to constant circulation.

    If a single zone has TRVs on the rads as you mentioned, yes any ∆P circulator will improve operation.

    Even without TRVs or zoning , the ECM circulators use 40% or more less electricity in fixed speed operation. So if nothing else you save some electrical consumption on those zone pumped circuits.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Steve Thompson (Taco)
  • leegej
    leegej Member Posts: 30
    I fully understand the delta p pump in radiators with TRVs, that’s a no brainer. I have two other delta p pumps ready to go in, but then realized I’ll never have any pressure change in a single zone. I’ve come to the conclusion that delta t pumps aren’t used much, would it make sense to use a delta t pump on a single zone? Or when the load got very small would you be barely pumping to get even a 10 degree delta?

    Also the I series 3 way mixing valve will be ODR.

    I’m striving for constant circ (or almost constant) mostly to prevent expansion noises in the floor. If it does shut off some it certainly won’t be the end of the world. Which hopefully the ODR on the boiler and on the mixing valve will mitigate any expansion noises in the plates.
  • hot_rod
    hot_rod Member Posts: 16,315
    I'm not a fan of constrained ∆T operation. In some cases it does no harm, I have yet to see a lot of value in a basic distribution circulation application. For an oversized boiler it can extend run cycles by pulsing the energy into the system.

    I believe the delta in any hydronic should be allowed to move around a bit with a dynamic load that it serves. The load changes constantly, let the ∆ also change to best match that load, thermal equilibrium is what it is called. ODR and constrained ∆ are trying to do two different tasks.

    I think you are on the right path for "near constant" circulation.

    IF you did want to pipe a specific constant circulation, here are some options.

    https://www.pmmag.com/articles/100586-continuous-circulation-in-floor-heating-circuits

    Idronics 23 is a good read for understanding heat transfer in hydronics.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Steve Thompson (Taco)
  • leegej
    leegej Member Posts: 30
    Sounds good! I’ll slap in the delta p pumps and let them run constant speed. My boiler is oversized by about 50%, but I’ll be adding DHW to it in the near future. The boiler was less than 5 years old when I sold my dairy herd so it’s getting repurposed from the milk house.
  • Steve Thompson (Taco)
    Steve Thompson (Taco) Member Posts: 200
    Hello leegej. Good questions to bring to "The Wall".

    Couple of comments, why pay for (and deal with more complex settings) by using a Delta P on a constant speed application? We have the 007e single speed circ and a 3 speed 0015e ECM specifically for that application... Or we have the 0018e with Bluetooth where you can almost see inside the pipe using our app - it's pretty cool.

    Also, the Delta T vs Delta P is an ongoing debate (discussion). Some (like myself) openly admit there are applications for both (that's why Taco has Delta t and Delta P).
  • hot_rod
    hot_rod Member Posts: 16,315

    Hello leegej. Good questions to bring to "The Wall".

    Couple of comments, why pay for (and deal with more complex settings) by using a Delta P on a constant speed application? We have the 007e single speed circ and a 3 speed 0015e ECM specifically for that application... Or we have the 0018e with Bluetooth where you can almost see inside the pipe using our app - it's pretty cool.

    Also, the Delta T vs Delta P is an ongoing debate (discussion). Some (like myself) openly admit there are applications for both (that's why Taco has Delta t and Delta P).

    Taco has done a nice job of filling in the gaps and offering some affordable ECM options for a no frills circulator.

    One question, why did it take so long :)

    A discussion we had here back in 2007

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Dave H_2
    Dave H_2 Member Posts: 503
    @leegej
    I fully understand the delta p pump in radiators with TRVs, that’s a no brainer. I have two other delta p pumps ready to go in, but then realized I’ll never have any pressure change in a single zone. I’ve come to the conclusion that delta t pumps aren’t used much, would it make sense to use a delta t pump on a single zone? Or when the load got very small would you be barely pumping to get even a 10 degree delta?


    The DeltaP circs used in a zone pump application like your project won't vary their speeds but will find the speed that it needs to. Actually it will pump as much as the size of the pipe allows.
    Depending upon the size of the zone, a DeltaT could work very well, but I am assuming that these are small zones and the DeltaT circ has a minimum speed that it needs to run at which may end up being over sized for your needs. I would rather see zone valves used with small zones in a projects with a DeltaT circ.


    Also the I series 3 way mixing valve will be ODR.

    The i-Valve is a good choice over a thermostatic to modulate the water temperature based upon ODR. It will give you longer run times and trickle the heat into the space.


    I’m striving for constant circ (or almost constant) mostly to prevent expansion noises in the floor. If it does shut off some it certainly won’t be the end of the world. Which hopefully the ODR on the boiler and on the mixing valve will mitigate any expansion noises in the plates.


    That's exactly how I have my house; all radiant floor (slab and plates), boiler using it's outdoor sensor and two i-valves on their own ODR. I do have DeltaT circs in my case as I have used actuators for the zoning. I get very consistent temperatures in the house as the thermostats typically act as high limits in the winter.

    Dave H.
    Dave H
  • leegej
    leegej Member Posts: 30
    I’ll have to look into the taco pumps and see what I think. Although I hate the idea of trying to return the pumps I bought back in November, I’m sure there will be a restocking fee!

    My three zones consist of 1 High temp zone of 4 panel rads, a low temp radiant zone with 6 loops in the living/dining room and kitchen (so certainly not small), and a low temp zone of 2 loops in the bedroom (2 fairly short loops of less than 200 feet). So the alpha won’t be a problem on the larger 6 loop zone, but the small bedroom zone I guess could be problematic but I’ve got my fingers crossed.

    As I work on the boiler piping while I have time, I’ve gotten to the point of the 3 way mixing valve. I have 2 zones that need to be mixed down. Can I do that off of one 3 way valve? Or do I need a mixing valve for each zone?
  • hot_rod
    hot_rod Member Posts: 16,315
    edited April 2020
    A common 3/4- 1" thermostatic mix valve will have around 3Cv. 6 maybe 7 gpm is probably about the max. you want to try and pump thru it.

    Here is what 6 gpm looks like thru a 3Cv valve, psi drop and ' of head.
    I think you mentioned a 3 way ball valve mixer? If so size it by Cv. Try to match the Cv of the valve to your desired flow of all the zones connected to it

    You really don’t want to oversize a ball style control valve
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream