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Flow (GPM) in zones won't go beyond 1/2 gpm

nicholsm4
nicholsm4 Member Posts: 18
edited October 2019 in Radiant Heating
I have a system with 11 loops on 6 zones with a primary secondary heating loop system. I can't get any loop to go above 1/2 gpm no matter the number of zones activated and with all zones activated gpm indicated on flow valves really drops. The pump I have is the Grundfos Alpha 15-55F and I have a Taco 5000-2 mixing valve . It will go up to 3 gpm with all zones on but not above that. I somewhat understand the relationship of resistance in the pipe or head and how the pump just circulates vs pressurizes the system. Any recommendations on where to start troubleshooting. I don't have original specs for the system. This is radiant in floor heat in a home 2350 sq ft. Thanks for any suggestions!

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 22,972
    Is this the original pump? If not, how was the replacement chosen?

    If it is check for air in the system -- or a partly closed valve somewhere. That is, assuming it ever worked right...

    If not, you will need to calculate the head loss -- flow resistance -- in the loops, and compare that to what the pump ought to be able to do.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • GroundUp
    GroundUp Member Posts: 1,868
    1/2 GPM is pretty standard for a 1/2" pex loop 250-300 ft long especially if there's glycol in it and the mixing valve has a rather large pressure drop and a Cv rating of only 2.3. The Alpha runs on delta P and will change speed depending on how many zones are open to maintain that pressure differential, not necessarily to maximize the flow and besides, it's not a large enough circ for 11 loops anyway. Are there 11 actuators on a single 11 loop manifold or how's it set up? What if you set the Alpha to constant pressure speed 3, does it then get past 3 GPM? Does the readout on the Alpha match what the flowmeters are saying with everything open? Pictures would be very handy. I've come to notice the Alpha1 circs don't always function like they should when used with radiant in delta P mode.
  • nicholsm4
    nicholsm4 Member Posts: 18
    No glycol. I double checked total GPM with all 11 valves open - 4 GPM at constant pressure speed 3. There are 2 manifolds one 7 and one 4 each fed by 3/4" pex. Flow meters drop very low with all 11 open approx .2 gpm each which doesn't add up the the 4 at the pump. The pump was a replacement recommended on a rough estimate of need. I purchased the home and the system has not ever worked as it should. They compensated by running high floor temp. The system is non-oxygen barrier pex with a Lochinvar cast boiler, which I understand is a problem but its what I have for now. I have a magnetic trap and drain and system is treated with no current rust. Hope to replace boiler next summer and any recommendations would be appreciated. Without knowing system design, not sure to go about calculate head loss.
  • nicholsm4
    nicholsm4 Member Posts: 18
    I can post pics, what would be of benefit? Thanks!
  • Jamie Hall
    Jamie Hall Member Posts: 22,972
    "The pump was a replacement recommended on a rough estimate of need. I purchased the home and the system has not ever worked as it should. "

    Right. Wrong pump. Someone -- such as it might be you or a qualified engineer or technician -- needs to determine what the flow characteristics (head loss vs. flow) are for the system, and then pick a pump which will work.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    nicholsm4
  • hot_rod
    hot_rod Member Posts: 21,898
    Ideally you would have a system design that indicated the required gpm per loop. .5- .6 gpm is about what most 1/2" pex designs around. All the piping in the circuit, including devices needs to be calculated. 11 loops at .6 gpm= 6.6

    6.6 gpm thru a thermostatic valve 3Cv would look like this.

    .6 gpm in a 1/2" 300 foot loop about 4' head.

    If you need more output from the system, increasing temperature may be a better option.

    I would not bet the farm one the gpm readout on circulators. A real flowmeter is a better way to get an accurate number.

    Steps you need to size a circulator are in this journal.https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_16_na_0.pdf

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    IronmanZman
  • Ironman
    Ironman Member Posts: 7,354
    Non-barrier tubing can cause many issues including premature failure of the boiler, circulator, expansion tank, etc. I would recommend that you isolate the tubing from the boiler with a generously sized plate heat exchanger and properly sized stainless steel circ on the floor side. You'll also need the normal ancillary components: expansion tank, relief valve, etc.

    With only a 3/4" line feeding the manifold, you're only gonna get about 4 gpm through it. It should be 1".

    Still, as stated, about .5 - .6 gpm per loop is about the best to be expected.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    GroundUp
  • Dave H_2
    Dave H_2 Member Posts: 547
    edited October 2019
    Is the circulator between the mixing valve and the manifold?

    I have to ask, that is probably one of the highest mistakes that happen when the circ is not in that position.

    Add a pic of the system if you can.

    Dave H.
    Dave H
    Ironmanrick in AlaskaGroundUp
  • nicholsm4
    nicholsm4 Member Posts: 18

  • nicholsm4
    nicholsm4 Member Posts: 18
    Circulator is just beyond the mixing valve in the photo (hard to see). I am doing heat loss calculations, and attempting to determine head loss/flow. If I can only expect .5 to .6 with 11 loops, 7 on one manifold and 3 on the other fed by 2 - 3/4" feeds it would seem like I need a pump that would put out about 5-6 gpm and this one is only hitting 4 with all zones demanding heat and then flow through each zone really drops. As long as only half of the system is demanding heat I am ok, its when we get a quick dip in temps, the system just can't keep up. So it looks like I have some work to do or find an expert in my area, Albuquerque, NM, to work the system over. I know at some point I need to change out the boiler due to non-oxygen barrier pex. I would probably benefit from a modulating system. Really happy with my on-demand DHWH system. If I can tune this system up for this winter maybe next summer I can replace it. Any recommendations are appreciated as are all those I have already received.
  • hot_rod
    hot_rod Member Posts: 21,898
    What supply temperature are you running? Increasing heat output on cold days might be easier by just turning the knob on the mix valve and increasing temperature. Add a gauge if there isn't one to see what the actual SWT is.

    1/10 of a gpm increase will not accomplish much. Increasing circulator size may increase noise and wear due to excessive velocity. 10° increase in supply temperature will make a noticeable difference, if the boiler is able to keep up.

    Really, 6- 7 gpm thru a 3 Cv valve is about what you want to flow on a continuous basis.

    Here is what 7 gpm looks like.

    Is that a DHW expansion tank on the boiler? Make sure the pre-charge was adjusted.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    nicholsm4
  • nicholsm4
    nicholsm4 Member Posts: 18
    Bob - I have a gauge and running a supply temp of 110 just beyond the circulator pump. The zone on the north side of the house could not maintain temp. last night dropped about 2 degrees, I will take your advice and increase it today to 120 in anticipation to temps in the low 20's tonight and see if that makes a difference. I adjusted the pressure on the tank prior to install, as I recall I set it at 15 psi, looking at literature it looks like 12 psi is standard, I will pull it out and check charge. The system is running between 12 - 15 psi when up to temp according to the gauge on the boiler. I am running the boiler at 180. If all zones are turned on the boiler temp will drop to just over 100 so it is being pushed to keep up. The boiler is a Lochinvar RBN090 with input rating of 90k btu. I plan to do a heat loss calculation to give me one more data point as I move forward. The house is single story 2300 sq ft living area, single floor standard 2 x 6 construction frame stucco with 10' ceilings. At this time I can only read gpm as indicated on the pump and never see over 4 gpm. One of my challenges is I get a large solar gain thru south windows during the day and the temp will easily go over 80 even on a 40 degree day but drops rapidly at night. So the slab doesn't get heat thru the day then at night the slab is cool but there is a need for heat. This house probably should have not been built with in floor radiant. I would probably benefit from a more advanced system that can take into account outside temp, slab temps, also a new mixing valve with more advanced features. I would like to make incremental changes up to boiler change out, just not sure what the best starting point might be or even if this is a good idea. Any advice is appreciated.
  • hot_rod
    hot_rod Member Posts: 21,898
    those passive solar gain homes are tough, tough to control High mass heating systems compound the control issues

    Any indoor and outdoor response you can add will help somewhat

    At the least a means to modulate Swt
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    nicholsm4DZoro
  • Jamie Hall
    Jamie Hall Member Posts: 22,972
    @hot_rod 's comment is an understatement. Radiant is very slow to respond -- as you have noted -- and worse if the floor is high mass, but from what you are saying I suspect that the floor really isn't high mass. What is needed is to figure out some way to move that extra heat out of the areas which are overheating during the day. Ideally, you would be able to store it somewhere, such as in a high mass slab or wall.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • DZoro
    DZoro Member Posts: 1,048
    @Jamie Hall
    On a side note, don't mean to get off track but...
    If he had a good odr control system set up properly. Would a constant pump set up, move some of the hot in the solar gain crete to the cooler crete? Basically keep constant temp in the concrete throughout the home? So when stat does call for heat (sun down) It is working with a entire slab of almost the same temp, and not trying to bring up cold rooms and over satisfying the sun rooms.
    Just some thought....
    D
  • hot_rod
    hot_rod Member Posts: 21,898
    How large of a slab gets that over-heating solar gain?
    To move the heat from the various room you would need to have them zoned and a means to turn off the boiler while you move from zone to zone. Keep in mind a 4" slab at say 85- 90 degrees is not going to store a lot of excess heat to move around, maybe a few hours worth?
    It may not be worth the piping and control costs to chase that passive gain stored in a slab.

    Your comment about radiant slabs not being the ideal system for this home is correct.

    A low mass floor, like a thin over the top wood product, or panel rads are much better for homes that need rapid start and stop systems. You have a huge flywheel in that slab.

    The best improvements would be indoor and outdoor reset. Hopefully the home is zoned so cold non passive gain zones could heat while the passive gain rooms turn off. Trying to not over-heat slabs that'll see that solar gain.

    Controlling the solar gain with motorized shades is another method to help prevent over-shoot in high solar gain rooms.

    An age old challenge that dates back to the cave dwellers I suspect :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    DZoro