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Questions on Radiant Hydronic Systems (using in floor distribution method)Open Vs Closed loop

chingo Member Posts: 22
I was wondering if anyone could answer a few questions.

1. which system would provide more flow using exact same equipment an open loop or a closed loop????
2. If i have the exact same equipment but installed in 2 different locations (same length of pex etc...) should i not achieve similar flow????
3. What would cause the pump to see a large amount of resistance in 1 system and not the other (given same equipment AND no air in system)????
4. If system is running quiet and smooth and heated water is shown to be circulating via temp. gauges (SEND and RETURN) on manifold of zone then shouldn't the pump be considered to be good even though i am not getting calculated flow. OR might it still be defective.?????
5. Have you ever heard of getting 3 defective pumps in a system (system was put together by WATTS)

Using purge cart hooked to system i can get a flow rate through system. 3GPM divide by 8 =.375gpm
PURGE CART = 1hp submersible pump in 50 gallon tank and connected to system via 1/2" hose IN FLOW (at fill point) OUTFLOW (just before boiler) OPEN LOOP SYSTEM to and from 50 gallon opened air tank.

any questions answered OR input would be appreciated.

thanks neil


  • Ironman
    Ironman Member Posts: 7,353
    edited October 2015
    The difference between an open and closed loop is that with an open loop elevation (static head), and friction loss (dynamic head), must both be overcome by the pump. In a closed loop, elevation is not a factor for the circ. Proper static fill pressure is required to overcome elevation in a closed loop. Think Ferris Wheel.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rod
    hot_rod Member Posts: 21,882
    What type of 1 hp pump? Is it a sump pump, high flow low head? Or a submersible well pump?

    All pumps have flow curves available somewhere.

    In either case 1 hp is a lot of pump to purge a typical residential system where the loops are able to be isolated and purged one at a time. Most installers do fine with 1/2 hp transfer pumps.

    If 1 hp only gives you 3 gpm, depending on the pump, it still sounds like you have some blockage.

    All the valves fully opened? Sometimes ball valves look open by handle position but may have a broken stem.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Gordy
    Gordy Member Posts: 9,546
    Pics of the install?

    Designed by watts, but installed by others. Was the watts design followed to the T?
  • chingo
    chingo Member Posts: 22
    1 hp pump was a submersible sump pump Everbilt SP07502VD
    4800gph of water@ total feet of lift 5ft.
    if i can get 2gpm flow (ran for 10 min.) through a isolated run would that not mean all air is out of run.
    I used such a big purge because in modern hydronic heating 2nd edition written by john siegenthaler, PE that is what he recomended to make sure that no air was in system.

    As to Gordy comment system was designed by HRAI certifed designer. Installed by others. Design followed
    not sure how many pics you can upload but i have whole project on file, here are a few

    appreciate any and all input
  • chingo
    chingo Member Posts: 22
    Again what is stumping me is why all runs are exhibiting same limiting characteristics of resistance to flow.
    On previous project i had no issues.
    One system hooked to city water.
    THis system hooked to Axiom pres. fill tank
  • Gordy
    Gordy Member Posts: 9,546
    Flow meters are fully open? I would not be shocked by smashed tubing that pump hose is heavy along with the coupler on the pump hose on top of wire mesh that is surely being mucked up off the ground( sarcasm). I guarantee it was dragged around not lifted, and moved.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Silly question, but are you certain you are flowing water in the correct direction? The flow meters could be causing the restriction if water is being pushed through them backwards.

    Purging correctly is an art as much as a science. You want to start with the lowest zones closest to the physical plant and work your way outward. Once that level is confirmed as clear (purge each circuit individually, or not more than 2 circuits at a time) and verified by no bubbles coming back in the submerged return hose of the purge cart, then go to the next higher floor, closest to the the pump, and then again move outward.

    Keep repeating until all floors are confirmed as purged. Important note: CLOSE ALL automatic air vents. When subjected to negative pressure ( like will be seen during siphon) they become a vacuum breaker, allowing air to be entrained into the flow.

    Once completely purge, residual pressure at bottom of system should be 1/2 PSI per vertical foot of system elevation, PLUS 5 PSI. 12 PSI is the typical minimum fill pressure to ensure correct NPSH required for proper pump operation.

    If you're absolutely positive that you have a fully pressurized and purged system, the circulator should work as designed. Large DT = slow flow. Small DT = high flow (assuming flow is actually occurring) heat source cycling will confirm wether or not the appliance is locked into the load. Short cycle = no or low flow. Long cycle = good flow, good purge heat going to slab.

    I'd have stopped replacing pumps at the 2nd one and started looking elsewhere. It's kind of like a suspected air binding problem on upright radiators. If you don't get air out of the radiators, it's not an air problem. In this case, it's not a pump problem. Something else is causing the issue.

    BTW, the definition of an open versus closed system has more to do with fresh potable water being used and induced into the system, I.e. common connection to the potable water you use for washing and bathing. Although allowed by both national plumbing/mechanical codes, it is not a suggested use by practicing qualified plumbers due to potential of generating high bacterial counts in the tubing during summer months. No amount of flushing or chlorination (within reason) will protect you from those bugs. What you are describing is a closed pressurized system that is not directly connected to the potable system (axiom).

    Check pump flow direction and make certain that flow direction is correct, and there are no obvious internal restrictions to flow.

    On initial startup, the slab will suck up every BTU you throw at it (30 to 40 degree DT). Once slab is charged, DT should be between 10 and 20 degrees.

    It's NOT a pump problem. If you can post the actual in slab circuit lengths, plus any distribution piping size and lengths from mechanical package to the manifold, and the calculated heat loss for the area being served, one of us can run Siggy's pump sizing program to make certain it is correct.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • chingo
    chingo Member Posts: 22
    I can acheive heat through every run(loop) if i isolate it.
    A delta of 20F
    When combined the reduced flow does not cut it.
    This also tells me that flow is in correct direction.
    System isolated Axiom pre/fill tank