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Circulator pump moving water slowly on hydronic radiant floor system

MarksTrying
MarksTrying Member Posts: 5
in Radiant Heating
I installed a hydronic radiant heating system into my home last spring.  I am using a takagi-jr tankless water heater in a closed loop system.  I am having a problem with the water not flowing quickly enough through the system.  I have blead the lines multiple times and i have an air eliminator installed.  I have an expansion tank set at the correct pressure (12psi) and I have an auto fill valve for the system set at 12psi.  I have a bell and gossett circulator pump (i sized it up to this from a taco, but with no significant change) installed after the expansion tank and before the 7 loop manifold.  Each loop consists of approx. 250' - 300' of 1/2" pex tubing.  If i open the bleed valve on the return manifold i see an instant increase in the gpm of the pump.  Once i close it, it slows way down.  I have adjusted the valves to turn varying loops on or off with no signifcant change in performance.  This problem is causing the heat to be distributed to my house very slowly.  The pump seems to be functioning, the system is working, just moving water too slowly, the expansion tank seems to be set correctly and the water heater is operating properly.  Anyone have any ideas?  I have attached a picture to show the system.

Comments

  • BobbyG
    BobbyG Member Posts: 79
    wow

    you need to call a professional.  There are too many things here wrong for me to try and help you.  See if there are any contractors in your area in the "Find a Contractor" at the top of the page.
  • MarksTrying
    MarksTrying Member Posts: 5
    Only one problem

    The only problem is that the circulator pump is not circulating water quickly enough.
  • Slimpickins
    Slimpickins Member Posts: 348
    only problem?

    I'd say your big problem is using the wrong appliance for your application.
  • Ironman
    Ironman Member Posts: 7,516
    I've Got to Agree

    There are multiple problems here. Especially using a tankless instead of a boiler. I must ask: who designed the system? Many times Internet sales people claiming to be experts sell these setups to folks who think they've found a cheaper, and thus a better way to get a radiant system installed. Some unscrupulous wholesalers will also do this to turn a quick buck. I don't know what your situation is, but if a tankless could take the place of a boiler, they'd stop making boilers and just make tankless.



    Pardon me for venting, but I come across this too often and it's the consumer who's getting ripped off as well as the pro who would have done it right and made an honest dollar.



    A couple of major problems beyond the tankless issue:



    1. You have the wrong pump. A pump must be sized according to required flow and friction loss (head) of the piping system.

    2. This should have been piped primary/secondary due to the high head loss through the tankless.



    I too, would suggest a professional.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Piping

    The rest of the group that responded are all correct and voice the same opinion I have. A tankless is a domestic hot water appliance and not a boiler. It's the cheap way out of trying to gain an efficiency heating plant.  There are all sorts of mistakes made in the provided picture.

    Attached should get you out of trouble.

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  • MarksTrying
    MarksTrying Member Posts: 5
    Pumping and Piping

    Thank you Ironman and HVHEHCCA for more informative postings.  It is clear that nobody is in favor of the tankless water heater, but can someone help explain why the pump is pumping so slowly in this situation.  I see from the diagram in the last posting that the system shows pumps on each zone plus another pump on the return side before the boiler.  Is this because of loss in flow caused by the tankless water heater, or is this to aid in a system that uses multiple zones that may require a second pump when only varying zones are on.  In my system i am not actually zoning any of the loops individually.  I understand the concept of head pressure casued by elevation change and friction in the pipe and bends, but it seems like the runs of tubing are not the issue.  If i open the bleed valve on the return manifold the pump triples in speed.  This leaves me to believe that the resistance is coming from the heater on the return side.  Is that correct?  How can i compnesate for that resistance?
  • CMadatMe
    CMadatMe Member Posts: 3,086
    The Mixing Valve

    You cannot pull enough through the mixing valve. You have to take into consideration it's CV rating (head). You used a tankless heater there is no need of a mixing valve. You set the water temp on the tankless for the water temperature you need on your design day.



    If you eliminate the mixing valve and don't do primary/secondary then you have to take the tankless pressure drop (ft of head) plus the head loss through the greatest loop and size the pump based on these. It means you need a big expensive pump. That is why you pri/sec pipe. Smaller pumps.



    A tankless unlike a condensing boiler will provide the radiant floor the same water temperature every day which is a water temperature you do not need every day. Like I said its a cheap way of trying to achieve efficiency and also a bad way to achieve comfort.



    You bought it, installed it so you might as well pipe it correctly. Personally I would pri/sec then save my pennies and install a Taco RMB to control the radiant/system side. Set the tankless to design water temp and let the RMB modulate via outdoor reset the radiant to provide maximum comfort.

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  • heatboy
    heatboy Member Posts: 1,468
    edited October 2010
    The reason is simple........

    Even at a modest flow rate through the heat echanger in the heater of 6 GPM, the presure drop through it is 20'+.  You need a Taco 009 just to get the water through at  a 20 degree rise.  Your system should be seperated with the heater and 009 on one side and the systemwith your pump on the other.  If not, replace the B&G with either a Taco 0011 or 0013. 

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  • BobbyG
    BobbyG Member Posts: 79
    give and take on information

    since you got the information to help you, can you explain how you got into this predicament?



    Since they've given you the info to make the system work, I should help you make it SAFE.  Make sure you have a pressure safety valve that is rated for 30# and DO NOT use the one that may have come with the tankless which is a temp. (210 deg. F) and press. (125#) relief valve



     Where did you get the materials and did someone give you a piping diagram or did you try to use something you found somewhere?
  • MarksTrying
    MarksTrying Member Posts: 5
    edited October 2010
    Great Information

    That is a lot of great information.  I am going to start by removing the mixing valve and see how things change.  If i end up still needing more, i will add back in the taco pump, i already have, as a secondary to help. As far as the concern for pressure release, I am going to look now and change it if necessary.  Thanks for the warning on that one. To answer the questions about how i ended up here; I pieced together this system myself based on the mounds of conflicting information I was able to gather from the internet and books on the topic.  I designed the layout myself combining a collection of diagrams that I researched. 
  • CMadatMe
    CMadatMe Member Posts: 3,086
    So You Found Us

    After the fact? I find it surprising that you can goggle for heating help from the get go and not find this site.



    Removal of the mixing valve alone is not what I was hoping for in this case. Don't try to band-aid this and just "get away" and take the easy path. You really need to pri/sec this. Did you know that you voided the warranty on the tankless as soon as you made it a "heating plant?" Now the best avenue is to do it right and protect the investment you made as best possible.

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  • heatboy
    heatboy Member Posts: 1,468
    Unless it's.....

    ..... a Taco 0011, it will not work any better if you are trying to run this with one pump (mixing valve or not) due to the extreme tightness of the heater's heat exchanger.  These units, no matter what anyone ele tells you, were not designed as heating appliances. 

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  • MarksTrying
    MarksTrying Member Posts: 5
    Still Trying

    I too am disappointed that I found this site after the fact HVHEHCCA, but the internet is a big place and sometimes neccesity drives discovery.  As far as the comments on the Takagi-Jr as a heating unit for radiant system, the manufacturer does recommend and warranty these units for this purpose.  This may not make it the right appliance for the purpose, but it is designed for it nevertheless.  I understand that adding the secondary may be the right solution, and since i have the pump it makes sense to.  The pump add is a bigger challenge since the pipe is closer to the wall.  I want to get this system right.  I am just trying to solve it one step at a time.

    Thanks again for all of the great information and advice.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited October 2010
    Best of Luck

    If it was designed for heating it would have an "H" stamp which it does not. Tankless heaters are advertised as a heating appliance due to their water temp delivery and the mfg's know that they can deliver the water temp needed for radiant systems. It still is not a heating appliance... Chaulk it up to another consumer getting caught up in the world of marketing...

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,858
    Pressure drops in series....

    The pressure drop of the longest small bore tube circuit is in series with the pressure drop of the heat exchanger the way you have it piped. You should have done it primary/secondary with the boiler as a secondary and its own dedicated pump. Then you can maintain the 3 way mixer.



    You also MUST keep that boiler from seeing too low of a return temperature, or it is guaranteed a slow death due to condensate corrosion.



    ME

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  • Ironman
    Ironman Member Posts: 7,516
    One Other Thing...

    You're looking for a 10deg. delta T on a radiant floor. This means twice the gpm. of a 20deg. delta T. Size your pump accordingly.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
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