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Should I direct pump this boiler...radiant floor with one zone.

nickh1nickh1 Posts: 16Member
I have a 7000 sq ft shop built in the mid 80's with radiant floor heat. It was heated with 2 40 gallon water heaters until this fall. I just put in a HTP UFT-80W boiler and it is humming along great. It was suggested by the boiler supplier and many things I read that it should be piped primary/secondary. The supplier spec'd out Grundfos 15-58 pumps.

There are 9 loops of 3/4" pex, but I honestly don't know how long they are. What I do know, is the pipe is only in the center 3500 sq ft. My assumption and by feeling the floor as it warmed up is they are on 2' centers, which would make them 200'ish loops. With the secondary pump on the lowest speed, I am getting about 10-15 degree's delta T. I currently have the boiler set at 115 and the return water is around 100. Both Primary and secondary pumps are one the low speed.

I'm content how it is operating, my question is if I'm wasting power with the 2 pumps and I would get the same results with one. It would not be a big deal to take out the extra pump/tee's and I have a need for a pump on another project so it would save me some cash to do so.


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Comments

  • Mark EathertonMark Eatherton Posts: 5,840Member
    Unless you have the ability to prove whether or not the existing distribution system has a low head pressure drop, I'd stick with the two pump plan.

    The parasitic cost of operation of these pumps are minimal, and it ensures peak performance from the heat source. If the heat source has it's own circulator, then it knows what it is supposed to be doing, and can "see" the influence of the connected loads and respond accordingly.

    Will it work with just one pump? Probably, but not as thermally efficient as it would with two separate pumps.

    I'm certain others will express different opinions, but based on personal experience, these are mine.

    ME
    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.
  • ZmanZman Posts: 4,428Member
    It looks like you have a pressure gauge on both sides of the secondary circ. With that pressure difference and the circ performance curve (15-58?), you should be able to determine the flow.
    Can you post that info with the circ at the 3 different speeds?
    I agree with Mark that if you don't know, you should play it safe.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Paul48Paul48 Posts: 4,492Member
    I don't see any means of balancing the loops. When you say you're getting a 10-15* DT, I assume you mean across the manifolds. The water will take the path of least resistance. With some electrical tape on each supply and return, and a cheap IR thermometer you can check the DT of each circuit. You can determine the length of each circuit, by flip-flopping the numbers for the Universal Hydronic Formula, in conjunction with the pex manufacturers info on head loss , and the pump curve. GPM= BTU / ( DT x500)
  • Bob Bona_4Bob Bona_4 Posts: 2,082Member
    Best to decouple boiler from an unknown system. P/S.
  • nickh1nickh1 Posts: 16Member
    Thanks for the responses. I will get the pressure readings and post. I also have a thermal camera, I haven't used it on the loops but thought about it. I charge it up and take some pictures.

    I debated about replacing the old manifold with a newer one that would allow balancing. In my brief search, I didn't find any that had adapters to 3/4 pex. I also figured that I would have to buy two for sizing and to deal with where the pipe comes out of the floor. The original setup had a fairly large pump on each water heater that each ran half the loops. The current manifold has I believe 1" female straight pipe thread on the pex adapter with a washer. Would there be any modern manifolds that use 1" npt vs bsp?

    I was going to fill the loops with water and blow it into a bucket to measure the volume of each loop, but figured in the end I can't change the outcome so I didn't' take the time. But if they were unbalanced, it would make a case for a new manifold.

    I personally would be surprised if they are much over 200'. This shop was built in the middle of the 80's farm crisis years and my family has a genetic history of being minimalists. 7000 sq ft is small by today's standards, but I'm very thankful to have it, even more when the floor is warm.
  • HatterasguyHatterasguy Posts: 6,058Member
    edited December 2016
    You're getting a DT of 12F (average).

    If this is at the maximum output of the UFT-80, the flow rate is 12 GPM.

    However, the fact that the 15-58 is on speed 1 tells that you're nowhere near 12 GPM. More than likely you're flowing at about 5 GPM with 5' head and delivering 30K to the floor. You can confirm this by taking a look at the fan speed on the boiler. From memory, 30K is about 2800 rpm.

    The loss in the HX with 5 GPM is only 1 foot so you'd be perfectly OK with running a single circulator and pumping direct.

    The only way this approach would not be recommended is if the 15-58 was on high speed and the DT was 15. Now, the additional headloss from the HX might result in an undesirable drop in the flow rate and resulting climb in DT.

    Also, the suggestion that the system is more "thermally efficient" with two pumps is factually incorrect. One pump means less piping and less loss and is always the preferred way to pipe the boiler if the boiler can accept the system flow rate.

  • ZmanZman Posts: 4,428Member
    I do believe that primary/secondary can increase the efficiency of a system.

    By controlling the flow across the heat exchanger, you can achieve efficiency gains. Lowering the return water temp by controlling these flow rates will increase efficiency. Not really sure if this is considered "thermal efficiency".

    In the system in question, I would be a bit surprised if these efficiency improvements would be worth the additional operating and installation costs associated with the additional circ. In reality, it would take a pretty thorough study to figure it out and it probably doesn't matter much.

    In the end these debates usually end up being an exercise in hair splitting.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • HatterasguyHatterasguy Posts: 6,058Member
    Zman said:

    I do believe that primary/secondary can increase the efficiency of a system.

    By controlling the flow across the heat exchanger, you can achieve efficiency gains. Lowering the return water temp by controlling these flow rates will increase efficiency. Not really sure if this is considered "thermal efficiency".


    This is correct.

    However, it is impossible to reduce the RWT to the boiler without simultaneously reducing the RWT from the system. Once you make the effort on both sides, you might was well pipe it direct and simply control the system RWT.

    There is a fallacy in the industry that accepts the mistaken notion that one can achieve efficiency gains strictly by reducing flow in the primary loop.
  • Paul48Paul48 Posts: 4,492Member
    Everything being proper..... nothing can be more efficient than using the most btus produced by the boiler. Directly pumping the boiler allows for that. How is that even debatable?
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,196Member
    @Zman I've fo7nd that unless the primary (boiler circ) is flowing less than the secondary (radiant circ) than the return Temps to the boiler will be higher and reduced condensing the result. If the secondary flows are sufficient, then wouldn't a direct pipe guarantee the lowest return Temps back to the boiler. Not short circuiting and warming up the return Temps.

    Taylor
    Master electrician specialising in boiler and burner controls, multiple fuel systems, radiant system controls, building controls, and universal refrigeration tech.
  • nickh1nickh1 Posts: 16Member
    I check the psi on the different secondary speeds. It didnt change much.

    Low was 20/18.5, medium was 20.5/19 and high was 21/19.

    I have a 12 psi pressure reducing valve on the makeup water and filler/flushed it with cold water. Is 20ish psi in the ballpark?
  • GordyGordy Posts: 8,478Member
    In P/S pumped system. The system side flow must be greater than boiler side to avoid btu constipation at the boiler.
  • HatterasguyHatterasguy Posts: 6,058Member
    edited January 2017
    You can run the boiler side slower, within reason...........it just doesn't buy you anything.

    In reality, it's very difficult to run the boiler side slower on a residential system unless you heavily throttle it. The headloss is typically insignificant.

    So, it's an issue that effectively cannot occur without intervention.
  • GordyGordy Posts: 8,478Member
    edited December 2016
    6 gpm on low, 11.5 gpm on med, and 13 gpm on high
    nickh1 said:

    I check the psi on the different secondary speeds. It didnt change much.

    Low was 20/18.5, medium was 20.5/19 and high was 21/19.

    I have a 12 psi pressure reducing valve on the makeup water and filler/flushed it with cold water. Is 20ish psi in the ballpark?


    If loop lengths are identical divide values by 9 for individual loop flow rates. Rough guess at best.
    Measuring loop deltas is most accurate when done correctly.
  • ZmanZman Posts: 4,428Member
    There is some inherent inaccuracy in measuring slight variations with the gauges you are working with. You should absolutely check that they both read the same with the system off.
    Based on the info provided, you could eliminate the primary secondary and leave the remaining circ on low. You would maintain minimum flow rates, increase delta t and save electricity.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • GordyGordy Posts: 8,478Member
    The pex dia of 3/4" and assumptions of loop lengths with the above psi differential readings would, and do indicate low system pressure drop.

    However as zman said accurate gauges 0-30 psi, and accuracy between the two gauges can change the readings a lot.
  • GordyGordy Posts: 8,478Member
    One question does the UFT cycle?
  • HenryHenry Posts: 841Member
    it has 10 to1 modulation
  • nickh1nickh1 Posts: 16Member
    I checked it with it off. They appear very similar, but they are 0-60 so it is hard to tell.

    I checked the return lines with my flir camera and as I suspected, some were around 94, others were 97-98. Would I be able to radiate more heat if I slowed flow down? Or would it just even out the floor temp more. My assumption is if I increase delta t at the expense of gpm btu's stay the same.

    I also looked at the floor and the pipe is 24-36" on center. The floor temps range from 60 between and 75 on top of the line. Not ideal, by today's standards, but we aren't wearing t shirts either. The sides of the building without pipe had a floor temp of 55.

    Thanks for the thoughts guys.
  • nickh1nickh1 Posts: 16Member
    No it is not cycling. The ignition counter counts 10x and it still reads 0. The unit has been running for 3 days. It is currently modulating at 52%.

    There is a backup modine heater in the building, so it wasn't completely cold in here, but the floor definitely wasn't warm.
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,196Member
    Also, I'm guessing from the look and the age of that install that is PB tube. No oxygen barrier, the circulators and the little bit of iron fittings may not fair well long term. Keep it all nonferrous including the expansion tank. I'd also give each loop a good flushing until the water runs clear.

    Taylor
    Master electrician specialising in boiler and burner controls, multiple fuel systems, radiant system controls, building controls, and universal refrigeration tech.
  • Paul48Paul48 Posts: 4,492Member
    Two to 3 ft spacing is not good.
  • Rich_49Rich_49 Posts: 2,512Member
    edited December 2016
    I've always wondered what might happen in the long term when a P/S system was piped incorrectly and the boiler circ was placed on the supply . Will you keep me informed of what happens ? Can it even be considered P/S when piped the way this boiler is ?

    Supplies are on the left and returns are on the right , top and bottom . RTFM !



    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC 732-751-1560
    Serving most of New Jersey , Eastern Pa .
    Consultation , Design & Installation
    Rich McGrath 732-581-3833
  • nickh1nickh1 Posts: 16Member
    I flushed everything for 20-30 minutes.

    I wondered if it was barrier pex. I guess time will tell.


    That diagrahm showed the pump on the supply line, but it is P/S it should be on the return?

    The spirovent instructions said to place it after the boiler, and I was told to pump away from the tank, so that is what I did.
  • GordyGordy Posts: 8,478Member
    It appears the primary is using the top supply , and bottom return in this case. However im not sure why other than room for x tank, and air removal.

    The manual for the UFT shows a definitive approach of indirect bottom set, and ch top set. Or vice versa. Not sure if using top and bottom s/r in this case is okay.

    Rich has a deep understanding of this boiler.

    Seems cycling is non existent.
  • Rich_49Rich_49 Posts: 2,512Member
    All the diagrams published show the circ on the supply on direct piped examples . All P/S examples show circ on return . All examples whether P/S or direct show PONPC on system piping .

    To make what you have correct , you must remove tees and lower circ , replace tees with 90*s . That would then be direct piped .

    If you want P/S you must move the air eliminator , make up water and expansion tank to the system piping , move the boiler circ to the return .

    Instructions are tricky things . We all must determine which instructions are most important , in your case choosing the instructions that come with the most costly and dangerous piece of equipment would have been prudent .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC 732-751-1560
    Serving most of New Jersey , Eastern Pa .
    Consultation , Design & Installation
    Rich McGrath 732-581-3833
  • kcoppkcopp Posts: 3,170Member
    edited December 2016

    Also, I'm guessing from the look and the age of that install that is PB tube. No oxygen barrier, the circulators and the little bit of iron fittings may not fair well long term. Keep it all nonferrous including the expansion tank. I'd also give each loop a good flushing until the water runs clear.



    Taylor

    I noticed the Poly Butylene straight away. You are a at a slight advantage that's its a slab install and not an above grade install. (Less tubing exposed to free air) I would certainly hit it w a cleaner, flush and add a good inhibitor.... This may effect your warranty if you don't.
    Fernox, Sentinel and Rohmar are reputable products.
  • ZmanZman Posts: 4,428Member
    Rich makes good point about PONPC. If you got rid of the lower circ and the tees and just connected the pipes those issue will go away.
    The grey PB tubing generally does not have an O2 barrier. It is less of an issue when embedded in concrete.Running low temps will also help. If the 15-58 does not hold up, switch to stainless.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • nickh1nickh1 Posts: 16Member
    Once again, thanks for the input. I'll work on some changes and post a sketch.
  • HatterasguyHatterasguy Posts: 6,058Member
    edited December 2016
    Rich said:

    I've always wondered what might happen in the long term when a P/S system was piped incorrectly and the boiler circ was placed on the supply . Will you keep me informed of what happens ? Can it even be considered P/S when piped the way this boiler is ?

    Supplies are on the left and returns are on the right , top and bottom . RTFM !



    I don't think that a boiler circ on the supply is going to cause any issues for the UFT long term.

    However, when that circ is placed so the flow is going INTO the boiler supply, that's the real question? Flow returns to the boiler via its supply and leaves the boiler via its return.

  • GordyGordy Posts: 8,478Member
    This becomes a good discussion for the OP as to why?

    Sometimes pictures only paint part of the story.
  • HatterasguyHatterasguy Posts: 6,058Member
    Zman said:

    Rich makes good point about PONPC. If you got rid of the lower circ and the tees and just connected the pipes those issue will go away.

    They won't go away.

    You'd need to turn the upper circ around.
  • nickh1nickh1 Posts: 16Member
    I'm not sure I follow what you mean on flow going back to the supply. It is pumping away from the boiler on the supply and I dont intend on reversing it.

    As to why I plumbed it like I did, I dont have a good reason, other than I came out the top thinking having the air vent and blead valve high would help get rid of the air. I returned on the bottom just because I didnt think there was a real need to return to the top. The top and bottom fittings are connected by a copper tube inside that is teed in the middle to the heat exchanger.
  • HatterasguyHatterasguy Posts: 6,058Member
    edited December 2016
    nickh1 said:

    I'm not sure I follow what you mean on flow going back to the supply. It is pumping away from the boiler on the supply and I dont intend on reversing it.

    Go up to the circulator and look for a small arrow on the side of the cast iron flange right next to the plastic housing (it's between the back wall of the room and the plastic case). Tell us which way the arrow points (up or down).
  • GordyGordy Posts: 8,478Member
    The manuals can be confusing.

    Usually the boiler manufactures want the circ pumping into the hx so the circs pressure differential is raising the psi in the hx preventing the possibility of the water in the hx flashing to steam.

    Pumping away from the hx the circs differential would lower the pressure in the hx. This was more of an issue with higher head loss hx designs.
  • nickh1nickh1 Posts: 16Member
    edited December 2016
    I'm fairly certain it faces down, as was my intent. I did turn the motor so the cord came out the bottom however.
  • GordyGordy Posts: 8,478Member
    That explains it.......
  • nickh1nickh1 Posts: 16Member
    I know a lot of acronyms, but you got me with PONPC.
  • GordyGordy Posts: 8,478Member
    Point of no pressure change. (The expansion tank.)
  • ZmanZman Posts: 4,428Member
    Point of no pressure change.
    In a closed system, the expansion tank is the PONPC.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
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