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Radiant floor not making setpoint

paul_81
paul_81 Member Posts: 27
in Radiant Heating
I have a radiant floor zone using Zurn thermal track that can't heat the room up to thermostat setpoint of 70 F.  Manual J heat loss for the space is 7000 BTUH.  There are five 160 foot loops of 3/8" tubing, manifolds are piped in 1" copper, less than 15 feet total copper supply and return combined.   Supply water is 116 from a geothermal powered buffer tank.  Other zones in the house are fine(one other Zurn thermal track, one Warmboard, one extruded aluminum heat transfer plates). Delta T is only 10 - 12 degrees.   House has been extensively remodeled and insulated with spray foam insulation.  We have inspected surfaces with infrared camera and found no large voids in the insulation.  When it is cold overnight, say -5 to 0 F outside, inside is about 64.  When daytime temps run up to 30, inside temp goes to 68, maybe 69. If the floor can put out 20 - 22 BTU/sq. ft, why can we not make setpoint?

Comments

  • Mark Eatherton
    Mark Eatherton Member Posts: 5,858
    edited March 2011
    Generally speaking...

    If you can't make set point, even when you are not near design condition, it indicates a major infiltration issue.



    What did the IR imagery show what kind of average surface temperatures you were seeing on the floor?



    Have you had a blower door test done yet?



    Also, what is the design temperature for your application?



    This is one of the reason I don't like depending on GSHP as the sole source for heating. You can't turn it up any higher than what it already is... and you are dealing with situations (excess infiltration) that CAN control you...



    ME

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  • Gordan
    Gordan Member Posts: 891
    Something's weird

    The heat output of the floor is roughly proportional to the difference between the room temperature and the floor temperature. As the room temperature drops, the average floor temperature should drop less - so, given a constant supply temperature and flow rate, your heat output to the room should increase, and so should your delta-T, unless you're somehow constrained by too much R value between the tubing and the space (or your GSHP is simply not keeping up, meaning that your supply temp is dropping.)
  • Gordy
    Gordy Member Posts: 9,546
    Floor coverings?

    Is another variable to consider in the trouble area. 
  • CMadatMe
    CMadatMe Member Posts: 3,086
    What's the water temp

    So at design water temp is 116 what is the water temp at 30? What's the sub floor? What's the finished floor surface? Are their any large area rugs?

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  • paul_81
    paul_81 Member Posts: 27
    searching for clues

    The IR showed no cold spots on the walls or ceiling, and very uniform temperatures across the floor.  No Blower door yet, that will be tomorrow.  Design temperature for the system is -5 F.  The floor assembly is joist cavities filled with sprayfoam over enclosed crawlspace, 3-6" of foam, 3/4" sub floor, thermal track, old 3/4" flooring(pine 8 - 10 " wide, sanded many times in it's long life so in many places it is only 5/8" thick), no carpets or rugs.  Other 3 zones make setpoint no problem, GSHP cycles normally, so not a GSHP capacity issue.  The room does have a vaulted ceiling, could this be an issue?
  • paul_81
    paul_81 Member Posts: 27
    searching for clues 2

    Should also mention that supply temp is constant, no OD reset.
  • Gordy
    Gordy Member Posts: 9,546
    Can lighting infiltration

     In that cathedral ceiling?  Is there many can lights?



     Have you double checked flow rates, and delta t of loops in troubled room?
  • paul_81
    paul_81 Member Posts: 27
    delta T is Low

    Don't think there are can lights at all...Loops all are at .42 GPM, but very low delta T: 9-12 F
  • paul_81
    paul_81 Member Posts: 27
    delta T is Low

    Don't think there are can lights at all...Loops all are at .42 GPM, but very low delta T: 9-12 F
  • CMadatMe
    CMadatMe Member Posts: 3,086
    New Look

    Could you please post a drawing of the room with all the proper dimensions, windows, insulation etc. Are you running 100 percent water or is there antifreeze in the system?

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,858
    edited March 2011
    The math says it IS working....

    5 loops at .42 GPM each = 2.1 GPM



    2.1 * 8.33 X 60 = 1,050 lbs of water per hour.



    1,050 X 12 degree delta T = 12,600 btuH



    You said the load calced out to 7,000 btuH.



    Something is not telling the truth... (Flow meters. thermostat, humans :-))



    How cold was it outside when you looked through the eyes of the IR camera?



    Double check all of your numbers, because it appears that the floor is delivering almost

    twice the amount of energy that the calculations said it should need.



    Is the room physically uncomfortable? 70 degrees F in my experience is HOT in an all radiant heat application.



    Something ain't right, obviously. If it were right, you wouldn't be here, now, would you :-)



    Last question,and it is a silly one, but I have to ask it. The thermostat isn't on an outside wall is it?



    ME

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  • paul_81
    paul_81 Member Posts: 27
    dimensions and R values

    The living room is the trouble area.  -5 F design temperature

    ceiling is 5" 2 lb spray foam, floors are 3-4" foam, walls are 3" foam

    windows north: 22sf  south 80 sf west 11 sf  all 2 pane low e

    Peak in living room is 14'10" from floor

    100% water

    What I cannot understand is that when -5 outside, room is 64, when 30 outside, room is 68.
  • paul_81
    paul_81 Member Posts: 27
    more answers

    It was a cold winter day when we looked thru the IR, maybe 15-20 outside. Tstat is not on an outside wall, it is on the wall to the North of the fireplace.  The doorway to the stairway has been blocked off with plastic sheeting as the finish carpenters work on the second floor.  The second floor is also Zurn thermal track, it is working fine.  The mudroom to the west is in the thermal boundary, just received the Myson bench rardiator that will go in there.  Electric baseboard has been the mudroom heat source, mudroom is typically 50 -60F, but even cranking the heat to 70F had no effect on the living room.  The chimney chase is sealed with foam board.  The kitchen, dining room, bathroom zone is extruded aluminum heat transfer plates under floor, also working fine.  The bedroom zone is Warmboard, also working fine.   
  • Gordy
    Gordy Member Posts: 9,546
    Tstat

     Are you sure the thermostat is not getting any direct sun during the day, or warm air flow from the blocked off doorway? A leak in the plastic by the tstat could throw it off.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Paul

    What is the floor surface? I'll take a peak at your diagram with my morning coffee.

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  • meplumber
    meplumber Member Posts: 678
    To follow Gordy's lead.

    Are you sure that the Thermostat is wired to the right zone?  Don't laugh.  I found one recently that a fellow contractor (friend of mine and a smart guy) had chased for almost a year.  Turned out that 2 of the 6 zones had their tstat wires crossed.  The other zone was in an rarely occupied area of the house so no one noticed.



    We got lucky when we found it.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    crossed thermostats

    I once worked for a little company that occupied a large airplane hanger building that had been divided into offices, laboratories, etc. The dividers did not go all the way up to the ceiling, but it was heated with Reznor type gas hot air heaters near the ceiling. In two adjoining areas were two thermostats and two heaters. The thermostats were crossed, but if they were both set to the same temperature, things worked pretty well. But one day a secretary felt cold, so she turned up the nearest thermostat a degree or two. A technician in the other area felt hot, so he turned down the nearest thermostat a degree or two. Then the secretary felt even colder, so ... . You get the picture. I was doing electronic engineering there, designing feedback control systems. It did not take long to guess what the problem was and fixing it was pretty simple too.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Supply Water Temp is Not Enough

    I just ran based on the drawing and info in the thread. Based on the sqft 3 loops of 200 - water temp is 145. I used 20 degrees as below temp in the crawl space with R-30 insulation value in the floor. Your floor r-value is high.... 1.78

    Take a peak as I converting the heat loss and radiant panel report to a PDF. If there is anything you see that needs a changing in the what I used in the heat loss please let me know and I will adjust. I guessed at the size of the windows made them 3x5's..



    Chris

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,858
    Well.....

    He says 7K, you say 9K and I say its getting 12K delivered to the load with 115 degree F water.



    SOMETHING is not right SOME WHERE...



    I still suspect infiltration, because based on his information (assuming flow meters are decently correct) it SHOULD be working, and even when he;s not anywhere near design condition, it's not comfortable, and in my experience, that points to infiltration.



    Almost half of your load is infiltration, so it would appear that you have it covered in your load calcs.





    I'm thinking a blower door test might be the next good move.



    ME

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  • Gordy
    Gordy Member Posts: 9,546
    edited March 2011
    Chris

     I noticed you used suspended tube with plates. He is using Zurn thermal track in the questioned area an over the top sandwich method. Maybe I'm reading the radiant pdf wrong. And he has an enclosed crawl space. Highly unlikely that it gets below 45* in that area, My crawl space is uninsulated block wall, and only gets to about 55* at -10 outside.





     I think the fireplace is doing some vacuming, or as meplumber made a good point something is array with the tstat.



    Gordy
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited March 2011
    Good Point

    I flipped it to Quik Trak and change floor r-value just to get an idea. Its' attached.  Big difference. I adjusted my air changes because of the fireplace. Generally I would be using a .35 air change not a .5. My setpoint is also only 68 if I boost it to 70 then that water temp goes up to 120. Loss changes a little do to downward loss.



    If I move that air change up to .75 which I generally use for a baseboard loss that water temp rises to 130. Mark is right on with the blower door test. Its most likley an infiltration issue. 

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  • paul_81
    paul_81 Member Posts: 27
    checking in

    Thanks for all the replies.  I have checked the thermostat wiring several times, and even changed the tstat out.  The Thermal Track uses 3/8" tubing, there are 5 loops at 150 feet.  The crawlspace temperature is 55F.  The subfloor below the thermal track is sprayed with foam, as well as the crawlspace walls.  I willl be going Thursday with the blower door to see if that reveals anything.  The other day it was 41 F outside, and the room hovered at 69 and calling for Heat!
  • Gordy
    Gordy Member Posts: 9,546
    edited March 2011
    Paul

     Are you SURE all 5 loops are purged completely, and getting flow? The infra red should have told the tale.  Are all 5 loops getting reasonably the same delta ts? if so what are they? I know you posted 9-12* earlier, but is that each loop, or what the manifold thermometers are saying.





    Gordy
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