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  1. #1
    Join Date
    Jun 2012
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    18

    Radiant floor not coming up to temp in two rooms

    Hello,

    We have a new house with radiant floor heating. The heat is provided by an air-to-water heat pump. For the most part the system works well. But we have two rooms that never quite get up to temperature. I can get most rooms hotter than we would want (24C), but these two won't go over 21 even with all the other zone valves closed. I'm suspicious that there's a flow restriction. The HVAC contractor feels that the temperature differentials would be greater that what they are (2C) if there were a restriction. There are no flow meters in the system. The contractor is a good guy but he's run out of ideas. Does anyone have any suggestions as to what we should be looking at?

  2. #2
    Join Date
    Jan 2004
    Location
    PA
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    68,789
    Circulator sizing.
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    How many times must one fix something before it is fixed?

  3. #3
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376
    Flow test the problematic circuit. Should be a manifold to this zone where a flow test could be done. Whoever designed the system should know how much flow that zone requires.

    Is this house slab on grade or are the radiant tubes beneath wooden subfloors? Could be an insulation issue either way.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  4. #4
    Join Date
    Jun 2012
    Posts
    18
    The downstairs is slab on grade. One of the problem rooms is down there. Upstairs we have tubes set in concrete on top of the subfloor with plank alder finish floor. We've had him confirm the design, I've run the numbers using some online tools I found and we had another contractor run the numbers as well. And realistically, the problem rooms don't have any big differences in heating parameters than rooms right next to them that work fine. So again, I can't help but think it's a flow issue. As far as measuring flow, the manifold is soldered copper pipe with tubing banded directly to it. Putting in flow meters will be a pain. That's why I'd hoped to confirm his notion that low flow could be ruled out by the temperature difference.

  5. #5
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376
    The space between the first and second floor (known as an interstitial space in building science terms) in your house...is it sealed and insulated at the band joist, which is where the floor joists meet the top of the first floor walls? If not, you could be losing a good deal of heat in this space due to air movement and conduction.

    Was insulation installed beneath the radiant loops upstairs AND under the slab loops?
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  6. #6
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,775
    Air in zone piping or thermal envelope issue. Could be kinked line or a number of other issues. Without being on site it is difficult to diagnose. Good luck

  7. #7
    Join Date
    Dec 2010
    Location
    Toronto
    Posts
    1,253
    What are the loop lengths, number of loops on each floor and the pump model?

  8. #8
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Are there zone vavles to each room? Balancing valves to each zone, or it is one big circuit?

    If you can put a pressure gauge on the supply and return pipe to each zone, you can measure flow by pressure drop.

    Then the question is, how the the heat loss and gain of the different rom compare in relationship to the length of piping... i.e. amount of BTU's being delivered to each room. The colder rooms might simply have less insulation, less solar heat gain or more windows.

  9. #9
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376
    Quote Originally Posted by motoguy128 View Post
    If you can put a pressure gauge on the supply and return pipe to each zone, you can measure flow by pressure drop.

    Then the question is, how the the heat loss and gain of the different rom compare in relationship to the length of piping... i.e. amount of BTU's being delivered to each room. The colder rooms might simply have less insulation, less solar heat gain or more windows.
    I was going to suggest Pete's Plugs (pressure taps) in one of my replies, but then thought about what it would entail to derive any meaningful info from a pressure drop reading, so left that out. IMO one would need to know a lot of info about the loop in question for a PD reading to cross over to a flow rate.

    Therefore I suggested to the OP, as you have, to investigate other potential causes. He did state that with all other zones valved off that performance in the problem zones does not improve. That narrows it down to a few remedies, either increase the temperature setpoint of the entire loop, which uses more energy, increase flow to the problematic zones (which may be limited by loop and pipe size, ensure each loop is completely purged of air, look for ways to slow heat loss from the rooms in question, or check insulation levels beneath each loop.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  10. #10
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Could be as simple as a balance issue. Maybe there aren't balancing valves.

  11. #11
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    11,376
    Quote Originally Posted by motoguy128 View Post
    Could be as simple as a balance issue. Maybe there aren't balancing valves.
    OP said they can throttle down on valves in other zones and the problematic zones do not improve in temperature.

    The first hurdle to clear is to determine if the problem zones are flowing enough water. If they are, the problem may lie in heat going the wrong direction, meaning either into the ground where the slab is, or into the space between floors on the upstairs problematic zone. While a common response to this thought may be "heat rises", the truth is that heat itself goes in all directions. Heated air "rises" due to density variances, but radiant heat moves in all directions. Meaning...if there is not insulation below the radiant loop in the problem zone, or the insulation is inadequate, installed incorrectly, or whatever, heat could be escaping that should rather go into the problematic zone.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  12. #12
    Join Date
    Jun 2012
    Posts
    18
    There are balance valves although they are all fully open. But in my mind we've ruled this out by the fact that a problem zone doesn't change even when all the other zones are secured.

  13. #13
    Join Date
    Jun 2012
    Posts
    18
    The loop lengths appear to be around 300'. There are 7 upstairs with three control zones, and 6 downstairs with 5 control zones. I'm currently away from home so I don't have the pump info in front of me. Sorry.

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