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Radiant Cooling

Timothy Member Posts: 3
Does anyone know if it would be possible to send cold water through a slab during the summer? I understand they do this in Europe. The space I'm considering this for is an 80' x 60' shop. The slab is insulated along the perimeter as well as underneath. We have 3 pex loops installed.

We have plenty of well water available and could just send it through the tubing and then use it for irrigation. Would this work OK? Would there be condensation problems?



  • Aidan (UK)
    Aidan (UK) Member Posts: 290
    Slab radiant cooling

    The European methods usually involve high level radiant ceiling panels or chilled beams. See


    I think this gives the ratio of cooling from a suspended slab as about 80/20% to the room below/above respectively.

    The problem is usually with high humidities. As the temperature decreases, the air's relative humidity will increase although the moisture content will stay the same. 75% or 80% Rh is not comfortable. You will usually need a dehumidification system to take moisture out of the air.

    You could also get problems with condensation forming within the slab or in adjoining walls or floor coverings. If you try it, let us all know how it works. Good luck.
  • Aidan (UK)
    Aidan (UK) Member Posts: 290
    radiant cooling

    That link should have been;


  • Timothy
    Timothy Member Posts: 3

    I checked out the link. Thanks, Aidan.

    A few quotes from the article have me puzzled:

    "cooling power is limited due to small temp difference between supply water & room air" ...seems to me the difference in temps could be 40* F or more. That doesn't seem small to me.

    "floor surface temp should not be less than 66* F" ...Why?

    "the dew point of the indoor air has to be kept below the supply water temperature(condensation)." ...I'm not sure what the dew point is.

  • Mike Norgan
    Mike Norgan Member Posts: 24

    How many loops do you have installed, I hope you have more than three installed.

    Mike Norgan
  • Timothy
    Timothy Member Posts: 3
    What I meant

    to say is that the area to be heated and hopefully cooled is 36' x 24'. There are 3 loops of 1/2" pex approx 12" on center. Each loop is 290'.
  • don_9
    don_9 Member Posts: 395
    dew point

    Is the temperature at which water vapor turns to liquid.

    Dew point of air at any given condition correspond to the drybulb or wetbulb temperature at which air become completely saturated(100% relative humidity)

    So if you would to look at a psychrometic chart and you had a drybulb temp at 75 degree with a relative humidity of 90%
    you will have a 73 degree dew point temp.So i would assume that you would have to keep your water temp above 73 degree
    in order to keep the floor from sweating.not sure if this is the case.Only guessing here
  • RB_2
    RB_2 Member Posts: 272
    radiant cooling performance

    It's late so forgive me if the numbers are not exact...at 79 deg f room temp between 60 and 70% rh, surface dew point should be between 64 deg f and 68 deg f.

    At 66 deg f floor surface temperatures 10% occupants would not be happy or 90% would be happy…anything cooler and occupant discomfort will go up.

    With a 66 deg f low limit floor temp & 79 deg f high limit room temp the output on floor cooling is appx. 16 btu/sf sensible cooling based on a 1.29 cooling coefficient. ( Can be boosted with ceiling fans)

    Assuming a floor resistance of R1.4 above the tubes, negligible absorption from ground below slab, 12 inches on center, fluid temperature would have to be a nominal 44 deg f which is why radiant floor cooling systems in this scenario design for a narrower delta t of 10 deg f instead of 20.

    In a 860 sf area, I would estimate your total flow for the zone is just under 3 US gpm or 1 US gpm per loop at about 2 ft/sec in ½” pex…about 1.6 psi/100 ft…(give or take)

    The above takes care of some or all of the sensible loads…the latent is another discussions and system.

    Your project…860 plus sf…wouldn’t pass an economic test if you consider the proper controls required to control dew point and low limits…

    If you just want to experiment be careful not to create a mold machine...I hear the sharks are drooling over this topic.

  • radiant cooling info

    i pump 56 degree well water through my radiant heating system and it cools my floors to 68 degrees and without any condensation on the floors. it works great.
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    Nice to see you Robert...

    Excellent post as usual...

    And you thought YOU were up late...


    To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"
  • John R. Hall
    John R. Hall Member Posts: 2,246
    Hoover Dam

    Perhaps the biggest "radiant" cooling job was the cold water run through 27 miles of piping in the Hoover Dam project. It was necessary for the cement cooling process. Otherwise, the cement today would still be curing. A seven-story refrigeration plant provided the cool water.
  • RB_2
    RB_2 Member Posts: 272

  • RB_2
    RB_2 Member Posts: 272
    condensation, cooling and mold....

    A source for humidity and condensation issues is


    for specific information on condensation and cold surfaces see:


    Mark...3:00 am...early riser? jeesh....

  • Bill Clinton
    Bill Clinton Member Posts: 75
    Applause to Mr. Bean

    Sure is nice to hear from someone who knows something. To often the rest of us (that includes me) are actors in the old tale of the blind men groping at various parts of an elephant, each, on the basis of his immediate experience, forming an opinion as to the "true nature of elephantness" and loudly proclaiming the others wrong and heretical.


  • RB_2
    RB_2 Member Posts: 272

    They say the gestation period for an elephant is two years...

    and for a really good technician...a lifetime.

    Merrily groping away sir...

  • RB_2
    RB_2 Member Posts: 272
    The dam project...

    is very cool indeed.

    A respected radiant engineer, Dr. Simmonds and his team designed a 2,153,000 sq. ft. radiant cooled floor for the International Airport in Bangkok...

    See you soon.


This discussion has been closed.