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Pex tubing insulation

  1. Jun 25, 2011 #1
    Hello Everyone.
    As an engineering student, I've been reviewing this forum many years. This is my first question.
    My team and I are designing a radiant floor heating system using pex tubing.
    The inlet water to pex tubing is 180 F, we assume that the outlet temperature will have a delta T loss of 20 F. This return temperature will be mixed with a mixing valve and sent back to the floor at a temperature between 160-170 F. The second loop will again have a 20 F loss and again this returning water will be mixed giving a temperature of 150-160 and thus the eventually the temperature in the tubes will be lowered down to 120-130 F and maintained there until the house zone temperature is reached.

    My Question is:
    Will it be viable to install insulation on top of pex tubing to protect the cork floor since the inlet water is at such a high temperature. The manufacture recommends that the cork floor be subjected to 120-130 F temperatures. Since the system uses a mixing valve we can lower the temperature down to this point, but there will be a delay(not sure exactly how long).

    So, is it viable to use insulation to protect the floor. Since this seems rudimentary that we are insulating against something that we are trying to heat, I'm really not sure.

    Thank You.
  2. jcsd
  3. Jun 27, 2011 #2
    Hi, normally you dont start with a hot feed temp and then let it cool down gradually.
    The thermal shock is often to much for a new floor to handle.

    Best practice calls for a cold startup, so total re-circulation, with blending valve set to full floor return. Once running, you SLOWLY blend in the warm water, in increments of 5 degC and leave it for a few hours, before again increasing the temp.

    If you follow this method, to the max allowable temp, then the floor will be just fine and no insulation will be needed.
    Insulation will will only ever hamper the heat transfer to the floor which is waht you want to avoid!

    Never take the floor to the max allowable temp. There are always tolerances on your control systems and response times to temperature readings and subsequent controls.

    Good Luck!
  4. Jul 3, 2011 #3
    I am not an ME. Just a Master Plumbing, Heating and Air contractor. Radiant flooring must be designed at a contact temp not to exceed 85 deg F. This is a comfort issue. Try walking barefoot across asphalt at 90 deg and tell me how comfortable it is.

    My question is the installation method. Most pex manufacturers have recommendations for at least an R-19 underfloor installation and at least 2" of foam under a slab. In either case, we usually only send 100-110 deg water to the slab and only as high as 140 to under floor applications that utilize aluminum heat transfer plates. In either method, we temper the water via a mixing valve before sending it to the floor distribution manifold.

    As previously stated, the thermal shock of slowly cooling the fluid is too great.

    Also, 20 deg delta T is too high for radiant. Most residential and commercial systems that I have been involved with over the last 20 something years are lucky to see 10 deg deltas.

    Good Luck. Sorry if my non-educated opinion is unwanted.
  5. Jul 5, 2011 #4
    Of course your opinion is welcome, we want to hear what works, not what people (engineers, myself included) think will work.
  6. Jul 5, 2011 #5
    Thank you MRFMEngineer.

    My son is an aspiring engineer and physics nut. He visits this site frequently.

    I wanted to comment on this thread and one other, but was unsure of the boards rules as they apply to us "unlearned" ones.
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