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Emmons
Registered Users
New Member
Posts:8
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| 04/20/2009 7:47 PM |
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Sorry for the foolish question, but what is PEX? I saw a radiant floor installation using what I think was an aluminum tube covered in what looked like some kind of poly(propylene/ethylene). Is that PEX or a variation of it? EDIT: Never mind this question. I found the answer at Blueridge's site.
Second question contingent on the answer to the first question, doesn't the plastic covering inhibit the transfer of heat? I am looking for tubing that is flexible and has high transfer of heat characteristics. I want to do some radiant cooling, not heating.
Thanks in advance for any responses. Tommy |
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Brock
Registered Users
Basic Member
Posts:444
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| 04/21/2009 9:28 AM |
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Yes, pex is plastic tubing. It is funny; in the local home store I bought mine from it listed one of the advantages of using pex to plumb your house is less heat loss compared to copper. In a radiant system you WANT the pex to have heat loss. Anyway…
Copper will give up heat much faster than pex but it costs so much more it's not really an option. Most people use aluminum plates that straddle the pex to pull the heat out.
Using radiant to cool you can run in too many issues, mostly condensation, take a look around this board and you will find some good info on it.
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Green Bay, WI. - 4 ton horizontal, 16k gallon indoor pool, 1.8kw solar PV setup, 3400 sq ft |
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NRT.Rob
Registered Users
Advanced Member
Posts:733
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| 04/21/2009 9:32 AM |
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| the PEX itself is not really a bottleneck in most cases. It's the medium around the PEX that is normally the bottleneck which is why aluminum plates are generally important in a non-concrete situation. PEX is "conductive enough" to meet any radiant panel heat situation I am aware of. |
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-=Northeast Radiant Technology=-
NRTradiant.com |
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Dana1
Registered Users
Advanced Member
Posts:702
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| 04/21/2009 9:38 AM |
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PEX doesn't have great heat-transfer characterisics from an emissivity or air-contact point of view, but not terrible either. But in direct contact with a more refractory material (eg: an aluminum heat spreader, or concrete), the R-value of the thin tubing wall is QUITE small and can be ignored. PEX is the right stuff to use- as are heat-spreader panels & cement slab materials. If not slab-embedded, spreader panels have a large effect on system efficiency. Extruded panels have a greater guaranteed-contact-area with the PEX and will outperform the thinner sheet-metal stampings, but either is preferable to none since you'll be able to heat/cool with much smaller delta-Ts (the difference between water temperature and room temperature) than with PEX alone.
If you intend to use it primarily for radiant cooling, consider make at least 1/4-1/3 of the radiant area ceiling or wall- you'll be able to suck 3x the heat out of the equivalent ceiling area as you would a floor at the same chilled-water temp, and you'll get there using temps that won't be uncomfortable to bare-feet-on-slab. In an all-floor radiant system you have the issue of the coldest air pooling at the floor level, forming an insulating boundary layer from the rest of the room area. Chilled ceiling or wall areas induce convection currents, constantly replenishing warmer room air contact with the radiant surface on the wall, which also breaks up the boundary layer at the floor.
Since using chilled surfaces for cooling deals with sensible-loads only, it's important to be able to use chilled-water temps well above the dew point to avoid condensation &/or mold conditions (over 60% relative humidity) within the radiant wall/ceiling/floor structure. (Not usually a problem except in more tropical climes, but think about where it'll be on the psychrometric charts, and the average cooling season dew points.) If you have high latent loads, mechanical dehumidification may still be necessary for health & comfort. |
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