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Old 10-01-13, 10:34 AM   #11
AC_Hacker
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Default Black Sludge...

I have a book here, written by a radiant heating guy that worked in the New England area. As I recall, he is retired now.

His experience went all the way back to the days of iron pipes buried in cement. An he actually had a significant part of a chapter on black sludge. In his view it was an excellent sign, because it indicated that the active elements in the circulatory part of the radiant system were as reacted as they were going to get. In fact he commented on the foolishness of inexperienced workers who wanted to flush and replace all the beautiful black stuff, which set up a situation such that the chemical reactions would re-commence.

I tell you, stories like that give me nightmares.

Please tell me that we have come farther than that.

I have studied some papers that looked at the role that fouling plays in the efficiency of brazed plate heat exchangers, of which I am so very fond. They even had some formulas that calculated the rate of fouling over time and the subsequent loss of efficiency.

Of course, in an open loop system fouling was nearly uncontrollable, save what particulate could be filtered out, but dissolved minerals would get through most filters.

In closed loop systems, the fouling rate was more controllable and could be reduced through PH control, etc.

The most interesting part of the paper was that by using distilled water, fouling could be reduced to a vanishingly small fraction. I mean, most women that I know would never think of putting tap water in their steam irons... Could they be that smart?

So, how about in-line filters? Nobody has mentioned in-line filters. They do exist. Are they just another gizmo?

-AC

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Old 10-01-13, 11:43 AM   #12
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Default PEX diameter...

Daox,

The following is in regards to Low-Exergy radiant heating and is a departure from radiant heating conventional wisdom...

I'm not sure what your expectations are for your floor, but I did some research on Low-Exergy radiant heating, and there's not so much direct information here in North America. The design considerations of a Lo-Ex floor are substantially different from a typical install.

But, I did download a copy of the free Watts Radiant design software, and by pushing the software and trying lots of different combinations, I was able to get an inkling of what would be involved. They even have someone who will respond in a timely and helpful manner to oddball issues such as very high efficiency radiant floors (AKA: Low-Exergy).

Anyway, what I learned is the obvious, that the closer spaced the PEX, the lower the required feed temperature.

There is an unfortunate design limitation in the Watts Radiant software, in that it will not recognize spacings that are closer than 6". In my estimation, this is a real bummer. But it is possible to see what the trends are and if you happen to be obstinate and resourceful, you can record your data from various runs, and do a graph or a regression analysis on your data and get some good predictions that go beyond (closer) than 6" spacings.

Piwoslaw mentioned a book in Polish that he (thought) he had access to that described European approaches to radiant floors, and spacings of 6" and 4" were not uncommon. Unfortunately, that resource never made it to our forum.

BUT, one thing I learned from all this is that if you want to operate in the range of VERY low feed temperatures (very Low-Exergy), you need to increase your flow rate. To accommodate this efficiently you need larger PEX.

I have heard mention of 5/8" PEX being used, close-spaced, in Low-Exergy installations.

But this all is in keeping with what I know about solar and heat pump systems for forced-air systems that are designed from scratch, rather than being a retrofit...

When doing a retrofit solar or heat pump installations, installers usually do not rebuild the existing ductwork because the extra expense may cause them to be underbid and lose the job.

The delta-T of heat exchange surfaces is solar or heat pumps is smaller, so to get the required BTU rate, extra air velocity is required. When you push extra air through existing ducts there is most often an increase in ventilation noise.

My girlfriend recently changed her house over from oil to ASHP forced air.

Her house is now comfortable, but there is a nearly constant background sound of ventilation noise.

So, for Low-Exergy installations, keep in mind that higher volumes could be required.

Something to consider...

-AC
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Old 10-01-13, 11:55 AM   #13
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Default

Thanks guys. I guess I will go with 1/2" O2 barrier pex for this install. I'd rather spend a bit more as solarmike said and be safe than try to cheap out and save a few bucks but have issues later.

Keep the info coming though, this is good stuff.
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Last edited by Daox; 10-01-13 at 11:57 AM..
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Old 11-07-13, 09:25 AM   #14
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good stuff indeed. I have only done tubing in concrete, so the very first reply baffled me for a moment. Then I proceeded to learn a whole bunch more.
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Old 11-27-13, 12:39 PM   #15
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I do it all the time.
As the pipe heats up it will expand like a can of worms, can be a esthetic issue, also makes noise if rubbing house framing.
Look at your specs, pressure rating goes down as temp goes up!
Most radiant pex heat systems run 140F or less, baseboard will run up to 180-190F.
And don't forget to use oxy barrier pex or you have to keep everything in the system non-ferrous.
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Old 11-27-13, 01:42 PM   #16
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Quote:
Originally Posted by TronHopper View Post
I do it all the time.
As the pipe heats up it will expand [and] also makes noise if rubbing house framing.
I invented a little trick that works wonders... I found some thin-wall polyethylene tubing that is meant for sprinkler systems... it's really cheap.

You cut lengths (maybe 4" to 8" or so) and slit them, then you can easily slip them over the PEX and center them at the points where the PEX goes through the framing.

No more expansion noise.

You can thank me later...


-AC_Hacker
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Old 01-22-14, 10:47 AM   #17
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That is what I have been using for years every time I have to run copper water or heating lines through joists or studs. Still waiting for my thanks
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Old 01-22-14, 11:07 AM   #18
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Quote:
Originally Posted by Minimac View Post
That is what I have been using for years every time I have to run copper water or heating lines through joists or studs. Still waiting for my thanks
No one appreciates an invisible miracle any more.

-AC
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Old 01-22-14, 11:24 AM   #19
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I'll thank you up front and hope I get to use it

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