[Greenbuilding] Al Pex for Solar Heating System

[Keith Winston]

One challenge one runs into with radiator and other unusual (from a 
house plumbing point of view) hoses is pressure: as long as you keep 
your system at heating-system pressure (i.e. 12 psi or so) they can 
work, many of them can't take higher pressures when they are hot I 
believe (isn't a car pressure relief around 12-15 psi?). On a 
multi-story install that might be hard for the full height of the 
system, though using them just at the top might be made to work... I got 
some special high-temp plastic hose from US Plastics for one stretch, it 
was a bit pricey (I think $3/ft). Thanks for the link to Gates, I don't 
know them yet.

Always check pressure/temp curves, when you can get 'em, for things like 
hoses and tubing. Between silicone, teflon and all other types of 
high-temp blah blah hose, there's some amazing things out there. It 
raises the challenging question of bringing increasingly exotic 
materials into the picture (with their entire manufacturing/disposal 
life-cycle implications). Interestingly, Dupont (I think it is) has a 
silicone based heat transfer fluid that can happily operate at 500F. 
It's expensive, and only has 1/2 the heat capacity of water (meaning 
slower heat transfer, sorta). I don't remember anything about the 
thermal conductivity, or the melding of these two factors, the thermal 
diffusivity... I don't recall if it's as low-toxicity as Polyethylene 
glycol...

Keith


Bob Korves wrote:
> ----- Original Message ----- 
> From: "Clarke Olsen" <colsen at fairpoint.net>
> To: "Bob Korves" <bkorves at winfirst.com>
> Cc: <greenbuilding at listserv.repp.org>
> Sent: Sunday, January 06, 2008 7:00 AM
> Subject: Re: [Greenbuilding] Al Pex for Solar Heating System
>
>
>   
>>    Isn't it possible that automative hose will last longer in an  enclosed 
>> application
>>    with no vibration and a narrower temp. fluctuation?
>>    Clarke Olsen
>>    Spencertown, NY
>>     
>
> Yes, it is certainly possible that the black, butyl rubber automotive hoses 
> would last longer in a household application.  My biggest worry would be 
> about any direct exposure to sunlight, since they are not exposed to direct, 
> prolonged sunlight in automotive use.  Maximum temperatures would be lower, 
> and they do not get contaminated with motor oil.  Vibration is not a problem 
> for automotive hoses anyway -- that is their world!.  Silicone rubber hoses, 
> which are usually red, green, or blue in color, are better in almost every 
> respect compared to the black butyl ones, except they are softer and if they 
> rub against things then they will rapidly wear through unless protected. 
> Sometimes, at 500,000 or more mile engine overhauls on big trucks, when 
> everything is renewed, the silicone hoses are re-used if they look OK. 
> They're that good.
>
> In a glycol filled solar system the price of the glycol and the worry about 
> pollution from leakage would certainly send me toward the silicone hoses, 
> which should only be needed for short distances anyway.  There are also lots 
> of special shapes and many sizes of these hoses made for specific 
> applications so things like 30 or 180 degree bends with different inside 
> diameters at each end are available.  Heater hose in standard sizes of 1/8 
> inch increments from 1/8 inch to 1 1/4 inch inside diameter are available. 
> Here is a link to the Gates catalogue.  Goodyear offers a similar line. 
> Radiator and heater hoses are what you are looking for.  Custom shapes will 
> not be shown in the catalogue.
>
> http://www.gates.com/catalogs/index.cfm?site_section=catalogs&location_id=524
>
> -Bob Korves 
>
>
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