[Strawbale] PEX tubing in floors

[Corwyn]

On Apr 30, 2007, at 21:13, David Neeley wrote:

> Shody,
>
>> I see, so a deicing loop would only be needed on a
>> evac tube collector because of its insulation and
>> shape, flat plate (closed loop) will deice itself.
>
> No, a deicing loop would likely *not* be necessary on an evacuated
> tube system, as the vacuum is the ultimate insulation. The tubes will
> not freeze. The manifold wherein the water is heated at the head of
> the tube would normally be well insulated, though, since at night the
> tube would not be making it hot and so avoid icing--although it could
> also be done as a drain-down system with not enough moisture left
> there to matter at night.

I think Shody was talking about a deicing loop to remove snow and ice 
from the exterior of the collectors.  I had an evacuated tube salesman 
trying to convince me that they didn't need it since heat gain through 
snow was not reduced too much.  I didn't buy it mostly because he also 
tried to convince me that the tubes would keep outputting heat even 
when receiving no some (since the were insulated).  Anyone have real 
numbers on tubes collecting sun through a layer of snow?
>
> Furthermore, a flat plate collector *will* freeze, which is why many
> people use antifreeze in them to avoid that problem by lowering the
> freezing temperature of the working fluid below any temperature your
> climate will present. Antifreeze is less efficient than plain water,
> however, and then of course you have the heat exchanger which is also
> less efficient--meaning you need more collector area for the same
> effective heating than you would for a direct-gain
> collector...although that is mostly a theoretical distinction.

I would put antifreeze in a tube manifold as well.  It isn't _that_ 
well insulated (especially if you consider the external pipes).

>  Thus, when you cool it the moisture it can
> no longer carry is dropped in the form of water or water vapor. The
> air exiting the radiators would be less moist (other than any water
> vapor carried physically along with it) than the warmer entry air,
> with water being deposited on and around the radiators.

I would say that it contains less water, it may actually be a higher 
relative humidity.  Air leaving a  cooler which is cooler than the dew 
point will be near saturation levels.  Of course it will quickly mix 
with hotter air, lowering the overall humidity.

BTW: I think you mean 'water droplets' or 'steam' rather than 'water 
vapor'.  water vapor is gaseous water (in other words humidity), steam 
is tiny drops of condensed water (clouds or the breath).

>> If the relitive humidity increases, for
>> the comfort of humans, should dehumidifcation also
>> take place, hense the popularity of regular A/C
>> because it does both?In many places, summer air is both warm and 
>> humid.

'regular AC' is really nothing more than a fan blowing air over a cool 
radiator (plus some mechanisms for making the radiator cool).  So. 
there would be no noticeable difference in effect.


Thank You Kindly,

Corwyn


-- 
Corwyn
Kermit didn't know the half of it...
http://www.greenfret.com/
corwyn at greenfret.com