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Re: A wall warmer with a fan



<daniel@daystar.laser.net> wrote:
 
>I'm real confused.

Doesn't stop you from stating the "facts" that follow, Dan :-)
But it's a free country, this net-world, with lots of virtual soap boxes... 

>(Nick Pine) wrote:
>> This is supposed to replace vinyl siding.
> 
>Why not leave the siding in place to protect the sheathing when [not if,
>when] the glazing begins to leak?

I suppose in time, everything will leak, even this stuff, which they say has
a 25 year lifetime for solar transmission, which I assume is shorter than the
mechanical lifetime. By that time, we may have basement fusion power or mostly
superinsulated houses, and I may be dead. I spent part of this evening lying
in a hammock strung between the collar beams in my attic, watching the rain
and lightning through the new roof, 14' up, which so far doesn't leak a drop,
even through the turbine vents, with the doors open underneath, even after
an afternoon of golfball-sized hail. The main reason for taking the old siding
off is that it is hard to attach anything on top of it, since it is neither
flat nor rigid, and it is cracking and falling off anyway.

>What about condensation?

What about condensation? Would you expect a lot of condensation in an air
heater, when the sun is shining and air is flowing through it, being heated 
to a higher temperature than when it went in? Or when the sun is not shining,
and no air is flowing through it?
                                                             
>What is the purpose of sloping the shade cloth [absorber ?] futher away
>from perpendicular to the sun?                    (yes)   a--^^--r

It's not a matter of solar geometry, but of increasing the cross-sectional
area of the "duct" to allow more airflow or less pressure drop. BTW, the
fan manufacturer (800) 5-HOLMES says their $11 HABF-20 20" box fan makes
500, 950 and 1350 CFM free air delivery, with both grilles on, at speeds
1, 2 and 3, whilst consuming 0.68, 1.08 and 2.08 amps at 110VAC. 

>>if the air
>>goes into the wall at 68F, it will emerge at about 68 + 150K/2K = 140F.

I guess I should double that temperature rise now, since the fan doesn't
make as many CFM as I thought, altho taking the grilles off should help.
Or maybe I need to spend more than $11 for a fan. Or use two of them.
Norman Saunders uses 1/4 HP motors with his fans.
 
>Whoa! At what ambient air temp? 

Whoa! At 32 F, like I said in the original posting. You have my numbers, Dan.
Where are your numbers? Do you believe in "Ohm's Law for Heatflow," or are
you possessed of a Higher Thermal Consciousness? If so, I stand in awe.

>Maybe if it's 70°-80° F outside already.

Assuredly so. But then the warmed air, if any, considering the wall will be
shaded, will flow out of the wall to the outside world, not into the house.
 
>What is the R value of this glazing?

About 1.

>Is this anything like the double glazed Lexan?

It's only one layer of polycarbonate plastic, strong, corrugated, and very
clear, at least to begin with, not milky or fibrous. It needs support on
4' centers as a roof, but I built a small wall warmer in January, with
vertical sleepers on 5 1/2' centers. I suppose you could go farther apart,
if it's not in a windy location and you don't mind floppy walls. 

>>  They sell black polypropylene Sundown 80%-absorbing shadecloth
>
>I respectfully submit that 80%-absorbing shadecloth is no such thing.

Ah, what is it then? Please tell me the true nature of this substance.
Once again, I stand in awe, respectfully. 

>The people who market this product [and those that buy it] couldn't care less
>if 80% of the light is absorbed, reflected, refracted, reradiated or eaten
>by little green light monsters. All they care about is that only 20% of
>the light passes thru the sheet to further heat the greenhouse.

True, but this stuff is black, so I think it really will absorb most of the
80% that does not get through. And my greenhouse engineering book says the
polycarbonate glazing will pass less than 4% of any long-wave reradiation.
Tell me more about your little green light monsters, Dan...

>A vinyl sheet with 20% holes

This is carbon-impregnated polypropylene, and it looks like about 50% of
the area is holes, but I haven't attempted to measure them. I just naively
believe what I read in the nice Stuppy (800) 877-5025 catalog (just got
a new one, 3/4" thick :-), lacking your shattering insight into the True
Ground of Polypropylene. Or do you only speak ex-cathedra on vinyl? :-)

Stuppy sells Ludvig Svensson aluminum/polyester "environmental screens" in
30, 40, 50, 65, 75 and 99.9% opacity, as well as black Sundown polypropylene
shade fabric in 30, 47, 55, 63, 73, 78, 80, 92 and 100% opacity. There is a
price jump above 80%, which costs $0.139/ft^2, and the more absorbent kinds
are less porous for airflow, so I'm using the 80% kind. This is a compromise. 
Stuppy now has a new product called Reemay spun poly 45% shadecloth, which
comes in pieces 148' wide x 300' long (wow), item number 2352, costing $130.
That's 0.292 cents/ft^2, 341 ft^2 for a dollar :-) They also sell 66% green 
shadecloth for 22 cents/ft^2, item number 23810.

"California Fire Marshall Approved" 78% fire retardant green shadecloth goes
for a hideously-expensive 55 cents per square foot. Fire is another story...
Asphalt shingles burn really well, and I've seen burned vinyl siding. The
polycarbonate glazing is difficult to get started, but once going, it burns
well too, if you hold it at the right angle, dropping off little liquid
fireballs that make an interesting buzzing sound in the air. I would not
recommend doing this with a house.

>will come no where near the absorbtion capacity of copper or aluminium
>[or any metal for that matter] with no holes and covered with a selective
>surface.

Yawn. This sounds expensive. And what do you mean by "absorption capacity"?
Is this something to do with the little green light monsters? Or perhaps
the plastic army soldiers you mentioned in your previous posting? I'm still
not sure what to do with them, and the hot water... Army soup?

>Come to think about it, why not cover the outer surface of the wall with
>aluminium foil to reflect that 20% back to the shade cloth?

My architect thought of that... I dissuaded him, saying that 20% of that
20% will keep on going through the shadecloth, back out of the wall. It
might look weirder that way too, altho that's never deterred me.

>Don't get me wrong Nick, I'm not discounting your device, but I do think
>that you have WAY overestimated it's potential.

So where are YOUR numbers, Dan? Or better yet, how would you improve the
price/performance ratio of this design? I'm looking hard for labor-saving
ideas... Perhaps you can help, instead of just throwing rocks here,
rhetorically-speaking. 

>At 30°F ambient air temp, 90°-100° is a lot closer to real

Ah, numbers. Where do these come from?

>[certainly nothing to sneeze at].

Faint praise! :-)

>Another thought, if you reversed flow to make the warm air enter the room
>from floor level, it would have to travel past furniture and people on
>it's way up, possibly increasing the effective performance.

Perhaps in Australia, where hot air sinks. Or we could crazy-glue little
plastic army men all over the ceiling, upside down. That might help.
This is somewhat outside of my expertise. What do you think? 
 
>> Who will be the first to build one of these?
>
>You!

I wouldn't mind being the second... :-)

Nick


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