Subject: A wall warmer with a fan

From: [email-masked] (Nick Pine)
Date: 12 Jul 1995 07:44:13 -0400

A local siding contractor gave me a verbal quote of $2 per square foot
including materials, to build my passive wall-warmer, which I thought was
pretty good... But when I asked for that in writing, he came back with
a reluctant $5/ft^2, and other contractors wanted more like $10 or $12. Yipes.
This is supposed to replace vinyl siding. Who woulda thunk it was 90% labor...

So I've redesigned it now, adding an $11 fan and changing the 4 32' long slots
along the top and the bottom and the 2 long plywood doors and 32' piano hinges
at the top for passive airflow, to a couple of 2' x 2' holes in the wall at
the top and the bottom diagonal corners. I guess it can't be called passive
anymore (sniff), but that doesn't seem too important. The wall can now be
controlled by thermostats, which is nice. The total cost of materials is
about $800, or about $1.50/ft^2, and the wall should save about 600 gallons
of oil per year, at a cost of about (63 cents + $12 (Gulf War)) per gallon,
as well as a few human lives. Below is an ascii picture. 

                        32'
                 s4                            
      ---------------------------------------      --------------------
     |    |    |    |    |    |    |    |fvfv|   plywood  / f. f .6T2 g fv
     |           s3                     | fan|     Door /  f . a .7\  g
     |----|----|----|----|----|----|----|----|        /  f    -n--2   g
     |    <-4'->                             |               w   w  c g
     |           s2                          |            T1 w   w  c g
16'  |----|----|----|----|----|----|----|----|     (inside)  w   w  c g S ->
     |                                       |               w   w  c g
     |           s1                          |               w   w  c g
     |----|----|----|----|----|----|----|----|               w   w  c g
     |    |                                  |             .f    6    g
     |vent|      s0                          |             . f   7 /  g
     |____l____|____|____|____|____|____|____|        _________f_2______

                                                      f is plastic film 
S4:  wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww        c is shadecloth
     |    |    |    |    |    |    |    |    |        g is rigid plastic
     |    |    |    |    |    |    |    |    |        . is hardware cloth
3.5" |    |    |    |    |    |    |    |    |        w is the original wall
     |    |    |    |    |    |    |    |    |     
     cccccccccccccccccccccccccccccccccccc             The fan is a Holmes
     ggggggggggggggggggggggggggggggggggggggggg        20" Slimline, 3-speed
                                                      HABF-20 box fan,
               (views from above)                     $11 from K-Mart.
S3:  wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww
     |    |    |    |    |    |    |    |    |        fv are Leslie-Locke
2.6" |    |    |    |    |    |    |    |    |        FV-1B automatic
     |    |    |    |    |    |    |    |    |        foundation vents,
     ccccccccccccccccccccccccccccccccccccccccc        $10.83 each from
0.9" |    |    |    |    |    |    |    |    |        Home Depot.
     ggggggggggggggggggggggggggggggggggggggggg
                                                      T1 is a an attic fan
                                                      thermostat, 2E340
S2:  wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww        $15.48 from Grainger
     |    |    |    |    |    |    |    |    |
1.75"|    |    |    |    |    |    |    |    |        T2 is a house 
     ccccccccccccccccccccccccccccccccccccccccc        thermostat, 2E158
     |    |    |    |    |    |    |    |    |        $14.05 from Grainger
1.75"|    |    |    |    |    |    |    |    |
     ggggggggggggggggggggggggggggggggggggggggg        To the left of these
                                                      words, air rises up
                                                      between the shadecloth,
S1:  wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww        c and the glazing g,
0.9" |    |    |    |    |    |    |    |    |        moves sideways from
     ccccccccccccccccccccccccccccccccccccccccc        South to North through
     |    |    |    |    |    |    |    |    |        shadecloth c and then 
2.6" |    |    |    |    |    |    |    |    |        further up and sideways
     |    |    |    |    |    |    |    |    |        from West to East until
     ggggggggggggggggggggggggggggggggggggggggg        it is pulled into the
                                                      house by the fan.

S0:  wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww        At the bottom of the 
	  cccccccccccccccccccccccccccccccccccc        wall, the shadecloth
     |    |    |    |    |    |    |    |    |        is stapled to the 
3.5" |    |    |    |    |    |    |    |    |        original wall sheathing
     |    |    |    |    |    |    |    |    |        At the top, it is 
     |    |    |    |    |    |    |    |    |        stapled to the vertical
     ggggggggggggggggggggggggggggggggggggggggg        spacer just under
                                                      the glazing.

The glazing could be Dynaglas (408) 997-6100, or Replex (800) 726-5151 
clear corrugated polycarbonate plastic, which comes in standard lengths,
12' long and a bit over 4' wide, eg from D & L Grower Supplies in Leola, PA
(800) 732-3509, and custom lengths up to 38' long in large quantities. It
costs a bit over $1 per square foot in small quantities and overlaps and
requires support on 4' centers. Replex also makes this in a flat form,
0.20" thick, sold in rolls 4' wide and 50' long. This material has a 10 year 
guarantee against yellowing and an expected solar transmission lifetime
of at least 25 years. It is widely used in commercial greenhouse roofs.
In fact, the South roof of my house is now covered with this stuff, and
it just survived some golf-ball-sized hail with no damage. You could also
use glass for the glazing...

Shadecloth is available from Stuppy Greenhouse Mfg. at 1212 Clay Street,
North Kansas City, MO 64116, (816) 472-1512 or (800) 877-5025 voice/
(800)423-1512 fax. They sell black polypropylene Sundown 80%-absorbing
shadecloth as item number 23691 for a basic price of $0.139 per square
foot. Shadecloth also comes in other colors, like red and green. (Stuppy
also sells plastic film greenhouses for 55 cents per square foot :-)

The vertical spacer/sleepers could be ripped from 2 x 4s. I would make
them about 1' long, with a 3' gap between them. The items marked 672
are Hart and Cooley 672 30" x 30" return air grills, $24.05 each, wholesale,
installed with the 40 degree vanes pointing up towards the outside at the
bottom of the wall, and up towards the inside of the house at the top of
the wall. Each 30" x 30" vent hole in the wall would have one stud of the
original house wall running through it vertically, up the center.

Here is a wiring diagram for the fan and thermostats:

                  T1, 70F        T2, 100F
         ---------|--------------X-----------------
                  house          fan              |
                  thermostat     thermostat      --- 
110 VAC           opens on       closes on      |fan|
                  temperature    temperature     ---
                  rise           rise             |
         ------------------------------------------

I would guess that the free air delivery of the fan is about 2000 CFM,
so in full sun, with the wall receiving 300 x 512 = 150K Btu/hour (that's
about 44 kW, or 18 cents per peak watt, for you PV people :-), if the air
goes into the wall at 68F, it will emerge at about 68 + 150K/2K = 140F.

When the house is warm enough, the fan will stop and the wall will continue
to heat up, until perhaps the automatic foundation vents open, if their
bimetallic springs have a little bit of wall air flowing over them. The
polycarbonate plastic can easily withstand 130F on a continuous basis,
with higher peak temperatures. In the summer, the vents will open to let
warm air flow out of the wall to the outside. Each vent is about 8" x 16",
not enough area to cool the wall very well, so it might be a good idea to put
some screw eyes through the glazing or hang some ropes or wires from the eaves
and grow some grapes, runner beans, trumpet vines, or clematis in front of
the wall. Or add an overhang. Or hang another piece of shadecloth over the
front, perhaps as an awning that goes to some guyed poles on the lawn...

Who will be the first to build one of these?

Nick

---

From: [email-masked] (Nick Pine)
Date: 12 Jul 1995 19:20:26 -0400

Scott Martin <[email-masked]> wrote:

>There is a product on the market called a "Solarwall." Made by Conserval...
>It consists of a black metal cladding with small holes in it...

Right. Thin black painted aluminum with about 2% of the area covered with
1/32" holes. I've talked with them and looked at their literature. This is
usually used in warehouses, etc, as the exterior skin, with suction from a
blower bringing air into the wall transversely, with no glazing! Since it
warms outside air, it is not too useful for houses. It attains an impressive
solar collection efficiency of 80%, and they say that glazing would reduce
that by at least 20%, but with some glazing, you could make indoor air hotter,
instead of just heating outdoor air from, say 32F to 40F. I think NREL is
doing some closed system testing, to evaluate this product for heating indoor
air, with glazing. That will probably work fine, BUT...

It costs $4/ft^2, vs greenhouse shadecloth at 13 cents/ft^2. Perhaps
shadecloth won't be as efficient as a transverse airflow solar absorber,
but it probably still makes more sense, at that price.

Nick

---

From: [email-masked] (Nick Pine)
Date: 18 Jul 1995 16:27:14 -0400

Dan Settles <[email-masked]> wrote:
>[email-masked] (Nick Pine) wrote:
>><[email-masked]> wrote:

>Why did you use glazing on the roof? 

Mainly, I wanted to blow down some warm air into the rest of the house from
this 32' long (E-W) x 14' high attic during the winter. But it also seems
to have made it a much more interesting space. I'm not sure what's next. 

>I suppose this might be nice in the winter on a sunny day, but doesn't
>this turn your attic space into an oven in the summer?  

That's what the two 1' turbine vents near the ridge are for, combined
with the 4 2' x 3' attic windows near the floor. But you are right, it
still gets up to 120 F or so when the sun is shining in the summer, altho
it's reasonably cool at night. I had planned on 2 4' x 4' skylights for
ventilation originally, but when those seemed expensive and not great 
ventilators, since they only opened a few inches, I switched to turbine vents,
3 as planned, 2 as installed, after the contractor started complaining and
re-interpreting the specs. I shoulda stuck to my guns. The summer venting
and shading up there can still be improved, tho.

>I was wondering how you plan to actually build this with the sloping shade
>cloth.  In the original plan the vertical shade cloth could be easily
>attached between the glazing and the side of the house.  How will you now
>attach the glazing to this sloped surface.  I know this is not impossible,
>but I'm wondering what you may have thought of that I haven't considered
>as yet.

Perhaps it was not clear from my last posting, but the vertical sleepers
in this case would not be continuous, they would be only say, 1' long, with
3' vertical gaps between them, still on 4' centers. The center of each sleeper
would be located at horizontal seams in the glazing panels. 

The one at the bottom would be a solid 2 x 4 on edge, with the shadecloth
underneath, stapled to the original wall, and the glazing 4" away from
the original wall. The next one, 4' up, would be a 2 x 4 ripped into a
1' piece and a 3" piece (nominally) with the 1" piece attached to the wall,
then the shadecloth, then the 3" piece, then the glazing on top of that
sandwich. The next one up would be 2 2 x 2's with the shadecloth in the
middle. Etc. So the glazing would attach to a plumb vertical surface, a
constant 4" away from the wall, even tho the shadecloth is sloped.
 
At some point (soon I hope) I'll have another big detailed drawing
from my architect. Perhaps this time he will include the lap fasteners
along the horizontal glazing seams, every foot or so.

>I was also wondering if you plan to cut out the shade cloth in front of
>the 2' X 2' vents as I saw in a previous post?  Is this just so you can
>reach the exterior vents through this area?
 
It seems like a good idea to have no shadecloth in front of either vent,
so the airflow resistance would be smaller in that particular area, which
is the bottleneck. That was the idea, at least. In this redesign, there is
no need to operate the (upper) exterior vent manually. It uses a couple of
$10 automatic foundation vents instead. 

>> >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.
>
>Yes, warm air rises, but since this is no longer a passive system maybe
>there could be some benefit from reversing the air flow with the fan if
>you'd rather have the warm air on the bottom floor.

Maybe. It isn't hard to make warm air flow downhill with a fan, but
why do that? I'd still like this thing to be able to operate by natural
convection without a fan, at low solar intensities. And it seems to me
that either way, the air will be pretty well mixed up in the room, a
fairly uniform temperature, when the sun is shining.

>An alternative would be to just attach the outflow to new or present air
>ducts and distribute the heat through the whole house.

Well, yes. Or add an oil burner, and put new vinyl siding back on :-)
This particular house has a fairly open plan, and a hot air heating system,
so it should work pretty well without extra ducting.

>Maybe me.

Wonderful! :-)

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

Nick

---

From: [email-masked] (Nick Pine)
Date: 18 Jul 1995 03:58:53 -0400

<[email-masked]> 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

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! :-)

>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? 
 
>You!

Nick