Subject: A translucent solar window collector?

From: [email-masked] (Nick Pine)
Date: 16 Aug 1996 11:25:28 -0400

Thermal shades are nice for windows on winter nights, but they are usually
opaque, so we have to open them to get solar heat and light into a room in
the morning, and close them again at night. If they are closed all day, they
don't provide daylight, and they prevent heat loss at best, vs collecting
solar heat... 

Full sun is about 10,000 footcandles, but a well-lit room is only 50 fc, so
we could attenuate the sun by 200:1 and still have lots of light in a room,
if the whole south wall were a window. Or have a 20:1 attenuation with 10%
of the south wall. 50 layers of very thin plastic might have an R-value close
to 50, and an attenuation of 200, and provide diffuse light for a room...

That's a lot of layers. Fewer would be less bulky on a roll-up window blind.
Should some of them be tinted or reflective? How efficient could 3 layers be?

Cathy Woodgold is thinking about using 10 layers of thin plastic glazing
inside a south window, with a possible improvement: seal the lower edge and
sides of each layer but leave the top open somehow, so if the air temp inside
a glazing cavity is less than the room temp, the air stays there, but if it's
warmer, it rises into the room... This would reduce the heat loss back out
of the window, by keeping some of the glazing cavities cooler than if they
were all sealed. But a large area sandwich with thin airspaces might have
a thermal resistance from one layer to the next that is a lot less than the
convective resistance for vertical airflow, so leaving the top open might
not help a lot... Would it help to seal some of the cavities, with a little
water inside, to try to make heat pipes? Would this thing get so hot inside 
that the plastic would melt?

A square foot of collector might look like this, schematically, with
no upward convective airflow:

        90%    90%
         | R1  | R1  | etc |     |     |     |     |     |     |
32 F     |     |     |     |     |     |     |     |     |     |  72 F
         |     |     |     |     |     |     |     |     |     |
300 -->  |     |     |     |     |     |     |     |     |     |  105 -->
Btu/hr   |     |     |     |     |     |     |     |     |     |  Btu/hr
         |     |     |     |     |     |     |     |     |     |

The equivalent electrical circuit might look like this

         T1    T2    T3    T4    T5    T6    T7    T8    T9    T10
         |     |     |     |     |     |     |     |     |     |
32 --ww--|--w--|--w--|--w--|--w--|--w--|--w--|--w--|--w--|--w--|--ww-- 72
         ^     ^     ^     ^     ^     ^     ^     ^     ^     ^
         |     |     |     |     |     |     |     |     |     |
         I1    I2    I3    I4    I5    I6    I7    I8    I9    I10

ie a string of resistors with small current sources (the sun absorbed
by each glazing) feeding each node...

Here's a little BASIC program that estimates the temperatures of 10 layers of
glazing, with full sun shining in the window, when it's 32 F outside and 72 F
inside, with a US R-value of 1 for each glazing cavity and an absorptance of
0.1 for each glazing, and no reflectance, with still air inside and outside
the house:

10 'calc temps for series glazing
20 I=300'solar input in Btu/hr-ft^2
30 T=.9'transmittance of each glazing layer
40 R=1'US thermal resistance of each glazing cavity
50 TA=32'outdoor temp (F)
60 TI=72'indoor temp
70 I(1)=I*(1-T)'sun power absorbed by window (Btu/hr)
80 PRINT INT(I(1)+.5);TAB(6);
90 FOR N=2 TO 9'calc and print sun power sources
100 I(N)=T*I(N-1)
110 PRINT INT(I(N)+.5);TAB(6*N);
120 NEXT N
130 I(10)=T*I(9)
140 PRINT INT(I(10)+.5)
150 TE(10)=TI+R*I(10)'Thevinin equiv temp of innermost glazing
160 RT(10)=1'Thevinin equiv resistance of innermost glazing
170 FOR N=9 TO 1 STEP -1'calc rest of Thevenin equiv temps & resistances
180 TE(N)=TE(N+1)+R*I(N)
190 RT(N)=11-N
200 NEXT N
210 FOR N=1 TO 9'print Thevenin equiv temps
220 PRINT INT(TE(N)+.5);TAB(6*N);
230 NEXT N
240 PRINT INT(TE(10)+.5)
250 FOR N=1 TO 9'print Thevenin equiv resistances
260 PRINT INT(RT(N)+.5);TAB(6*N);
270 NEXT N
280 PRINT INT(RT(10)+.5)
290 TG(1)=TA+(TE(1)-TA)/(RT(1)+R)*R'window temp (F)
300 PRINT INT(TG(1)+.5);TAB(6*1);
310 FOR N=2 TO 9'calc rest of glazing temps
320 TG(N)=TG(N-1)+(TE(N)-TG(N-1))/(RT(N)+R)*R
330 PRINT INT(TG(N)+.5);TAB(6*N);
340 NEXT N
350 TG(10)=TG(9)+(TE(10)-TG(9))/(RT(10)+R)*R
360 PRINT INT(TG(10)+.5)

The I's above (rounded) are:

 30   27    24    22    20    18    16    14    13    12    (house)

The "Thevenin equivalent temperatures" for each glazing layer, looking to
the right (an electrical model that simplifies calculations) are: 

 267  237   210   186   164   145   127   111   97    84

The "Thevenin equivalent resistances" for each layer are:

 10   9     8     7     6     5     4     3     2     1

And here are the glazing temperature estimates:

 53   72    87    100   109   115   117   116   109   96

It looks like there is a max temp in the center, which makes sense, because
there are low thermal resistances on each side, but the center glazing isn't
very hot, even in full sun.

This calculation mgiht be expanded to estimate the solar collection efficiency
including glazing reflections, different thermal resistances at the ends,
selective upwards convection from each space, tints, selective surfaces, heat
loss at night, daylighting, summer performance with the shade turned upside
down, etc...

Nick

---

From: john <[email-masked]>
Date: Sat, 17 Aug 96 08:55:18 GMT

One question I wonder about transfering the warmer air in the glazing, to the 
room when it is warmer than the room, would there be just to much for a fan or 
heat pipe to transfer it without making a noise.
I've seen greenhouse vents that open at a certain temperture silently.
With a little warming electronics they could open at differant tempertures as 
required. -- 

Yours sincerely....John G.*?*?*?*?*? Us Neuron's don't KNOW that much, period.
*?*?*?*?*?*?*?*?*?*?*?*?*?*?*?*?*?*?*?*?*?*?
(Everybody wants to be certifiably nice on this tide of awesome tech' power.)c?
(Posts mispelt or not should be written with content to be worth saving
so as apathy doesn't drown lurkers)c?

---

From: [email-masked] (Nick Pine)
Date: 18 Aug 1996 09:14:11 -0400

>heat pipe to transfer it without making a noise.

A PV fan? Hmmm. I dunno.

>With a little warming electronics they could open at differant tempertures as 

Bias them with a little resistive heater? Interesting idea. I seem to recall
that some HVAC hydronic zone valves work that way.  
 
Nick

---

From: [email-masked] (Nick Pine)
Date: 18 Aug 1996 10:31:13 -0400

Youth hostels now have educational goals, ie "programming," including posters
and demonstrations. A nearby hostel has a "sustainable living" theme, and
its keepers Beverly and Arnold would like to redo a 10x12' shed on a concrete
pad in the backyard into a 100% solar-heated structure, a room for two people
to stay in, with no other means of heat. This could be a way for some people
to try out a sunspace/solar closet house, and say to themselves "Hey, it's
warm in here and cold outside, and there's been no sun for a week, and this
is a simple system!" (With one voice :-) And a place to put our Lambert data
logger and modem this winter. The shed has electricity now, and there's a
pnone line nearby. 

The hostel runs on a shoestring, with some 600 yearly visitors, even though
they can put up 24 people. (How many hotels charge $12/night and have a 7%
occupancy rate? :-) They would like to be able to house a classroom or
schoolbus full of people, now that they are in the education business.

Right now the shed is just 2x4 studs with clapboard on the sides, on a
concrete pad, with slightly rotting sills, and 2 2x6' single pane skylights
and 2 6'x6' single pane windows recently installed by young architect Eric.
The south side is a blank 12' wall, facing a state park road. 

                      | 
    main building     |                                ^
 ---------------------                               S |
                                               20'
                                      --------------------
                                     |                    |
         view from above             |        pond        | 16'
                                     |                    | 
                                     |                    |
                                      --------------------
                                          |   sunspace    | 4'
                                           ---------------
                           solar closet-->| dd|     .     |
                                          | dd| sky . sky | 10' 
                                          | dd|     .     |
                                           --- -----------
                                            4'      12'

                                         campfire/picnic area

                -----     (gable roof)              .
                -----                     .....           .
             . |     |                    | dd|  window/  | 8' window
     pond   .ss| sc  |                    | dd|    door   |
  ---------------------------       --------------------------------

        view from the east                view from the north

The sunspace might look like this from the east, larger:

                         ---------------------------------------
    sun                 |                 10'                   |
                        |                                       |
                      .  ---------------------------------------
                    .   |  data logger                          |
                        |                                       |
                  .     |                                       |
                        |  drum  drum  drum  drum      sauna?   | ~8'
                 .      |                                       |
                        |                                       |
                        |                                       |
     pond       .  4'   |  drum  drum  drum  drum               |
----------------------------------------------------------------

The sunspace might be $1/ft^2 0.020" very clear flat Replex (800) 726-5151
polycarbonate plastic from a 49" wide x 50' roll, with a 10 year guarantee,
attached to curved beams on 4' centers, made from 2 8' 1x3s screwed to some
spacers between them. It might have a railroad tie "foundation" spiked to
the ground with 4' of rebar, and a layer of dark green shadecloth hooked to
the inside of the 1x3s in winter, and hanging over the outside in summer. 

Some Tyvek on the inside of the shed might stop the wind from blowing through
the clapboards (long-haired hostel friend George, from West Virginia, who
added the skylights and reshingled the roof, recently treated the outside
of the clapboards with his secret formula of old crankcase oil and kerosene),
and insulate it and add on a 4' wide x 8' tall x 8' deep solar closet, perhaps
with no inner glazing, so the shallow sunspace, eg "solar siding" or plastic
film lean-to greenhouse, would be about 8' tall x 16' long, gathering about
118K Btu/day. An EPDM-rubber-lined pond 16' wide x 20' long x 1' deep along
the south wall might increase this to 157K Btu/day when it's frozen, making
a skating pond and leaving less grass to mow. With a sunspace glazing loss
of 6 hr x (80-36)6x16/R1 = 34K Btu, it might gain 123K Btu/day (36 kWh/day,
like $50K worth of PVs :-), net. 

If the insulation inside were US R20 (5 1/2" of compressed fiberglass, with
some horizontal 1x3s over that, and a vapor barrier and drywall, (visiting
green German architect Claudia suggests a straw/clay mixture instead), and we
could somehow board up all those architecturally-interesting windows and
skylights with R10 shutters on December nights, the shed would have a total
thermal conductance of about 96 ft^2/R10 = 9.6 Btu/hr-F for the glazing and
another 584 ft^2/R20 = 29.2 for the walls and roof, ie 38.8 Btu/hr-F, so
it would need 24(68-36)38.8 = 30 K Btu to stay warm inside on an average
36 F Phila December day, with no sun, and over 5 days it would need 150K Btu.
If the solar closet had 16 55 gallon drums in it, the water would need to
lose 150K/16x500 = 19 F to provide that heat, so it might have a steady-state
temperature of 100 F, after a long string of average December days, with some
sun, if an 80 F solar closet could keep the room at 68 F. The room needs
1250 Btu/hr on an average day, and C cfm of airflow 12 F warmer than the
house would move about 12C Btu/hr, ie C = 104. 

Maybe this could this work by natural convection. An H foot chimney with warm
air inside and vent areas A ft^2 at top and bottom has an airflow of about
16.6 A x sqrt(H DT), ie 163 A = 104, so A = 1.6 ft^2. We might want a small
low-power fan that seldom turns on, as well as a motorized damper, eg a
1' x 2' piece of foil-faced foamboard attached to a $50 Honeywell ML6161A1001
direct-coupled damper motor about the size of a cigarette pack with a 24 VAC
motor the size of a ping-pong ball that uses 2 Watts when it is moving and
0 Watts when it is not.

If 157K Btu flowed into the sunspace on an average December day, and 30K of
that heated the house (altho the south wall will be warm), 127K might flow
out of the 128 ft^2 of sunspace glazing, so 1000 Btu = 6 hours x (T-36)/R1,
and the average sunspace temperature might be 36 + 1000/6 = 203 F. Probably
not, but it looks like the sunspace-house heating airpath can definitely work
by natural convection, and maybe the sunspace-solar closet airpath (although
a PV-powered fan would be useful). We might need to leave some of the shed
windows open during the day...

The ASES solar house tour is October 18 :-)

Anyone else want to help with this project?

---

From: Larry Coutlee <[email-masked]>
Date: Sun, 18 Aug 1996 10:24:50 -0700

>  ---------------------                               S |

geeze louize!!!!  with the walls treated with motor oil and kerosene, it 
sounds like a fire trap or a perfect space for toxic fumes when all that 
heat starts circulating! My first step would be to rip off all the wood 
treated with the "secret formula!" Then start with the sealing of all air 
leaks, insulation, thermal spaces etc. It will work but if your not 
carefull this will get expensive real quick.

---

From: "Brian A. Rock" <[email-masked]>
Date: Sun, 18 Aug 1996 12:23:08 -0700

> carefull this will get expensive real quick.

Old engine oil has carcinogens (amines) and pollutes ground water too!

-- 
-----------------------------------------------------------------------
Brian A. Rock, Ph.D., P.E.        Voice:  (913) 864-3434
The University of Kansas          Fax:    (913) 864-5099
Architectural Engineering Dept.   E mailto:[email-masked]
Marvin Hall                       Home page: http://www.arce.ukans.edu/
Lawrence, Kansas 66045-2222       Rock Chalk, Jayhawk, KU!
-----------------------------------------------------------------------

---

From: [email-masked] (Nick Pine)
Date: 18 Aug 1996 16:15:39 -0400

>geeze with the Nick Pine wrote:
 
Geeze didn't help with this. Would He prefer the Gulf War, as projects go?

>>pad in the backyard into a 100% solar-heated structure...

>>...(long-haired hostel friend George, from West Virginia, who

>heat starts circulating!

I imagine this structure will end up pretty air-leaky. We didn't hear much
about this problem until we started building expensive airtight houses...
George makes up for this environmental insensitivity by heating his house
with no insulation in West Virginia with 9 cords of environmentally-friendly
renewable wood a year. He's old, and he has a long beard and pony tail.

I'm working on the materials list for this proj now. So far we have wood,
fiberglass and foam insulation, polyethylene film, polycarbonate plastic,
straw, clay, flashing, screws, chicken wire, wire, turnbuckles, solid state
relays, microprocessors, modems, stucco, lead-based paint and misc (benzine,
paraquat, and diazinon, with a pinch of arsenic and cadmium dust.)
  
>My first step would be to rip off all the wood 
>treated with the "secret formula!"

Gee Larry, thanks for volunteering! :-) Email for directions. My neighbor Jim
says he will donate 1 or 2 hours a day too. He says we need to lift up the
shed and put some pressure-treated 4x4s under the sill plates. This may be
easier if we remove all that wood first, ie the walls. 

>Then start with the sealing of all air leaks,

Like, um, where all the walls used to be? 

Good idea :-)

Nick

("Cement? I can't BELIEVE you are going to use CEMENT!" --anon, Tom Lawand.)

---

From: [email-masked] (JustMe)
Date: Tue, 20 Aug 1996 11:29:44 GMT

On 16 Aug 1996 11:25:28 -0400, [email-masked] (Nick Pine) wrote:

*mostly snipped*

=>Cathy Woodgold is thinking about using 10 layers of thin plastic glazing
=>inside a south window, with a possible improvement: seal the lower edge and
=>sides of each layer but leave the top open somehow, so if the air temp inside
=>a glazing cavity is less than the room temp, the air stays there, but if it's
=>warmer, it rises into the room... This would reduce the heat loss back out
=>of the window, by keeping some of the glazing cavities cooler than if they
=>were all sealed. But a large area sandwich with thin airspaces might have
=>a thermal resistance from one layer to the next that is a lot less than the
=>convective resistance for vertical airflow, so leaving the top open might
=>not help a lot... Would it help to seal some of the cavities, with a little
=>water inside, to try to make heat pipes? Would this thing get so hot inside 
=>that the plastic would melt?

Interesting....
Melt point would likely depend on the plastic used, BUT
I had a set a plastic mini-blinds mounted _inside_ a window (between the
interior and exterior glazing) and used some of the temporary plastic
heat-shrink type stuff that's used for temp. insulated glazing (?).
The blinds are now kinda wavy (!). SO, I'd say use thin glass rather than
plastic. Or make sure the plastic used can withstand high temps w/no ill
effects.

=>Nick
=>

Not gonna try to follow the calcs. Just giving you an answer from MPE.

---

From: [email-masked] (Philip Kabza)
Date: Tue, 20 Aug 1996 22:06:03 GMT

I remember reading a recipe once for fixing carp.  This solar shack
project  reminded me of that recipe, you know, the one where after you
nail it to a board, smoke it and marinate it and bake it, you throw
away the carp and eat the board.  

Also thought of that old saying about a silk purse and a sow's ear.

Last time I did a project like that, my mason came to me later and
said he would give me a hundred bucks toward the bulldozer time if I
got tempted to do another one.

Human energy is worth a lot of conserving too, and investing it where
the payback is worth it makes sense.  Maybe you could sell the shack
to the county historical folks and start fresh.  

Speaking of human energy, did you include the internal load of the
occupants body heat?  If these are young people, and there's two of
them in one room all night. . . it could be quite a bit.

Best of luck.
Philip Kabza CSI AIA
Progressive Architecture Engineering Planning
Grand Rapids Michigan USA
[email-masked]

---

From: [email-masked] (Nick Pine)
Date: 21 Aug 1996 13:22:44 -0400

>away the carp and eat the board.  

Hi Philip,

We are calling it a cabin now :-) Several people have put some significant
time and energy and money into it now, so the core shack may have to stay.
And it may be easier to fix up an old building than build anew here, permit-
wise. Plus the hostel director likes the look of the wood on the outside
(aesthetic tyrants again), and this IS recycling... And they really don't
have much money. Altho more than some poor rural east Indians... They can
afford things like chicken wire and cement. 

My New Zealand friend Dave looked at the place and also suggested tearing
it down, saying he'd now learned well that it takes a lot less work to build
something new. He also mentioned that down under, they have "demolition
centers," vast indoor warehouses full of used windows and doors, and even
2x4s for sale. And many people prefer to use those old materials for new
construction, not only because they cost less. Some people make interesting
distressed furniture out of the old house lumber, which is basically better
in quality than what is available today... 

But I agree with you in general, recalling the soybean recipe, where you
put some soybeans in a pot with a rock, and when the rock has dissolved,
they are done, and some people who tell me they would rather wear the box
the shoes came in than the shoes.

>got tempted to do another one.

So you've learned that lesson too. I sort of naively like the idea of 
not having to completely start from scratch, since the biggest thing I've
ever built is our 2' x 2' x 8' solar closet test structure. 
 
>to the county historical folks and start fresh.  

Good idea. And labor is not all that plentiful here. But I'm not sure
how historical it is...

>them in one room all night. . . it could be quite a bit.

Interesting thought. It would depend on what they are doing. Perhaps
600 Btu/hr, out of the 1250 Btu/hr I guessed would be needed to keep
it warm on a cloudy day, if all those architecturally-interesting single
glazed windows and skylights could somehow be boarded up in December...

>Best of luck.

Thanks,

Nick

---

From: Philip Griffiths <[email-masked]>
Date: Wed, 21 Aug 1996 13:47:38 +0100

Interesting thread.  Have you read the book by Brian Norton
"Solar Thermal energy Technology" published by Springer-Verlag
1992.

It contains chapters on Collectors and passive and hybrid
solar design of Buildings.

He is also the assistant editor of the Solar Energy journal
in charge of collector technology.

regards
-- 
----------------------------------------------------
Dr Philip Griffiths,     PROBE, University of Ulster
TEL:+44 (0)1232 368238              Northern Ireland
FAX:+44 (0)1232 368239 E-MAIL [email-masked] 
----------------------------------------------------

---

From: Elaine Gallegos <[email-masked]>
Date: 28 Aug 1996 01:08:01 -0700

Philip Griffiths <[email-masked]> wrote:
: Interesting thread.  Have you read the book by Brian Norton
: "Solar Thermal energy Technology" published by Springer-Verlag
: 1992.

  One of the tract houses around the block from me has an interesting
solar collector. The one story house has a squarish gable running the
length of the roof. It is lined with windows, facing south.
  Talking with the owner, she stated that these windows heat the house up
like a son-of-a-bitch.  the area is uninsulated.  I think that I would
cover the windows up in the summer.

-------------------------------------------------------------------------------
Elaine Gallegos
[email-masked]                  
-------------------------------------------------------------------------------

---

From: Philip Griffiths <[email-masked]>
Date: Fri, 30 Aug 1996 11:48:55 +0100

> cover the windows up in the summer.

One of the main problems which everyone seems to raise on this newsgroup
is the failure of solar energy ideas, designs, products etc in use,
especially overheating.

The installation of solar collectors on a house is not adhoc like the
purchase of television set.   It is obvious to me that a small degree of
thermal modelling would have highlighted the overheating problem BEFORE
installation.

regards

---

From: john <[email-masked]>
Date: Sat, 31 Aug 96 01:41:26 GMT

> thermal modelling would have highlighted the overheating problem BEFORE
Is there a simple way or formulae for estimateing amount of storage of hot & 
cool?
On the old duttch wind mills there was adjustabl slats to be alterd for 
diferent wind, why isnt there somthing like it today for shade & sun alteration
as we've got the z80 micro computer all these years? 
-- 

*What is existance without socialising?*?*?*?*?*?*?*?*?*?*?*?*?

---

From: Raymond Bahm <[email-masked]>
Date: Sun, 01 Sep 1996 21:50:20 -0600

> cover the windows up in the summer.
What you are describing sounds like what we term "clerestory" window.
South-facing windows on a solar home usually have an overhang that
blocks the summer sun's rays.  Since the sun is lower in the sky in
the winter, they are not blocked in the wintertime.  This is standard
passive solar design technology.
-- 
Ray Bahm  --  [email-masked]