Subject: Sunspace cogeneration

From: [email-masked] (Nick Pine)
Date: 4 Nov 1996 09:06:11 -0500

In the usual way of making electricity, about 2 kWh of heat go up the cooling
tower, etc, for every 1 kWh of electricity produced. Cogeneration makes more
efficient use of fuel, since that "waste heat" (2/3 of the fuel energy :-)
is used, and the electricity is more reliable, given a grid connection, too.
Small scale cogen makes more sense, as in the Intelligen system (about $10K
for 5 kW, ie $2/peak watt), since it's hard to move heat over large distances.
Intelligen built their first cogen system about 8 years ago, and now they have
about 80 systems in the field, which burn home heating oil. They are building
10 prototypes that will burn natural gas or propane. Their system has an 11 HP
Diesel engine attached to a 5 kW motor, ie an "induction generator." When the
house needs heat, the motor starts the engine from the grid, and the engine's
cooling water circulates through house radiators, a water-air heat exchanger,
an indirect-fired water heater, a fan coil unit, a swimming pool heater, etc,
while making the electric meter run backwards. When the house thermostat says 
the house is warm enough, the system shuts down and waits for the house to
cool off. In the winter, the electric company sends the homeowner a check
every month, or credits for summer usage. The electric bill comes out close
to $0.00 for the year, and the heating bill stays about the same, since over
90% of the energy in the oil is used to make heat and electricity.

But cogen using fossil fuels has to be an interim step, vs. a solar future,
since those fuels will become progressively more expensive as the atmosphere 
keeps getting dirtier. Combining PV and space or water heating seems like a
natural form of cogeneration, since PVs are less than 20% efficient, ie we
waste 4 kWh of heat for every 1 kWh of PV output, and PV cells cost a lot
more than mirrors. Running them hotter makes them a tad less efficient (not
much for the amorphous sort, 50 W/m^2 at 25 C vs 45 W/m^2 at 60 C), so this
is a compromise, but it can work well. Sunwatt makes a 150 W PV panel that
makes 1600 watts of water heating at the same time, using 2:1 concentration.

Putting PV panels or bare PV cells or bare solar water heating collector
plates (eg Big Fins, Zomeworks' most popular product) inside a sunspace is
another way to use the waste heat from PV or water heating to heat a house,
with sunspace air warmed by PVs or collector plates with water inside, not
antifreeze, and no pumps or heat exchangers or controls, just warm-water
thermosyphoning with a plain old 3/4" copper pipe loop to an insulated tank
or a conventional water heater or insulated upstairs, with a heating element
that rarely turns on. A simpler way to make gravity-feed hot water is to put
a few plastic 55 gallon drums on the floor above, and let warm air from the
sunspace rise up behind another layer of glazing on its north wall and heat
the drums, which are supplied with fresh water using a float valve. 

What is this PV mania? Why are a few people going bananas about the small and
shrinking electrical slice of their home energy pies, while mostly ignoring
much more cost-effective solar house and water heating systems?

Suppose we have a "superinsulated" house with average R20 walls and ceilings. 
This might be an ordinary house, with fairly airtight construction, eg a good
polyethylene film vapor barrier inside, and 5 1/2" of fiberglass insulation,
and _just a few windows_ in the walls of the house itself. Why do houses have
so many heat-losing windows? Richard Komp of Sunwatt thinks houses have so
many windows because of the popularity of early "solar houses," ironically.
Pat Hennin at the Shelter Institute thinks it has something to do with massive
magazine advertising of windows, or perhaps the FHA. Marc Rosenbaum, PE,
thinks the BOCA code requires that 4-8% of the floor space of a house be
windows. Do houses have so many windows for daylighting? Direct beam sunlight
is 200 times more intense than a brightly lit office, so if we spread it
around a room well, eg with a reflecting lightshelf below and a white ceiling
above, we only need about 1 ft^2 of window for every 200 ft^2 of floorspace,
ie about 10 ft^2 of windows in a 2,000 ft^2 house. A single 3'x4' south window,
passing Steve Baer's "sameshine" from a heliostat outside? Or a 1'x 1' window
passing a 1kW beam of 10:1 concentrated sun into the house, onto a solar oven? 

Do houses have so many windows so we can see the world outside? At night???
If not, let's put all those house windows in a thermally-isolated low-thermal
mass sunspace that heats the house proper during the day, and enjoy the
sunspace and the view during the day, and go inside and let the sunspace
get cold at night. We do not have an obligation to heat the "outdoors" :-)

I have a engineer friend who lives in a conventional house near Phila, who
has a winter heating bill of about $300. In the winter, he covers almost all
of the windows of his house on the inside with white foamboard, expanded
polystyrene coffee-cup material, which costs about 15 cents per board foot.
He just stuffs the foamboard into the window frames. A fire hazard, but he
lives with that. Malcolm Wells used to cover most of the windows in his
underground office annex with foamboard too, but he had a thin coat of nicely
stenciled stucco on the side of the foamboard that faced the office. For
south windows, we might put some dark stucco or window screen on the side
of the foamboard facing the window, and leave a 2" air gap between the window
and the foamboard, and leave a few inches of window exposed at the top, to
make those windows into passive solar air heaters in the winter. 

If we don't try to keep the sunspace warm at night, we don't need to make it
with R8 house windows that cost $40/ft^2, filled with heat mirrors and argon
gas, or even $5 R2 double glazed patio door replacement panes. We can make
a sunspace out of inexpensive single pane glass, or polycarbonate plastic
at $1/ft^2, or even polyethylene film at $0.05/ft^2, should we desire more
frugality or privacy.

Suppose our two-story R20 house is 32'x32'x16' tall. The thermal conductance
would be about 1,000 ft^2/R20 for the roof and 2,000/R20 for the walls, a
total of 150 Btu/hr-F. How much sunspace glazing would the house need, for
100% solar house heating? That depends on where the house is...

                Mon  Ta  I    I/(68-T)  Qd    SSG   SSA  Q5    ND  SCW

Prescott, AZ    Jan  36  1570    49     114K  1379   83  570K  23   8'
Albuquerque, NM Jan  34  1640    48     122K  1437   85  610K  25  10'
Phila, PA       Jan  30  1000    27     135K   774  174  675K  27  10'
Portland, ME    Dec  27   940    23     149K   691  216  745K  30  10'
Concord, NH     Dec  24   880    20     157K   618  254  785K  32  12'
Elkins, WV      Dec  32   710    19     130K   494  263  650K  26  10'
Seattle, WA     Dec  41   420    15      99K   255  388  495K  20   8'

The first column is the difficult month for solar house heating. The second
and third are NREL's average outdoor temperatures (F) and amounts of sun
that fall on south walls in Btu/ft^2/day. I/(68-T) is sun/degree days, a
measure of solar heating ease. Qd=24(68-T)150 is the amount of heat our house
needs on an average day in that worst-case month. SSG=I-6hr(68-T)1ft^2/R1 is
the daily solar gain per square foot of sunspace glazing. SSA=Qd/SSG is the
sunspace glazing area needed to keep the house warm on an average 24 hour day.
Q5 = 5 Qd is the amount of heat needed to keep the house warm for 5 days
with no sun. ND=Q5/(130F-80F)55x8)) is the number of 55 gallon drums full of
water 130 F water needed inside a solar closet to store that heat. SCW = ND/3,
rounded up to the nearest 2', is the east-west solar closet width required to
hold the drums stacked 3 deep and 2 high, in a box 8' high and 6' deep. The
size of the solar closet does not depend on the amount of sun, in this model,
just the average outdoor temperature. It is proportional to the difference 
between indoor and outdoor temperatures, ie the number of heating degree days.
The sunspace glazing area decreases with the amount of available sun. 

If the sunspace were 16' tall, with insulated endwalls and roof, the 32' south
wall of our R20 house might look like this from above, in various cities: 

                 32'                              
      12'        
|________________________________|     Concord, NH
|           |     |
|     SC    |     |
|           | SS  | 8'
|-----------      |
 -----------------
	16'

      10'        
|________________________________|     Portland, ME 
|         |     |
|     SC  |     |
|         | SS  | 8'
|---------      |
 ---------------
	14'

      10'        
|________________________________|     Phila, PA 
|         |   |
|     SC  |   |
|         | SS| 8'
|---------    |
 -------------
	12'

      10'        
|________________________________|     Elkins, WV 
|         |       |
|     SC  |       |
|         | SS    | 8'
|---------        |
 -----------------
	16'

      10'        
|________________________________|     Albuquerque, NM
|         |  |
|     SC  |  |
|         |SS| 8'
|---------   |
 ------------
	10'

      8'        
|________________________________|     Prescott, AZ 
|       |  |
|     SC|  |
|       |SS| 8'
|-------   |
 ----------
	8'

      8'        
|________________________________|     Seattle, WA 
|       |                  |
|     SC|                  |
|       |SS                | 8'
|-------                   |
 --------------------------
	24'

If some nut fills up the sunspace with PV cells, it won't make any difference
in the size required for house heating, since they are so inefficient, and 
most of the heat from the electrical energy they produce will end up heating
the house anyway. If sunspace air heats water for showers, or it contains bare
collector plates for water heating, it should be about 4' wider. If the solar
closet heats water via 16' of fin-tube pipe near its ceiling and a warmwater
convection loop, the closet should be 8' wider, and double-glazed... 

Nick

It's a snap to save energy in this country. As soon as more people become
involved in the basic math of heat transfer and get a gut-level, as well as
intellectual, grasp on how a house works, solution after solution will appear.

                                          Tom Smith, 1980

---

From: [email-masked] (Nick Pine)
Date: 5 Nov 1996 08:58:57 -0500

Here's a little calculation that might be useful for curved sunspace design:
it finds the approximate bending radius Re and helps estimate the length Le of
the 2 1x3s needed to make a spaced sunspace beam. Picking a length La gives an
estimate of the actual effective bending radius; 10' seems like a good radius.
Much less than that, and cheap 1x3's (10 cents/linear foot) tend to snap.
Much more than that, and headroom and snow loading become problems.

10 H=8'height of an approximate quarter cylinder lean-to sunspace
20 D=10.75'depth of sunspace
30 C=SQR(H^2+D^2)'length of diagonal chord (use for prebending with a wire)
40 RE=C/SQR(2)'approximate radius of bending
50 LE=3.1416*RE/2'approximate length of 1x3
60 PRINT C,LE,RE
70 LA=14'actual length of 1x3 used
80 RAE=LA/SQR(2)'estimate of effective radius of bending
100 RA=RAE'save last estimate
110 RAE=C/2/(SIN(LA/(2*RA)))'refine estimate
120 IF ABS(RAE-RA)>.01*RAE GOTO 100'iterate to 1%
140 PRINT,LA,RA' Note: at Ra = 8', 1/3 of cheap 1x3s snap, when bent.

RUN

13.40009      14.8838       9.475297
              14            12.38271

A typical beam might have flat 1x3 spacer blocks every 2', screwed between 2
12' 1x3s with 2" deck screws, with the bottom 1x3 sticking out (tab A) an inch
below a horizontal purlin serving as the last spacer, with tab A tucked inside
a pressure treated 2x4 staked on edge to the ground with 3' of 1/2" rebar
through a 5/8" hole every 6'. The top tab might stick out from another purlin,
and tuck under a 2x4 screwed flat along the wall of a house, with another 2x4
under that. A slightly diagonal center purlin is useful for alignment and
racking strength. The glazing can be very clear, long-lasting polycarbonate,
at $1/ft^2 in 49" wide rolls, or 3 year UV-stabilized greenhouse polyethylene
film which comes in much wider rolls, with some nylon twine stretched over
the poly from top to bottom between each beam to reduce wind fatigue.  

Dr. Erdos might have offered a dime for the solution to this math problem :-)

Nick

Dr. Paul Erdos died of a heart attack this spring at age 83, while attending
a conference in Warsaw. He lived a celibate, monkish and nomadic life devoted
to mathematics. He had no home, lived out of a single suitcase and traveled
the world attending conferences and visiting mathematicians. Above average
mathematicians might publish 20 papers in their lifetimes; great ones might
publish 50. Erdos worked on mathematics for 19 hours every day, and was the
author of more than 1500 works. He received the immensely prestigious World
Prize, at $50,000 the highest-paying award in mathematics. Despite a spotty 
income, he gave most of it away, offering $10 prizes for easy unsolved
mathematical problems, $100 for hard ones, and $1000 for impossible ones.
He defined the word "mathematician" as "a machine for turning coffee into
theorems." Told by many colleagues to slow down, he always replied "There'll
be plenty of time to rest in the grave." He was 5'6" tall and weighed 130
pounds, with white hair, glasses and an unruly beard. He lived on a diet
consisting largely of caffeine, antidepressents and amphetamines. He was
a master of the Japanese board game go.

---

From: [email-masked] (Nick Pine)
Date: 6 Nov 1996 07:44:57 -0500

Dave Robison <[email-masked]> writes:

>New super-windows are R3-R5, which is pretty good.

But super-prices and lower solar transmissions are not.
Nor 5 year guarantees. What happens after the argon leaks out?

Consider 2 houses on an average day in Philadelphia in December, with an
average outdoor temperature of 36 F and an average 1,000 Btu/ft^2/day of sun
that falls on a south wall: a super-house with 200 ft^2 of R5 super-windows
in the R20 south wall, with a solar transmission of 60%, and a house with a
32' wide x 16' tall x 12' deep lean-to R0.8 polyethylene film sunspace on the
R20 south wall, with a solar transmission of 92%, covered with shadecloth
in the summer, with just a few windows in the house wall proper, and a 16'
x 48' x 2' deep shallow frozen pond, made from a single 20 x 50' piece of
EPDM rubber in front of the sunspace that augments the solar input by 30%:

                        super-house         sunspace house

Solar gain              120K Btu/day        612K Btu/day

Thermal loss             43K Btu/day        123K Btu/day

Cloudy day loss          43K Btu/day         20K Btu/day

Net energy gain          89K Btu/day        489K Btu/day
                         (26 kWh/day)       (143 kWh/day)

Cogen possiblities:
      solar closet      no                  yes
      water heating     no                  yes
      PV                no                  yes

Summer solar gain       120K Btu/day           0 Btu/day 

House wall
Maintenance             more                less 

Sunspace glazing                            $25 and 2 hours
recycling               none                every 5-10 years            

Gutter
maintenance             more                none

Lawnmowing              more                less

Water storage           0 gallons           12,000 gallons 

Skating rink            no                  yes

Tertiary sewage 
treatment pond          no                  yes

Duckweeds, ducks, 
frogs, goldfish,
bass, reeds, etc.       no                  yes

Mosquitos               no                  ?

Aesthetics              "pretty"            a matter of taste 

Resale value            N/A                 ?       

Removable or      
convertible to
a grape arbor, etc.     N/A                 1 day

Privacy                 not good            better

Cost                    $8,000              $1,000

Additional 
wallspace for
bookcases, etc.         0 ft^2              512 ft^2

Additional floorspace
for daytime use,
December gardening, 
hot tubs, storage, etc. 0 ft^2              384 ft^2

Second story deck       no                  possible (8x32')

Nick

---

From: [email-masked] (Nick Pine)
Date: 7 Nov 1996 02:13:10 -0500

I wrote:
 
>Cogen possibilities:
>      PV                no                  yes...

A little more explanation:

The practice of heating a house with a low-thermal-mass isolated sunspace is
not new, altho adding a solar closet inside one may be. These are called
"solaria" in Canada, as popularized by the Brace Research Institute in
Montreal. I'm building a 2-story version of a polyethylene film "Solar Room"
as pioneered by S. R. Kenin and others in Taos, NM, and described in William
Shurcliff's book _New Inventions in Low-Cost Solar Heating--100 Daring Schemes
Tried and Untried_. The materials for this will cost about $500, and I expect
it will take me about 2 weeks to build.

Some ways to get an idea of what these curved plastic film sunspaces look like
are to visit a local greenhouse grower or greenhouse supplier or to get a
$5 catalog from Stuppy at (800) 877-5025 or E. C. Geiger at (800) 4GEIGER,
http:/www.hortnet.com, or X. S. Smith in New Jersey. The materials to build
one of these greenhouses can cost less than $1/ft^2.

I'm attaching curved galvanized pipe half-bows ($36 each) from a gothic-arch-
type greenhouse to the south side of my house this week. They come from
Geiger's 30' wide "Northerner" plastic film greenhouse, which is 13' 3" tall
in the middle, as normally set up. The straight end that is normally at the
peak of this greenhouse will be at the ground, with the curved end that is
normally at the ground at the top, in this case. The pipes are 20' long
corner to corner and about 22' long along the curve, and 1.66" in diameter,
and get attached to the fascia board of the house with 2 small pieces of
angle iron and 3 bolts to make a hinge, in X S Smith's lean-to detail. The
overall pipe length can be adjusted by slipping more or less of the straight
end of the pipe into a concentric ground post pipe, 50", 60" or 70" long, with
a 3/8" through bolt to hold it in place. The ground posts serve as foundation,
attached to a pressure-treated 2x10 on edge running along the ground.

These pipes will be set up on 4' centers, using 9 of them to cover the
32' x 16' south wall of my house, and the resulting sunspace will be about
12' wide at ground level, ie it will have about 12'x32' of floorspace,
covered with black plastic and pebbles, or maybe gravel and slate.

Greenhouse polyethylene film comes in wide rolls, up to 40'x150' long, and
one standard roll size is 24' x 100' ($122 for 0.004" thick material) so
I'll adjust the pipe length to 24' along the curve, and use a single layer
of 24' wide poly with some nylon twine stretched over the outside between
the bows from top to bottom, following their curve, Mediterranean-style,
to tension the film against wind fatigue. The film will have a large piece
of greenhouse shadecloth covering it in the summer, which should make it
last longer than the 3 year guarantee. Rutgers prof David Meer told me about
his greenhouse in the shade, covered with 6 year old poly film that is still
in good shape. Greenhouse film is often recycled, vs discarded.

I'll be using some aluminum extrusion clamps ("Uni-Lock," Geiger catalog
number 33-SL16, or Stuppy's 10081/10082, at about $1/linear foot) to make the
film easy to change. A less expensive and more labor intensive alternative
is to make curved 1x3 spaced beams for about $5 each, and use cedar 1x3 cap
strips with deck screws to hold the film at the perimeter. 

The usual commercial practice in the US (which has about 15,000 acres of
poly film greenhouses) is to use 2 layers of film, and statically-inflate
them with a continuously running 50-100 watt blower to tension the film.

Nick

---

From: [email-masked] (Carl Windnagle)
Date: 7 NOV 96 11:31:23

Nick,

I appreciate your contributions to these groups.  While I don't necessarily
agree with your general concept of a low-cost, unheated solar-clost it
obviously has merits worth considering.

I have a few questions about the following scheme though.  Why does
one scenario have a reflecting pond and the other does not?  It seems
that the pond could have been used in both to give a more fair comparison.

I also don't understand why the house has so much less window area than
the lean-to.  If you assume that the house has a wall of windows on
the south side it would have less glazing that an equivalent sized lean-to
wall because of the structural supports, but if you started with the
same size building, the lean-to would have a shorter south wall because
of the slant of the roof over the 12 foot depth of your lean-to.

I have a house that I selected because the rear of the house faces within
20 degrees of South.  I plan on adding a garage with a large room above
it primarily for entertaining.  I can't really consider your lean-to
idea because it needs to be permanent and used for more than just heating.
The room hasn't been designed yet, but I'm considering having the roof
of the room angle directly up to the south side so it's at its highest
point there.  Amusingly, this style of roof is referred to as "lean-to".
The south wall would be mostly windows and have an automatic insulating
shade that would open in the morning and close in the evening.  Since it
will only be used for entertaining it seems that it shouldn't need much
heating if there is enough thermal mass to keep it warm into the late evening.

/carl

Sorry for deleting the end of your post, my newsreader made me do it.

In article <[email-masked]>, [email-masked] (Nick Pine) writes...

---

From: [email-masked] (Nick Pine)
Date: 9 Nov 1996 05:51:09 -0500

>Nick,

Hi Carl,

>I appreciate your contributions to these groups.

Good :-)

>While I don't necessarily agree with your general concept of a low-cost,
>unheated solar-clost it obviously has merits worth considering.

An unheated solar closet? Not our concept. And our concept is very specific,
not at all general, altho specific implementations can take a wide variety of
architectural forms, with equivalent thermal performance. Perhaps you are
talking about a low-thermal-mass sunspace that gets cold at night, something
like a $1/ft^2 transparent lean-to tent covering a part of the south side
of a house, or a $100/ft^2 aluminum or redwood and glass sunspace. It's the
same configuration, from an engineering point of view, but it can have many
architectural forms, with different costs, real-estate taxes, aesthetics, etc.

A solar closet is diametrically different from a sunspace, as physics prof
Dr. Paul Bashus and I described it in our paper. It's a high-thermal-mass
energy storage element, and its internal temperature changes slowly. It stores
solar heat for about a week without sun. It might live in the sunspace, with
its own glazing. It definitely stays warm overnight, completely surrounded
by insulation. Someone just told me that years ago, he added a 15' cube of
water on to his house in New Jersey, for seasonal heat storage. A solar closet
is sort of like that, but smaller and easier to build, and easier to get
heat into and out of, using air, and it only provides heat during cloudy
periods, while the sunspace provides heat for the house on a statistically
average winter day, with an average amount of sun. The sunspace takes care
of the statistical mean, and the closet takes care of statistical deviations.

The National Renewable Energy Laboratory's Solar Radiation Data Manual for
Buildings lists monthly weather data collected over the last 30 years for
239 US cities, with statistical means and deviations. It says a south wall
in Philadelphia receives an average of 1000 Btu/day of sun in January, with
a standard deviation of about 7%.

>From  a less statistical point of view, a sunspace is like a stereotypical
husband who only works when the sun is shining, and moves fast, a yin person
who has no memory for tomorrow. The solar closet is his yang farmer wife, who
puts every penny of her egg money into the cookie jar, and doesn't spend a
penny on heat until a cloudy week comes along, when she leaves her husband
out in the cold (sniff) and keeps her human children warm in the house, her
highest calling. She thinks ONLY of future rewards and delayed gratifications, 
and has few concerns for today, moving slowly, tilling the soil protected
by the sunspace.

The larger the solar closet, the lower the R-value of the house can be, and
still be 100% solar heated. David Boyer's 20 x 100' greenhouse with R1 walls
(2 layers of polyethylene film) was over 80% solar heated last winter, with
a propane heating bill of $1500 vs $8000 the year before. The only thing we
did was to add lots of thermal mass, 200 55 gallon drums full of water, about
a hundred thousand pounds of water. With R10 walls, we might have the same
performance with only 10,000 pounds of water, but the greenhouse was already
there, and the drums were free, and David mainly wants to grow plants and
people, not build solar structures.

What would the R-value of the walls of a 32'x32'x16' tall sunspace house
have to be, for 100% solar heating, if the sunspace contained an 8' tall x
8' deep x 16' long solar closet, under a deck? It might have 55 gallon drums
4 deep x 8 wide x 2 high inside, 64 of them, about 32K pounds of water 
completely surrounded by R20 insulation, with an air heater over the south
wall of the closet: a single 16'x 8' layer of polycarbonate glazing with an
air gap between the glazing and the south wall closet insulation, and openings
in that wall at the top and bottom to let solar warmed air into the closet
during the day, with an insulated damper to cover the top opening at night.
What would the average water temperature be, inside that closet?

The sunspace might be 68 F on an average December day, filled with house air 
flowing into the sunspace from an opening in the house wall near the bottom.
That 68 F air might travel upwards and sideways, from south to north through
a mesh absorber, eg a piece of 50% solar-absorbing green greenhouse shadecloth
with sun shining on and through it, hanging a few inches from the house wall.
That air might become warmer, say 120 F in that thin space, and re-enter the
house through an opening at the top with a motorized damper and a couple of
thermostats to keep the house warm on a statistically average day. 

Meanwhile, the sun would also be shining through the sunspace glazing and
then into the solar closet glazing, inside the sunspace, with no shadecloth
in front of that. Approximately 16'x8'x1000Btu/ft^2/dayx0.9x0.9 = 103K Btu
of sun would enter that solar closet on a statistically average December day,
where I live, with no reflecting pool. The air heater would warm closet air
which would circulate through the solar closet, heating the drums full of
water inside. Each 2' diameter x 3' tall drum has a surface area of about
25 ft^2, so 64 of them have 1600 ft^2, vs the 128 ft^2 of solar glazing,
a large 12.5:1 ratio, which means the drum temperature would be about the
same as the air temperature, when the sun is shining.

On an average December day in Philadephia, the solar closet might lose heat
to a 68 F sunspace during the day and a 36 F sunspace at night. I assume an
average solar collection day is 6 hours long in December in Phila. After a
long string of statistically average weather days in December, if the slowly-
changing water temp in the closet is T, ignoring the floor, we have 

103K Btu = 6hr(T-68)128ft^2/R1    for the south wall, during the day
        + 18hr(T-36)128ft^2/R20   for the south wall at night
        +  6hr(T-68)128ft^2/R20   for the deck, during the day
        + 18hr(T-36)128ft^2/R20   for the deck, at night
        +  6hr(T-68)128ft^2/R20   for the end walls, during the day
        + 18hr(T-36)128ft^2/R20   for the end walls, at night
        + 24hr(T-68)128ft^2/R20   for the north (house) wall
	  
         = 6(T-68)128 + 6(T-68)256/20 + 18(T-36)384/20 + 24(T-68)128/20
	 = (768+76.8+153.6)(T-68) + 345.6(T-36) = 998.4(T-68) + 345.6(T-36)
         = 1344T - 80333, so

T = (103K + 80333)/1344 = 136 F.

If the drums can provide heat for the 68 F house until they reach 78 F, we
can store (136-78)32K = 1.86 million Btu in the closet. On a average cloudy 
day, our sunspace house with about 3000 ft^2 of walls and ceilings with an
average R-value R might lose 24hr(68F-36F)3000ft^2/R = 2.3 million/R Btu.
It might need about 11.5 million/R Btu to stay warm inside for 5 days in
a row with no sun. If 1.86 million = 11.5 million/R, then R = 6.2. One might
even build the whole house out of R8 windows, except for the R20 south wall,
if one were rich and crazy. Houses with sunspaces and solar closets do not
have to be superinsulated and airtight to be 100% solar-heated.

>one scenario have a reflecting pond and the other does not?

Most houses don't have ponds to the south, and I was trying to
compare a conventional house to something different, and better. 

>It seems that the pond could have been used in both to give a more
>fair comparison.
 
Sure. That would reduce the amount of sun that falls on the sunspace by about
30% in December (-->, below), while increasing the lawnmowing, etc, so the
sunspace house would collect less sun. Instead of collecting 5.44 times as
much sun as the super-house, the sunspace house would only collect about
4 times as much, which is still a lot more, and a lot more than needed for
100% solar heating, with reasonably-insulated walls and air infiltration. 

Solar gain              120K Btu/day        612K Btu/day --> 471K Btu/day

Net energy gain          89K Btu/day        489K Btu/day --> 348K Btu/day
                         (26 kWh/day)       (143 kWh/day)-->  102 kWh/day

>of the slant of the roof over the 12 foot depth of your lean-to.

I'm trying to give the super-window-house a break. Direct gain houses have
an optimal ratio of heat load to south window area. Too many south windows,
which are poor thermal insulators, vs a house wall, and the thermal loss of
the house during the night or a cloudy week go way up, which kills the
performance unless you live in the sunny southwest. Too few windows, and you 
have a superinsulated house with no solar gain. And those windows are very
expensive. Sunspace houses have no such performance limitation. They can have
as much sunspace glazing as they want, since that glazing causes no thermal 
loss for the house at night, or on a cloudy day. The sunspace also eliminates
the average daytime loss from the south wall area covered by the sunspace,
but that doesn't mean much, since at high solar fractions, what matters most
is house performance on cloudy days. 
 
>20 degrees of South. 

Nice to be free from aesthetic tyrants :-)

>I plan on adding a garage with a large room above it primarily for
>entertaining.

That is to say, occasional use?

>I can't really consider your lean-to

Nothing is permanent, but X S Smith says their curved galvanized pipes should 
last for at least 40 years. The plastic film needs replacing and recycling
every 5-10 years, if it is covered with shadecloth in the summer. That might
take an hour or two, on a calm day. Polycarbonate plastic is clearer, like a
window, and would last longer, perhaps 30 years if covered with shadecloth
in summer, but it is also more expensive, about $1/ft^2, and attaching it
is more work, since it only comes in 4' wide rolls, vs 40' wide rolls that 
only need be attached at the edges.  

Is it better to build permanent structures, eg concrete Monolithic Domes
with a lifetime of some 2000 years, by their estimate, or to build things
with shorter lifetimes, and allow them to adapt or disappear over time? An
old Californian specifically asked an architect to design him a house that
would not last much longer than his lifetime. Suppose we covered the earth
with Monolithic Domes over the next few years, leaving a permanent legacy 
for our children, and their children, and so on. Would their lifestyles be
different from ours? Would they see this as an architectural disaster? Would
they establish a superfund, with traveling concrete grinders to reduce them
to dust, so they could build more appropriate houses?

>The room hasn't been designed yet, but I'm considering having the roof of the
>room angle directly up to the south side so it's at its highest point there.

Sounds good.

>Amusingly, this style of roof is referred to as "lean-to".

Sounds like a clerestory, that doesn't lean.

>shade that would open in the morning and close in the evening.

Good luck. Those things seem very expensive to me, and if they leak ANY air
around the edges, the R-value becomes a lot lower than what is claimed. And
how does the claimed R-value compare to an R20 wall?

>Since it will only be used for entertaining it seems that it shouldn't need
>much heating if there is enough thermal mass to keep it warm into the late
>evening.

Something seems backwards here. If the room use is occasional, perhaps it
should have very low thermal mass, so you can heat it up quickly for parties
at night, eg with warm air from the house, and let cool off quickly. It
sounds like a fine sunspace, one that might even heat the rest of your house,
unless you fill it with thermal mass.

Why not make the south wall of the garage below transparent, and let that
"sunspace" warm air flow up into your new room when the sun is shining, and
into the house, with no nighttime penalty? How about some clear corrugated
polycarbonate "solar siding," with a dark, low-thermal-mass surface and an
air gap behind it, or an old-fashioned glass garage door, or perhaps a
translucent fiberglass version? 

Nick

Nicholson L. Pine                      System design and consulting
Pine Associates, Ltd.                                (610) 489-0545 
821 Collegeville Road                           Fax: (610) 489-7057
Collegeville, PA 19426                     Email: [email-masked]

Computer simulation and modeling. High performance, low cost, solar heating and
cogeneration system design. BSEE, MSEE. Senior Member, IEEE. Registered US
Patent Agent. Solar closet paper: http://leia.ursinus.edu/~physics/solar.html

---

From: Duncan Baird <[email-masked]>
Date: 10 Nov 1996 22:00:54 GMT

If you would like natural daylighting in your house to replace your
electric lights during the day, visit 

http://pages.prodigy.com/duba/sohome.htm

So-Luminaire Daylighting Systems Corp makes a system that tracks the 
sun and reflects the light into your house.  You will find info at 
this web site.

Thanks,
Duncan Baird

---

From: [email-masked] (Nick Pine)
Date: 12 Nov 1996 20:32:16 -0500

Carl Windnagle <[email-masked]> wrote:

>>into the house, with no nighttime penalty? 
 
>Actually I was planning on extending the windows all the way down to the
>ground level

Sounds good. An ideal passive house might have a sunspace on a lower level,
thermal storage above that, and living space above that, so heat could be
collected and stored and distributed entirely passively, since hot air rises.

>It seems like making that space a solar closet instead would solve many
>problems.

It sounds like you are talking about putting the solar collection and
storage on the ground floor. I was just suggesting putting a "sunspace"
on the ground floor, with no thermal storage.

>I won't have to worry about freezing.  The glazing for the solar closet 
>would be dramatically less expensive than high R-value windows used
>in the living space. 

Good... Do you have clearly in mind that solar closets work best inside
some sort of larger sunspace glazing, or at least with 2 layers of glazing
in front of them, with house air circulating between the glazings, to make
this a more efficient solar collection and storage system, in a sort of
symbiotic relationship? You write about a solar closet on the ground floor,
but you don't mention its surrounding sunspace partner.

>I should also be able to set it up so that when the large room is not being
>used, I can send excess collected heat from the solar closet into the rest
>of the house.

The way I figure it, if the solar closet is inside or behind some sort of
sunspace (which can take a number of forms, eg transparent siding for a house)
there will always be excess heat available from that sunspace while the closet
is charging up to a higher temperature, but the closet will never supply heat
to the house while the sun is shining, by design. When the sun is shining, 
heat is most efficiently extracted from the sunspace, a less expensive
structure operating at a lower temperature. If the closet were to supply heat
to the house when the sun were shining, it would have a have to store heat at
a lower temperature than if not. In my mind, solar closets themselves should
supply little heat for the house on an average day, except as accidental
thermal losses.

This is a vague word picture of some conclusions that can be made
more precise and seen more clearly with some solar arithmetic...

Nick

---

From: [email-masked] (Carl Windnagle)
Date: 12 NOV 96 10:49:26

Thanks for the clarification.  I have to admit I hadn't fully understood
the solar closet concept until now.  It seems like that would nicely
solve some of the problems I had been trying to figure out.

In article <[email-masked]>, [email-masked] (Nick Pine) writes...
>architectural forms, with equivalent thermal performance. 
>Solar closet paper: http://leia.ursinus.edu/~physics/solar.html

>unless you fill it with thermal mass.
My line of thinking had been that I could let it cool off, but then I
realized that most of the time it would be used would be after sunset.
I also thought that the room would most likely be excessively warm
during the day so some thermal mass would help.

Actually I was planning on extending the windows all the way down to the
ground level and putting a wall between the garage and the sunspace so
there would be more sunspace to heat the room and thermal mass.  I was going
to use simple unglazed, passive hot water collectors with the storage tank 
above so it would be completely passive.  I was worried that there was a chance
that the bottom of the collector could freeze though since it would be the
lowest point of the room and right next to all those windows.

It seems like making that space a solar closet instead would solve many
problems.  I won't have to worry about freezing.  The glazing for the
solar closet would be dramatically less expensive than high R-value windows
used in the living space.  I should also be able to set it up so that
when the large room is not being used, I can send excess collected heat
>from  the solar closet into the rest of the house.  And of course the solar
closet could be used to heat the large room when necessary.

I still don't think I'd use the lean-to, galvanized pipe frame sunspace
because it would obscure the view out the south windows.

/carl