Subject: Re: Seek Passive Solar Design FAQ/Guide

From: [email-masked] (Nick Pine)
Date: 8 May 1996 12:41:11 -0400

William R Stewart  <[email-masked]> wrote:
>george p swanton wrote:
>> 
>> Can anyone offer a pointer to a set of formulae for glazing/
>> mass/temperature/etc calculations involved in passive solar
>> design? I am interested primarily in direct gain residential
>> space heating applications.
>
>These calculations are somewhat complex, if you are considering passive
>solar as your main heat source.  The Passive Solar Industries Council
>has a complete book and software program for this engineering problem.
>
>     Passive Solar Industries Council
>     1511 K St., #600
>     Washington, DC 20005
>     (202) 628-7400

Yeah, the brick people :-) Give them a call if you want to fill up your
sunspace with thermal mass and cripple the performance, while raising
the price dramatically :-) Or if you want your "main heat source" to
provide less than half the heat for your house.

Two views on sunspace design:
 
   It is hard to think of any other system that supplies so much heat
   (to an existing house) at such low cost...
 
   One could shorten the warm-up time of the enclosure and increase
   the amount of heat delivered to the rooms by making the enclosure
   virtually massless--by greatly reducing its dynamic thermal capacity.
   This can be done by spreading a 2-inch-thick layer of lightweight
   insulation on the floor and north wall of the enclosure and then
   installing a thin black sheet over the insulation. Then, practically
   no heat is delivered to the massive components of floor or wall;
   practically all of the heat is promptly transferred to the air.
   And since the thermal capacity of the 100 or 200 lb. of air in
   the room is equal to that of one fourth as great a mass of water
   (about 25 to 50 lb. of water), the air will heat up very rapidly.
   I estimate that its temperature will rise about 40 F. degrees in about
   two minutes, after the sun comes out from behind a heavy cloud cover.
   At the end of the day, little heat will be "left on base" in the 
   collector floor or north wall and, accordingly, the enclosure will
   cool off very rapidly.
 
     New Inventions in Low Cost Solar Heating--
     100 Daring Schemes Tried and Untried
     by William A. Shurcliff, PhD, Physics, Harvard
     Brick House Publishing, 1979, 293 pages, $12
 
   A sunspace has extensive south-facing glass, so sufficient thermal mass
   is important. Without it, the sunspace is liable to be uncomfortably hot
   during the day, and too cold for plants or people at night.
 
   However, the temperature in the sunspace can vary more than in the
   house itself, so about three square feet of four inch thick thermal
   mass for each square foot of sunspace glazing should be adequate...
 
   The sunspace floor is a good location for thermal mass. The mass floors
   should be dark in color. No more than 15-25% of the floor slab should be
   covered with rugs or plants... Another good location for thermal mass
   is the common wall (the wall separating the sunspace from the rest of
   the house)... Water in various types of containers is another form of
   energy storage often used in sunspaces.
 
     Passive Solar Design Guidelines--
     Guidelines for Homebuilders
     for Philadelphia, Pennsylvania
     Passive Solar Industries Council
     National Renewable Energy Laboratory
     Charles Eley Associates 
     Current (1995) edition, 88 pages, $50 
 
So, which is the most energy-efficient sunspace in a partly cloudy climate
like Philadelphia?
 
Shurcliff's plastic film sunspace, wearing the green uniform in this
contest, might cost about $1/ft^2, and on an average December day at 36 F,
it would receive about 1000 Btu/ft^2 of sun, like the PSIC sunspace. Let's
assume that both sunspaces have a perfectly insulated wall between them and
the house, to avoid the thermal disaster of a poorly insulated Trombe wall
in a partly cloudy climate, and let's assume there is no air infiltration
>from  the outside in either case. The sunspace air would be circulated
through the house with some dampers or fans, keeping the sunspace at 80 F,
say, while the house remains at 70 F. With single glazing, about 900
Btu/ft^2 of sun might enter the sunspace during the day, and the amount of
heat lost through a square foot of Shurcliff's sunspace over a typical day
would be about 6 hr (80-36)/R1 = 264 Btu/ft^2/day, for a net gain of 636
Btu/ft^2, ie his $1/ft^2 sunspace would be about 64% efficient, as a solar
collector. A 16' x 32' sunspace like this costing $500, along with a solar
closet containing 20 55 gallon drums full of water, could provide all of
the heat and hot water needed for an attached 32 x 32' two-story house with
an average R20 envelope. As an auxiliary living space, it could be heated
up instantly on some starry night for a party, by moving some warm air from
the house into the sunspace.
 
This sunspace might have a single layer of mylar glazing made by Bayer or
Dow chemical, distributed by Replex or Armin Plastics, stretched over some
curved galvanized pipes, with their curved ends tucked under the south eave
of a two story house. The film might be attached with aluminum extrusion
clamps around the perimeter of the sunspace, with a landscaping timber
foundation, staked to the ground with 4' of #4 rebar. The sunspace might
have a layer of green colored greenhouse shadecloth hanging inside to help
absorb the sun. Opening some vents and hanging the shadecloth over the
outside in summertime would keep the sunspace and house cooler, and prolong
the life of the glazing. The sunspace might have a crushed stone floor over
black polyethylene film, with a shallow reflecting pond in front, made from
a single layer of EPDM rubber draped over a low perimeter earth berm. A
transparent motorized damper in a first floor window would allow house air
to flow into the sunspace, if the sunspace were warmer than 80 F and the
house were cooler than 70 F, and a second floor window fan with a one-way
plastic film damper would move air from the sunspace into the house when
the house needed heat, with the first floor damper open. The fan would also
operate on windy days and nights, perhaps with the downstairs damper
closed, to create a slight vacuum inside the sunspace, to avoid plastic
film fatigue. 
 
The PSIC sunspace, wearing the brown uniform, would perform better with
double glazing. It might cost $10/ft^2, with a 4" concrete thermal mass
with an official PSIC heat capacity of 8.8 Btu//f-ft^2. Say the concrete
absorbs 100% of the sun that falls on it, vs the official PSIC solar
absorptance of 0.65 (table K, page 57.) Then about 800 Btu/ft^2/day of sun
will enter the double glazing and be absorbed by the concrete, and the
concrete surface will warm up the sunspace air, and that warm air can be
used to heat the house when the sunspace temperature is more than 80 F.
Suppose the concrete loses no heat at all to the soil below (I'm giving
quite a few handicaps to the PSIC sunspace in this efficiency race.) The
concrete might start the day at temperature T, and charges up in the sun to
a max temperature of T + dT, and return to temperature T at dawn. How can
we calculate T and dT? The equivalent electrical circuit looks something
like this:
 
                             Ts sunspace temperature
                             |
                      R2     |            D 
       36 F ---------wwww-----------------|-------------------- 70 F
       outdoors      glazing |            open damper to heat   house 
                             w
                             w  R0.5 concrete - sunspace air resistance 
               800 Btu/ft^2  w
                   per day   |
            |      ---       |
          | | ----|-->|------|--Tc concrete temperature
            |      ---       |
               sun current   w
                   source    w  R0.4 concrete bulk thermal resistance
                             w
                             |
                          ------- 26.4 Btu/F thermal mass of concrete
                          -------           
                             |
                            ---
                             -
 
Let's simplify this by assuming the thermal mass of the concrete is
infinite, vs 8.8 Btu/F-ft^2. Lots of concrete, or a water wall, or
something with so much thermal mass that the temperature inside the
sunspace never changes at all from day to night over a long string of
average December days, with some sun. This is an optimal sunspace with more
than "adequate" or "sufficient" thermal mass by official PSIC standards.
Let's also assume that the two small resistors have a value of zero, ie
let's ignore the R0.4 bulk thermal resistance of the concrete, that makes
the surface heat up more than the inside, while the sun is warming it up,
and makes it harder to get heat out of the inside of the concrete and into
the sunspace air, and the R0.5 concrete-sunspace air resistance, by
assuming both are R0 conductors. What will Tc be in that simplified case?
 
The sun shines into the sunspace during the day and adds 800 Btu to our
concrete capacitor, and over 24 hours, 24(Tc-36)1ft^2/R2 = 12 Tc - 432 Btu
flow out of the capacitor. If Ein = Eout (providing no heat for the
attached house), then Tc = (800+432)/12 = 103 F. Pretty nice, but this
sunspace is not providing any heat for the house, just keeping itself warm
on an average day, and losing lots of heat on a cloudy day. Suppose we
allow some heat to flow from the sunspace into the house, ie close the
switch, ie turn on the fan or open the damper between the sunspace and the
house often enough to limit the maximum sunspace temp to 80 F instead of
103 F. Then the heat loss to the outside world over the course of a day is
24(80-36)1 ft^2/R2 = 528 Btu, and the rest of the heat that enters the
double glazing, ie 800 - 528 = 272 Btu/ft^2/day goes into heating the
house, so the solar collection efficiency of this $10/ft^2 sunspace in
terms of useful heat provided for the attached house is 27%. As an
auxiliary living space, the temperature of this sunspace is largely out of
our control. It takes a long time and a lot of house heat to warm it up on
an evening or cloudy day, and after we leave the space, it stays warm for a
long time, giving up precious house heat to the outside world.
 
How curious that by carefully following the current official guidelines of
the Passive Solar Industries Council, we can reduce the performance of
Shurcliff's low-thermal-mass sunspace from 64% to 27%, while increasing the
price from $1/ft^2 to $10/ft^2, unimproving the cost-effectiveness of the
sunspace by a factor of 12, even with all these PSIC-slanted assumptions...
 
Here's a quote from the Acknowlegements section of the PSIC guidelines:  
 
   _Passive Solar Design Strategies: Guidelines for Home Builders_          
   represents over three years of effort by a unique group of organizations 
   and individuals. The challenge of creating an effective design tool that
   could be customized for the specific needs of builders in cities and t   
   towns all over the U. S. called for the talents and experience of        
   specialists in many different areas of expertise.
 
   _Passive Solar Design Strategies_ is based on research sponsored by the
   United States Department of Energy (DOE) Solar Buildings Program, and
   carried out by the Los Alamos National Laboratory, the National          
   Renewable Energy Laboratory (NREL)... and the Florida Solar Energy       
   Center (FSEC.) 
 
   The National Association of Home Builders (NAHB) Standing Committee on
   Energy has provided invaluable advice and assistance during the
   development of the Guidelines.
 
   Valuable information was drawn from the 14 country International Energy
   Agency (IEA) Solar Heating and Cooling program, Task VII on Passive and
   Hybrid Solar Low Energy Buildings...
 
   Although all the members of PSIC, especially the Technical Committee,
   contributed to the financial and technical support of the Guidelines,
   several contributed far beyond the call of duty. Stephen Szoke, Director
   of National Accounts, National Concrete Masonry Association, Chairman of
   PSIC's Board of Directors during the development of the Guildlines; and
   James Tann, Brick Institute of America, Region 4, Chairman of PSIC's
   Technical Committee during the development of these guidelines... 
   gave unstintingly of their time, their expertise, and their enthusiasm. 
 
>Some of the variables involved in such a design include;

>What is the heat loss rate of your structure?

Yes, that's a good thing to know... "Ohm's law for heatflow"... Note glass
is a very poor insulator... A 30 x 30' x 2 story house with R20 walls and
ceiling might have a thermal conductance of 2000 ft^2/R20 = 100 Btu/hr-F.
Make 10% of the wall area windows by adding 200 ft^2 of R2 glass and this
doubles to 200 Btu/hr per degree F--unless the glass is in a thermally
isolated sunspace, in which case the thermal conductance and heat loss
of the house go down, not up... 

>What is the solar insolation in your area and when does it occur?

Also good to know, eg the amount of sun that falls on a south wall on a
December day, as well as the average temperature in December. If your
house stores heat for several days, these averages are good enough for
design. You don't need to know much more detailed weather data. (Altho
it is very nice to be able to simulate the performance of a house design
easily, hour by hour, over the last 30 years, if you want to do that,
with the NREL/NOAA CD-ROM data.)

>http://solstice.crest.org/renewables/solrad/index.html
 
Joe McCabe, PE, lives there :-)

>What are your backup systems (eg, masonry fireplace, ground-source
>heat-pump, etc)?

Ideally none. This is how some people define a "solar house," ie one with
no other form of heat... Simple, no? Such a house can be easily designed
with some high school physics and algebra, as licensed Professional Engineer
Norman Saunders has been doing in cold, cloudy New England since 1944.

Or... you can follow the orthodox Passive Solar Industries guidelines above,
which say that no matter how hard you try, you can't provide more than 41%
of the heat needed for a house in the (warmer, sunnier) Phildelphia area
using the sun, if you fill up your sunspaces with bricks, that is :-)

                     *       *        *

Here's the scoop. The way to do this is simple. Start by finding 3 numbers:

1. Find the heat loss for your house, eg 200 Btu/hr per degree F.

2. Find the average temperature in December where you live, eg 36 F.

3. Find the average amount of sun that falls on a south wall in December
   where you live, eg 1000 Btu/ft^2/day, using NREL's numbers for
   Philadelphia, assuming a little more ground reflection.

Size a low-thermal-mass sunspace to provide 100% of the heat for the house
on an average December day, with some sun. There are several steps here:

4. Find how much heat your house needs on an average December day. If it
   needs, say, 200 Btu/hr/degree F, using "Ohm's law for heatflow," on
   an average 36 F day, it will need 24 hours (70-36) 200 = 163K Btu/day
   to stay at 70 F inside. 

5. Find how much net heat a square foot of low-thermal-mass sunspace can
   gather on an average day where you live. Suppose the sunspace takes
   in 1000 Btu/ft^2/day with R1 single glazing. Then if we let the sunspace
   temperature rise to, say, 80 F during an average 6 hour December day,
   so it can provide warm air to heat the 70 F house, the loss will be about
   6 hours (80-36)1 ft^2/R1 = 264 Btu, for a net gain of 736 Btu/ft^2/day.

6. Size the sunspace glazing. In this case, we need 163K Btu/day divided by 
   736 Btu/ft^2/day, ie 221 ft^2 of low-thermal-mass sunspace. This might be 
   a lean-to sunspace 16' tall and 16' wide and 8' deep, made with 5, 20' long
   curved galvanized pipes on 4' centers, costing $35 each, with some clear
   mylar film costing 10 cents/ft^2 stretched over the pipes and a "foundation"
   consisting of railroad ties ("landscape timbers") spiked to the ground
   with 4' of rebar, with a floor made of black poly film covered with round
   pebbles. Or it might be an "expensive" sunspace made with $80 worth of
   2x6s with some clear single layer polycarbonate plastic costing $1/ft^2,
   or one might just use the clear polycarbonate plastic instead of vinyl
   siding on the south side of the house, as "solar siding." 

7. Size the thermal mass in a solar closet or pure attic warmstore to provide
   heat for the house for a week or so without sun. For 5 days, say, we need
   to store 163K Btu/day x 5 days = 815K Btu of heat. If we use 55 gallon
   drums full of water starting at 130 F, and cooling to 80 F over 5 days,
   each storing 25K Btu of heat, we need 815K/25K = 32 of them, each 3' tall
   by 2' in diameter, tucked away somewhere, receiving the sun thru an inner
   layer of glazing on the back wall of the sunspace, with some insulation
   behind that glazing to make a passive air heater.

8. Other options: add a water heater and 10' of fin tube pipe inside the
   solar closet or warmstore to make domestic hot water, using a little
   more glazing, or add a sauna, or a place to dry clothes...
  
                     *       *        *
		  
There, that wasn't hard, was it? That's how to design an inexpensive 100%
solar house, with no backup heating system, that also makes hot water, just
like Norman Saunders has been doing since 1944...

There are a few more little details to check, but this isn't rocket science,
or even college physics. It's somewhere between figuring out a restaurant tip
and doing a simple beam strength calcualtion, as architects know how to do.

>Do you plan to use a Trombe wall, free-standing thermal mass, floor mass, etc?

Ah yes, you might use a Trombe wall, invented by Felix Trombe in 1964 (and
patented by Edward Morse of Salem, MA, in 1881) or a picture window in the
living room, with a masonry floor in front of that... A "direct loss" house,
like the one architect George F. Keck called a "solar house" in 1934 :-) 

A few years ago, I spent some time explaining to a local architect, a more
technical person than most, who had taken a few engineering courses on the
way to architecting, that a "Trombe wall" with some insulation on the outside
and some passive plastic film dampers to the inside of the house, that
opened up during the day, was probably a lot more efficient at collecting and
keeping solar heat in the house than a plain old "traditional" Trombe wall,
with masonry right behind the glass, with no insulation. Here's what I said:

  A "Trombe wall" with insulation on the outside, and 1 square foot of South-
  facing single-glazed area and an R-value of 20, will receive about 1000
  Btu/day of heat on an average 32F December day, where I live. If the room
  behind it has a constant temp of 70F, and the sun shines 6 hours a day,
  on the average, the energy that leaks out of the glass will be about 6 hours
  x (70F-32F) x 1 ft^2/R1 = 228 Btu during the day, and 18 hours x (70-32) x
  1 ft^2/R20 = 34 Btu at night, a net gain of 1000 -228 -34 = 738 Btu/day.
  Simple, no? (750 Btu, net, with double glazing, which passes less sun.)

  A standard unvented Trombe wall (Table IV-14b of Mazria's book says vented
  ones don't work much better) with a very large uninsulated thermal mass
  right behind the glass and an R-value of, say 2 (roughly 1' of masonry),
  would have an average temperature at the outside wall surface of about
  32F + R1 x (70F-32F)/(R2+R1) = 45F, if there were no sun. If you add a
  heatflow of 1000 Btu/day of sun to that model, falling on the outside
  of the wall, the outside wall surface will have an average temperature
  of about 45F + 1000/24 x (R=2/3) = 72.4F, which contributes 24 hours x
  (72.4F- 70F) x 1 ft^2/R2 = 29 Btu/day to the room behind the wall.

  So the "improved Trombe wall" above, (actually an air heater with the
  thermal storage inside the house) is more than ***25 times*** as efficient
  (738/29) at collecting and keeping heat in the room behind it, than
  the usual Trombe wall. This is somewhat oversimplified, of course...

And do you know what the architect said? "I agree with you completely, but
if you do that, you will violate the integrity of the traditional Trombe wall,
which has a magical, wonderful way of *flywheeling*, and transporting the
heat through the wall, so it is available at the other side *precisely* when
it is needed, the next morning!" And he went on and on about this conceptual
delight, this conceit, completely ignoring numerical performance... :-)

Trombe walls are also thermal disasters during long strings of cloudy days.
When the sun goes in for a week or two, they lose their stored heat in less
than a day, and then leak house heat badly, dramatically raising backup
heat or other solar thermal storage requirements.

I'm amazed that so many people, even in these newgroups, are still so
interested in Trombe walls, or their passive solar equivalents, like
direct gain houses or high-thermal mass sunspaces. A lot of people are
apparently still willing to settle for high-cost, low-performance passive
solar house heating techniques, that get them a 30% yearly savings in backup
space heating costs over a 20 year payback period, vs. warmstores, solar
closets, sunspaces and transparent siding, which really can save close to 100%
of the space heating energy needed for a house AND provide close to 100% of
the hot water needed for a house, as well.

>You'll find water is far and away the highest-capacity, non-phase change
>storage medium, in the form of freestanding tanks...

Agreed.

>How do you plan to provide for effective daylighting while preventing glare?

How about skylights with reflective south-facing sunscoops over the top?

Or a transparent steep south roof with some reflective motorized dampers
in the insulated attic floor, or a bubble-ceiling?

>I'm presently looking for windows that block UV radiation...

You would want to look for windows made out of glass, or polycarbonate
plastic with a UV light transmission of less than 1%...

>but are not low-E (because of the amount of infrared radiation they block). 

You seem to be seriously confused, Will. For solar heating, blocking IR is
GOOD, as is passing visible light... Window glass and polycarbonate plastic
pass 85% of the solar radiation between 380 and 2,000 nanometers (the sun
being like a 10,000 degree F black body) and block more than 98% of the IR
re-radiation between 4,000 and 10,000 nanometers from an 80 F room. This
"greenhouse effect" has been around long before ozone concerns.

>UV will fade furniture

Something fades furniture next to south-facing windows... Is it the visible
light or the heat or the tiny amoutn of UV that gets through the glass? 
At any rate, an intelligently-designed solar home (not yours, apparently)
will not have a lot of glass opening into the living space.

>and increase skin cancer likelihood.

I doubt you would ever get skin cancer with glass between you and the sun.

>I am in the middle of a similar design effort myself, and a utilizing the
>designs of a modular home manufacturer that has participated with DOE
>on this subject (see Solar Today, Sept/Oct 1995).

Kurt Smith at Avis? :-) He should know how to design better solar houses
by now... DOE also sponsored the Passive Solar Industry Council Guidelines.
Perhaps we should abolish them, if they continue to do more harm than good.

>If anybody has any additional info, I'd be interested as well.

I'm trying to help you...

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, residential
solar heating and cogeneration system design. BSEE, MSEE. Senior Member,
IEEE. Registered US Patent Agent. Fluent in French.

---

From: William R Stewart <[email-masked]>
Date: Wed, 08 May 1996 08:14:25 -0400

george p swanton wrote:
> I've searched some of the web sites that claim 'passive solar'
> info but have only found pretty pictures and sweeping
> generalizations with no mathematical analysis.

These calculations are somewhat complex, if you are considering passive solar as your 
main heat source.  The Passive Solar Industries Council has a complete book and software 
program for this engineering problem.

You may have visited here already, but 
http://www.greenbuilder.com/Sourcebook/PassSolGuide1-2.html gives a lot of overall 
design clues.

What is your heating profile and when does it occur?
In other words, how many degree-days of heating is required in your area?

What is the heat loss rate of your structure?  Even landscaping comes in to play here, 
such as berming, evergreens planted to the north to act as  nothern wind breakers, etc.

What are your backup systems (eg, masonry fireplace, ground-source heat-pump, etc)?

Do you plan to use a Trombe wall, free-standing thermal mass, floor mass, etc?  You'll 
find water is far and away the highest-capacity, non-phase change storage medium, in the 
form of freestanding tanks (wall-shaped or cylindrical).

How do you plan to provide for effective daylighting while preventing glare?  I'm 
presently looking for windows that block UV radiation but are not low-E (because of the 
amount of infrared radiation they block).  UV will fade furniture and increase skin 
cancer likelihood.

I am in the middle of a similar design effort myself, and a utilizing the designs of a 
modular home manufacturer that has participated with DOE on this subject (see Solar 
Today, Sept/Oct 1995).

Regards,

Will Stewart

---

From: William R Stewart <[email-masked]>
Date: Thu, 09 May 1996 08:34:31 -0400

Nick Pine wrote:
> the price dramatically :-)

Thermal storage does not 'cripple' the performance of a sunspace, it simply evens out the temperature 
swings.  Brick is only one of several materials that can be utilized, including even water.

> Or if you want your "main heat source" to

You would have to provide the figures to support your assertion, as I have seen passive solar homes where 
solar provided in excess of 85% of the heating requirements.

[199th repost of solar closet deleted]

>    virtually massless--by greatly reducing its dynamic thermal capacity.

So that energy isn't stored for the evening and night hours?  A mistake of some early passive solar 
designs.

>    collector floor or north wall and, accordingly, the enclosure will

I fail to see the advantage of such a system; what do you do for heat at night?

>    during the day, and too cold for plants or people at night.

Just the opposite of what you state above.

>    mass for each square foot of sunspace glazing should be adequate...

How did you arrive at that size?  And what material would you use for the thermal mass, as energy 
capacities vary widely?

>    should be dark in color. 

Like brick?  :-)

No more than 15-25% of the floor slab should be
>    energy storage often used in sunspaces.

Yes, a water wall is an effective thermal storage device.
 
> from the outside in either case.

Two major assumptions that are unacceptable in a real world situation, especially the lack of air 
infiltration.  That would negate the benefits of an air storage attempt in a sunspace.
[deletion]

> of the house go down, not up...

Try using R4 windows with window quilts for even more night insolation.  And the sunspace you refer to 
with mylar windows will have less than an R1 rating, so energy retention in the sunspace, including air 
infiltration, will be negligent.
 
> design. 

This is a little over-general, as passive solar mistakes have borne out in the past.

> Norman Saunders has been doing in cold, cloudy New England since 1944.

Again, the specifics of the weather play an important role, because if you have 6 days of cloudy or rainy 
weather in January, then you will freeze without supplementary heating of some form.

> 1. Find the heat loss for your house, eg 200 Btu/hr per degree F.

A fairly well-insulated house.

>From  http://solstice.crest.org/cgi-bin/solrad , we get 2.9 kWh/m2/day for a vertical wall surface in 
Philedelphia in December.

Out of "Principles of Solar Engineering", Kreith/Kreider, we find for 40o north latitude;
Dec 21, we find 702 BTUH/ft2 for an ideal day, with no overcast or other insolation impediment.

>    6 hours (80-36)1 ft^2/R1 = 264 Btu, for a net gain of 736 Btu/ft^2/day.

What is the surface area of the sunspace?  It wouldn't be identical to the floor square footage, or else 
you would have the typical solar collector.  I would estimate you would have roughly 3 times the surface 
area to floor space ratio, at a minimum.  That makes an enormous difference in your calculations.  And 
don't forget air infiltration.

> or even college physics. 

You need to construct one, collect data, and provide empirical results.  Otherwise, there are a lot of 
loose ends for you to tie up in the mean time.
 
> like the one architect George F. Keck called a "solar house" in 1934 :-)

You are making specious claims.  Trombe wall effectiveness has been proven with empirical data. 

> delight, this conceit, completely ignoring numerical performance... :-)

Perhaps you should have listened to his argument for a change.  

> direct gain houses or high-thermal mass sunspaces. 

What you have described is a direct gain air collector with no thermal mass for storage.

>A lot of people are

You make these claims yet provide no empirical data to back them up.  When you construct such a system 
and it performs to the satisfaction of the occupants, then show us the data and we will examine it.  
Until then, you need to fix a number of oversights in your calculations.

> How about skylights with reflective south-facing sunscoops over the top?

What are the R-values?  How many lumens do they provide?  What do you do when you have day lighting 
requirement in the basement and 1st floor of a two-story building?
 
> GOOD, as is passing visible light... 

I don't want to block incoming infrared, which the low-E glazings do.  Check the stats for window 
comparisons at the NREL site.

> will not have a lot of glass opening into the living space.

You imply that I am not intelligent, but I will simply reply that you need to consider yourself first 
before making such a statement.

> Perhaps we should abolish them, if they continue to do more harm than good.

You need to make a *much* better case first.
 
Cheers,

Will Stewart

---

From: [email-masked] (Nick Pine)
Date: 9 May 1996 14:55:07 -0400

William R Stewart  <[email-masked]> wrote:
>> >... if you are considering passive solar as your main heat source.
>> >The Passive Solar Industries Council has a complete book and software
>Thermal storage does not 'cripple' the performance of a sunspace,

I disagree. This basic high school physics is now well-understood, being
over 300 years old, invented by Newton and others. In rhetoric, an assertion
demands no more than a counterassertion. I've gone beyond that already.
You have my numbers. Where are your numbers, Will?

>it simply evens out the temperature swings.

That it does, but that's not all it does. It also stores lots of solar heat
during the day, most of which radiates back out thru the sunspace glazing
at night, since that is a poor insulator. Again, this is simple physics.

>Brick is only one of several materials that can be utilized,
>including even water.

Less delightful for the brick people, no doubt :-)

>You would have to provide the figures to support your assertion,

I'm confused here, Will. Or perhaps you are. I said that there are a number
of houses in the US that are 100% solar heated, with no backup heating
systems at all, some of which have long track records, in cloudier, colder
places than Philadelphia. I also said that if you carefully follow the
orthodox PSIC "Passive Solar Design Strategies: Guidelines for Home
Builders," you will end up with a house in the Philadelphia area that is
no more than 41% solar heated (see the 13th line on the right hand side
of the table on page 31 of those guidelines.) This PSIC target seems
surprisingly low, given all these solar houses with no other form of heat.

>...I have seen passive solar homes where solar provided in excess of
>85% of the heating requirements.

So have I. But they were not built using those rotten PSIC guidelines.

>[199th repost of solar closet deleted]

Perhaps you should read it and understand it once, Will, instead of just
deleting it over and over... :-)

>So that energy isn't stored for the evening and night hours?

Correct. No heat lost via the sunspace at night, because the heat is
stored elsewhere. This is Bill Shurcliff, PhD, physics, talking...

>what do you do for heat at night?

A solar closet, an attic warmstore, a rock bin, massy house walls,
an indoor pool, concrete furniture, a 5 year supply of Diet Coke, etc.

>Just the opposite of what you state above.

Right. I'm quoting the PSIC brick people here, not Bill Shurcliff, PhD,
physics, Harvard prof and author of a dozen or so well-respected books
on solar heating. Bill Shurcliff does not sell bricks :-)

>How did you arrive at that size?

I didn't. The brick and concrete people did. I found this pearl of wisdom
on page 27 of my Philadelphia PSIC Guidelines.

>And what material would you use for the thermal mass, as energy 
>capacities vary widely?

I would use sealed containers of water myself, but I would not put them in
a sunspace. I'd keep them somewhere inside the house, ideally above room 
temperature inside a solar closet, where they wouldn't lose all of their
heat overnight or during a week without sun to the outside world thru the
glazing, which is a good heat conductor. I'd let the sunspace itself get
icy cold very quickly at night, so it loses little heat.

>>    The sunspace floor is a good location for thermal mass. The mass floors

Sure, if you sell bricks :-)

>Yes, a water wall is an effective thermal storage device.

It is indeed, if it has insulation between itself and the outside world.

>Two major assumptions that are unacceptable in a real world situation,
>especially the lack of air infiltration.

OK, put in an imperfectly insulated wall, say R20, and some air infiltration,
eg 2 air changes per hour. The results hardly change at all. Trust me, I know
what I'm doing. I won't bore you with those details.

>That would negate the benefits of an air storage attempt in a sunspace.

Nobody's trying to store heat in air... (?)

>Try using R4 windows with window quilts for even more night insolation.

R4 is poor, compared to a wall. And try using the word "insolation" for sun,
and "insulation" for heatflow. And recall that people don't use manual movable
insulation for long. They get tired of operating it. Nobody seems to have
come up with good, simple, cheap, automatically-movable window insulation,
after all these years. For one thing, it's not easy to seal the edges. 

>And the sunspace you refer to with mylar windows will have less than an
>R1 rating, so energy retention in the sunspace, including air infiltration,
>will be negligent.

For starters, I guess you mean "negligible" instead of "negligent" (as in
"The great American colonial composer William Billings was said to be
'a man of uncommon negligence,' since he spent a lot of time in the gutters
of Portsmouth.") More substantively, air infiltration should be minimal in
a sunspace made with a very large piece of plastic film, and I assume that
by "energy retention" you mean something having to do with solar collection
efficiency, not heat storage... I can't find very complete information about
the thermal resistance of Mylar (polyester) film in my greenhouse engineering
book, perhaps because it has not been used for a long time in greenhouses,
but it does say that Mylar has an IR transmittance of 30%, vs 50% at the
same temp for R0.8 polyethyene film, so it must be at least R0.8. So instead
of a loss of 6 hr (80-36)1 ft^2/R1 = 264 Btu/ft^2 for a 74% solar collection
efficiency of a single-layer glass sunspace in the Phildaelphia area, we
might have a loss of 330 Btu/ft^2/day and a solar collection efficiency of
67%, so we would need a few more square feet of sunspace glazing. No big deal,
at 10 cents/ft^2 (?)

>have borne out in the past.

I disagree. I've posted some detailed computer simulations that prove this.
Perhaps you would like me to email you a 262,980 line solar simulation for
such a house using hourly NREL data for the last 30 years.
 
>Again, the specifics of the weather play an important role, because
>if you have 6 days of cloudy or rainy weather in January, then you will
>freeze without supplementary heating of some form.

I don't think you will freeze, but you might have to put on a sweater every
35 years or so, the way Norman Saunders, PE, calculates these events, on a
statistical basis, like 100 year floods... Of course one can never build a
"100% solar house," as you say, because no matter how much thermal storage
a house has, Mother Nature will eventually supply a string of cold cloudy
days that exhaust it, and the house temp may dip to 67 or 66 F (horrors!)
despite our best laid plans. My best laid plans might include a simple solar
house simulation based on hourly local NREL/NOAA data for the last 30 years.
It seems to me that most people would be happy over the next 30 years if
their house would not have needed any backup heat for the last 30 years...  

>A fairly well-insulated house.

True. And why not. As Steve Baer says, the greatest discovery of solar
investigators has been that if you use lots and lots of insulation, a
house will need very little heat, from the sun or any other source. However,
insulation does cost money, and it doesn't make hot water. Perhaps future
houses will have more glazing and thermal mass and less insulation. Perhaps
not. Perhaps they will have backup heating systems, perhaps not. This is
a matter of economics, inter alia. But, there will always be purists, sailors
who like to sail boats without motors, and heroic natural homeowners...

>From http://solstice.crest.org/cgi-bin/solrad , we get 2.9 kWh/m2/day
>for a vertical wall surface in Philedelphia in December.

Fine.

>Out of "Principles of Solar Engineering", Kreith/Kreider, we find for 40o
>north latitude; Dec 21, we find 702 BTUH/ft2 for an ideal day, with no
>overcast or other insolation impediment.

That sounds more like an average day, not an ideal day, especially since
you mention the latitude. Your 2.9 kWh/m^2/day NREL number (919 Btu/ft^2/day)
with a built-in 0.2 ground reflectivity is probably more accurate for an
average day... Either one can be improved with something more reflective
lying on the ground in front, eg snow or ice with a 0.6 reflectivity. .   

>What is the surface area of the sunspace?

I had in mind a fairly shallow sunspace, perhaps some south "solar siding."

>It wouldn't be identical to the floor square footage,

True. It would be quite a bit larger. Making a 16' tall x 12' long lean-to
sunspace 8' deep instead of 8" deep adds another 128 ft^2 or so of endwall
losses, so if the original sunspace were designed to collect (1000-264)x16x12'
=141K Btu/day, the 8' deep one would want to collect enough sun with the
south facing glazing area A so that (1000-264)A=128*264+141K Btu/day, making
A about 238 ft^2, ie we might use a 16' x 16' sunspace.

>I would estimate you would have roughly 3 times the surface area to floor
>space ratio, at a minimum. 

Let's check that: (16x16'+128')/16x8' = 3. Exactly :-) 

>That makes an enormous difference in your calculations.

No, this is just one of those little refinements I mentioned before. Using
a deeper sunspace than solar siding requires a little more glazed area.

>And don't forget air infiltration.

OK, I won't forget that. Should we forget internal heat generation?

>You need to construct one, collect data, and provide empirical results.

Like the one with the electronic data logger inside that has been up on
the roof of the local college since November 4? No, I don't need to do that.

>> ...you might use a Trombe wall, invented by Felix Trombe in 1964 (and
>You are making specious claims.

I disagree. Trombe walls are even poorer performers than sunspaces full of
bricks, since they have little thermal resistance. At least you can put an
insulated wall between your living space and your brick sunspace, so most of
your backup heat stays in the house during a cloudy week. You have my numbers.
Which number is incorrect? Where are your numbers? Most people don't even
need numbers to see this.

>Trombe wall effectiveness has been proven with empirical data. 

They work pretty well in the Southwest, in places with less than 5 cloudy
days per year, but even there, people call these "direct loss houses" :-)
In cloudier climates, they are thermal disasters.

>>And the architect said, "I agree with you completely, but if you do that,
>>you will violate the integrity of the traditional Trombe wall, which has
>>a magical, wonderful way of *flywheeling*, and transporting the heat
>>through the wall, so it is available at the other side *precisely* when

I did listen... 

>What you have described is a direct gain air collector with no thermal mass

Perhaps you didn't have time to read this carefully.

>>A lot of people are apparently still willing to settle for high-cost,
>>low-performance passive solar house heating techniques, that get them a
>>30% yearly savings in backup space heating costs over a 20 year payback
>>period, vs. warmstores, solar closets, sunspaces and transparent siding,
>>which really can save close to 100% of the space heating energy needed for
>>a house AND provide close to 100% of the hot water needed for a house...

>You make these claims yet provide no empirical data to back them up.

I have some data. Norman Sauders has lots of data, and many people with
firmer grasps on simple high school physics can understand how well this
works without building a thing.

>What are the R-values?  How many lumens do they provide?

Perhaps you have heard people say "Asking questions is the mark of a fool"? :-)

>What do you do when you have day lighting requirement in the basement
>and 1st floor of a two-story building?

I don't know. What do you do? Windows, transparent floors, light pipes,
a walkout basement?

>I don't want to block incoming infrared, which the low-E glazings do.

It is nice to pass solar IR, from 0.78 - 3 microns. It is not nice to pass
80 F IR re-radiation at 3 microns and over... One way to do this is to use
plain old glass in a low-thermal-mass sunspace. Another is to use inexpensive
single layer polycarbonate glazing. Polyethylene film is not good at blocking
either kind of IR.

>You imply that I am not intelligent...

Let's just say that you don't seem to understand how to design an inexpensive,
energy-efficient solar house, and you have been bamboozled by PSIC. That's OK.
Ignorance is no crime, save when combined with arrogance, stupidity, rudeness,
direspect, stubborness, short-sightedness and superficial orthodox thinking.
 
Perhaps you should take up religion, or law.

Still trying to help...

Cheers,

Nick

---

From: William R Stewart <[email-masked]>
Date: Sat, 18 May 1996 01:35:43 -0400

gcp wrote:
> [etc - snip!]
> (sounds like a solar panel to me :-)

Yep.

> There is a philosophical difference here that boils down to whether
> you want the sunspace to be part of the living space.
> If you like sunspaces, fine!

Thank you!  I've been trying to get the point across that some people
have their own preferences.

> I am going to suggest that a dedicated sunspace need not be part of
> the design for space heating.
> If you design your house to be superinsulated, it has been shown that,
> even for houses orientated to minimise passive solar gain, addittional
> energy costs for space heating can be made insignificant.  With
> windows available now (R-10+) and orientation to make best use of
> winter sun I think it is possible to reduce space heating costs to
> zero in an otherwise normal house.  These houses cost little more than
> a normal house and that is paid for quickly.
> Then the main effort needed is to reduce lighting and water heating
> costs.
> On the latter a recent design here in the UK (Scotland in particular)
> has aimed at reducing cost rather than increasing efficiency of a
> solar panel.  Most panels have a dual circuit arrangement, because of
> problems of freezing. This design uses a type of rubber, in a single
> circuit, to allow the water to safely freeze!  The cost is
> considerably reduced and it has survived one of the hottest summers
> and coldest winters here in recent times.
> Any comments?

These have been used in the US, and I heard of one story
that a hotel in the West used one in the 1800s
The cost is minimal, due to the lack of expensive materials and controls.
The efficiency is low, but the sun is free, so what's to complain about?

> >I don't want to block incoming infrared, which the low-E glazings do.  Check 
> >the stats for window comparisons at the NREL site.
> Can you provide a URL

http://www.nrel.gov/documents/erec_fact_sheets/acrobat.html
"Advances in window glazings"
"Energy Efficient Windows"
(and for Nick, "Sunspace Basics", though they include sunspaces that he 
disagrees with)

One thing neither of these files have that I remember seeing is a table comparing
solar conductance (SC) by type of glazing and layers.  I'll see if I can locate it.

> You are right normal glass does not sufficiently block UV (you may
> need to reduce the higher energy range of the visible spectrum to
> reduce fading aswell - but you are better to check on this) although
> you wont get a tan in a hurry.
> I don't understand your aversion to low-E windows though.  The amount
> of IR you stop getting in is more than made up for by the amount you
> stop getting out (unless it is hotter outside - in which case you
> probably want to keep it that way!)  The way it works is that light
> comes in as high energy visible (or UV) is absorbed by amongst other
> things your furniture (fading it) then re-radiated as lower energy IR
> which the window does not transmit as well - low-E only makes this
> better.

Some of the low-E windows I have seen lately have been close to what
Nick had mentioned; one was SC=.59 and another 'heat mirror' SC=.41

These sorts of figures *do* concern me.  If you have another take, I'd 
like to hear it, especially if it has to to with spectral-selective
glazings.

Cheers,

Will Stewart

---

From: William R Stewart <[email-masked]>
Date: Mon, 20 May 1996 07:42:43 -0400

Nick Pine wrote:
> Good snip.
> But they are also very expensive, and normally live on the roof, which makes
> them fundamentally different from these inexpensive sunspaces. 

Sure, but they will last 10-30 times longer than a sheet of mylar stapled to a
wooden frame.  Before someone makes a decision about which route they will take,
they have to consider whether or not weather considerations prevent the long term
use of mylar staple (or nailed or glued, etc) sheets.  In my area (Washington, DC),
we get just enough high wind bursts every year to make a flimsy sunspace impractical
for serious consideration.

Even if the force of the wind didn't carry it off in the first 2 months, wind-swept
items, such as sticks or other debris, would puncture and rip the surface, 
requiring replacement or unsightly patching.

These panels
> are often heavy boxes added on to houses, mounted on brackets, shipped from
> afar at great expense and manufactured in relatively small quantities, with
> ducts and plumbing that go through the house roof, and pumps and blowers
> that eat lots of electrical energy every year. 

You yourself said that heat distribution from your solar closet would require
HVAC elements that required electricity (controls, blower, etc.)

(Yes, that electrical energy
> can come from PVs, altho they are very expensive now and usually waste 90%
> of the sun that falls on them, the very same solar energy we are trying to
> collect with the add-on boxes :-)

Fuel costs with solar are minimal :-)
 
> Some solar air heating panels have low thermal mass. Water heating panels
> have more thermal mass. I saw a new rooftop-type water heating panel for
> sale for about $40/ft^2 with lots of intentional thermal mass. It was about
> 4x8x1' thick, and contained 30 gallons of water, a batch heater with no
> insulation between the water and the absorber plate and the glazing as
> far as I could tell. They also had a 50 gallon model...

This is only one particular implementation of a water-based solar heating
panel.  In cold climates, water storage is almost always contained within
the structure.

> Brick sunspaces have LOTS of thermal mass behind glass with no night
> insulation, as do many Trombe walls and direct gain houses. This is a
> very inefficient way to heat a house in a partly cloudy climate, because
> the thermal mass stores lots of solar heat during the day, and most of that
> solar heat disappears through the glazing at night. 

This ignores the sunspaces with insulating materials, that are tracked and
easy to move.  Just look through you back issues of Home Energy or Home Power
for examples of window coverings between R4 and R8.

>During a week without
> sun, an isolated sunspace can just get cold, even if it is full of bricks,
> which is OK. But a Trombe wall or a direct gain house with south glazing in
> the living space will lose a lot of backup house heat to the outside world
> through the relatively low thermal resistance of the glazing.

This ignores the use of insulating curtains to prevent exactly that.  Too bad
you could'nt have come down this weekend for our yearly Tour of Solar Homes.
One house I visited had virtually the entire south wall covered in windows (R3)
with two large track-guided R8 shades (4 sheets of reflective mylar with air 
spaces).  The house had less than .2 ACH, was heavily insulated, and the 
occupants said their fuel bills were less than $30/month in winter.

> Of course people have preferences and that's fine. But let's recognize
> that that's a lifestyle choice involving a compromise with aesthetics and
> money and fossil or wood fuel consumption. Let's not drag in false physics.

Let's not focus on one or two aspects of physics, and forget about infiltration,
re-radiation, and convection.  That would give one false results in any
thermal energy equation trying to determine overall Qin to Qout.

> A low-thermal-mass sunspace could be a commercial plastic film greenhouse
> adjacent to a house, costing 50 cents/ft^2, put up by 1 person in one day,
> more like a tent than a building. The glazing might be poly film costing
> 5 cents/ft^2, with a 3 year guarantee, changed every 3 years in an hour,
> and recycled. 

If it withstands weather conditions for more than 3 months and your neighbors
still talk to you.
 
> Or it might be flat very clear polycarbonate glazing, costing $1/ft^2,
> with a 10+ year solar lifetime, that comes in rolls 49" wide, so it might
> be simply attached to 2x6s on 4' centers in a simple lean-to sunspace that
> forms the weather south wall of a house.

Again, you have the serious concerns of infiltration, neglible insulation (>RI)
and weather to overcome, not to mention the sickly yellow appearance after 
a year in the sun.  If that's not a problem, by all means, knock yourself out.
  
> Another way to make a low-thermal-mass sunspace is to make the steep south
> roof of a house with the same single-layer corrugated polycarbonate plastic,
> with an insulated attic floor. Again lower first cost than normal
> construction (no shingles, no tarpaper, no sheathing, and 4' x 12' panels
> that attach with a few hex head screws) and it can collect solar energy,
> with a low power fan that blows warm air from the peak of the attic down
> a large cheap uninsulated duct (eg a poly film tube duct that costs 50
> cents per linear foot), into the house when the sun is shining. House air
> might return to the attic through a $200 2' x 2' motorized damper that lets
> daylight into the house when it is open. The value of such daylight might
> be $200/year of electrical power savings, vs the fluorescent equivalent,
> if it is well distributed inside the house, as well as the aesthetic value
> of daylighting.

One point you seem to miss over and over is the lack of a thermal 'flywheel' by
which to dampen the large temperature swings large amounts of solar gain can
induce.  If you lessen this by reducing the solar insolation received, then 
you lessen the amount of solar heat your structure can utilize.  The lessons
learned by overheating in the day have been hard won; don't ignore them by
offering simplistic paper drills that have too many questionable assumptions.

I you have a separate thermal storage, such as your solar closet, then active
controls and blowers are necessary.  I don't consider that to be undesirable,
but I myself prefer to use passive techniques, at least for the majority of 
my space heating.  

> I agree.
> >> energy costs for space heating can be made insignificant.
> 
> Absolutely true. But at what price?

Perhaps this is the crux of your argument.  I will address this as it applies 
to me.

1.  The house I am in the middle of finalizing will have a 'normal' amount of
windowspace.  The south side, however, will have approximately 50% of the
windowspace.  My wife prefers a certain level of natural light, so I must
satisfy her desires as well.  My first inclination was to have an earth-
sheltered home, with full exposure to the south, but she felt that would
be like living at the mouth of a cave.  

So there will be no added costs for windowspace or window type. 

2.  I will be using the same amount of window insulation that I would
if I didn't have solar gain, given that I am an energy-efficiency nut.
Therefore, no additional costs will be incurred for extra window
insulation.

3.  The only added cost will be for the installation of thermal storage
containers next to the south facing windows.  Previous installations have
totalled $2000.  Given the thermal flywheel effect, they will pay for 
themselves in around than ten years.

4. I still intend to have supplemental heat, as well as cooling.  I am in the
final stages of determining if I will have a masonry heater stove and a small,
efficient window A/C or whether I will have a simpler efficient fireplace and 
a small ground-source heat pump.  My wife insists on *some* kind of fireplace.

> >> With windows available now (R-10+) and orientation to make best use of
> >> zero in an otherwise normal house.
> 
> I agree, IF you are willing to live with very few windows.

I could, but my wife won't.  :-|
 
> >> These houses cost little more than a normal house
> 
> Whoa!!!
> 
> >> Then the main effort needed is to reduce lighting and water heating costs.
> 
> True. And how do you reduce water heating costs? Superinsulation doesn't
> heat water. Can we try to look at more of the whole picture here, and make
> new houses that have these functions as beautiful integral parts, rather than
> adding on kludgey afterthoughts, box after box after box, more expensively?

Solar water heating will be in my design from the start.  It will be active, and
will be supplemented by the ground source heat pump on overcast days.
 
> >> solar panel.
> What a strange and excellent idea :-)
> 
> They are also more expensive...

I would be using them anyway, in order to reduce heat loss in winter and heat
gain in summer.

Cheers,

Will Stewart

---

From: [email-masked] (gcp)
Date: Thu, 23 May 1996 18:42:41 GMT

William R Stewart wrote:
and
Nick Pine wrote:
And if you can't tell one from the other...

Just to tidy up some bits.

> (sounds like a solar panel to me :-)
(I wrote that!)
>> them fundamentally different from these inexpensive sunspaces. 
There's inexpensive and there's cheap  :-)
Maybe a false economy?
>> solar heat disappears through the glazing at night. 
Didn't I mention something about TIM somewhere?
>> Absolutely true. But at what price?
This is from a case study book published by the RIBA (Royal Institute
of British Architects) - so it's kosher!
Two types of house were built on a site (in Milton Keynes) one to
building regulation standard the other superinsulated.  That was the
only difference i.e. window style was normal;  indeed, orientation of
the house was to minimise solar gain!
The 'super' houses cost 2000 pounds more to build than standard, and I
think there would be less difference now.  (At a guess the market
value of the houses would be >100,000 so you see this is not a
significant sum - and the 'super' houses sold first.)
Space heating costs were then 10 to 20 pounds a year.
>> I agree, IF you are willing to live with very few windows.
No.  I believe (but I have been known to be wrong  :-)
That in the RMI (Rocky Mountain Institute) these sort of windows
contribute more heat than they lose -  North facing in the winter.
(I would check this before I committed to build though!)
>> >> These houses cost little more than a normal house
See above. 
>> What a strange and excellent idea :-)
That's what I thought and as someone has already asked me, and to
satisfy my own curiosity, I shall attempt to find out more.
(Though I am of the opinion, if it is not a retrofit, highly efficient
nonimaging optics systems plus storage is the solution(!) for hot
water.)

---

From: [email-masked] (Nick Pine)
Date: 24 May 1996 08:24:19 -0400

gcp <[email-masked]> wrote:

Who is this UKsian gcp, anyhow? :-) Will he/she unlurk, with a real name?

>William R Stewart wrote, and Nick Pine wrote [blah blah blah...]

>Just to tidy up some bits.

OK...

>There's inexpensive and there's cheap  :-)

And 'frugal.'

>Maybe a false economy?

Maybe. To me, rooftop panels make no sense at all, economically.
Putting bare water heating panels in a sunspace makes more sense.
What we use for glazing is a tradeoff between aesthetics, cost, and
replacement maintenance. A matter of personal taste, when all is said.

Physics is not a matter of taste: panels in a sunspace gather more heat
than rooftop panels. Low-Thermal-Mass Sunspaces (in many forms) are more
efficient than HTMS at heating attached houses. Isolated sunspaces work
better than direct gain houses, Trombe walls are the pits, performance-wise,
and heat stored in a high temp store can keep a house warm longer than
heat stored in the same thermal mass in the house itself, etc.
(Repeating obvious truths to people who won't listen.)

>Didn't I mention something about TIM somewhere?

I don't recall that. What's a TIM? Or is this your friend Tim?

>>> >> If you design your house to be superinsulated, it has been shown that,

Love that phrase... Like "thus we can easily see..." skipping over
pages and pages of hard mathematics, or enshrouding shaky assumptions...

>of British Architects) - so it's kosher!

I suspect architects, even kosher ones. Altho they were the guys who
inspired US solar architects in the 1800s... Have they evolved with
the same fervor as the British Admiralty over the years?

>the house was to minimise solar gain!

OK. (Architects at work.) Where is Milton Keynes?
Are these Cornwall houses, surrounded by palm trees and pirates? 

>significant sum - and the 'super' houses sold first.)

I could see that a house like this might not cost more than its "normal"
neighbor, if all one does is stuff another layer of 1L/m^2 R3 (UK) fiberglass
in the wall, but not if it means tightening up the house to 0.1 natural
air changes per hour, vs 1 or 2. Perhaps the "normal" house had 0.1 ACH
already...? What sells first may be largely a matter of hype.

>Space heating costs were then 10 to 20 pounds a year.

Unbelievable. I'd like to know more of this story,
eg their climate and electrical consumption. 
And the window type and area... 
How big are these houses? 

Are they bathing machines full of incandescent bulbs?
Do people live in them in the winter?
Is there a winter?

>No.  I believe (but I have been known to be wrong  :-)

Let's check this with a few numbers if possible, gcp... 
Can we do a little thermal arithmetic here, or do you rely on Unseen Forces?

>contribute more heat than they lose -  North facing in the winter.

That sounds possible, esp in a cloudy climate with lots of diffuse
solar radiation, which comes from all over the sky, not just the south.
But what's the whole picture here?

>>> >> These houses cost little more than a normal house
I repeat. Whoa!!! In rhetoric, an assertion demands no more than a
counterassertion. I've supplied some numbers, and well-known physicks
accepted by all but a few self-styled AE gurus, who shall remain nameless,
like you, and you've supplied an incomplete anecdote thus far, I ween. 

>satisfy my own curiosity, I shall attempt to find out more.

Good. But we still have that inescapable economics, that if ALL a "solar
collector" does is collect solar energy worth S pounds per square meter
per year, and the complete system cost is C pounds per square meter, with 
labour and all the bits and pieces, it will take at least C/S years (ie
forever) to pay for itself, not including maintenance, hail, hurricanes,
reroofing problems, roof penetration leaks, and the cost of electrical
power to run it. Of course we do things now that never pay back, but
wouldn't it be nice if a solar heating investment paid off better than
putting money in a bank account? Wouldn't that make it more interesting
for Nigel Average?

And solar collectors should go in warm sunspaces if possible, where they can
collect heat more efficiently or work without insulation, and their "waste
heat" can heat an attached house, vs being blown away in the wind, and where
if they never freeze, they won't need antifreeze, heat exchangers or pumps
(IMHO.) Not that I'm trying to tell you what to do, mind you. Go waste your
money on ugly expensive complex inefficient systems if you like.

>nonimaging optics systems plus storage is the solution(!) for hot water.)

I like non-imaging opticks :-) I lent my laser pointer to the father thereof
at a lecture a couple of weeks ago. He brought along a Cassegrainian version
(~1mx3m for the primary reflector) of what may become a standard for roofs
of large buildings, and set it up on the roof of the Franklin Institute in
Philadelphia to let us all watch it work. But there was no sun :-( Hence,
yes, storage... But you know, Prof Winston came very close to saying that
his optics are expensive overkill if all you want is hot water for showers,
vs. higher temperatures for process steam or tropical icemaking or LiBr
absorption air-conditioning. (Many would say the same for Thermomax.)

I like Richard Komp's version, a 4' x 8' panel with 2:1 CPCs that fail to
focus the sun on half the normal number of PVs, which are somehow attached
to "Big Fins" (I think) that are clipped to copper pipes. These things make
150 W of electricity and 1600 Watts of hot water at the same time. Now if
we could do similar solar co-generation with some sort of transparent
electrodeposited PVs which can produce lots of power at high temperatures
and cost $1/peak watt, and plate them on to a window or some polycarbonate
plastic, or glue them on to some big fins attached to some copper pipes
inside a sunspace, or collect their "waste heat" with an air-water heat
exchanger, as they are starting to do in Appleby restaurant sunspaces,
that would be even more interesting, even without the NI optics... 

Cheerio,

Nick

---

From: [email-masked] (gcp)
Date: Sat, 25 May 1996 17:06:45 GMT

>Who is this UKsian gcp, anyhow? :-) 
argumentum ad hominem?  
>Will he/she unlurk,  ?
Why, would that change your opinion of what I say?
>>William R Stewart wrote, and Nick Pine wrote [blah blah blah...]
Now, I didn't say that last bit!  :-)

>I don't recall that. What's a TIM? Or is this your friend Tim?
Strange.  I had a short email correspondence with you about
Transparent Insulation Material.  I even used my real(?) name - first
one anyway.  Unless there are two Nick Pines?  And will the real one
please step forward?

>pages and pages of hard mathematics, or enshrouding shaky assumptions...
Shown, as in built - real world!
>>the house was to minimise solar gain!
Otherwise it wouldn't have been a test of superinsulation.
>Are these Cornwall houses, surrounded by palm trees and pirates? 
52 3N  0 42W
No.
I have to point out though, that the UK is a less variable climate
than the US both at a particular place, and from place to place.
Definitions of superinsulated will thus vary.
However, insolation is also less here.
But a superinsulated house is basically designed to operate (most of
the time) without addittional space heating.
>already...? What sells first may be largely a matter of hype.
Less than 0.1air change per hour (ventilation off).
Demonstrated by pressure-testing and also tracer gas.
These were an off-the-peg Scandinavian system.
>>Space heating costs were then 10 to 20 pounds a year.
This is old prices, but inflation has not been large in the
intervening period, and gas prices have gone down in real terms.
So it may be at the upper rather than lower end of that range.
>How big are these houses? 
Semi-detached, two storey, three bedroom approx. 75 square metre floor
area - pretty normal there.
>Are they bathing machines full of incandescent bulbs?
Compact flourescents haven't fully caught on yet!
>Do people live in them in the winter?
These houses were sold on the open market.  Real, normal people lived
in them and that is what it cost them.  Though as I said originally
this is addittional cost - cooking, lighting, the refrigerator and
other appliances (and living) will contribute to space heating. 

>Can we do a little thermal arithmetic here, or do you rely on Unseen Forces?
Unseen Forces - every time  ;-)
I think it was a reasonable assumption for these houses on that site.
And I meant normal in windows as well.
In the more extreme US climate(s) much more rigorous design would be
required.  Such as in the RMI.
They know a lot more than I do - gurus may even be applicable.

>But what's the whole picture here?
OK, you really need to design for a particular site.
I gave an actual example - how applicable that is is for you to
decide.
The point was efficient space heating design need not require a
dedicated sunspace.  (Hot water is a different matter.)
What is needed is good insulation eg. windows that lose no more heat 
than a good wall.  ('One prototype now being developed has actually
performed better on a daily average in field tests than a highly
insulated (R-19) wall.  At night the superwindow loses a little more
energy than an R-19 wall, but during the day even a minimal amount of
sunlight is sufficient to turn the winbdow into a net energy
provider.':  Scientific American Sept. 1990.  The same article says
they have a payback period of 2 to 4 years - you wont get that from a
bank! (and also that they block UV that fades furniture!))
Just another anecdote. (And I'm not sure about the R-19 as at one
point it mentions R-50 in the same context!)
>like you, and you've supplied an incomplete anecdote thus far, I ween. 
This was not theory, but real houses, and in Scandinavia they are
fairly normal.  (They just cost a bit more to heat there!)

---

From: William R Stewart <[email-masked]>
Date: Fri, 24 May 1996 23:16:18 -0400

> replacement maintenance. A matter of personal taste, when all is said.

Smartest thing you ever said.

> than rooftop panels.

Evidence by assertion.

> Low-Thermal-Mass Sunspaces (in many forms) are more
> efficient than HTMS at heating attached houses. 

This might be true, but discounts extra living space/time most
HTMS have (assuming people won't want to spend time in a room
with plastic wrapped around cheap piping that is cold as soon as
the sun dips).

>Isolated sunspaces work better than direct gain houses,

More evidence by assertion, and ignores daylighting benefits
of direct gain houses.

> Trombe walls are the pits, performance-wise,

Could you be less technical here, Mr. Wizard?

> heat stored in the same thermal mass in the house itself, etc.

Hmm, same mass, same potential energy, same Qout but different results...
Is this the "new math" we've heard about?

> (Repeating obvious truths to people who won't listen.)

The Oracle of Thermodynamics - "R-values include radiation and convection"

> pages and pages of hard mathematics, or enshrouding shaky assumptions...

Like 'assuming the interior temperature remains at 72 F" and other
'enshrouding' assumptions of yours in the past.
> I suspect architects, even kosher ones.

Admit it, you suspect 99% of the people in the field.

> Altho they were the guys who
> I've supplied some numbers, and well-known physicks

You overestimate your flock...

Cheerio,

Will Stewart

---

From: [email-masked] (gcp)
Date: Thu, 30 May 1996 19:24:31 GMT

[email-masked] (Nick Pine) wrote:

>>Transparent Insulation Material.

>Sorry, I'd forgot the acronym, and I thought you were talking about a posting.
>Who makes this TIM, and is it available commercially, and how much does it
>cost and what is its solar energy transmittance and R-value?
Sorry,  I used just the acronym as a dig at you   :-)
I'd have to get back to you on that, but there is a web site.

>Can you explain this a bit more?
This was an investigation of superinsulation by the Polytechnic of
Central London, they only wished to investigate this variable, so
passive solar input was minimised in the superinsulated and control
houses.  Fairly normal experimental procedure.

>I wonder what the average temp and amount of sun that falls on a south
>wall is in the coldest month in Milton Keynes? 
Looking at my atlas 3 Celsius and about 1.5 hours bright sunshine in
January.  In short:  I don't know!
Perhaps you can work it out using the latitude?
>Very nice, but I think you are saying that superinsulated houses need very
>little heat, from the sun or any other source. No argument there.
Yes - but a combination of superinsulation and solar may be optimum.

>OK. Were they hideously expensive?
No - I said they were then 2000 pounds more than the controls which
were built to pretty much bog-standard energy-wise. 

>Do you mean 75 m^2 on each floor, ie 1600 ft^2 of floorspace in the house,
>or 75 m^2 altogether, ie 800 ft^2 of floorspace?
Um, I was hoping you wouldn't ask  :-)
Looking at the information I have I would say the value is a bit
greater than 75, but is the total.  Therefore I would probably
reassess the  house value at <100k but I still think that 2000 is not
particularly large as part of that considering the gains.
Total energy saving then ~ 100 a year on control - both were fitted
with high efficiency boilers.
You might have got a better deal from the bank in this case -
(remember solar gain was minimised), but is that the whole point?

---

From: [email-masked] (gcp)
Date: Thu, 30 May 1996 19:28:43 GMT

>satisfy my own curiosity, I shall attempt to find out more.

The item on solar heating was broadcast on SCIENCE NOW, tx:04/05/96, 
Radio Four.
You can contact the designer direct:
Dr Kerr MacGregor
Mechanical Engineering Department
Napier College
Edinburgh
EH14 1DJ
If you would like a transcript of the programme please send a cheque
for 
3.00, made payable to British Broadcasting Corporation, to:
Science Now
Room 7079 Broadcasting House
London  W1A 1AA

Bit of advertising for the Beeb there.  :-)
I do have other things to do, so feel free to make your own enquiries
in the meantime!