Seek Passive Solar Design FAQ/Guide

Question:

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        outdoors      glazing |            open damper to heat   house                              w                              w  R0.5 concrete – sunspace air resistance                800 Btu/ft^2  w                    per day   |             |      —       |             |      —       |                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 … read more »

Response:

- Hide quoted text — Show quoted text – 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 :-)

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 provide less than half the heat for your house.

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] 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.

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

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

Just the opposite of what you state above.    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…

How did you arrive at that size?  And what material would you use for the thermal mass, as energy capacities vary widely?    The sunspace floor is a good location for thermal mass. The mass floors    should be dark in color.

Like brick?  :-) 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.

Yes, a water wall is an effective thermal storage device. – Hide quoted text — Show quoted text –      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.

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] 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…

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. 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.

This is a little over-general, as passive solar mistakes have borne out in the past. http://solstice.crest.org/renewables/solrad/index.html 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.

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. 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.

A fairly well-insulated house. 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.

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. 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.

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. There are a few more little details to check, but this isn’t rocket science, 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. 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 :-)

You are making specious claims.  Trombe wall effectiveness has been proven with empirical data. – Hide quoted text — Show quoted text – 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,

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Response:

– Hide quoted text — Show quoted text – … 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 :-) 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 :-) Or if you want your "main heat source" to provide less than half the heat for your house. 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… :-) 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. 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… – Hide quoted text — Show quoted text –    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. I fail to see the advantage of such a system; 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.    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. 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 :-)    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… 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    should be dark in color. Like brick?  :-)

Sure, if you sell bricks :-)    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. Yes, a water wall is an effective thermal storage device.

It is indeed, if it has insulation between itself and the outside world. 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. 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… (?) 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… 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 (?) – Hide quoted text — Show quoted text – 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. This is a little over-general, as passive

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Response:

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. 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.      Passive Solar Industries Council      1511 K St., #600      Washington, DC 20005      (202) 628-7400 You may have visited here already, but http://www.greenbuilder.com/Sourcebook/PassSolGuide1-2.html gives a lot of overall design clues. Some of the variables involved in such a design include; 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 is the solar insolation in your area and when does it occur? http://solstice.crest.org/renewables/solrad/index.html 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). If anybody has any additional info, I’d be interested as well. Regards, Will Stewart

Response:

[etc - snip!] 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.    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.

(sounds like a solar panel to me :-) 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! 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? I’m presently looking for windows that block UV radiation… 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… 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 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.

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.

Response:

[etc - snip!]

Good snip.    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. (sounds like a solar panel to me :-) Yep.

But they are also very expensive, and normally live on the roof, which makes them fundamentally different from these inexpensive sunspaces. 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. (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 :-) 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… 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. 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. 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.

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. 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. Or it might be clear mylar glazing, slightly more expensive and longer lasting, if this inexpensive sunspace leans against a house wall. 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. And to me, a "low-thermal-mass sunspace" can also be $1/ft^2 clear plastic "solar siding," ie a sunspace 2" thick, that takes the place of, say, vinyl siding on the south wall of a house, with no sheathing underneath and only 3 1/2" of insulation in a 2×6 wall. This costs _less_ than normal house construction (no sheathing, less labor), and it collects solar energy. 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. I am going to suggest that a dedicated sunspace need not be part of the design for space heating.

I agree. 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.

Absolutely true. But at what price? 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.

I agree, IF you are willing to live with very few windows. 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? 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.

What a strange and excellent idea :-) 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

They are also more expensive… Cheers, Nick

Response:

[etc - snip!] 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.    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. (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. – Hide quoted text — Show quoted text – 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’m presently looking for windows that block UV radiation… 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… 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. – Hide quoted text — Show quoted text – 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. 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

Response:

- Hide quoted text — Show quoted text – [etc - snip!] Good snip.    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. (sounds like a solar panel to me :-) Yep. 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. 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. 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 am going to suggest that a dedicated sunspace need not be part of the design for space heating. I agree. 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. 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 winter sun I think it is possible to reduce space heating costs to 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. – Hide quoted text — Show quoted text – On the latter a recent design here in the UK (Scotland in particular) has

… read more »

Response:

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. (sounds like a solar panel to me :-) 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.

I suppose they might, but why would you do that? I might attach my 30 x 20′ sheet of very clear Mylar only around the perimeter of a sunspace, stretched over some curved galvanized pipes. If you were to look in a catalog, like http://www.hortnet.com, or visit your local commercial greenhouse supplier, you’d see some nice aluminum extrusion clamps like UNI-LOCK (Geiger 33-SL16, $0.80/linear foot on page 101 of their current catalog) which make recycling 5 cent/ft^2 poly film as easy as changing a big bedsheet (on a calm day :-) every 3 years, or less often, if you hang some 80% greenhouse shadecloth (eg Stuppy’s 23691 polypropylene product at $0.139/ft^2) over the outside in the summer and inside in the winter. Only 2% of the oil in the US is used to make plastic, BTW, and most greenhouse poly film IS recycled. Unfortunately you won’t find the very clear Mylar in either catalog yet… We have to wait a few months until Bayer or Dow start making it again, and Armin and Replex plastics start distributing it again. This polyester film was once used extensively in 100% solar-heated Japanese greenhouses, but people stopped making it for a while, because oil was so cheap. It should last longer than poly film eg 5-10 years, longer with a seasonal shadecloth cover, and cost a bit more (10-20 cents/ft^2 ?) For now, it seems reasonable for reasonable and serious alternate energy enthusiasts (if any) to start with greenhouse poly film over curved galvanized pipes, and upgrade to Mylar some time in the next 3 years. 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.

If you look on page 106 of the Geiger catalog, you will see their small 01-4C442 blower and 01-2CK610 blower fan installation kit used to inflate two layers of poly film for better insulation and protection from wind fatigue. This particular technique was invented at Rutgers years ago, and it works, in winds short of hurricanes. Most growers let their 50 Watt blowers run all winter, keeping their $2000, 3,000 ft^2 greenhouse walls inflated. But nowadays, now that electricity is more expensive ($1/Watt/year), it seems better to have a wind switch, something made with an outdoor microswitch from Grainger, and just turn on the blower when it’s windy outside. Once inflated, the poly pillows should stay inflated for a few minutes. It seems even better and cheaper and more ephemeral, as Bucky Fuller used to say, to use only one layer of plastic film for a lean-to-sunspace on the south wall of a house, and put a transparent motorized damper in the bottom half of one window and a window fan and a plastic film one-way damper in the upper half of another window, blowing air into the house, and turn on the fan and open the motorized damper during the day when the house is cooler than 68 F and the sunspace is warmer than 80 F, say, using two thermostats in series with the fan, and turn on the fan with the damper closed whenever the wind blows hard and the house does not need heat, to make a slight vacuum in this reasonably airtight sunspace. and 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.

Heavens. Thousands of greenhouse growers gone wrong… 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.

I have no desire to interfere with your twice-daily rituals, but you haven’t yet answered my question about the effect of air leaks around the edges on the actual R-value of those tracked and easily-movable and inexpensive (?) curtains, which would insulate several times less effectively than a house wall, IF they worked perfectly. Consider if you will, Will, or if you can, the effect of a 1 CFM air leak on an 8′ x 8′ "R8" curtain in front of an R2 window on a 30 F day. Chacun a son systeme. My taste is for inexpensive, high-performance, automatic systems. Too bad you could’nt have come down this weekend for our yearly Tour of Solar Homes.

If I’da knowed I’d been there. I like those tours. Helped run some, even. 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).

Lovely. I saw something like that in a barn conversion designed by architect Harrison Frakur in Washington’s Crossing, PA, on a solar house tour in 1980. It was very dramatic, as many architectural entertainments are. It was only two layers of partly-aluminized mylar film, a single piece that deployed as a U shape with tracks on the sides and a dead-weight roller at the bottom, and a motorized roller at the top. These were over some 8 x 8′ sliding glass doors mounted way up on the west wall of a 3 story barn with a cathedral ceiling, completely open above, and when the sun went down, they would come down too, automatically, "reducing the heat loss by 90%." It was said you could still see through them dimly when they were closed. They were open when I was there. I wonder if these are a commercial product now, and how much they cost, and what their real R-value is, including air leaks… You still haven’t answered my question about which brand of movable window insulation you plan to use, and how much it costs, including installation. How about an insulated frame wall with a fan or a motorized damper and a couple of thermostats, for "movable window insulation"? Those barn people had a woodstove in the middle of their barn, with a bare black exposed 30′ chimney, going right up thru the ceiling, dramatically. They could well have used a double or triple wall fluepipe with a fan at the top to blow down outside air or air from the ceiling inside the outer pipe… I wonder if you will have such an air-air heat exchanger in your house. Harder to do this with a fireplace, especially without a fan, since to make it work naturally, the air outlet from the house needs to be above the air inlet to the house. But a small fan like that would have a high COP, and it would keep the flow from reversing on a summer day. What will your fireplace efficiency be, vs a woodstove? Do you care? The house had less than .2 ACH, was heavily insulated, and the occupants said their fuel bills were less than $30/month in winter.

Good. Unbelievable, even. Were they counting their electrical fuel bill? 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.

I agree. Perhaps we can more usefully talk about that when you understand how conduction and thermal mass work. And RC time constants. This time constant idea is useful. Once you learn it, you can instantly eyeball the solution to that simple differential equation, and find how the temperature of a passive solar structure changes with time, when the sun is not shining. Find the R, and find the C and multiply them together. Bang: 200 hours for that 4′ cube, 800 hours during a cloudy week, 53 hours for your new house. Here is your house starting a cloudy week in January in Richmond, where the average outdoor temperature is 36 F. Suppose the thermal curtains are closed 24 hours a day, and you are neither burning wood nor electricity, and the house starts off at 76 F, water walls and all. T(t) = 36 + (76-36) exp(-t/53), where t is in hours, ie        76 after 0 days,        61 after 1 day,        52 after 2 days,        42 after 3 days. 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.

I’d just say "Faith without works is dead." :-) Or maybe "Works without faith are dead." Or "10,000 growers can’t be wrong." Or "It’s my house, not yours." And stick out my tongue. – Hide quoted text — Show quoted text – 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

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and

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!) Yep. But they are also very expensive, and normally live on the roof, which makes them fundamentally different from these inexpensive sunspaces.

There’s inexpensive and there’s cheap  :-) Maybe a false economy? 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.

Didn’t I mention something about TIM somewhere? Me again: 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. 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. As I said: 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. 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!) – Hide quoted text — Show quoted text – These houses cost little more than a normal house Whoa!!! See above. 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? Read on (again): 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. 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.)

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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… (sounds like a solar panel to me :-) (I wrote that!) Yep. But they are also very expensive, and normally live on the roof, which makes them fundamentally different from these inexpensive sunspaces. 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.) 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. Didn’t I mention something about TIM somewhere?

I don’t recall that. What’s a TIM? Or is this your friend Tim? Me again: 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… even for houses orientated to minimise passive solar gain, addittional energy costs for space heating can be made insignificant. 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!

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? 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!

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

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? As I said: 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. I agree, IF you are willing to live with very few windows. 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? That in the RMI (Rocky Mountain Institute) these sort of windows 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 Whoa!!! See above.

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. 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. 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.

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. (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.)

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

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What we use for glazing is a tradeoff between aesthetics, cost, and replacement maintenance. A matter of personal taste, when all is said.

Smartest thing you ever said. Physics is not a matter of taste: panels in a sunspace gather more heat 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? 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.

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" 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…

Like ‘assuming the interior temperature remains at 72 F" and other ‘enshrouding’ assumptions of yours in the past. This is from a case study book published by the RIBA (Royal Institute of British Architects) – so it’s kosher! I suspect architects, even kosher ones.

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

You overestimate your flock… Cheerio, Will Stewart

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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!  :-) Didn’t I mention something about TIM somewhere? 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? Me again: 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…

Shown, as in built – real world! 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!

Otherwise it wouldn’t have been a test of superinsulation. OK. (Architects at work.) Where is Milton Keynes? 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. 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.

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. 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?

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? Is there a 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. As I said: 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. I agree, IF you are willing to live with very few windows. 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?

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. That in the RMI (Rocky Mountain Institute) these sort of windows 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?

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!) These houses cost little more than a normal house Whoa!!! See above. 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.

This was not theory, but real houses, and in Scandinavia they are fairly normal.  (They just cost a bit more to heat there!)

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Who is this UKsian gcp, anyhow? :-) argumentum ad hominem?  

I wasn’t attacking your character, just enquiring who you were. Will he/she unlurk,  ? Why, would that change your opinion of what I say?

I tend to believe people more when they are willing to identify themselves in public… Didn’t I mention something about TIM somewhere? I don’t recall that. What’s a TIM? Strange.  I had a short email correspondence with you about 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? 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! Otherwise it wouldn’t have been a test of superinsulation.

Can you explain this a bit more? OK. (Architects at work.) Where is Milton Keynes? Are these Cornwall houses, surrounded by palm trees and pirates? 52 3N  0 42W No.

OK… 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.

I wonder what the average temp and amount of sun that falls on a south wall is in the coldest month in Milton Keynes? But a superinsulated house is basically designed to operate (most of the time) without addittional space heating.

It sounds like these houses did :-) 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. Less than 0.1air change per hour (ventilation off). Demonstrated by pressure-testing and also tracer gas.

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. These were an off-the-peg Scandinavian system.

OK. Were they hideously expensive? Space heating costs were then 10 to 20 pounds a year.

VERY nice. 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? Semi-detached, two storey, three bedroom approx. 75 square metre floor area – pretty normal there.

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? Nick

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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. 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! Otherwise it wouldn’t have been a test of superinsulation. 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. These were an off-the-peg Scandinavian system. 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. Semi-detached, two storey, three bedroom approx. 75 square metre floor area – pretty normal there. 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?

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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. 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.

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!

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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.

So how about double glazing with two different materials?  I think a layer of polyethylene on the outside, and glass on the inside might be the best combination since pe is cheaper than mylar and with the glass inside you don’t need to block the longwave IR.  Or at these temperatures do you lose more from the transmission loss than you gain from the increased R value? Just thinking out loud :-) . Regards,

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– Hide quoted text — Show quoted text – … 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 :-) 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 :-) Or if you want your "main heat source" to provide less than half the heat for your house. 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… :-) 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. 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… – Hide quoted text — Show quoted text –    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. I fail to see the advantage of such a system; 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.    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. 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 :-)    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… 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    should be dark in color. Like brick?  :-)

Sure, if you sell bricks :-)    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. Yes, a water wall is an effective thermal storage device.

It is indeed, if it has insulation between itself and the outside world. 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. 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… (?) 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… 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 (?) – Hide quoted text — Show quoted text – 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. This is a little over-general, as passive

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- Hide quoted text — Show quoted text – 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 :-)

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 provide less than half the heat for your house.

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] 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.

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

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

Just the opposite of what you state above.    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…

How did you arrive at that size?  And what material would you use for the thermal mass, as energy capacities vary widely?    The sunspace floor is a good location for thermal mass. The mass floors    should be dark in color.

Like brick?  :-) 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.

Yes, a water wall is an effective thermal storage device. – Hide quoted text — Show quoted text –      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.

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] 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…

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. 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.

This is a little over-general, as passive solar mistakes have borne out in the past. http://solstice.crest.org/renewables/solrad/index.html 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.

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. 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.

A fairly well-insulated house. 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.

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. 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.

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. There are a few more little details to check, but this isn’t rocket science, 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. 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 :-)

You are making specious claims.  Trombe wall effectiveness has been proven with empirical data. – Hide quoted text — Show quoted text – 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,

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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        outdoors      glazing |            open damper to heat   house                              w                              w  R0.5 concrete – sunspace air resistance                800 Btu/ft^2  w                    per day   |             |      —       |             |      —       |                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 … read more »

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