Talk:History of passive solar building design

Double Shell Envelope House
Suggested edits:

Lee Porter Butler's 1975 Double Shell thermal envelope design received wide publicity after the U.S. solar energy tax credits were created in 1978. Versions were on the cover of Better Homes and Gardens and Popular Science magazines.


 * (Any other peer-reviewed publications referring to this design?)

Lee misunderstood how and why his accidental double shell discovery worked:


 * 'Lee originally attributed the success of his design to:'. (Provide reference for Lee's alleged statement)
 *  'Further analysis by other researchers suggested there were flaws in the original design.' (Provide references to published editorials/commentaries of this)'
 *  (Attempt to achieve more neutral language directed to individuals)

''
 * He had an (unnecessary) rock bed under the house to store daytime heat (it actually interfered with the geothermal night time effect and slowed warming in the morning).
 * He used a lot of inefficient roof-angled glass (See [[sun path[[), which created a solar furnace in the summer and lost heat in the winter.
 * He often had an equator-side porch that shaded the lower floor where solar gain was needed the most.
 * He wasted a foot-and-a-half of space for the double north wall, and created a potential fire hazard.
 * Dark roofs and no radiant barrier was used, increasing summer cooling requirement.
 * He used a fireplace as backup, which drew in unconditioned outside air for combustion, and exhausted heat up the chimney.
 * Interior clothes dryers sucked conditioned air outside, and thereby drew in unflitered, unconditioned outside air.
 * Butler also falsely claimed that his double shell would work "everywhere" (which is obviously false near the poles).
 * 'Butler suggested his design could be used widely in a number of locations. Analysis suggested that this would be unlikely in regions near the poles' ('Falsely' may suggest a deliberate attempt to mislead')

''
 * He was discredited by scientific performance monitoring.


 * '' 'Formal performance monitoring revealed inefficiencies in the design'. ('Discredited' is a value-laden term and has negative connotations about Butler's integrity)

'' In 2008, there are several builders still duplicating many of Butler's errors, although few give him credit.


 * 'Several commercial builders have modeled their designs on the original concept without addressing the later criticisms.' (Provide referenced examples of building design that have demonstrated this.   The bigger issue is whether they have claimed credit for the innovation.

The double shell designs perform much better than conventional homes, but not as well as other isolated passive solar gain buildings have been proven to do.


 * (Require a citation which has formally compared double shell with other isolated gain designs)

Butler's original double shell had a lot of documented "dirty bath water" (above) that needed to be discarded, and therefore it created much controversy and was never well accepted by most architects or builders.


 * (Need to elaborate on 'dirty bath water'. Discuss other concerns about the design including cost / fire codes etc.  Discuss current methods that address this.  Provide editorials or references)

But, the essence of Butler's gravity-fed natural-convection flow loop concept is an excelent baby that has been nutured to maturity by others.


 * 'Butler's initial concept preceded a generation of similar designs that have continued to refine his work

When the U.S. Solar Energy Tax Credits were created in 1978, Larry Hartweg (a second generation energy research scientist working in one of the nation's largest energy research labs) used much help from his scientific collegues to refine the double shell design, remove all of Butler's above documented design errors, and build his own near-zero-energy double-shell home in 1979.[www.ZeroEnergyDesign.com]


 * 'An experimental house created in 1978 addressed the original issues with Butler's design. Anecdotal reports suggest marked improvements in efficiency and near-zero-energy performance. (Provide references of formal evaluation if possible. Eliminate reference to author - sounds like an advertisement.  If possible describe further the salient differences between the original design)

He became the most popular invited guest speaker at the huge National Energy Expositions, and the largets exhibitor building entire houses insdie the exposition buildings. At the recent U.S. Department of Energy / Oak Ridge National Laboratory Tenth Tri-Annual International Buildings Conference, Hartweg was invited as the most qualified speaker to prepare and present his popular Three Decades of Passive Solar Heating and Cooling Lessons Learned Workshop


 * (See above and advertising)

The following discussion applies to northern latitudes from roughly 25 to about 64 degrees. North and south are reversed in the southern hemisphere.

In a direct-gain passive-solar building, verticle glass on the south side can make southern rooms uncomfortably warm when the winter sun is low, and cold north wind make northern rooms uncomfortable cold, especially those with windows.

The double shell creates a recirculating air flow path that uses warm (less-dense) air rising in a south-side solarium, and cooler (more dense) air falling on the north side to create pressure differentials that automatically move excess solar thermal gain from the south to the north side of the building - equalizing the temperature with no mechanical equipment or thermostats. The large the temperature differential, the faster the air move, up to a very-high cfm velocity.


 * 'The double shell assists a natural convection loop between the heated south-side solarium and cooler north wall' (Attempt to combine this with terminology from pre-exisiting principles)

In the summer, shading devices eliminate all direct solar gain. Vents are opened at the top of the well-insulated attic (see cool roof], [[green roof, and radiant barrier). Fresh air intake uses ambient temperature Earth to cool and dehumidify replacement air at the base.

Part of why a double shell works is the increased total R-value of two walls, instead of just one.


 * 'It has been stated that the efficiency of the double envelope is related to the total R-value of the two walls' (Provide citation)

But actually it is the thermal buffer zone (TBZ) between them that is the most thermally-effective design pattern element.


 *  'However, it has been suggested that the convection air space provides an additional buffer to heat transfer'. (TBZ is a neologism which is not broadly understood.) 'It is known that the rate of heat transfer is proportional to the temperature gradient between two compartments (Fourier's law} The addition of an intermediate compartment retards the net transfer rate of heat.

On cold winter days, the TBZ is tempered with solar-heated air that is often above 85 degrees F, when outside air is below freezing. On winter nights, the TBZ is buffered by warm ambient-temperature Earth under the floor (which is partially recharged by the natural convection flow loop during each winter day). In the summer, the TBZ is tempered with near-ambient-temperature Earth replacment air, and warm air exhaust by natural convection - fans, thermostats and electricity may not be required in many moderate locations.


 *  'During the day, sufficient heat is drawn from solar radiation to significantly raise the temperature of the air space and be stored in the earth-coupled thermal mass.  'At night the air space continues to be maintained from the heat stored earlier in the earth [[thermal mass]' (Use pre-existing terminology).   

The interior living quarters "think" they are in a place with moderate outside temperates (even when the seasonal temperatures are extreme).


 *  According to anecdotal reports, despite extreme external temperature, the interior temperatures are maintained at a comfortable level.(Alternatively state a formal evaluation that has been performed)Dymonite (talk) 10:34, 17 January 2008 (UTC)

Building costs
Having trouble finding an independent source to back up this reference. Only reliable stats I can find is:

http://www.eia.doe.gov/oiaf/ieo/enduse.html

Says that industry (including construction) is 37%, transport is 20%, residential 11%, commercial 5%. Construction + building consumption may exceed everything else but hard to tell from this.Dymonite (talk) 13:31, 17 January 2008 (UTC)

TBZ house vs Direct mass/high mass/high glazing design
Has there been any other analysis of what may contribute to how a TBZ house functions?

There are a number of uncontrolled factors that could have improved performance unrelated to the convective barrier:


 * High amounts of glazing - increased solar gain
 * High amount of thermal / earth coupling mass in the construction - increased heat storage

Has a conventional direct gain configuration with the same amount of glazing/thermal mass been tested against a TBZ system?

How does the TBZ significantly alter heat transfer from the living space? Still air has low thermal conductivity but moving air increases heat transfer through convection. Is the TBZ just preferentially shedding stored heat from the thermal mass rather than 'buffering' the interior air. What are the heat losses at night from the extensive north glazing?

If the TBZ is part of the conditioned space e.g. north zone = solarium, south zone = utilities area, is it technically a double envelope system? Or is the function of the TBZ predominantly a passive heat distribution system?

How livable would the TBZ north zone be if had no significant thermal mass?

Presumably earth coupling in a TBZ requires a sub-floor. How would this compare simply with exposed floor mass in a conventional direct gain system?Dymonite (talk) 10:38, 21 January 2008 (UTC)

Historic observations
Hippocrates - his treatise on 'Air, Waters and Places' not 'Air, Light' contains what would sound like a pre-scientific discussion on the relationship between natural phenomena (sunlight, water, wind) on disease rather than a specific tome on passive solar design. A direct quote will probably be required from his Treatise to demonstrate his appreciation.

Cites of Priene/Zippori - it is not clear whether these specific cities were designed in specific regards to solar orientation or other considerations were made. For instance in the Priene Wikipedia entry, the city was based on the foothills facing an ancient sea. More evidence is needed to show that an entire generation of ancient Greek cities demonstrated passive solar design. For instance I could say that 1/2 of the houses on my street face north and therefore they appreciated the value of proper orientation. Dymonite (talk) 10:24, 31 January 2008 (UTC)

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