1

Properties and Methodology of Earth Structures

GSD 6400: Energy and Environment

Michelle Addington

John Middendorf

Harvard Graduate School of Design

January 2001

2

Abstract

Earth construction offers benefits often under utilized in the developed world, and

global energy concerns encourage the use of low-embodied materials such as earth.

Understanding the material characteristics of soil can assist in the use of earth as

an ecological on-site building material. Earth is modifiable using additives that can

be added to obtain desirable properties, and earth construction is possible with

a wide variety of building methods for potentially diverse architectural expression.

The thermal storage properties and humidity balancing effects of earth can be an

important component of passive design.

Index

Introduction/Embodied Energy

Earth as Material

Building Methods

Thermal and Comfort Aspects

Design Considerations

Appendixes

Bibliography

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Introduction

Earth is one of the oldest architectural materials, dating back 10,000 years,

with archeological evidence of earth construction found in the earliest cradles of

Middle Eastern and Asian civilizations. The Egyptians, Greeks and Romans

all developed interesting

methods of building with

earth, not just for housing

and storage, but also for

grand monolithic struc-

tures. Earth is one of

the most widely used

construction materials in

human history, and every

continent has a heritage

of building with earth.

Today, it is estimated

that more than two billion

people live in buildings con-

structed of earth.

Why Earth?

Earth as a building material is available everywhere, existing in many different com-

positions that can be processed in a myriad of ways. In developing countries, earth

construction is economically the most efficient means to house the greatest number

of people with the least demand on resources. In developed countries, people are

re-discovering the beneficial thermal comfort and healthy aspects of earth walls.

In addition, earth structures are

completely recyclable with mini-

mal resource requirements. All

over the world, the awareness of

the embodied energy of materials

and the global impacts of carbon

dioxide emissions encourages the use of low-embodied energy materials. It is

clear that the use of earth for the built environment will continue to be a strong

component in the future of humankind.

Above: Egyptian mud-brick storage rooms (3200 years old).

Above: Modern Rammed Earth Buildings in Australia

Above: Village in Yemen

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Energy Considerations

According to the Environmental Resource Guide, produced by the American Institute

of Architects, more than 30% of the energy consumed in the United States goes to

making and maintaining buildings. This includes both operating energy--the energy

required for space heating and cooling, lighting, refrigeration, water heating and

other building functions--and energy embodied in the physical structure. Earth

construction can reduce both categories of energy requirements.

Embodied Energy

Although most earth construction methods are more labor intensive than other

methods of construction, earth walls are significantly lower in embodied energy than

other structural materials. Energy costs related to the transportation of building

materials can be reduced with the use of materials found on or near the site. To

prepare earth for building, only a fraction of the energy needed for the production,

transport, and handling is required compared to timber or reinforced concrete.

Above: Embodied Energy of common building materials

Comparison of Masonry Materials

In 1984, Paul McHenry compared the embodied energy of common masonry materi-

als, and found that even mechanically processed adobe bricks had significantly less

embodied energy compared to bricks and concrete. In addition, the use of adobe

avoids the localized atmospheric detriments of concrete production. For comparison:

PRODUCTION ENERGY COSTS OF MASONRY MATERIALS

Common Fired Brick: 218 Btu/in3

Concrete Block: 28.3 Btu/in3

Adobe Brick: 4.46 Btu/in3

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Earth as Material

In order to understand the process of building with earth, it important to understand

the mechanics of the material and how to make best make use of the soil on site.

This requires a close look at the macro-structure of soil and an understanding of

the properties that make it a viable building material. If necessary, on-site material

can be modified appropriately by either refining or adding material brought to the

site such as sand or lime. Even with a sizable proportion of the material is brought

in from other sources, a considerable overall energy savings can be achieved. As

in all architectural efforts, an in-depth knowledge of the material is essential for

good design.

Properties of Soil

Soil is the result of erosion of rock. The characteristics of soil depend on the

transformation from the parent rock, which involves physical, organic and chemical

processes that take place over geologic time periods. Soils derived from a strong

parent rock (e.g. granite) create a strong material for earth construction. The

properties of soil vary depending on location, and different types of soil are more

appropriate for different construction methods.

Composition

Soil is a mixture of aggregates, sand, silt, clay, water, and organic material. Organic

material may consist of living flora and fauna, decomposing plants and animal waste,

and colloids other than clay including humus and bacterial glues. Generally in earth

construction it is advantageous to use soil without organic material, which gives a

musty odor and may decompose, although pure peat houses are common in some

parts of the world. Sub-soil dug at least 12” below the surface is generally free

from significant organic material.

Component Size

Components in soil larger than 20mm in diameter (pebbles and stones) are generally

not beneficial to the architectural properties of soil and can be sifted out prior to

using soil as a building material. Gravel between 2mm and 20mm in diameter can act

as a skeleton of the soil. Sand (particles between 0.06mm to 2mm in diameter), and

silt (particles ranging from 0.002mm to 0.06mm) are particles of silica, quartz

and other minerals, and are indistinguishable from a physical and chemical point of

view, yet have different swell and shrinkage properties. Generally, the smaller the

particle, the greater the swell in contact with water. Clay grains are the majority of

particles smaller than 0.002mm. Particles smaller than 0.002mm also exist in soil,

notably smaller quartz crystals silicates, and extremely fine crystals of limestone,

magnesium, and iron oxides. A simple test to

determine the ratios of each component can be

made by adding water and soil in a jar, mixing

thoroughly, and allowing to settle. The compo-

nents will separate according to size with the larg-

est on the bottom allowing a visual representation

of the proportions.

6

Water in Soil

There are several categories of water found in soil. Most water (free water) in soil

will be removed by a normal drying process, which can cause the material to shrink.

Pore water is water bound in the pores of the material and will evaporate at normal

temperatures over a longer period of time. Absorbed water is water electrically

bound to the grains of the soil and can only be removed if the soil is heated to

at least 100 degrees Celsius. Water is also found as hydroxyl groups bound to the

clay particles; this type of water is called the water of crystallization. The water of

crystallization is beneficial to the binding forces in the clay and will only be removed

from the soil if it is heated to 600 degrees Celsius.

Soil Binding Forces

Gravels, sand and silt enhance the compressive strength of the soil, but not

significantly to the binding forces. Clay, the smallest component, acts as the

primary binder in soil, just as cement acts as the primary binder in concrete.

Other less influential binding forces in soil result from the friction among particles,

cementation (the binding of particles as a result of chemical agents), capillary forces

(attraction between particles and water molecules trapped in the pores of the soil),

and Van der Walls’ forces (the electromagnetic cohesive force).

Types of Clay

Clay minerals, in chemical terms, are hydrated alumino-

silicates. Clays particles are elongated and platelike,

and therefore have a much greater surface area than

the other particles in soil, which are generally more

spherical. The flat structure of clay allows it to bind

strongly together, and while the larger particles in soil

are electrically neutral, particles of clay are generally

either negatively or positively charged, resulting in a

strong electro-chemical bond. There are three main

types of clay: kaolinites, illites, and montmorillonites.

Each has a different swelling response to water: whereas

kaolinites are generally stable in contact with water,

illite and especially montmorillonite clays are less stable

with water and swell considerably. In general, soil with

between 15 and 30% clay makes for good building

material.

Balanced Construction Soil

Suitable soils for construction purposes need to have a balanced amount of sand,

silt, and clay. Soil with excessive sands and silts will tend to crumble when dried out,

while soils rich in clays will shrink excessively and form cracks in the drying process.

Suitable testing of the soil is required prior to construction, and additional clay or

sand may need to be added to create a balanced natural building material.

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Properties of Soil for Building

The main properties to consider when using soil as a building material are the

potential for structural integrity related to density and strength, and the amount of

shrinkage as the material dries out. Material with too high a clay content will shrink

excessively when drying and cause cracking. Other advantageous factors of finished

soil include moderate moisture absorption, high resistance to erosion and abrasion,

and moderate thermal expansion/contraction characteristics.

General Indicators

Simple tests can determine a soil’s properties and consistency. One can be

performed by sampling soil that is as dry as possible (moisture content 15 to

30%) yet still able to be formed into a ball. Dropping the ball of soil from

head height onto a hard surface

will indicate general characteristics.

If the ball of soil explodes, it is

too sandy and cannot be used as

a building material. If it flattens

slightly and does not crack, it will

probably have too much clay and

must be thinned by adding sand.

A good soil will retain its shape

and crack only slightly after being

dropped. Another conceptual indicator of the soil is given by a cohesion test. The

cohesion of a soil can be measured roughly by first kneading moist soil and then

rolling it into a thread about 1/4 inch in diameter. The thread is flattened and

then pushed over an edge until it breaks. The length

of the material at breakage indicates the amount of

cohesion: if it breaks after a few inches, the material

has little cohesion and will require additional binding

agents (clay). If it breaks at more than 8”, the

material may have too much clay requiring additional

sand. Prior to building, accurate testing of the soil

properties of the site can be determined by digging

a trench two meters deep and taking soil samples

at varying layers in the trench. Composition of each

layer can be determined by a geotechnical labora-

tory, or by additional tests made with specialized

equipment. Often an optimal soil can be made by

mixing various quantities of individual layers. Other factors such as color may also

be modified by mixing soils found on site.

Density

Density and strength in soil are generally proportionally related, and higher densities

are preferred for thermal storage aspects. The density of freshly dug soil typically

varies between 1000kg/m3 and 1500kg/m3. Compatibility of a soil is the measure

of the soil’s potential to reduce its porosity to a minimum, and is measured by the

Soil Sampling. Right: too sandy. Left: good clay content.

Above: Cohesion test

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Proctor compaction test. To achieve maximum compaction, the soil must have an

optimal water content, which allows the particles to slide into a denser configuration

without too much friction. It is also possible to over compact the soil so that the

strength is compromised. Rammed earth after normal compaction will have a density

between 1700kg/m3 and 2200kg/m3.

Strength

The strength of dry building elements

varies depending on composition and

processing method. The quality and

type of clay, and the grain distribution

of silt, sand, and larger aggregates

affect the basic strength. Compres-

sive strength of processed soil can

vary from 300 to 700psi (for com-

parison, typical concrete varies from

2000 to 6000psi). Calculations on a

five story rammed earth house built in

1828 and still standing, it was found

that the maximum compressive force

at the bottom of the building was

only106psi.

Shrinkage

Controlling shrinkage can be a major

challenge when building with earth.

Shrinkage is related to the water con-

tent: soil swells when water is added and shrinks as the water dries out. Shrinkage

is highly dependent on the type of clay, and on the grain distribution of silt and

sand. Typical soil without additional additives will shrink between 3% and 12% with

wet mixtures, and between 0.4% and 2% for drier mixtures (such as soil used for

rammed earth or compressed adobe blocks). Generally, shrinkage can be controlled

by increasing the percentage of sand to the soil, and by increasing the drying time.

Other additives, including whey, straw and hair fibers, and gypsum, can also be

incorporated into the soil mixture to control shrinkage. The effects of additives are

not universal, and varying sources give contradictory information on the effects of

individual additives, especially regarding gypsum (hydrous calcium suphate). This

is likely attributable to the varying proportions of the types of clay found in earth,

which respond differently to different additives. Clearly this is a promising future

field of additional research.

Other Additives

Lime, cement and bitumen are common additives to soil. Cement in proportions

from 2 to 8% is used generally for sandy soils to increase stabilization, strength,

and durability. A slow drying time is required for cement stabilized soil, otherwise

the addition of the cement can result in detrimental effects. Non-hydraulic slaked

Above: 1828 five-story rammed earth building in

Weilburg, Germany.

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lime (CaOH)

2

is often used with clayey soils in proportions from 2-5%. Slaked

lime strengthens the binding action of the clay and limits the penetration of water

into the fine particles, reducing shrinkage. Quicklime (CaO) is also used, but is

more difficult to work with as it caustic and absorbs water quickly. Hydraulic and

agricultural limes have little beneficial effect on soils. Bitumen (2-3%) is often used

for soils with a low clay content to add to the weather resistance of processed

soil. Here again, different sources cite widely varying results of additives, and

specific testing is required on the local soils. Finally, other additives can be added

to enhance the thermal properties of earth. Earth itself is not a good insulator.

The use of a natural material like expanded perlite can enhance the insulating

properties.

Part 3: Building Methods

There are many methods of building

with earth, and the type of soil and

the building method should be consid-

ered together. For example, a sandy

soil may be more preferable for mono-

lithic construction, while a clayey soil

may be more appropriate for seg-

mented construction. The main types

of monolithic constructions include

rammed earth (known as pise de terra

in France), and poured earth. Mono-

lithic formwork can either be remov-

able or integrated into the structure

(lost form methods). Segmented con-

struction can include abobe (uncompressed dried bricks), compressed blocks, daub

(shaping earth using a built framework), and various ways of stacking wet soil with

balls of soil or extruded sections (cob, stranglehm, and direct forming). All methods

offer unlimited possibilities for unique architectural expression and effective thermal

design.

Several new technologies are being developed for earth construction. David Easton

has developed methods for spraying earth using existing gunite (sprayed concrete)

tools. The earth is mixed with concrete and walls of 16” thick can be produced by

spraying the earth on a formwork panel.

Above: Sliding Formwork for Rammed Earth

Left: Adobe

Site Work.

Right: Daub

Techniques

of laying

earth on a

framework.

10

Although pouring earth

into formwork is an old

technique, new interest is

sparked by the economics

and wide availability of

concrete mixing equip-

ment. In 1985, Ruhi Kaf-

escioglu from the Techni-

cal University of Istanbul

studied the effects of

gypsum and found it

to moderate shrinkage.

Recently, Michael Frerking

in Arizona has become a

proponent of building with

a poured earth/calcined

gypsum mix. Additional

retarders are added to

manage the gypsum’s set

times. Using concrete technology, a large house with 24” walls can poured in a

day. Poured earth using lost fabric formwork has been experimented with by Gernot

Minke and the Research for Experimental Building (FEB) center at the University

of Kassel, Germany, and the results offer an interesting surface textures. Further

research will determine the longevity of poured earth in lost fabric construction the

effects of the fabric on the humidity balancing factors of such construction.

A method being investigated by the author is using a lost form method using a

fabric box with one vertical surface made of rigid insulation for the external surface.

The insulating surface would also give structure to the container which then can

be filled with earth.

Above: Lost fabric formwork for poured earth.

Above: Fabric box with one side of rigid insultion

for building segmented earth wall.

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Part 4: Thermal and Comfort Aspects of Earth Construction

“There is a certain magic to living in buildings with thick earth walls. It’s hard to describe, but easy

to notice. Just take a step inside one on some warm summer day and you’ll feel it immediately. It’s

cool, of course—everyone knows adobe houses are “warm in winter and cool in summer” but there’s

something else, too, a little harder to put your finger on. “It’s quiet, feels somehow incredibly solid

and sturdy, very different from other houses, timeless even.” I once had a happy homeowner tell me

walking into her rammed earth house was like walking into her lover’s outstretched arms.

--from The Rammed Earth House, David Easton.

Comfort

In addition to the lower energy requirements of using earth mass for structure due

to its inherent thermal mass which can store the daytime heat for extended periods,

there are also significant advantages in terms of human comfort. Additional reasons

for why earth makes for comfortable interiors is seen is when you consider the 4

methods of how the body transfers energy form and to the environment:

? Conduction

? Convection

? Radiative

? Evaporative

Of these, the last two (radiative and evaporative) play an important role in earth

construction.

Radiative Heat Transfer

The benefits of a warm or cool wall contribute to human comfort significantly. For

example, on a cold day, occupants of a room in a traditional insulated timber house

with large windows can feel cold even if the air temperature in the room is 80

degree F. Similarly, people can feel hot in a room with a lot of hot surfaces even if

the air temperature is less than 65 degrees F. The characteristics of earth walls to

maintain average temperatures contribute to the radiative aspect of comfort.

Radiative Properties

Emissivity (e) and absorptivity (a) and are prop-

erties of a material which determine radiant

exchange of a surface with its environment.

Emissivity is the main factor which determines

the heat exchange response of long wave (ther-

mal) radiation. The emissivity is high (e =

0.9) for masonry surfaces. Radiation heat trans-

fer is measured by Boltzman’s equation which

indicates that the heat transfer is dependent

on the emissivity and the temperature to the

fourth power. From the mathematics we can

get an idea of the beneficial aspects regarding

comfort in having moderate interior surface

temperatures.

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Solar Absorptivity

Absorptivity, on the other hand, is the main factor in determining the temperature

response to the absorption of short-wave (solar) radiation, and is dependent largely

by color. The surface tempera-

ture can be measured by the

ambient temperature and the

amount of incoming solar radia-

tion:

T

sol-air

= T

o

+ (a*I/h

o

) - LWR

where I is the incident solar

radiation, h

o

is the external sur-

face coefficient, and LWR is

a function of the long-wave

radiation to the sky (~6

o

for

clear sky, 0

o

for cloudy sky).

The absorptivity for earth walls

allows them to absorb and

store the daytime energy.

Porosity-the Miracle of Earth Walls

Humidity is another major factor in

experiencing comfortable conditions.

The ability of earth walls to balance the

indoor climate by absorbing and releas-

ing humidity and thus creating a healthy

interior is unmatched by other materi-

als. Recent research by the University

of Kassel in Germany has shown that

the first 1.5cm thick layer of an unfired

mud brick wall is able to absorb about

300grams of water per square meter

of wall surface in 48 hours if the humid-

ity is increased from 50% to 80%. Com-

parison with other material are shown in

the chart. In addition, recent research

has shown that earth walls can actually

absorb air pollutants. The choice of

interior finish is critical if the absorption

quality of earth walls is to be preserved.

Gernot Minke recommends for aesthet-

ics and ease of cleaning casein (pure

or mixed with lime) or linseed oil as a

interior finish.

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Thermal Mass Basics

Thermal mass refers to materials

have the capacity to store thermal

energy for extended periods. Ther-

mal mass can be used effectively to

absorb daytime heat gains (reduc-

ing cooling load) and release the

heat during the night (reducing

heat load). The use of thermal

mass in shelter dates back to the

dawn of humans, and until recently

has been the prevailing strategy

for building climate control in hot

regions. Today, passive techniques

such as thermal mass are ironically

considered “alternative” methods to

mechanical heating and cooling, yet

the appropriate use of thermal mass

offers an efficient integration of structure and thermal services.

Heat Storage and Diffusivity

The basic properties that indicate thermal behavior of materials are the density,

specific heat, and conductivity. For earth and most masonry materials the specific

heat ranges from 0.2 to 0.25Wh/kgC. The total heat storage capability is related

to the density and volume of material (mass). Diffusivity is the measure of how

fast heat travels through the material, and is a function of the conductivity divided

by the product of the density and specific heat (units: area/time). The time lag

between outside and inside peak temperatures is a function of the thickness of the

material divided by the square root of the diffusivity. For solid masonry materials,

conductivity can be approximated as a function of density, though precise values will

vary according to moisture content :

k=0.072exp(1.35x(density/1000)).

Using these relations, we find that diffusivity has a non-linear relation to density.

For example, the diffusivity of 2200kg/m

3

earth walls (k=1.3) is only 1.8 times the

diffusivity of 600kg/m

3

(k=0.2) earth walls.

Thermal Time Constant

One of the more important mathematical constructs to imagine the behavior of

thermal mass is the Thermal Time Constant of an building envelope, defined as the

product of the heat capacity (Q) and the resistance (R) to heat transmission. The

TTC is representative of the effective thermal capacity of a building.

To calculate the TTC of an area, the heat capacity per unit area (Q

A

) is multiplied by

the resistance to heat flow of that area ( where Q

A

=thickness*density*specific heat,

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R=thickness/conductivity). In calculating the TTC

A

(TTC per area) of a composite

wall, the Q

A

R value of each layer, including the outside and inside air layers, is

calculated in sequence. The Q

A

R for each layer is calculated from the external wall to

the center of the section in question, thus:

Q

Ai

R

i

= (c

m

*l*p)

i

*(R

0

+R

1

+…+0.5R

i

)

For a composite surface of n layers, TTC

A

=Q

A1

R

1

+Q

A2

R

2

+…Q

An

R

n .

The TTC

s

for each surface is the product of the TTC

A

multiplied by the area. Glazed

areas are assumed to have a TTC of 0. The total TTC

total

of the building envelope

equals the sum of all TTC

s

divided by the total envelope area, including the glazing

areas. A high TTC indicates a high thermal inertia of the building and results in a

strong suppression of the interior temperature swing.

Example TTC Calculations

Diurnal Heat Capacity

The DHC is a measure of the building’s capacity to absorb solar energy coming into

the interior of the space, and to release the heat to the interior during the night

hours. The DHC is of particular importance for buildings with direct solar gain.

The DHC of a material is a function of building material’s density, specific heat,

conductivity, and thickness. The total DHC of a building is calculated by summing

the DHC values of each surface exposed to the interior air.

DHC

per area

=F

1

s

15

From Balcomb, the temperature swing can be

calculated from the DHC:

Delta T(swing)= 0.61Q

s

/DHC

total,

, where Qs is

the daily total solar energy absorbed.

Note that the DHC for a material increases

initially with thickness, then falls off at

around 5”. This behavior reflects the fact

that after a certain thickness, some of the

heat transferred to the surface will be con-

tained in the mass rather than returned to

the room during a 24 hour period.

TTC and DHC

Relative values of TTC indicate the thermal

capacity of the building when a building is

affected mostly by heat flow across the

opaque parts of the envelope (i.e., when it is unventilated, and when solar gain is

small relative to the total heat transfer through the building envelope). Relative

values of DHC, on the other hand, indicate the thermal capacity for buildings where

solar gain is considerable. The DHC also is a measure of how much “coolth” the

building can store during the night in a night ventilated building. Both measures

indicate the amount of interior temperature swing that can be expected based on

outdoor temperatures (higher values indicate less swing).

TTC and DHC Examples

Building which is externally insulated with internal exposed mass.

Here, both TTC and DHC are high. When the building is ventilated at night and

closed during the day, it can absorb the heat in the mass with relatively small indoor

temperature rise. Best for hot-dry regions.

Building with mass insulated internally.

Here, both the TTC is and DHC are low. The mass will store energy and release

energy mostly to the exterior, and the thermal response is similar to a low mass

building.

Building with high mass insulated externally and internally.

Here, the building has a high TTC, but a negligible DHC, as the interior insulation

separates the mass from the interior. When the building is closed and the solar

gain is minimized, the mass will dampen the temperature swing, but if the building

is ventilated, the effect of the mass will be negated. With solar gain, the inside

temperature will rise quickly, as the insulation prevents absorption of the energy

by the mass.

Building with core insulation inside two layers of mass.

Here the TTC is a function of mostly the interior mass and the amount of insulation,

and the DHC is a function on the interior mass. The external mass influences heat

loss and gain by affecting the delta T across the insulation.

16

Design Strategies

It is clear that with the many ways of forming earth,

a wide variety of architectural expression is possible.

Depending on the consistency of the soil, variations in

surface texture and color are also possible and modifi-

able. Good thermal design with earth follows the prin-

ciples of passive solar design, where mass is used in

areas which can absorb daytime heat gains. From the

analysis of thermal mass, it is also evident that insula-

tion can be used effectively on the exterior walls which

are not exposed to considerable solar gain, whereas

the south walls could be left uninsulated in moderate

climates to optimize external solar gain. Interior mass

can be optimized in areas exposed to direct sunlight

though the fenestration. Courtyard and other architec-

tural features may be considered.

Prior to the architectural design of

buildings with earth, it is important

to outline the general thermal perfor-

mance that is desired, for example,

in a hot climate, the parameters may

include:

•Slow rate of indoor heating in

summer (minimize solar gain).

•Fast rate of indoor cooling and venti-

lation in summer evenings.

•Higher indoor temperatures during

the day in winter.

•Slow release of stored heat during

winter night.

The outline of desired parameters can help integrate the design the ventilation

and cooling systems, window size and locations, and radiant heat systems. Other

factors to consider include acoustics, fire and earthquake resistance, and codes.

Many examples of architecture have proved that passive thermal engineering can

be integrated with the aesthetic design. Familiarity with the principles of the site

specific thermal aspects can help with optimizing choices.

Adobe Dome with skylight.

Above: Interior thermal “spine”.

Above: interior mass

walls near south glass.

Left: The plan of the original Pueblo Bonito in New Mexico

(built 900AD) has a southeastern orientation is aligned with

great precision to the angle of the winter solstice sunrise. This

orientation captures the maximum amount of winter sun when

warmth is needed. Behind the site on the North side is a tall

cliff which along with the orientation reduces the amount of

summer morning and evening solar gains.

17

Appendix 1: Computer analysis programs that include contributions of

thermal mass.

Sunrel (National Renewable Energy Laboratory)

A general-purpose thermal analysis program for residential buildings. The solution approach is

a thermal network using a combination of forward finite differencing, Jacobian iteration, and

constrained optimization. It was written to aid in the design of small energy efficient buildings,

where the loads are dominated by the dynamic interaction of the building envelope, the environment,

and the occupants. It is especially appropriate for buildings that incorporate energy efficient

design features, such as: moveable insulation, control of interior shading, energy efficient windows,

thermochromic switchable glazings, and thermal storage in Trombe walls, water walls, phase change

materials and rockbins. Energy efficient buildings tend to be more free floating than buildings which

are tightly controlled by large HVAC

systems, therefore, proper design is

essential for comfort and usability.

The goal was to create a program

that was simple to use with sophis-

ticated thermal models and yet

maintain flexibility to accommodate

additional computational modules by

researchers. Sunrel allows for the

description of the wall as composed

of one or more layers of material.

Each of these layers may consist of

either an R-value or a specified material described by its thickness, specific heat, density, and

conductivity. In this way, walls of almost arbitrary complexity may be treated. Additionally, if the

walls are part of an exterior surface and the user wishes to determine the effects of solar energy on

the wall, the azimuth, absorptance, and parameters for shading can also be specified.

Solar 5 (University of California at Los Angeles)

Displays 3-D plots of hourly energy performance for the whole building. SOLAR-5 also plots heat

flow into/out of thermal mass, and indoor air temperature, daylighting, HVAC system size, cost of

electricity and heating fuel. Only four pieces of data initially required (floor area, number of stories,

location, and building type), the expert system designs a basic building, filling in hundreds of items of

data; user can make subsequent revisions.

Energy 10 (Passive Solar Industries Council)

Design tool for smaller residential or commercial buildings that are less than 10,000 ft2 floor area, or

buildings which can be treated as one or two-zone increments. Performs yearly whole-building energy

analysis, including dynamic thermal and daylighting calculations. Passive Solar Industries Council.

BuilderGuide (National Renewable Energy Laboratory)

Design tool for residences that calculates annual heating and cooling estimates of loads based on

simplified, but validated, algorithms; especially suitable for evaluating passive solar houses. Uses

solar-load-ratio method (modified degree-day), diurnal heat capacity method, and simplified cooling

load method.

Micropas4 (Enercomp, Inc.) Energy simulation program which performs hourly calculations to estimate

annual energy usage for heating, cooling and water heating in residential buildings. Data is required

describing each building thermal zone,opaque surfaces, fenestration, thermal mass. Used extensively

for California code requirements. Calculates HVAC size and U-values.

Blast: (Building Systems Laboratory, University of Illinois)

Performs hourly simulations of buildings to provide accurate estimates of a building’s energy needs.

The zone models of BLAST (Building Loads Analysis and System Thermodynamics), which are based

on the fundamental heat balance method.

18

Appendix 2: A method of visualizing annual solar paths for design.

Above: Annual Solar Paths in relation to a building site.

By analyzing the visual representation of the sun paths from the winter to the

summer solstices, one can see how the building will experience solar gain throughout

the year. Programming can color-code of the sun paths depending on when daytime

gain is desired (winter), and when gain is undesired (summer). The color coded

paths can then be linked to color coded surfaces and shadows on the building. With

this visual information, architectural features can be modified to optimize thermal

performance, as well as the size and location of shading devices.

19

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