Integrated Passive Solar Design: The Essence of a Green Building

Passive Solar Design:
As green as green building gets

Recalling what we’ve forgotten.

Where we want to go
Provide you with the concepts, background, resources and
motivation to integrate passive solar design into your
homes—both existing and future.

Roadmap
• The big solar picture
– Recalling what we knew

• Why we should do this?
– It’s not just about saving $

• Passive solar fundamentals
– Eating low on the food chain
– 14 principles of passive solar design

• Understanding thermal mass

• Some simulations
– SketchUp visualization
– Energy 10
– Insulated brick-in-the-sun demo

• Real world examples and applications
– How to “solar-passivate” existing buildings
– How to build the ideal passive solar house

Recalling what we knew
• Anasazi understood these
principles
– The Anasazi Indians built
stone and mud dwellings in
the deeply carved canyons
of the desert Southwest.
Nestled into south-facing
canyon walls under natural
overhangs, their homes
were sheltered from the
intense summer sun. Yet as
winter approached, the low-
angled sunlight dropped
below the overhang to
provide warmth.

Recalling what we knew
• The Greek city Olynthus
– 500 years before that, the ancient
Greeks utilized solar energy to
heat their homes. They
understood the value of sunlight
so well they treated solar access
as a legal right.

– The Greek city of Olynthus was
laid out so that homes would
have unfettered access to the
sun—5th century B.C. (Chiras, p.
6)

Today’s Engineers
• Estimates of energy savings resulting from the
application of passive solar design concepts are
provided by:
– ASHRAE (1984)
– DOE (1980/1982)
– LBL (1981)
– Ed Mazria, architect and sustainability authority (1979)

• “Passive solar heating, cooling and lighting design must
consider the building envelope and its orientation, the
thermal storage mass, and window configuration and
design.”

– From ASHRAE Handbook –HVAC Applications 2007, Ch. 33.

From the sun to us…free
• The sun delivers to us, free of charge, 300 BTU/h/sf (88W/sf) of clean green
energy.

Making a friend of the sun
• This is about 176 kWh to the average house,
every hour, every day it’s sunny.

– The key question is: friend or foe?

So why are we not building solar-integrated
passive homes today?

• It’s too expensive.
• It’s too complicated.
• Energy is too cheap so why bother.
• Inconvenient.
• We will lose jobs, hurt the economy.
• Fear—loss of control.
• What else?

Benefits
• Americans spend about 54 billion dollars each year heating and
cooling their homes (ignoring the externalized cost of energy—
extraction, distribution, pollution, climate disruption, etc.)

– Passive design can cut this cost significantly, and that’s just the
beginning.

Benefits…
• Natural conditioning (as opposed to air conditioning) is

– Simple (no moving parts)

Benefits…
– Elegant (based on physics and natural laws—
biomimmickry)

• Designs that follow natural laws tend to be more successful
over the long term.

Benefits…
– More efficient:

• Using energy with minimal conversions is fundamentally
more efficient (compare electric heater vs. solar heating)
– By the time we use it, electricity from coal is 15% efficient

• We want to eat low on the food chain to minimize waste

Benefits…
• Natural conditioning (as opposed to air conditioning) is

– More comfortable (radiant heating rather than forced, etc.)
• Quiet, solid construction, warm in winter, cool in summer,
gradual temperature variations

Benefits…
– Attractive:
• Large windows, sunny, daylit interiors, open floor plans

– Results in a healthier house (indoor air quality is higher since
we’re not circulating pollutants)

Benefits…
– Lower life cycle cost
• increased economic security with rising energy costs

• In our “moderate” climate zone, utility bills of $300-$500 per month
in the summer and $150-$250 in winter are common and will go up.

Benefits…
– High level of owner satisfaction with increased resale
value
– Green (environmentally sound)

• A quality home need not be green, but a green home cannot be
low quality.

– What else?

In a Nutshell
The fourteen principles that follow can be summed up in the four
golden rules:

1. Harvest solar heat by proper building orientation with respect
to the site and annual solar path.

2. Keep that heat in the building by proper air sealing and
insulation (quality envelope).

3. Store the heat (and level temperature variations in both
seasons) with properly designed interior thermal mass.

4. Use efficient backup heat for long overcast spells and
imperfect designs.

Passive Solar Principle 1
Choose a site with good solar exposure

– On our site, we had to take down some eucalyptus trees and
plant lower canopy trees.
• This provided both sun and food.

Macadamia

Elderberry

Mulberry

To make optimal use of the sun we do get, we need to
understand solar motion.

• The sun reaches higher in the sky in summer than in
winter.
– This is the altitude angle.

• The sun rises further northward in the summer than in the
winter.
– This is the bearing angle.

Altitude angles

June 22
March 21
December 22

Bearing angles, summer:

Bearing angles, winter:

A Solar Pathfinder knows all this and will determine where
the shadows fall throughout the year.

Orient the long, east-west axis of a house within 10 degrees east or
west of true south

– Solar gain vs. degrees deviation from true south:
• 0° 100%
• 22° 92%
• 45° 70%
• 67° 36%

Passive Solar Principle 2…
Orient the long, east-west axis of a house within 10 degrees east or
west of true south

– In warm climates, more than 10-degree deviation may cause summer
overheating, especially late in the day.

• “Choosing a good building shape and orientation are two of the most
critical elements of an integrated design.”
– Sustainable Buildings Industry Council

• Locate most windows on the south side of a house
– “The right amount” of south facing glass is the solar
collection system.
• The Three Bears principle (more is not better)


– At the lowest solar altitude (winter solstice) the sun
can penetrate 20 ft into a house.

– With “proper” overhangs, solar collection diminishes
in summer (higher solar altitude)

• Minimize windows on the north, west, and east sides
and “tune” them to the orientation
– Too much glazing on east and west walls causes
summer overheating.
– Too much glazing on north walls results in excessive
heat loss.

– In general, we want to tune our windows thus:
• South:
– High solar heat gain coefficient (SHGC), >0.5
• East, west:
– Low solar heat gain coefficient (SHGC), <0.4
• All exposures:
– Low U-factor (<0.4) to minimize heat loss (best
insulation)
– Low-e glass for best overall performance both
seasons

• Provide overhangs and shading to regulate solar
gain
– For additional shading on east and west sides, use
exterior window shading
– Vertical trellis or long horizontal trellis can reduce
western late afternoon sun

No overhang:

Black Shaded

White Unshaded

Gray Partially
shaded

Green Sun below
horizon

Blue Sun above
horizon

With 2 foot overhang

Black Shaded

White Unshaded

Gray Partially
shaded

Green Sun below
horizon

Blue Sun above
horizon

• Provide overhangs and shading to regulate solar gain

Overhang calculated
for 32 degrees north
latitude

gain

– Choose roof and wall colors and emissivities that
reduce heat gain.

– Use interior color selection that brings solar heat and
daylight deep into the interior

gain
– Solar-integrated landscaping
• West and east side evergreen trees
– Summer cooling and winter heating (cut wind)
• South side deciduous trees
• Minimize heat-generating hardscapes and heat
island

• Landscaping: nature provides smart shading

Shades in summer

Mulberry in winter

• Un-shaded south facing glazing needed this
overhang.

• Jacaranda now cools the home in summer when
west facing rooms would overheat.

• Provide sufficient, properly situated thermal mass

– This is the critical element that deserves special attention

– “The basic strategy is to design the house so that its own
masses—mainly walls and floors—are so placed, proportioned,
and surfaced that they will receive and store a large measure of
incoming solar energy during the daylight hours and will gently
release this stored heat to the house interior during the night
hours or cloudy days.”

– Peter Van Dresser, Passive Solar House Basics


– “Light-colored walls nearest solar glazing reflect light
onto dark-colored thermal mass located deeper within
the structure to ensure greater and more even
distribution of heat.”
– Daniel Chiras


– The higher the density, the higher the heat storing capacity up to
about 4” thick.

Material Density (lbs/ft3)
Concrete 140
Concrete block 130
Clay brick 120
Lightweight concrete block 110
Adobe 100
Sheetrock ?

• How much thermal mass?
– We want the south-facing glazing area to be in proportion to the
thermal mass --the mass-to-glass ratio.

– Determine the glazing-to-conditioned-floor-area ratio (Gs / CFA):
• This is total solar glazing area (ft2) divided by the conditioned floor
area (ft2)

– The first 7% of this ratio is accommodated by the incidental
thermal mass (flooring, drywall, furniture, tilework, etc.)

– If the Gs / CFA exceeds 7%, then we need additional (intentional)
thermal mass.

• How much thermal mass?

Thermal Mass type Portion required

Sun-direct mass 5.5 ft2 per foot Gs

Sun-indirect floor mass 40 ft2 per foot Gs

Sun-indirect wall mass 8.3 ft2 per foot Gs

Where Gs is solar glazing area (ft2). Floor and wall mass must be 4”-6”
thick.

Thermal mass approximation example:

• You’re building a 2,500 sf house with 275 sf of south-facing glass.

• 7% of the CFA = 175 sf, so this amount of solar gain is
accommodated by the incidental thermal mass.

• The remainder, 275 -175 = 100 sf must be intentionally “massed”


• Here are the three options:
– Use solar-direct floor area:
• 100 x 5.5 = 550 sf of sunlit slab
– Use solar-indirect floor area:
• 100 x 40 = 4,000 sf of unlit floor slab
– Use solar-indirect wall area:
• 100 x 8.3 = 830 sf of unlit walls


• The most practical choice would be a combination of these three
thermal mass elements designed into the overall structure and
aesthetic.

• So let’s say we get 50 feet of the Gs from slab that we were going to
carpet. We could tile it or stain and seal. This requires

– 50 x 5.5/1 = 275 sf of exposed slab area. So we could uncover
and treat a 28 ft x 10 ft strip of sunlit slab near the windows, for
example.

Thermal mass approximation example, continued

• We can get 25 feet from indirect slab:

– 25 x 40/1 = 1,000 sf of indirectly lit floor slab. Perhaps the kitchen
or family room with some floor tiled or partially covered by throw
rugs. Using flexible coverings like throw rugs permits adjustments
to varying conditions.

• The remaining 25 feet of Gs could be indirect thermal walls:

– 25 x 8.3/1 = 208 sf of unlit wall area

• Insulate walls, ceilings, floors foundations and
windows
– In other words, build a quality envelope with low
uncontrolled conduction, infiltration and radiant gain.

• Insulate walls, ceilings, floors foundations and
windows

• Quality water barrier to protect insulation from
moisture

• Air barrier: build tight ventilate right.

• Design thin: each room should be heated--directly or
indirectly--by solar heat

• Avoid sun drenching: create sun-free spaces

Back up heating: provide efficient, properly sized,
environmentally responsible back-up heating.
– Tight ducts, etc.

• Protect homes from winds by landscaping or earth
sheltering

• Synchronize daily living with solar patterns.

Modeling
Let’s set up two buildings
located in San Diego. One
is “typical” construction, the
other is Passive Solar.

Comparing Energy Use: No
changes

With Passive Solar Measures
• Applying the following measures:
1. Tuned windows (not optimally
distributed)
– North, East, West:
– U = 0.286
– SHGC = 0.34
– South:
– U = 0.47
– SHGC = 0.77
2. Overhangs
– Set to 32°NL
3. Thermal mass
– 244 sf exposed slab equivalent

4. Insulation
– R23 walls
– R60 ceiling

Comparing Energy Use: Passive
Solar measures applied

-16%

-43%
-77%

Comparing Energy Use: Passive Solar measures + rotated
90 degrees

-11%

-34%
-44%

Comparing Energy Use: Passive Solar measures + moved
to Tucson

-23%

-33%

-50%

Summary
1. Harvest solar heat by proper building orientation with respect
to the site and annual solar path.

2. Keep that heat in the building by proper air sealing and
insulation (quality envelope).

3. Store the heat (and level temperature variations in both
seasons) with properly designed interior thermal mass.

4. Use efficient backup heat for long overcast spells and
imperfect designs.

Dadla Ponizil-- BPI certified BA, Shell
California Building Performance Contractor’s Association
Certifications:
•Building Performance Institute
•California Green Building Professional
•GreenPoint™ Rater
•Home Energy Rating Systems (HERS) rater
www.PonizilEnergy.com
760-487-1776
dadla@cox.net

References
The Solar House: Passive Heating and Cooling, Daniel Chiras.
The Passive Solar House, James Kachadorian
Green From the Ground Up, David Johnston
Natural Remodeling for the Not-So-Green House, Carol Venolia & Kelly Lerner
The Not So Big House, Sarah Susanka
Your Green Home, Alex Wilson
The Timeless Way of Building, Christopher Alexander
The Ecology of Commerce, Paul Hawken

Overhang calculator: http://www.susdesign.com/overhang_annual/
Energy-10: Sustainable Building Industries Council

Integrated Passive Solar Design: The Essence of a Green Building

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