passive solar design presentation

Passive Solar Design: As green as green building gets

Recalling what we’ve forgotten.

Where we want to goProvide 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 NutshellThe 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 1Choose a site with good solar exposure

Passive Solar Principle 1– On our site, we had to take down some eucalyptus trees and

plant lower canopy trees.• This provided both sun and food.

Elderberry

Mulberry

Macadamia

Passive Solar Principle 1To 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.

Passive Solar Principle 1Altitude angles

June 22

March 21

December 22

Passive Solar Principle 1Bearing angles, summer:

Passive Solar Principle 1Bearing angles, winter:

Passive Solar Principle 1A Solar Pathfinder knows all this and will determine where

the shadows fall throughout the year.

Passive Solar Principle 2Orient 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

Passive Solar Principle 3• 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)

Passive Solar Principle 3…• Locate most windows on the south side of a house

– 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)

Passive Solar Principle 3…• Locate most windows on the south side of a house

Passive Solar Principle 4• 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.

Passive Solar Principle 4…

– 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

Passive Solar Principle 5• 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

Passive Solar Principle 5No overhang:

Black Shaded

White Unshaded

Gray Partially shaded

Green Sun below horizon

Blue Sun above horizon

Passive Solar Principle 5With 2 foot overhang

Black Shaded

White Unshaded

Gray Partially shaded

Green Sun below horizon

Blue Sun above horizon

Passive Solar Principle 5…• Provide overhangs and shading to regulate solar gain

Overhang calculated for 32 degrees north latitude

Passive Solar Principle 5…• Provide overhangs and shading to regulate solar

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

Passive Solar Principle 5…• Provide overhangs and shading to regulate solar

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

Passive Solar Principle 5…• Landscaping: nature provides smart shading

Mulberry in winter

Shades in summer

Passive Solar Principle 5…• Un-shaded south facing glazing needed this

overhang.

Passive Solar Principle 5…• Jacaranda now cools the home in summer when

west facing rooms would overheat.

Passive Solar Principle 6• 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

Passive Solar Principle 6…• Provide sufficient, properly situated thermal mass


– “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 ?

Passive Solar Principle 6• 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.

Passive Solar Principle 6• 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.

Passive Solar Principle 6Thermal 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.

Passive Solar Principle 6Thermal 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

Passive Solar Principle 7• Insulate walls, ceilings, floors foundations and

windows– In other words, build a quality envelope with low

uncontrolled conduction, infiltration and radiant gain.

Passive Solar Principle 7…• Insulate walls, ceilings, floors foundations and

windows

Passive Solar Principle 8• Quality water barrier to protect insulation from

moisture

Passive Solar Principle 9

• Air barrier: build tight ventilate right.

Passive Solar Principle 10• Design thin: each room should be heated--directly or

indirectly--by solar heat

Passive Solar Principle 11• Avoid sun drenching: create sun-free spaces

Passive Solar Principle 12Back up heating: provide efficient, properly sized,

environmentally responsible back-up heating.– Tight ducts, etc.

Passive Solar Principle 13• Protect homes from winds by landscaping or earth

sheltering

Passive Solar Principle 14• Synchronize daily living with solar patterns.

ModelingLet’s set up two buildings

located in San Diego. One is “typical” construction, the other is Passive Solar.

Reference Case

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

-77%-43%

-16%

Comparing Energy Use: Passive Solar measures + rotated 90 degrees

-44%-34%

-11%

Comparing Energy Use: Passive Solar measures + moved to Tucson

-50%

-33%

-23%

Passive Solar design options

Summary1. 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.

Questions?

Dadla Ponizil-- BPI certified BA, ShellCalifornia Building Performance Contractor’s Association

Certifications:

•Building Performance Institute

•California Green Building Professional

•GreenPoint™ Rater

•Home Energy Rating Systems (HERS) rater

[email protected]

http://www.ponizilenergy.com/�

ReferencesThe Solar House: Passive Heating and Cooling, Daniel Chiras.The Passive Solar House, James KachadorianGreen From the Ground Up, David Johnston

Natural Remodeling for the Not-So-Green House, Carol Venolia & Kelly LernerThe Not So Big House, Sarah SusankaYour Green Home, Alex WilsonThe Timeless Way of Building, Christopher AlexanderThe Ecology of Commerce, Paul Hawken

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

http://www.susdesign.com/overhang_annual/�

passive solar design presentation

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