JPL Green Club Meeting27 September 2012Ann Tavormina 818-393-0581

DESIGNING A PASSIVE-SOLAR, FOSSIL-FUEL-FREE, GRID-NEUTRAL HOME

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High Level Goals•Return to individual research• Planetary science•Be surrounded by natural beauty•Get back to a rural environment• Truly dark night skies!• Live a healthful, sustainable lifestyle •Minimize fossil-fuel usage, direct & indirect• Home, Land Use, Transportation• Produce much of my own food, organically•Design for system maintainability • Be robust to infrastructure breakdowns•Devote more time to arts & music27 September 2012

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Near-term Objectives•Design and build a home that: • Enables comfortable living while stewarding the environment• Low carbon footprint (i.e. fossil-fuel-free home)• Takes advantage of California’s abundant sun and mild climate• Passive solar design (collect excess BTUs in winter; avoid them in summer)• Energy efficient design (attend to heat loss, in all directions, through all

surfaces)• Produces at least as much electricity as it uses (grid-neutral or better)• Active solar electric system• Is robust to power-grid outages and extended periods of cloudy weather• Backup heat source; backup power for critical systems

•Do it cost-effectively, so others see they can do it, too•Get the word out!• Blog construction, write articles, give talks!

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Why focus on fossil-fuel-free?

• Homo sapiens: 500,000 YA

• Homo sapiens sapiens (anatomically modern humans): 200,000 YA

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Big-picture Considerations• Desired climate (physical and political)?• How much humidity?• How much sun?• How much winter? • How long a growing season?• How red? How blue?• Desired population density?• How much land? • How much house?• One-story or two? • How many SqFt?• Grid-tied or Off-the-Grid?• Dig a well or use community water supply?27 September 2012

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Zeroing In• Kern County, Tehachapi, CA• Bear Valley Springs• Building Site:• Latitude: 35deg, 11.5min• Longitude: -118deg, 41.8min• Elevation: 3,750 ft• Rainfall: ~12.5 in/yr (LCF~21.5)

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Start with the Sun!• From “Sustainable by Design” website, determine sun positions through the year for the building site’s latitude/longitude• http://www.susdesign.com/sunangle/index.php

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Passive Solar Considerations• To optimize passive solar, orient house to true (not magnetic) North• Align the long axis of the house along true East-West line• The south side of the house is the “business” side of the house for

solar energy collection in winter – make sure you have GOOD SOUTHERN EXPOSURE!• Deep eaves (overhangs) provide protection from direct sunlight in summer • Clear (not low-e) glass on south side allows enough BTUs to enter during the

winter to provide daytime excess to store for nighttime use• Very important to provide night-time window insulation [good drapes (or better),

especially for south-facing “regular-e” windows]• Contain window area and use low-e glass on North side windows to

limit heat losses at night during winter• Contain window area and use low-e glass on East & West side

windows to limit morning and evening heat gain during summer• Collect local climate data, by month (ave. highs, ave. lows,

sunniness, etc) to support home energy balance/thermal model calculations

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The “Solar Slab” (goal: keep the furnace off overnight)• Developed and patented by James Kachadorian in the 1970’s • built by him through his company Green Mountain Homes in Vermont

for several decades • described in his book, “The Passive Solar House”, c2006• Purpose of solar slab is to provide sufficient thermal mass to store excess solar BTUs from winter days for use during winter nights.• Constructed of building materials that would be used anyway (at least in the Northeast) to build the home• trade a basement for a concrete foundation with built-in air channels

that provide • Sufficient total concrete mass to store the collected excess daytime BTUs and • Sufficient surface area via hollow concrete blocks to transfer BTUs into/out of

slab• Air circulation through the slab is both passive and active.• Thermal worksheets provided in book for energy balance calculations

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Draft Design with full-length “Solar Slab”

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Solar Slab Reduced by ~50% to reduce cost • Kept predicted daytime solar slab

temperature rise within recommended bounds (3 deg -> 6 deg)

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House “Section”, after reducing solar slab to approximately half original length• Deeper-dug center portion makes room for hollow-core

concrete blocks, laid north to south, with duct channel along center-line Center portion shows concrete blocks “end-on”• Right & left ends show insulated, encased duct lines under “regular” slab

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Key Design Trades (underscore indicates chosen option)• Ground-mounted solar electric vs. roof-mounted system• Grid-tied vs. off-grid for solar electric• Ground-loop Heat Pump/AC vs. electric FAU and whole house fan• 9-ft vs. 10-ft ceilings (~10% reduction in heated volume)• Attached garage or attached pottery studio (not room for both)• Solar thermal hot water vs electric water heater • House size – had to fit budget, with allowance for margin• Solar-slab size – whole length of house vs center section only

• PLUS: Get feedback on your design from friends, professionals, and others who have been down this custom-home road before you!• They’ll see things you won’t and• Will have learned lessons you don’t want to have to learn yourself!!

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Thermal Model – furnace should generally stay off• Kachadorian’s book provides sample worksheets to calculate heat

lost/gained given home construction and building location particulars.• R-value calculations for walls, roof, windows• Home Heat Loss Calculations for day and night, using local temperature data

(January is coldest month w/ average low ~36 deg; ave. high ~52 deg)• Solar heat gain, by month, using window performance values and published

“sunniness” and “atmospheric clarity” values • “Excess” BTUs generated in daytime are stored in the ~800 CuFt of concrete in

the solar slab (concrete heat capacity ~30.1 BTU/(CuFt*deg F)• Model predicts January daytime excess of ~143,000 BTUs • Solar slab has a thermal capacity of ~24,000 BTUs per deg F, so slab temp

will rise ~6 deg during typical January day• Home will lose ~138,000 BTUs between 8pm and 7am in January, so slab

temp will fall ~ 6 deg by morning and furnace will not have needed to turn on

• Without the solar slab, the furnace would have had to produce these BTUs and the house might have reached higher than desired temp during daytime

• Kachadorian’s worksheets were assembled into an integrated Excel spreadsheet• This allowed changes in component performance parameters to show

immediately the change in home’s predicted thermal performance.

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Overview of Building Site – facing South

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Final Approved Plans!

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Front & Rear Elevations

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Eave Design (“Overhang”)• South-facing windows should be protected from direct sun in summertime to avoid overheating• From Noon sun elevation, June 21 vs Dec 21, can optimize eave height and depth for building location• Result: Full illumination at Noon on Dec 21, full shade on June 21.

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Eave Design Reference Link• http://www.OurCoolHouse.com• Window “shade-drop” for eave (overhang) calculations by

season• The home at this link also uses a radiant heat floor system and

is built into the side of a hill for additional thermal buffering.• East Elevation showing overhang above south side windows:

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Active Solar Considerations• For roof-mounted active-solar features (solar electric or solar thermal), design roof so one of the roof faces points to true South• Optimize pitch angle of the roof (for roof mounted systems)• Steeper roofs favor winter solar production; shallower roofs favor

summer• If your system is roof-mounted, plan for a way to keep the panels

clean!!

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• Collect local weather data, in particular “sunniness” by month• To optimize for year-round total

production, set the roof pitch to approximately the latitude of the building site (if roughly equivalent sunniness in all seasons)

• Note: Builders use “Rise to Run”: e.g. 8’ over 12’ = ~34deg

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If you’re thinking of a ground-mounted solar electric system, plan to protect it!

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Garage Elevations (solar electric panel loc.)Note: Deck allows hosing off panels during dry season

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More on Solar Electric Production • sensitivity to panel elevation angle and time

of yearBased on Figure of Merit (FOM) proportional to sun position vs true perpendicular to panel, integrated 7am to 5pm, 1-hr steps

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Backup Heat – A Must! (& generally required by code)• You still need backup heat (for cloudier/colder weather than normal)• Electric FAU is first backup, but sometimes the grid goes down…• Masonry Heater provides “grid-down” back-up as well as lovely ambience• Needs to go in ~center of house – NEVER against an outside wall• Regular firewood charge burns for ~2 hrs, radiates thru the firebrick for ~12 hrs• Various sizes available for various size homes (see http://masonryheater.com)

• Bonus: you can get these with a bake oven that opens to back or front!

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Additional Considerations• Building Site should have good southern exposure

(did I already say this??)• Avoid shading south-facing windows in winter• Deciduous trees may be ok on south side, but not evergreens• Shade on east/west is ok and reduces heat load in

summer mornings & evenings• Won’t hurt winter-time input since sun rises in southeast and sets

in southwest• Avoid shading solar panels, whether ground or roof-

mounted, winter or summer – it impacts output by more than the percentage of shading

• Consider a separate circuit, powerable by generator, for freezer, fridge, and a few outlets for grid-down case

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• Find a builder who thinks your project is as cool as you do. • You need them to be invested in the project’s success!

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Project Progress to Date• Lots of reading, learning & preliminary designs – 2007 thru 2010• Initial plans submitted to Kern County – December 2010• House size reduction to keep within budget – Summer 2011 thru Spring 2012• Final plans turned in to Kern County for “Plan Check” – 6/12/12• Building Permit issued by Kern County - 6/28/12• Final approvals from Bear Valley Springs Home Owners Association – 7/25/12• Selected Solar Electric Installer – 7/26/12• Contract signed with Builder – 8/10/12• Grading for driveway and home site - 8/23/12• 5,000 gallon Fire Tank installation - 8/31/12 • Garage slab & Solar Slab (bottom-layer) concrete pour: TODAY!!• Estimated completion ~6 months from grading (~Feb-Mar 2013)• Stay tuned via: http://lightupontheearth.wordpress.com

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Grading Day: August 23, 2012, View to SW

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Grading Day: dirt from up top used to build driveway with gentle grade

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Home Site, View Approximately Southeast, Foundation digging underway

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House foundation, View to West, deeper section dug for “solar slab”, w/ 4 mil poly

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Solar slab foundation w/ 2-inch thick rigid foam insulation (R ~12) & taped joints

then 6 mil polyethylene

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Solar slab foundation: w/ 2 inches of sand (over 6 mil poly), ready for 2-inch layer of concrete

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Garage foundation, view to South, Ready for pouring (scheduled for today!)

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After the house is built. . . • Fence ~ 1-2 acres around house/garage to keep elk and deer out of the gardens & yard• Install car-charger in garage for planned Chevy Volt• Build greenhouse for citrus trees, winter vegetables• Build walled courtyard connecting house and garage• Plant orchard trees, berries, grapes, etc• Plant vegetable & herb gardens•Outbuildings/fencing for animals (chickens, honey bees, dairy goat, other?)•Outfit pottery studio (kilns in garage)• And, of course, monitor house performance and keep spreading the word ;-)

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References & Useful Links• “The Passive Solar House”, James Kachadorian, c.2006• Passive solar fundamentals, solar slab description, design concepts, good

drawings, thermal modeling spreadsheets & procedures• http://susdesign.com • “Sustainable by Design” website by Christopher Gronbeck• Many useful design tools: sun positions, overhang design, solar panel

shading, plus USA climate data for 250 cities• http://www.OurCoolHouse.com• Window “shade-drop” for eave (overhang) calculations by season• Lee & Anne Elson (lee.elson@yahoo.com) generously shared information

about the passive solar home they built in the Carson Valley in Nevada.• Especially helpful was the information on their masonry stove and their

“lessons learned”.• Follow progress via blog: http://lightupontheearth.wordpress.com• If you’d like more details on any aspect of this project (most

aspects go deeper), please don’t hesitate to contact me:• ann.tavormina@gmail.com

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