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Energy efficient residential construction: a closer look at a passive solar home

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Energy efficient residential construction: a closer look at a passive solar home

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Energy efficient residential construction: a closer look at a passive solar home

  1. 1. Straw, Mud and Sun A passive solar home
  2. 2. Today’s discussion <ul><li>Passive solar 101 </li></ul><ul><li>Thermal mass </li></ul><ul><li>Insulation </li></ul><ul><li>Roof cachement </li></ul><ul><li>Greywater </li></ul><ul><li>Domestic hot water </li></ul><ul><li>Photovoltaics </li></ul><ul><li>Embodied energy </li></ul><ul><li>Soapbox </li></ul><ul><li>Resources </li></ul>
  3. 3. Passive solar 101 <ul><li>Solar radiation </li></ul><ul><ul><li>enters through south facing windows </li></ul></ul><ul><ul><li>is captured by thermal mass </li></ul></ul><ul><ul><li>held inside by good insulation </li></ul></ul><ul><li>Everyone gets fired up about gadgets </li></ul><ul><li>Passive solar has no gadgets </li></ul><ul><li>The only moving part is the sun </li></ul><ul><ul><li>Reliability! </li></ul></ul><ul><ul><li>Efficiency! </li></ul></ul><ul><li>The south face of the house is the critical design point </li></ul><ul><ul><li>south facing glass </li></ul></ul><ul><ul><li>sun is higher in the summer – overhangs prevent overheating </li></ul></ul><ul><ul><li>sun is lower in the winter – south-facing glass lets in solar radiation </li></ul></ul><ul><li>Minimize other glass, especially north facing (in cold climate) </li></ul><ul><li>Shade west facing glass </li></ul><ul><li>Overhang length depends on latitude and window height </li></ul><ul><li>Other options: Trombe walls </li></ul>Note: this is written for the Northern hemisphere June 22 December 22
  4. 4. Passive solar – house design considerations <ul><li>Keep the footprint small </li></ul><ul><li>Orient the house within a few degrees of true south </li></ul><ul><li>Need a decent southern exposure </li></ul><ul><ul><li>McMansions to the south of the site are problematic </li></ul></ul><ul><ul><li>So are big evergreen trees </li></ul></ul><ul><li>South facing glass 7% to 12% of total floor space </li></ul><ul><li>Control southern exposure with overhangs </li></ul><ul><li>Exposed west facing windows can get very hot in the summer </li></ul><ul><li>Slanted glass can lead to overheating in all but coldest climates </li></ul><ul><li>Make good use of deciduous trees </li></ul><ul><li>South facing greenhouses are an option </li></ul><ul><li>Without interior thermal mass, none of this works - there’s no storage mechanism </li></ul><ul><li>Insulate, insulate, insulate </li></ul><ul><li>Open floor plans work better </li></ul><ul><li>To really go all-out, berm the north side (e.g. Earthships ) </li></ul>
  5. 5. Thermal mass <ul><li>Interior thermal mass is critical to making passive solar work </li></ul><ul><ul><li>Thermal mass stores heat </li></ul></ul><ul><ul><li>Radiates slowly back into the space throughout the night </li></ul></ul><ul><ul><li>Without thermal mass, heat dissipates quickly </li></ul></ul><ul><ul><li>Direct exposure is better, but indirect works also </li></ul></ul><ul><ul><li>Usually floors and walls </li></ul></ul><ul><li>Examples of thermal mass </li></ul><ul><ul><li>Concrete slab </li></ul></ul><ul><ul><li>Brick floors or dark colored tile </li></ul></ul><ul><ul><li>Adobe interior walls </li></ul></ul><ul><ul><li>Masonry fireplaces </li></ul></ul><ul><ul><li>Plaster </li></ul></ul><ul><ul><li>Planters </li></ul></ul>
  6. 6. Insulation <ul><li>So…You let in solar radiation and captured the heat in thermal mass </li></ul><ul><li>… now you have to keep it in the house </li></ul><ul><li>Design points </li></ul><ul><ul><li>Insulate under slab </li></ul></ul><ul><ul><li>Extra insulation in the roof </li></ul></ul><ul><ul><li>Straw bale walls </li></ul></ul><ul><ul><li>And yes, backup radiant heat </li></ul></ul><ul><li>About straw bales… </li></ul><ul><li>Existing building code in AZ, NM, others </li></ul><ul><li>Low embodied energy </li></ul><ul><li>Excellent insulation </li></ul><ul><li>Thick walls </li></ul><ul><li>MUST be kept dry </li></ul><ul><li>Need to “breathe” </li></ul><ul><li>Wonderful in dry climates </li></ul>
  7. 7. Roof cachement <ul><li>Fresh water is an issue worldwide – get used to the idea now that the more you can conserve, the better </li></ul><ul><li>Taos is a high desert </li></ul><ul><ul><li>Water rights </li></ul></ul><ul><ul><li>Respect for the land and climate </li></ul></ul><ul><li>Well vs. roof cachement </li></ul><ul><li>That’s not a roof, it’s a rainwater collector </li></ul><ul><li>Rainwater stored in underground cisterns (6800 gal capacity) </li></ul><ul><li>Three stage filtration: particle, carbon, and silver ceramic anti-bacterial </li></ul><ul><li>… and just in case… rough in for alternate water main (a future well if needed) </li></ul><ul><li>Could have dug a well, and done roof cachement for external irrigation only </li></ul><ul><ul><li>Can be very low tech! </li></ul></ul><ul><ul><li>An old olive barrel = a rain barrel in Tampa </li></ul></ul><ul><li>Cannot use asphalt shingle roof to catch drinking water </li></ul>
  8. 8. Greywater <ul><li>Greywater is: </li></ul><ul><li>Drain water from bathroom sinks, showers, tubs, washing machines </li></ul><ul><li>NOT from toilets (blackwater) or kitchen sink </li></ul><ul><li>The lynchpin that makes the roof cachement system viable </li></ul><ul><li>That’s not a hole in the foundation, it’s a greywater filtration system </li></ul><ul><ul><li>Greywater is kept separate from sewage </li></ul></ul><ul><ul><li>Planter is lined / gravel / filtration plants </li></ul></ul><ul><ul><li>Recirculation/oxygenation loop (small pump w/ solar panel) </li></ul></ul><ul><ul><li>1500 gal holding tank (would not want a holding tank without filtration) </li></ul></ul><ul><li>Building code for greywater in AZ, NM, CA </li></ul><ul><li>Systems can be much simpler than this one </li></ul><ul><li>Create an Oasis with Greywater , by Art Ludwig </li></ul>
  9. 9. Domestic hot water <ul><li>Lets recap for a minute – “solar energy” could mean: </li></ul><ul><ul><li>Passive solar design </li></ul></ul><ul><ul><li>Photovoltaics (generation of electricity from solar panels) </li></ul></ul><ul><ul><li>Solar water heating (directly heating water for household use with solar heat) </li></ul></ul><ul><li>Solar domestic hot water is one of the best solar technologies around </li></ul><ul><li>Usually a shorter payback than PV </li></ul><ul><li>Can be done almost anywhere </li></ul><ul><ul><li>In colder climates, systems circulate antifreeze </li></ul></ul><ul><ul><li>In warmer climates with no risk of freezing, can circulate water </li></ul></ul>Can also heat water for radiant in-floor backup heating (we chose not to do so in this house) Solar hot water panel (two skylights below – not part of system)
  10. 10. Photovoltaics (PV) <ul><li>1 Kw PV grid tie system with battery backup planned </li></ul><ul><li>Budget constraints – rough in and roof blocking only </li></ul><ul><li>Planned install in about 3 years – significantly reduced costs </li></ul><ul><ul><li>PV technology keeps improving </li></ul></ul><ul><ul><li>No contractor overhead </li></ul></ul><ul><ul><li>May owner-install </li></ul></ul><ul><ul><li>Buying wind power from local electric co-op in the meantime </li></ul></ul><ul><li>Things to know about PV </li></ul><ul><li>You MUST have good southern exposure </li></ul><ul><li>Grid-tie or off grid </li></ul><ul><li>Roof mount vs. pole mount </li></ul><ul><ul><li>Pole mounted may track the sun automatically </li></ul></ul><ul><ul><li>Panels adjusted seasonally for optimal efficiency </li></ul></ul><ul><li>Determining the angle of the panels – latitude and season </li></ul><ul><li>With current technology, any shade can seriously compromise system efficiency </li></ul><ul><li>“ Watch this space” – venture capital is being committed daily </li></ul><ul><li>Interesting side note: </li></ul><ul><li>Commercial production of electricity from solar heat rather than PV </li></ul>
  11. 11. Embodied energy <ul><li>How hard is your project on the earth? </li></ul><ul><li>What can you use less of? </li></ul><ul><li>How much energy did it take to make the materials you use? </li></ul><ul><li>Can you use any recycled materials? </li></ul><ul><li>Are the materials renewable? </li></ul><ul><li>Examples </li></ul><ul><li>Concrete is very high embodied energy – use it wisely </li></ul><ul><li>Straw bale is very low embodied energy – transportation, processing </li></ul><ul><li>Wood is renewable if it is sustainably harvested </li></ul>
  12. 12. Resources <ul><li>The Good House Book by Clarke Snell </li></ul><ul><li>Books by Dan Chiras : The Solar House , The Natural House </li></ul><ul><li>Building with Awareness (video of hybrid house construction) </li></ul><ul><li>Mother Earth News magazine </li></ul><ul><li>Natural Home magazine (“green Better Homes and Gardens”) </li></ul><ul><li>Home Power magazine </li></ul><ul><li>Create an Oasis with Greywater , by Art Ludwig </li></ul><ul><li>Just to see what’s possible: </li></ul><ul><li>El Monte Sagrado resort , Taos, NM – amazing on-site full waste treatment system </li></ul><ul><li>Greater World – earthship community outside of Taos, fully self sustaining </li></ul><ul><li>Earth: the Sequel , by Fred Krupp and Miriam Horn </li></ul>
  13. 13. Final thoughts <ul><li>Building is expensive - but building a non-green house is pretty much just as expensive </li></ul><ul><li>Your house should work for you … not some mythical resale buyer. </li></ul><ul><ul><li>Keep your living space as small as you can </li></ul></ul><ul><ul><li>If it works for you, it will work for others </li></ul></ul><ul><ul><li>Don’t be influenced by neighbors, Architectural Digest, or anyone making money off of your decision (realtors, builders) – they are all slightly crazy </li></ul></ul><ul><li>Without conservation, energy technologies amount to playing with new toys </li></ul><ul><li>Conservation does not equal deprivation </li></ul><ul><li>Demand energy efficiency in construction and real estate </li></ul><ul><ul><li>You vote with your wallet </li></ul></ul><ul><ul><li>Trends change in response to consumer demand </li></ul></ul><ul><li>Look at the whole picture in any construction project, whether remodel or build </li></ul><ul><li>Bring political pressure to level the playing field </li></ul><ul><ul><li>The current financial deck is stacked against energy innovation efforts </li></ul></ul><ul><ul><li>In the US, oil, gas, and coal all have enormous subsidies and benefits to the tune of $6 billion a year (that’s your tax $$, folks) </li></ul></ul><ul><ul><li>Need long-term policies to foster energy innovation </li></ul></ul><ul><ul><li>In 2007 dozens of Fortune 500 companies called for a national cap on carbon emissions, including GE, Alcoa, Caterpillar, Duke Energy, Shell Oil, and all three US automakers </li></ul></ul><ul><ul><li>Industry gets it, but if politicians don’t – inform them or vote them out </li></ul></ul><ul><li>100% of energy from renewable, carbon neutral sources should be our new “space race” </li></ul>

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