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Don Otto dpoconstruction

Comfortable homes that save the world Sustainable Environmental Economic Development October 27, 2007. Don Otto dpoconstruction.com. What Works “Sure, it works in practice, but does it work in theory?”. The physics of how buildings live in the environment

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Don Otto dpoconstruction

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  1. Comfortable homes that save the worldSustainable Environmental Economic DevelopmentOctober 27, 2007 Don Otto dpoconstruction.com

  2. What Works “Sure, it works in practice, but does it work in theory?” • The physics of how buildings live in the environment • Convection, Conduction and Radiation • Some math formulas you can’t live without • Design: planning spaces that meet your needs with the fewest square feet • Testing each home for performance--the whole heating system, too • Financing: finding an appraiser who values EE

  3. Some details of how I do it

  4. The science & math of energy flow Heat crosses the building envelope in only 3 ways: conduction, convection, radiation • Conduction (insulation) roughly accounts for 1/3 - 1/2 • Convection (air flow) also accounts for 1/3 - 1/2 • Radiation (electromagnetic) accounts for the rest Heat flow, (in Btu/hr) through insulation depends on conductance (U), sq. ft. area (A) and temperature difference from inside to outside (∆T): • Btu/hr = U x A x ∆T Heat flow by air movement depends on air flow rate (CFM), temperature difference inside to outside (∆T), and correction factor (1.08): • Btu/hr = CFM x ∆T x 1.08

  5. Some real-world examples The formula for heat flow through insulation, Btu/hr = U x A x ∆T For a 1-story,1,000 sq ft house, (a 32’ x 32’ house walls also = ~ 1,000 sq ft) an inside temperature of 70° and cold outside winter air temperature of 0°F, or year-round ground temperature of 50° Conductive heat loss Un-insulated basement floor(R-1, U=1.0) 1,000 x 1.0 x 20 = 20,000 Btu/hr (the temperature below grade is about 50°, so the difference is only 20°, not 50°) But what if we installed insulation under the floor to R-10? R-10 (U = 0.1): 1,000 x 0.1 x 20 = 2,000 Btu/hr

  6. How much energy do we lose by air leakage? (Air flow Btu = CFM x ∆T x 1.08) For 5 air changes per hour (ACH) and 1,000 sq ft: 1,000sq ft x 8’ x 5 ach/60min = 667 CFM. 667 CFM x 70° x 1.08 =50,350 Btu/hr Current ventilation standards(ASHRAE 62.2, 2004) recommend 7.5 CFM per person plus 1 CFM per 100 sq ft. For a three-BR house, a couple with 2 kids, per 1000 sq ft: 40 CFM x 70 x 1.08 = 3,024 Btu/hr That’s saving 94% of the energy we waste to heat the winter sky If we installed an energy recovery ventilation system, we could even recover 60 to 80% of that. Minnesota already requires one in all new homes.

  7. Photos of the science applied

  8. Design-meeting your needs with the fewest square feet

  9. Sight lines and focal points • Diagonal views are the longest possible. Focal points, like light from windows, attract the eye, making the space feel larger than it is

  10. Does doing all this make a difference? • A home in Solon costs $180 a year to heat • It keeps 36,000 lbs of CO2 out the air • It’s comfortable all the time • The benefits will last the life of the house

  11. How many ways do homes lose energy? How much? Where? • Inadequate insulation • Air leakage • Poor windows • Inadequate ductwork How do you know what to fix?

  12. Performance testing • Building envelope leakage w/ blower door & Infra-Red camera • Entire heating system performance • Furnace & A/C or heat pump • Ductwork, airflow delivery • As well as windows and insulation • (the whole test costs between $300 - $400)

  13. Financing energy upgrades Banks need appraisers who place a value on energy efficient features in order to include them on a loan. I know of one such appraiser: JIM POTTER, Preferred Appraisal, 319-373-6746

  14. THANKSThis presentation will be on my Website,dpoconstruction.com

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