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Conserving Energy

Conserving Energy. As in, not wasting it. Basic Conservation Ideas. Biggest savings are possible: applications with greatest consumption greatest unit cost cheapest improvements Efficiency vs. Sacrifice. Space Heating. Q. D T. = – kA. D t. D x. Conductive Heat Loss.

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Conserving Energy

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  1. Conserving Energy As in, not wasting it

  2. Basic Conservation Ideas • Biggest savings are possible: • applications with greatest consumption • greatest unit cost • cheapest improvements • Efficiency vs. Sacrifice

  3. Space Heating

  4. Q DT = –kA Dt Dx Conductive Heat Loss • Fourier Heat Conduction Law • rate of heat transfer: • Q is heat transferred • Dt is time increment • k is thermal conductivity, W/mK or Btu/ft·h°F • A is cross-sectional area • DT/Dx is temperature gradient

  5. Degree-Days (In/Out Temperature Difference)  (Number of Days) Or, DTDt Note that Q = –kADTDt/Dx Proportional to energy demand

  6. Q = –ADT /R Dt R-value • Thermal resistance of a material • RDx/k • So rate of heat transfer is • Unit: m2K/W or h·ft2·°F/Btu • Series R-values are additive

  7. Common Heat Losses • Air infiltration • substantial heat loss • benefit of ventilation • Standard fireplaces

  8. Energy in Transportation Capacity and Demand

  9. Engine Efficiency • Best at optimal power, rpm • Normal operation gives varying demand • efficiency gains from evening demand

  10. Power F·v

  11. Prominent forces • Acceleration F = ma • Hill climbing F = mgs Energy could be reclaimed by regenerative braking • Drag F v2 Lost to air turbulence

  12. Hybrid Vehicles • Regenerative braking • Peak power • More efficient engine, operating conditions

  13. Alternate fuels • Biodiesel, ethanol • Hydrogen • Methanol

  14. Fuel Cells • Not heat engines! • Less stringent constraint to efficiency • Fuels: Hydrogen, maybe methanol

  15. Lighting • Incandescent lighting is horribly inefficient • Fluorescent and LED are better • longer lifetime • issues with spectral quality • higher initial cost • hazardous materials in fluorescent tubes

  16. Recycling • Especially beneficial for aluminum • high energy cost to make metal from ore • Added benefit of reducing landfill use

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