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Methods of Heat Transfer: CONVECTION

Methods of Heat Transfer: CONVECTION. Infiltration – Heat Loss by Convection. Air Infiltration & Exfiltration. • Costs Homeowners $13 billion per year • Attic bypasses • Crawlspace/slab bypasses • Penetrations in walls • Ductwork • Exhaust fans. Average House with Lots of Windows.

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Methods of Heat Transfer: CONVECTION

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  1. Methods of Heat Transfer: CONVECTION

  2. Infiltration – Heat Loss by Convection

  3. Air Infiltration & Exfiltration • Costs Homeowners $13 billion per year • Attic bypasses • Crawlspace/slab bypasses • Penetrations in walls • Ductwork • Exhaust fans

  4. Average House with Lots of Windows

  5. Infrared Image

  6. Convective Loop “Windwashing”

  7. Installed R-Value vs. Wind Pressure

  8. Impact of R-Value: Caulking vs. Tyvek

  9. Good Air Sealing Practice

  10. Poor Sill Seal

  11. Incomplete Air Sealing

  12. Crawlspace Bypass

  13. Attic Bypass

  14. Convective Loop “Windwashing”

  15. Tough Spot to Insulate

  16. Attic Air Leaks

  17. Infiltration – Heat Loss by Convection

  18. Calculating Air Infiltration • Q = V x AC/hr x 0.02BTU/ ft²°F x T x t • For example: How much heat is replaced by infiltration in a 10,000 cubic foot home, with an Air Exchange Rate of 1.5Ac/hr, when it is 35°F outside and 68°F inside throughout one day? • Q = 10,000ft³ x 1.5AC/hr x 0.02 x 33°F x 24hrs • Q = 237,600 BTUs  ÷ 24 = 9,900  BTU/hrThe furnace would have to provide 9,900 BTU/hr to make up for the heat lost due to air infiltration.

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