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Unformatted text preview: temperature Energy balance, First Law of Thermodynamics for a closed system: Increase in system energy = Energy in across system boundary = Heat in - Work out: Incremental form: W Q U Δ − Δ = Δ Infinitesimal form: W Q dU δ − = Rate form: W Q dt dU & & − = Internal energy term: Write in terms of constant volume heat capacity dt dT C dt dU i vh = Heat mechanisms: Conduction, convection into system: ia i air h conv cond R T T A Q ) ( , − = & Outgoing radiation: 4 i rad T Q εσ = & Work done: Assume zero for house problem Complete balance eqs: Consider only conduction & convection through walls & roof (no net radiation into house): ia i air r ia i air w roof wall i vh R T T A R T T A Q Q dt dT C ] [ ] [ − + − = + = & & , specify air T Model Results Note energy saved as insulation is improved....
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- Fall '08
- Thermodynamics, Building Energy, interior temperature Ti