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Lecture Objectives:

Lecture Objectives:. Finish with Solar Radiation and Wind Define Boundary Conditions at Internal Surfaces. Solar radiation. Direct Diffuse Reflected (diffuse). Solar Angles. q z. - Solar azimuth angle – Angle of incidence. Direct and Diffuse Components of Solar Radiation.

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Lecture Objectives:

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  1. Lecture Objectives: Finish with Solar Radiation and Wind Define Boundary Conditions at Internal Surfaces

  2. Solar radiation • Direct • Diffuse • Reflected (diffuse)

  3. Solar Angles qz • - Solar azimuth angle • – Angle of incidence

  4. Direct and Diffuse Components of Solar Radiation

  5. Measurement of Direct Solar Radiation

  6. Global horizontal radiation IGHRand Diffusehorizontal radiation measurements

  7. 2.5 m Internal surfaces 8 m 8 m HW1 Problem You will need Austin weather data: http://www.caee.utexas.edu/prof/Novoselac/classes/ARE383/handouts.html

  8. Solar components • Global horizontal radiation IGHR • Direct normal radiation IDNR Direct component of solar radiation on considered surface: Diffuse components of solar radiation on considered surface: qz Total diffuse solar radiation on considered surface:

  9. External convective heat fluxPresented model is based on experimental data, Ito (1972) Primarily forced convection (wind): Velocity at surfaces that are windward: Velocity at surfaces that are leeward: U -wind velocity Convection coefficient: u surface u windward leeward

  10. Boundary Conditions at External Surfaces 1. External convective heat flux Required parameters: - wind velocity • wind direction • surface orientation N leeward Consequence: U Energy Simulation (ES) program treatsevery surface with different orientation as separate object. windward

  11. Wind Direction Wind direction is defined in TMY database: “Value: 0 – 360o Wind direction in degrees at the hou indicated. ( N = 0 or 360, E = 90,   S = 180,W = 270 ). For calm winds, wind direction equals zero.” N http://rredc.nrel.gov/solar/pubs/tmy2/ http://rredc.nrel.gov/solar/pubs/tmy2/tab3-2.html leeward U windward Wind direction: ~225o

  12. Internal Boundaries Internal sources Window Transmitted Solar radiation

  13. Surface to surface radiation Exact equations for closed envelope Tj Ti Fi,j - View factors ψi,j - Radiative heat exchange factor Closed system of equations

  14. Internal Heat sourcesOccupants, Lighting, Equipment • Typically - Defined by heat flux • Convective • Directly affect the air temperature • Radiative • Radiative heat flux “distributed” to surrounding surfaces according to the surface area and emissivity

  15. Internal Heat sources • Lighting systems • Source of convective and radiative heat flux • Different complexity for modeling

  16. Surface Balance For each surface – external or internal : All radiation components Conduction Convection Convection + Conduction + Radiation = 0

  17. Air balance - Convection on internal surfaces + Ventilation + Infiltration Uniform temperature Assumption Affect the air temperature - h, and Q as many as surfaces - maircp.airDTair= Qconvective+ Qventilation Tsupply Qconvective= ΣAihi(TSi-Tair) Ts1 mi Qventilation= Σmicp,i(Tsupply-Tair) Q2 Q1 Tair h1 h2

  18. Distribution of transmitted solar radiationDIRECT solar radiation

  19. Distribution of transmitted solar radiationdiffuse solar radiation

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