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Lecture Objectives:

Lecture Objectives:. Learn about Boundary Conditions at Internal Surfaces solar radiation and heat transfer through windows Internal heat loads Introduce HW Assignments 1b, and HW2. HW1b.

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Lecture Objectives:

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  1. Lecture Objectives: • Learn about Boundary Conditions at Internal Surfaces • solar radiation and heat transfer through windows • Internal heat loads • Introduce HW Assignments 1b, and HW2

  2. HW1b • Calculate solar Insolation (a measure of solar radiation energy received on a given surface area) for a real PV systems and real weather • PV system: • 32 panels of SunTech PV modules (total area = 32x1.28 m2) • http://www.platt.com/CutSheets/Suntech/SuntechSTP185S_24Adb+.pdf • 269 degree azimuth, 35 degree tilt • Recent weather (solar) data for August 29, 2012 • PV system production data provided at: • http://www.ce.utexas.edu/prof/Novoselac/classes/ARE383/Handouts.html • Compare total solar Insolation with the produced energy and calculate energy efficiency of the solar system

  3. Transmission for single and double glazed window , , ,

  4. Heat transfer for double glazed window

  5. Internal Boundaries Internal sources Window Transmitted Solar radiation

  6. Distribution of transmitted solar radiationDIRECT solar radiation

  7. Distribution of transmitted solar radiationdiffuse solar radiation

  8. 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

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

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

  11. 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

  12. Air balance – steady stateConvection on internal surfaces + Infiltration = Load Uniform temperature Assumption • h, and Qsurfaces as many as surfaces • infiltration – mass transfer (mi – infiltration) • Qair= Qconvective+ Qinfiltration T outdoor air Qconvective= ΣAihi(TSi-Tair) Ts1 mi Qinfiltration= Σmicp(Toutdoor_air-Tair) Q2 Q1 In order to keep constant air Temperate, HVAC system needs to remove cooling load Tair h1 h2 QHVAC= Qair= m·cp(Tsupply_air-Tair) HVAC

  13. Top view Glass T_oi Tsouth_i Tinter_surf Tair_in Surface radiation IDIR Idif Twest_i conduction Twest_o Tair_out Styrofoam Surface radiation Idif IDIR Homework assignment 2 2.5 m 10 m 10 m West South

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