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Lecture Objectives:

Lecture Objectives:. Review, Discuss HW1a, and correct some typos Define Typical Meteorological Year (TMY) Boundary Conditions at Internal Surfaces. Solar components. Global horizontal radiation I GHR Direct normal radiation I DNR.

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Lecture Objectives:

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  1. Lecture Objectives: • Review, Discuss HW1a, and correct some typos • Define Typical Meteorological Year (TMY) • Boundary Conditions at Internal Surfaces

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

  3. 2.5 m Internal surfaces 10 m 10 m North East East North HW1 Problem Solar angles and Solar radiation components calculation You will need Austin weather data: http://www.caee.utexas.edu/prof/Novoselac/classes/ARE383/handouts.html

  4. Other Boundary Conditions at External Surfaces 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

  5. 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

  6. 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

  7. Ground and sky temperatures Sky temperature Swinbank (1963, Cole 1976) model • Cloudiness CC [0-1] 0 – for clear sky , 1 for totally cloud sky • Air temperature Tair [K] Tsky4 = 9. 365574 · 10−6(1 − CC) Tair6+ Tair4CC·eclouds Emissivity of clouds: eclouds = (1 − 0. 84CC)(0. 527 + 0. 161e[8.45(1 − 273/ Tair)]) + 0. 84CC For modeled T sky theesky =1 (Modeled T sky is for black body)

  8. Ground and sky temperatures Sky temperature Berdahl and Martin (1984) model • - Cloudiness CC [0-1] 0 – for clear sky , 1 for totally cloud sky • Air temperature Tair [K] • Dew point temperature Tdp [C] !!! Tclear_sky = Tair (eClear0.25) eClear = 0.711 + 0.56(Tdp/100) + 0.73 (Tdp/100)2 - emissivity of clear sky Ca = 1.00 +0.0224*CC + 0.0035*CC2 + 0.00028*CC3 – effect of cloudiness Tsky = (Ca)0.25* Tclear_sky esky =1

  9. Ground and sky temperatures • For ground temperature: • - We often assume: Tground=Tair • or we calculate Solar-air temperature • Solar-air temperature – imaginary temperature • Combined effect of solar radiation and air temperature • Tsolar = f (Tair , Isolar , ground conductivity resistance)

  10. Weather data Design condition vs. Operation condition Design whether parameters: Winter • Temperature Summer • Temperature and RH - Solar radiation – clear sky no pollution

  11. Weather data for ES analyses • Representative (typical) data • Characteristic for the location and longer period of time • TMY , TMY2, TMY3 database • Typical Meteorological Year 2 (TMY2) • data files are created from the National Solar Radiation Data Base (NSRDB) • a solar radiation and meteorological database (1961-1990 for TMY2 and 1991-2005 for TMY3)

  12. Typical Meteorological Year • http://rredc.nrel.gov/solar/ • Large number of locations • http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/by_state_and_city.html • Very compact data base • http://rredc.nrel.gov/solar/pubs/tmy2/fig3-1.html • You need to use data reader (write your one ore use already developed) • http://www.eere.energy.gov/buildings/energyplus/ Find more about TMY3 at: http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3

  13. Typical Meteorological Year • Structure (many weather parameters) • Real data (no averaging) 1960 1961 1962 ………………….. 1990 January February December August

  14. Boundary Conditions at Internal Surfaces

  15. Internal Boundaries Internal sources Window Transmitted Solar radiation

  16. 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

  17. 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

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

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

  20. 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

  21. Distribution of transmitted solar radiationDIRECT solar radiation

  22. Distribution of transmitted solar radiationdiffuse solar radiation

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