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 zz  - Solar azimuth angle  – Angle of incidence

4. Direct and Diffuse Components of Solar Radiation

5. Measurement of Direct Solar Radiation

6. Global horizontal radiation I GHR and Diffuse horizontal radiation measurements

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

8. Solar components Global horizontal radiation I GHR Direct normal radiation I DNR Direct component of solar radiation on considered surface: Diffuse components of solar radiation on considered surface: Total diffuse solar radiation on considered surface: zz

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

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

11. Wind Direction Wind direction is defined in TMY database: “Value: 0 – 360 o 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.” U windward leeward Wind direction: ~225 o N http://rredc.nrel.gov/solar/pubs/tmy2/ http://rredc.nrel.gov/solar/pubs/tmy2/tab3-2.html

12. Internal Boundaries Window Transmitted Solar radiation Internal sources

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

14. Internal Heat sources Occupants, 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 Conduction All radiation components Convection Convection + Conduction + Radiation = 0 For each surface – external or internal :

17. Air balance - Convection on internal surfaces + Ventilation + Infiltration h1 Q1 h2 Q2 Affect the air temperature - h, and Q as many as surfaces - m air c p.air  T air = Q convective + Q ventilation mimi Ts1 Tair Uniform temperature Assumption Q convective = ΣA i h i (T Si -T air ) Q ventilation = Σm i c p,i (T supply -T air ) Tsupply

18. Distribution of transmitted solar radiation DIRECT solar radiation

19. Distribution of transmitted solar radiation diffuse solar radiation