1. Lecture Objectives: Discus HW 1a Define Solar Radiation Components
Solar angles
Solar components calculation process
Introduce Internal Surface Energy Balance

2. HW1 Problem You will need Austin weather data: West South
Internal surfaces
West
South
Solar angles and
Solar radiation components calculation
You will need Austin weather data:

3. View (Shape) factors FSS , FSW , FSI FWS , FWW , FWI FIS , FIW , FII
Part 1) Using the equations provided in the attached paper sheet and the basic properties of view factors calculate the view factors for internal characteristic surfaces:
FSS , FSW , FSI
FWS , FWW , FWI
FIS , FIW , FII

4. Solar radiation
Direct
Diffuse
Reflected (diffuse)

5. Solar Angles qz
- Solar altitude angle
– Angle of incidence

6. Calculation of Solar Angles
g – surface azimuth (from 0 to ±180°, east negative and west positive)
f - Latitude
d - Declination (function of a day in a year)
- Hour angle (function of Longitude defined distance from local meridian
Austin’s Latitude = ° N
Austin’s Longitude ° W
What is v ?
HW1a Part 3) Calculate q for two surfaces in your HW1a for each hour:
Use equation from the handouts.
NOTE: When you use excel be careful about degree and radian mode.
Default is radian ! 1
1 radian = 180/ degrees.

7. Direct and Diffuse Components of Solar Radiation

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. Global horizontal radiation IGHR and Diffuse horizontal radiation measurementsqz

10. Measurement of Direct Solar Radiation

11. External convective heat flux Presented 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

12. 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 treats every surface with different orientation as separate object.
windward

13. Wind Direction Wind direction: ~225o
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
leeward U
windward
Wind direction: ~225o

14. Boundary Conditions at Internal Surfaces

15. Internal Boundaries Window Internal sources 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 sources Occupants, Lighting, Equipment
Typically - Defined by heat flux
Convective
Affects the air temperature
Radiative
Radiative heat flux “distributed” to surrounding surfaces according to the surface area and emissivity

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