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

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: http://www.caee.utexas.edu/prof/Novoselac/classes/ARE383/handouts.html

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 http://www.thermalradiation.net/indexCat.html

Solar radiation Direct Diffuse Reflected (diffuse)

Solar Angles qz - Solar altitude angle – Angle of incidence

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 = 30.2672° N Austin’s Longitude 97.7431° W What is v ? HW1a Part 3) Calculate q for two surfaces in your HW1a for each hour: Use equation 1.6.2 from the handouts. NOTE: When you use excel be careful about degree and radian mode. Default is radian ! 1 1 radian = 180/ degrees.

Direct and Diffuse Components of Solar Radiation

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:

Global horizontal radiation IGHR and Diffuse horizontal radiation measurements qz

Measurement of Direct Solar Radiation

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

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

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 http://rredc.nrel.gov/solar/pubs/tmy2/ http://rredc.nrel.gov/solar/pubs/tmy2/tab3-2.html leeward U windward Wind direction: ~225o

Boundary Conditions at Internal Surfaces

Internal Boundaries Window Internal sources Transmitted Solar radiation

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

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

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