Lecture Objectives: Introduce Internal Surface Energy Balance

HW1 Problem 10 m 2.5 m Internal surfaces East South South West

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:

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 Directly affect the air temperature Radiative Radiative heat flux “distributed” to surrounding surfaces according to the surface area and emissivity

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

Distribution of transmitted solar radiation DIRECT solar radiation

Distribution of transmitted solar radiation diffuse solar radiation

Air balance - Convection on internal surfaces + Ventilation + Infiltration Uniform temperature Assumption Affect the air temperature - h, and Q as many as surfaces - maircp.air DTair= Qconvective+ Qventilation Tsupply Qconvective= ΣAihi(TSi-Tair) Ts1 mi Qventilation= Σmicp,i(Tsupply-Tair) Q1 Q2 Tair h1 h2

HW1b Problem Steady State Energy Model 2.5 m Internal surfaces 8 m