Lecture Objectives: Learn about Boundary Conditions at Internal Surfaces solar radiation and heat transfer through windows Internal heat loads Introduce HW Assignments 1b, and HW2

Transmission for single and double glazed window , , ,

Heat transfer for double glazed window

Internal Boundaries Window Internal sources Transmitted Solar radiation

Distribution of transmitted solar radiation DIRECT solar radiation

Distribution of transmitted solar radiation diffuse solar radiation

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

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

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

Air balance – steady state Convection on internal surfaces + Infiltration = Load Uniform temperature Assumption h, and Qsurfaces as many as surfaces infiltration – mass transfer (mi – infiltration) Qair= Qconvective+ Qinfiltration T outdoor air Qconvective= ΣAihi(TSi-Tair) Ts1 mi Qinfiltration= Σmicp(Toutdoor_air-Tair) Q1 Q2 In order to keep constant air Temperate, HVAC system needs to remove cooling load Tair h1 h2 QHVAC= Qair= m·cp(Tsupply_air-Tair) HVAC

Homework assignment 1b Top view T_north_o Tnorth_i Tinter_surf Tair_in IDIR Idif Glass Tinter_surf Teast_i Teast_o Tnorth_i T_north_o Tair_out Styrofoam Surface radiation Surface radiation 2.5 m 8 m 8 m conduction East North