Lecture Objectives: Answer questions related to HW 2

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Presentation transcript:

Lecture Objectives: Answer questions related to HW 2 Conduct energy balance Write energy balance equations

HW2 Problem East South Steady State Energy Model 2.5 m Internal surfaces East South Steady State Energy Model

Surface Energy Balance Energy coming in = Energy going out or Sum of all energy = 0 Direction does not matter except for Solar energy Radiation from Internal sources

In HW1 you defined External Boundaries

Internal Boundaries Window Internal sources Transmitted Solar radiation

Air balance - Convection on internal surfaces + Ventilation + Infiltration Uniform temperature Assumption HVAC need to neutralizes all heat gains and losses hconvective and Qconvective as many as surfaces Qinfiltration +Qconvective= QHVAC Infiltration Toa Qconvective_i= Aihi(TSi-Tair) Ts1 mi Qventilation= Σmicp,i(Tsupply-Tair) Q1 Q2 Tair h1 h2

Homework assignment 1b Top view Teast_o Teast_i Tinter_surf Tair_in Styrofoam Teast_o Tinter_surf Teast_i 2.5 m Tair_in Surface to surface radiation 8 m 8 m IDIR Idif Tsouth_i South East Tsouth_o IDIR Tair_out Idif Glass Surface to surface radiation

Homework assignment 1 Room energy balance 1) External wall (East) node Qsolar_ext_east+C1·A(Tsky4 - Teast_o4)+ C2·A(Tground4 - Teast_o4)+hextA(Tair_out-Teast_o)+Ak/(Teast_in-Teast_o)=0 Qsolar_ext_east=A·asolar_east (Idif_tot_east+IDIR_east) c1=esky·esurface_long_wave·s·Fsurf_sky 2) Internal wall (East) node C3A(Tinternal_surf4-Teast_in4)+C4A( Tsouth_in4-Teast_in4)+ hintA(Tair_in-Teast_in)+k / A (Tsouth_out--Teast_in)+Qsolar_to int _east_surf =0 C3=esouth_in·einternal_surfs· Feast_in_to_ internal surface Qsolar_to int _east_surf = portion of transmitted solar radiation that is absorbed by internal east surface

3) External glass (South) node …. 4) Internal glass (South) node … 3) External glass (South) node ….. 4) Internal glass (South) node …. 5) Air balance equation … Five equations five unknowns - we just need to solve them for each hour

MatLab Example Example code is posted on the class website MatLab at: http://www.ece.utexas.edu/it/student-licensing