1. Lecture Objectives:
Energy balance and modeling
HW1b

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

3. Air balance - Convection on internal surfaces + Ventilation + Infiltration
Uniform Air Temperature Assumption!
What affects the air temperature?
- h and corresponding Q - as many as surfaces
Energy balance:
Tsupply
-maircp.air ΔTair= Qconvective+ Qventilation
Qconvective= ΣAihi(TSi-Tair)
Ts1 mi
Qventilation= Σmicp,i(Tsupply-Tair) Q1 Q2
Tair h1 h2

4. 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

5. Homework assignment 1b Top view Teast_o Teast_i Tinter_surf Tair_in
conduction
Tair_in
IDIR
Idif
Glass
Tinter_surf
Tsouth_i
Tsouth_o
Teast_i
Teast_o
Tair_out
Styrofoam
Surface radiation
Surface
radiation
2.5 m
10 m
10 m
South
East