Lecture Objectives:

1
Lecture Objectives

• Energy balance and modeling
• HW1b

2
Announcements

• On October 3rd 930 am
• class will be in ARE302
• introduction to energy simulation software
• This Friday (September 27th) 8 am
• Intro in MTHLAB, relevant to HW1b
• class will be in ARE302

3
Surface Balance
For each surface external or internal
All radiation components
Conduction
Convection
Convection Conduction Radiation 0
4
Distribution of transmitted solar
radiationDIRECT solar radiation
5
Distribution of transmitted solar
radiationdiffuse solar radiation
6
Internal Heat sourcesOccupants, 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

7
Internal Heat sources

• Lighting systems
• Source of convective and radiative heat flux
• Different complexity for modeling

8
Surface to surface radiation
Exact equations for closed envelope
Tj
Ti
Fi,j - View factors
?i,j - Radiative heat exchange factor
Closed system of equations
9
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 ?Tair Qconvective Qventilation
Qconvective SAihi(TSi-Tair)
Ts1
mi
Qventilation Smicp,i(Tsupply-Tair)
Q2
Q1
Tair
h1
h2
10
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 SAihi(TSi-Tair)
Ts1
mi
Qinfiltration Smicp(Toutdoor_air-Tair)
Q2
Q1
In order to keep constant air Temperate, HVAC
system needs to remove cooling load
Tair
h1
h2
QHVAC Qair mcp(Tsupply_air-Tair)
HVAC
11
Homework assignment 1b
2.5 m
10 m
10 m
South
East