Lecture Objectives:

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Lecture Objectives:. Finish with Solar Radiation and Wind Define Boundary Conditions at Internal Surfaces. Solar radiation. Direct Diffuse Reflected (diffuse). Solar Angles. q z. - Solar azimuth angle – Angle of incidence. Direct and Diffuse Components of Solar Radiation.

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Lecture Objectives:

Finish with Solar Radiation and Wind

Define Boundary Conditions at Internal Surfaces

• Direct
• Diffuse
• Reflected (diffuse)
Solar Angles

qz

• - Solar azimuth angle
• – Angle of incidence

2.5 m

Internal surfaces

8 m

8 m

HW1 Problem

You will need Austin weather data:

http://www.caee.utexas.edu/prof/Novoselac/classes/ARE383/handouts.html

Solar components

Direct component of solar radiation on considered surface:

Diffuse components of solar radiation on considered surface:

qz

Total diffuse solar radiation on considered surface:

External convective heat fluxPresented model is based on experimental data, Ito (1972)

Primarily forced convection (wind):

Velocity at surfaces that are windward:

Velocity at surfaces that are leeward:

U -wind velocity

Convection coefficient:

u

surface

u

windward

leeward

Boundary Conditions at External Surfaces

1. External convective heat flux

Required parameters:

- wind velocity

• wind direction
• surface orientation

N

leeward

Consequence:

U

Energy Simulation (ES) program treatsevery surface with different orientation as separate object.

windward

Wind Direction

Wind direction is defined in TMY database:

“Value: 0 – 360o Wind direction in degrees at the hou

indicated. ( N = 0 or 360, E = 90,   S = 180,W = 270 ). For calm winds, wind direction equals zero.”

N

http://rredc.nrel.gov/solar/pubs/tmy2/

http://rredc.nrel.gov/solar/pubs/tmy2/tab3-2.html

leeward

U

windward

Wind direction: ~225o

Internal Boundaries

Internal sources

Window

Transmitted

Exact equations for closed envelope

Tj

Ti

Fi,j - View factors

ψi,j - Radiative heat exchange factor

Closed system of equations

Internal Heat sourcesOccupants, Lighting, Equipment
• Typically - Defined by heat flux
• Convective
• Directly affect the air temperature
• 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 :

Conduction

Convection

Convection + Conduction + Radiation = 0

Uniform temperature Assumption

Affect the air temperature

- h, and Q as many as surfaces

- maircp.airDTair= Qconvective+ Qventilation

Tsupply

Qconvective= ΣAihi(TSi-Tair)

Ts1

mi

Qventilation= Σmicp,i(Tsupply-Tair)

Q2

Q1

Tair

h1

h2