Lecture Objectives: -Define the midterm project -Lean about eQUEST -Review exam problems.
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Transcript of Lecture Objectives: -Define the midterm project -Lean about eQUEST -Review exam problems.
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Lecture Objectives:
- Define the midterm project
- Lean about eQUEST
- Review exam problems
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Midterm Project
Objective:
- Learn to use eQUEST
- Learn to conduct parametric analyses for design optimization
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Midterm Project• Use eQUEST to model 2 buildings: • Residential house
– Duplex – 2 floors single zone per floor– Focus on envelope, zoning, and internal loads
• Commercial Building – ECJ building
18’
60’
40’
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Midterm Project• Major Output: Energy consumption for both buildings
– Electricity and – Gas
• Part 1: Parametric analysis for residential building – Windows (glazing and shading)– Wall insulation – Wall surface properties– Shading
• Part 2: Complex geometry, internal loads, and detailed mode
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eQUEST
• Example of– Defining envelope and internal loads – Selecting HVAC system– Presenting results – Finding design cooling and heating loads– Extracting simulation detail
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Review• Heat transfer
• Thermal analysis of building elements
• External and internal boundary conditions
• Weather data for boundary conditions
• Modeling procedures– Numerical methods for solving equations
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Review of heat transfer
How to model:
– Convection at surfaces
– Radiation between surfaces
– Conduction through building elements
Steady state or unsteady state
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Building elements
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Weather data (TMY2 database)
Use them for External boundary conditions
Convection Long-wave Radiation
Solar radiation• Direct • Diffuse• Reflected (diffuse)
Externalsurface
Sky DiffuseDirect Normal
radiation
Reflected
n
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Discretization
F
C
L R
3
3
33
A air node
Ei
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Discretization for conduction
Faca
de s
lab
Insu
latio
n
Gyp
sum
Section considered in the following discussion
Discretization in space
2
2
xT
ckT
pDiscretization in time
T – temperature [C]
ρ – density [kg/m3]
cp – specific capacity [J/kgK]
k- conductivity [W/mK]
time [sec]
x distance [m]
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Finite volume (difference) method
( x) I- 1 ( x)I
x I
I-1 I I+1q I -1 to I q I to I+1
sourcep qxTkTc
2
2
q
xTTk
xTTkTTxc
I
II
I
IIIII
III
11
Boundaries of control volume
Fir each node conservation of energy:
q
xTTk
xTTkTTxc
I
III
I
IIIII
III 111
implicit
explicit
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Implicit methods - example wioww TTTTT 2)(3
iwii TTTT )(2.0
woiw TTTT 3)1()23(
iiw TTT )12.0()1(
=0 To Tw Ti
=36 system of equation Tw Ti
=72 system of equation Tw Ti
After rearranging:
2 Equations with 2 unknowns!
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Unsteady-state conductionImplicit method with linearization
1 2 3 4 5 6
Matrix equation
M × T = F
for each time step
Air Air
b1T1 + +c1T2
+=f(Tair,T1,T2
)
a2T1 + b2T2
+ +c2T3+=f(T1
,T2, T3
)
a3T2 + b3T3
+ +c3T4+=f(T2
,T3 , T4
)
a6T5 + b6T6
+ =f(T5 ,T6
, Tair)
………………………………..
M × T = F
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Numerical methods
System of equations for unsteady state process (nonlinear)
Explicit
Implicit
Linearization (Matrix solver)
Nonlinear (Newton-Raphson method)
For each time step
PROBLEM
Steady-state Unsteady-state
System of equations for steady state process (nonlinear)
Implicit
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Integration of HVAC and building physics models
Building Heating/Cooling System Plant
Building Heating/Cooling System Plant
Load System Plant model
Integrated models
Qbuiolding Q
including
Ventilation
and
Dehumidification
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Modeling steps• Define the domain• Analyze the most important phenomena and
define the most important elements• Discretize the elements and define the
connection • Write the energy and mass balance equations• Solve the equations (use numeric methods or
solver)• Present the result
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Practice for the ExamExample #1
Walmart store (L>>H, D>>H)
H-5m
L=200 m
D=100m
door
Plenum (air)
Room (air)
Floor
concrete
QHVAC
insulation
acoustic tile
TR
TF
Lconcrete
Linsulation
Lplenum
Ltile
mS ,TS
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Practice for the ExamExample #2
You are considering using the ventilated windows for ventilation of your new building and a sales person claims that it will reduce your annual energy bill by 10%. To check this claims you decided to model the performance of this window for your climate condition.
Air cavity open to outdoor air at the top, and to indoor air at the bottom
Building fan creates under pressure in the room
TRAQHVAC
TRAQHVAC Building fan creates
pressure in the room