Lecture Objectives:

- Define the midterm project

- Lean about eQUEST

- Review exam problems

Midterm Project

Objective:

- Learn to use eQUEST

- Learn to conduct parametric analyses for design optimization

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’

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

eQUEST

• Example of– Defining envelope and internal loads – Selecting HVAC system– Presenting results – Finding design cooling and heating loads– Extracting simulation detail

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

Review of heat transfer

How to model:

– Convection at surfaces

– Radiation between surfaces

– Conduction through building elements

Steady state or unsteady state

Building elements

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

Discretization

F

C

L R

3

3

33

A air node

Ei

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]

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

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!

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

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

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

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

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

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