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||Building physics 3: Energy Part 1

Energy in Buildings

Dr. Kristina Orehounig

1

These buildings are examples from Austria of very low energy buildings built according to the passive house concept.

||

Energy use in buildings

1. Heat gains/losses in a building

2. Steady state calculations

3. Influencing factors

27.02.2019 3

This lecture…


Energie in Gebäuden - Ziele

Energy issues in the context of buildings

Building stock responsible for about 50% of energy demand

40% of CO2-Emissions

Goal to reduce energy consumption by 50% until 2050

Strategies to improve the buildings energy performance

Low-Energy/low emission buildings

Insights into standards, calculation methods, and simulation

methods

Energy in Buildings

4


5

Content

Introduction

Definitions

Heat load calculation

Annual heating energy demand

-----------------------------

Influencing factors

Simplified methods

Situation in Switzerland


Motivation

Building

Micro climate

Systems

Occupant

Thermal

Performance

6


Energie in Gebäuden

Energy demand in private households

Source: Prognos 2013

Energy in Buildings

Space

heating

Domestic hot

water


Energy in Buildings

Change from 2000 to 2012

Source: Prognos 20138


New tendencies of energy efficient construction

9

Until 1975

conventional

approx. 220 kWh.m-2.a-1

Cantonal requirementsapprox. 48 kWh.m-2.a-1

9


Conventional

Low-energy (Minergie)

Passiv (Minergie-P)

Energie-autark

(Net-zero-energy)

E-Plus10

New tendencies of energy efficient construction


11

Content

Introduction



Influencing factors

Simplified methods



Heizwärmebedarf (Net energy demand)

Heizwärmebedarf

Definition

The energy which is required to

heat a building (or a zone).

It is independent from the

heating system or energy

carrier.


Heizwärmebedarf

Definition

Heizenergiebedarf (Brut energy demand)

Heizenergiebedarf

Erzeugung

Speicherung

Verteilung

Takes production, storage,

transmission and distribution of

heat into account.

Is equal to the net energy

demand divided by the

efficiency of the heating system

13


Heizwärmebedarf

14

Definition

Heizenergiebedarf (Brut energy demand)

Heizenergiebedarf

Erzeugung

Speicherung

Verteilung

Example:

Net energy demand for a

building: 38 kWh.m-2.a-1

100m²: 3800 kWh.a-1

Brut energy demand with e.g. oil

heating system:

3800/0.7 = 5430 kWh.a-1


15

Definition

Endenergiebedarf

Heizwärmebedarf

Heizenergiebedarf

Erzeugung

Speicherung

Verteilung

Final energy consumption

Final energy consumption:

• Domestic hot water

• Lighting

• Electrical appliances

+


16

Definition

Endenergiebedarf

Primary energy

Heizwärmebedarf

Heizenergiebedarf

Erzeugung

Speicherung

Verteilung

Primary energy

Generation,

conversion and

distribution of the

energy carrier

+


17

Definition

Net energy demand for heating

The energy needed for a zone / building when the total efficiency of the

installation for heating equals 100%

Brut energy demand for heating

The net energy demand divided by the efficiency of the heating system

(distribution and heat release)


18

Definition

Energy use

The energy used in a building for heating, domestic warm water, lighting and electric appliances . Also the energy used to make the heating system operational (pumps, fans, control system) is included

Primary energy use

The total energy used to produce and transport the energy necessary for the building


Heating demand calculations involves three

different types of calculations:

Heat load calculations – Used to design the

heating system

Annual heating energy demand – Used to determine the amount of energyneeded

Transients – Used to investigate time

dependent response of house and heating

system

19

Definition


-25

-20

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12

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03

.12

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24

.12

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Outside Dry-Bulb Temperature [°C]

Heat load calculation Annual heating energydemand

Transient

For dimensioning theheating system

For calculating theannual heating energy

demand

To calculate the time dependent behaviour

Reference temperature

Typical year Hourly values

20

Definition

HDDor

monthlyvalues


-25

-20

-15

-10

-5

0

5

10

15

20

25

30

01

.01

.

22

.01

.

12

.02

.

05

.03

.

26

.03

.

16

.04

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07

.05

.

28

.05

.

18

.06

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09

.07

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30

.07

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20

.08

.

10

.09

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01

.10

.

22

.10

.

12

.11

.

03

.12

.

24

.12

.



Transient



demand




21

Definition

HDDor

monthlyvalues


-25

-20

-15

-10

-5

0

5

10

15

20

25

30

01

.01

.

22

.01

.

12

.02

.

05

.03

.

26

.03

.

16

.04

.

07

.05

.

28

.05

.

18

.06

.

09

.07

.

30

.07

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20

.08

.

10

.09

.

01

.10

.

22

.10

.

12

.11

.

03

.12

.

24

.12

.



Transient



demand




22

Definition

HDDor

monthlyvalues


23

Content

Introduction



Influencing factors

Simplified methods



24


To dimension the heating system

What is the maximum heat load which the heating

system has to deliver based on a standardized indoor

temperature?

Gebäude-

kategorieRaumnutzung

Norm-

Innentemperatur

[°C]

Wohnen Schlafraum 20

Wohnraum 20

Küche 20

Industrie Arbeiten im Sitzen 20

leichter Aktivitätsgrad 20

mittlerer Aktivitätsgrad 18

Schwere körperliche

Arbeit15


25


To dimension the heating system

What is the maximum heat load which the heating

system has to deliver based on a standardized indoor

temperature?

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

01

.01

.

22

.01

.

12

.02

.

05

.03

.

26

.03

.

16

.04

.

07

.05

.

28

.05

.

18

.06

.

09

.07

.

30

.07

.

20

.08

.

10

.09

.

01

.10

.

22

.10

.

12

.11

.

03

.12

.

24

.12

.



26

Heat load calculations

How many radiators

How large radiators

Heat source requirement


27

Content

Introduction



Influencing factors

Simplified methods


Amount of heat, which is required over a year, to

maintain a certain indoor temperature within the

building

28



Energy performance of a building:

29

Heating demand

Solar

gains

Ventilation losses

Transmission-

losses

Internal

gains

Infiltration losses

Heating

load

tQ ISVTH


Transmission losses – Through walls, floor,

roof, windows, doors

30

What kind of heat losses does a house have?

Solar

gains

Transmission-

losses

Internal

gains

Heating

load


Ventilation losses – Heat lost by introduction

of cooler ambient air to the heated space

31


Ventilation lossesSolar

gains

Transmission-

losses

Internal

gains

Heating

load


Infiltration losses – Heat lost by leakage of

cooler ambient air into the house / heated air

outside the house

32


Infiltration-

losses

Solar

gains

Transmission-

losses

Internal

gains

Heating

load

Ventilation losses


What do losses depend on?

Source: Willems 2013

33

Indoor and outdoor temperature

Ventilation and infiltration flow rates

Area of walls, floor, roof, windows, doors

Insulation level of walls, floor, roof, windows, doors

U-values [W.m-2.K-1]

Building component Very bad bad middle good Very good

Roof >1.0 0.6 0.3 0.22 <0.15

Wall >1.5 0.8 0.4 0.3 <0.2

Window 5.2 3.5 1.8 1.4 <1.2

Typical U-values of building components

Source: hornbach.ch


34

Terminology

Protected (conditioned) volume V

The volume in a building, where thermal comfort is required and thus heating /

cooling

In residential buildings the protected volume

equals the habited volume.

External dimensions are used to calculate the

protected volume.

Reference area

Floor area in a building which is heated Quelle: Energieatlas


35

Definitions

Energy reference area (Energiebezugsfläche)

alle ober- und unterirdischen Geschossflächen, die innerhalb der

thermischen Gebäudehülle liegen

Building envelope area (Gebäudehüllfläche)

Fläche der thermischen Gebäudehülle (Aussenabmessungen)

Setzt sich zusammen aus Flächen gegen aussen, gegen

unbeheizte Räume und gegen Erdreich

Reduktionsfaktoren für Flächen gegen unbeheizt und Erdreich


36

Transmission heat losses

The transmission heat losses in a zone

Transmission heat losses to the outside environment

Transmission heat losses to other zones at different temperature (e.g. non-

heated spaces)


37

Building envelope area - dimensioning (SIA 416)

Building envelope area

Reduction factors for areas against unheated or to the ground


38

Building envelope area - dimensioning (SIA 416)

Building envelope area

Details


39

Building envelope area – an example

unbeheizt


40

AUT

The transmission heat loss for a building

component is given by

Heat transfer

coefficient

U-value

W/m2K

Heat flow

W, J/s

Surface m2

Temperature

difference




41

Heat transfer coefficient for the

thermal envelope

in

n

e h

ddd

h

U1

...1

1

2

2

1

1

Heat transfer

coefficient outside

W/m2K

Heat transfer

coefficient inside

W/m2K

Thermal

conductivity

W/mK

thickness

m

Number of layers


Heat transfer coefficient

42

Heat exchange between the environment and wall surface area is called the heat transfer coefficient(combined for radiation and convection).


Heat transfer coefficients - According SIA 180

43



44

Transmission heat lossesU-values according to SIA 380-1


Calculate the required thickness of an insulation material for ceiling construction of a

living room against a non heated attica space according to SIA.

1. Transmission heat losses

Mineral wool d=?, λ =0,04 W/mK

reinforced concrete ceiling d=140mm, λ =2,1 W/mK

gypsum plaster 15mm, λ=0,7 W/mK


Calculate the required thickness of an insulation material for ceiling construction of a

living room against a non heated attica space according to SIA.


in

n

e h

ddd

h

U1

...1

1

2

2

1

1

Mineral wool d=?, λ =0,04 W/mK

reinforced concrete ceiling d=140mm, λ =2,1 W/mK

gypsum plaster 15mm, λ=0,7 W/mK



47

The building envelope is composed of different

components, like walls, windows, glazing, roofs. The

transmission heat loss factor HT describes the total

heat loss through the building envelope.

Heat flow

WTemperature

difference

TT H

Transmission

heat loss factor

W/K



48

When the building is composed of N surfaces A1, A2, A3,

… and U values U1, U2, U3, … the heat loss factor is

given by

N

i

iiT UAUAUAUAH1

332211 ...

mTT UAH

the transmission heat loss factor is also given by

with Um the average U-value and AT the total surface

covering the protected volume



49

Thermal bridges (linear, point) are taken into account

using a linear heat transfer coefficient (W/mK) or

point heat transfer coefficient (W/K)

l

k

kk

m

j

jj

n

i

iiT zLUAH111

with Lj the length of the jth type of linear thermal bridges,

zk the number of repeating point thermal bridges

lijnvormig geconcentreerd

linear form point form


50

Thermal bridges according to SIA 380-1



51

Thermal bridges according to SIA 380-1



53

l

k

kk

m

j

jj

n

i

iiT zLUAH111

Transmission heat

transfer coefficient

W/K

Thermal bridgesTransmission heat losses


ΦT


6m

3m

3m

2m

Uw

1.1 W / m2 K

Uwall

0.2 W / m2 K

i 20C

e

1.1C

22°C

N

i

iiT UAUAUAUAH1

332211 ...

TT H

T HT ?


Limit and target values according to SIA 380-1 (Ausgabe 2009)

ΦT


Target valuesLimit values


59


Ventilation lossesSolar

gains

Transmission-

losses

Internal

gains

Heating

load

Infiltration-

losses


60

Ventilation heat (enthalpy) losses

The enthalpy heat loss due to ventilation can be due to air

exchange between the zone and the outside environment,

between different zones and due to air infiltration or

exfiltration of the ventilation (air heating) system


Natural ventilation

Mechanical ventilation

Air conditioning unit

Heat recovery ventilation

61


window ventilation duct ventilation


Natural ventilation: window ventilation

Ventilation through open

window. Usually, high, narrow

windows lead to a more

efficient air exchange than low,

wide windows.

Short time, fast ventilation=

Stoßlüftung/shock ventilation

62


Natural ventilation: duct ventilation

Vertical ducts, which

(specifically in winter) use the

thermal stack-effect. Additional

inlet air openings have to be

provided.

Suitable for rest rooms and

bathrooms.


Mechanical ventilationLow pressure ventilation (Unterdrucklüftung):

The air is sucked via a fan into the vent pipes. (Negative pressure in the interior, fresh air is sucked in

through joints and / or supply air openings)

Applications: sanitary area, large kitchens, rooms with high concentration of pollutant, targeted ventilation

possible (for example, „exhaust (kitchen) hood")

High pressure ventilation (Überdrucklüftung):

By generating an overpressure (fan in the supply air shaft) in the interior air escapes through joints and / or

exhaust ducts. Problematic: dust uptakes

Zentrale Ventilationsanlage im

Dachraum

Einzelventilatoren

64


65


eiaaV Vcn

3600

ca the specific heat (1000 – 1030 J/Kg.K),

n the air change rate per hour (1/h) also denoted ACH,

a the density of air (1.2 kg/m3),

V the volume (m3)

qV outside air flow rate

V

qn

V

Ventilation heat

losses


66


eiaaeiaaV Vcn

cG 3600

Ga the air flow (kg/s),

ca the specific heat (1000 – 1030 J/Kg.K),

n the air change rate per hour (1/h) also denoted ACH,

a the density of air (1.2 kg/m3),

V the volume (m3)

qV outside air flow rate



Typical ventilation and infiltration rates

67

Source: Gross et al. 2007

Window

tilted

Window

½ open

Window

fully openCross-

ventilation

Mech.

Vent.

with fans

Mech.

ventilation


68

Infiltration losses

Pressure difference between the indoors and outdoors cause leakage

through cracks near windows, doors, and corners of the house.

Usually the leakage is around 0.1- 0.3 ACH for new houses, and 0.5-1.5 ACH

for old houses.

The heat losses are calculated as the ventilation heat losses with the new

volumetric flow rate.


• For ventilation losses we introduce a heat loss factor HV

with rec the efficiency of the heat recovery system, when

using a infiltration / exfiltration ventilation system.

• Frequently we use the following simplified equation

69

recaaV Vcn

H 13600

VnHV 34.0



70

Heat recovery systems


V nL

3600V ca a i e

ΦV

3. Ventilation losses

nL

0.5 /h

a

1.2 kg/m3

ca

1000 J/kgK

QH T V g S I t


72

What heat gains does a building have?

Ventilation losses

Transmission

losses

Solar

gains

Internal

gains

Infiltration losses

heating

load


73

Internal gains

Solar radiation – heat which is gained through transmission of sun light

through windows which is absorbed by the indoor space, stored and released.

People – every person produces around 100-120 W/Person

Electrical appliances and lighting – thermal energy released from appliances

which is given to the environment.


75

The total solar irradiation on a surface with angle b,

consists of a direct and diffusive part. We consider the

diffusive radiation of the sky to be isotropic.

Direct radiation

Diffuse radiation

from the sky

Diffuse radiation

from the ground

Solar gains


76

Solar gains

The total irradiation depends highly on weather conditions especially on the cloudiness


Solar gains

77

The total irradiated solar energy depends on the time of the year(summer vs winter), the orientation and the inclination of the surface.

Example of a South oriented surface

Low

sun

altitude

during

winter

21th december

21th december

21th june


78

Solar gains The total irradiated solar energy depends on the time of the

year (summer vs winter), the orientation and the inclinationof the surface.

Example of vertical surfaces with different orientation


Solar gains

79

South Facing FacadesFor a predominately South facing facade,

effective solar shading can be achieved

using a fixed horizontal solar shading

system.

During the day in both summer and

spring/autumn, a fixed horizontal system

projecting out from the window can be

designed to shade the building during

office hours.

In the winter such a device cannot stop

direct rays of the sun penetrating the

building since the sun is much lower.

However the heat gain and solar glare is

greatly reduced in winter and therefore

this may not considered to be a major

problem.

summer

winter

Spring /

autumn


80

east west

Solar gains

East or West Facing FacadesWith a predominantly East or West facing facade, a

fixed system will not perform well throughout the

whole day as the altitude of the sun is much lower.

Sunlight will pass directly under most horizontal

shading systems as shown in the illustration below.

To overcome this problem, effective solar shading

can be achieved using a movable solar shading

system


81

STEsingle glazing

Transparent

component

irradiation EsT : the total solar

irradiation including

direct and diffuse parts

on the transparent

component (W/m2)

Solar gains through transparent components


82

STE

STS E

One part of the irradiation

is reflected with ρS the

reflection coefficient

one part is transmitted,

with τS the transmission

coefficient

one part is absorbed, with

αS the absorption

coefficient

reflection

Transparent

component

irradiation

STS Eabsorption

STS E

transmission

single glazing



83

STS E

STE Due to absorption the

glass pane heats up and

releases heat by

convection and radiation

to the environment

according to the heat

transfer coefficient hi for

inside and he for outside

Transparent

component

absorption

irradiation

single glazing



84

STE

The total heat admission through

glass is the sum of

the radiation transmitted through

glass

the inward convective /radiative

flow from the heated glass due to

absorbed solar radiation

the heat flow due to outdoor-

indoor temperature differences

Transparent

component

irradiation

STS E

transmission

STS Eabsorption

ie

single glazing



85

STE

Transparent

component

irradiation

STS E

transmission

STS Eabsorption

ie

Solar heat gain coefficient

or G-value

is the fraction of incident solar

radiation admitted through a

window, both directly

transmitted and absorbed and

subsequently released inward.

SHGC is expressed as a number

between 0 and 1. The lower a

window's solar heat gain

coefficient, the less solar heat it

transmits.


single glazing


86

STE

STS E

Transparent

component

irradiation

ie

SiS

hhhg

Overall solar heat

gain coeffcient for

single glazing or ‘g’

valuetransmission

STS Eabsorption



88

STE

STS E

Transparent

component

irradiation

Transmission coefficient

for double glazingtransmission

21

21

1

S

1 2



91

Solar gains

sTrs EgAF

The glass reduction factor Fr takes into account the

surface reduction due to the window frames

Other influencing factors

Shadowing (protection by the horizon, shadowing devices)

Soiling of the glass, use of curtains

g-value or solar

heat gain

coefficientHeat flow

W Surface m2

Solar irradiation

W/m2

Glass

reduction factor

Solar irradiation – Heat gained by mainly transmission of sunlight through

windows which is then captured by inside capacity, stored and emitted.


92

Solar gains

Reduction factor due to solar shading devices

Without shading

system

internal shading

system

external shading

system


Calculate the solar gains of a south oriented 2m2 big window in vertical wall

at the location of Vienna. (frame 20%, g=0,6)

4. Solar gains

sign desciption value unit

IS Irradiation- south 356 kWh.m2.a-1

IN Irradiation- north 150 kWh.m2.a-1

IO Irradiation- east 210 kWh.m2.a-1

IW Irradiation- west 210 kWh.m2.a-1

Ihorizontal Irradiation- horizontal 368 kWh.m2.a-1


Calculate the solar gains of a south oriented 2m2 big window in vertical wall

at the location of Vienna. (frame 20%, g=0,6)

4. Solar gains sTrs EgAF

sign desciption value unit

IS Irradiation- south 356 kWh.m2.a-1

IN Irradiation- north 150 kWh.m2.a-1

IO Irradiation- east 210 kWh.m2.a-1

IW Irradiation- west 210 kWh.m2.a-1

Ihorizontal Irradiation- horizontal 368 kWh.m2.a-1


95

What heat gains does a building have?

Ventilation losses

Transmission

losses

Solar

gains

Internal

gains

Infiltration losses

heating

load


96

Internal heat gains

Internal gains I based on SIA (Appliances, lighting, people)

People

Appliances


97

Electric appliances


98

Monthly heat balance for a zone (room)

tQ ISVTH

T : transmission heat losses

V : ventilation heat losses

s : Solar heat gains

I : Internal heat gains

t : the time of heating in a month

: the use factor

Net energy

demand J


Energy performance of a building:

99

Heating demand

Solar

gains

Ventilation losses

Transmission-

losses

Internal

gains

Infiltration losses

Heating

load

tQ ISVTH


100

Monthly heat balance for a zone (room)

tQ ISVTH

T : transmission heat losses

V : ventilation heat losses

s : Solar heat gains

I : Internal heat gains

t : the time of heating in a month

: the use factor

Net energy

demand J


How much of heat gains can be utilised within the building

When the losses are low and the gains are high, the inside temperature can rise above the comfort temperature, and gains become useless, or even cost energy (cooling)

101

The use factor

Small lossesHigh gains


102

The use factor

The use factor depends on the ratio between

heat gains and heat losses using the factor g

The use factor depends on the heat capacity or

heat storage of the building

00,

VT

VT

IS ifgg


103

Capacity of a building

The diurnal variations of the outside temperature (green line) result in heat flows into the building during the day, where part of the heat is stored in the material.

During the night, the heat flow is reversed (from the building to the environment).


104


The higher the

thermal mass, the

greater the time lag

and the smaller the

ratio between the

maximal variation of

internal and external

temperatures

(Timax/T0max).

Thus thermal mass

leads to increased

thermal comfort and

to reduced peak

loads for technical

systems.


105



106


The use factor depends on the capacity of a

building, which is expressed by the time

constant.

The time constant is given by the ratio between

capacity and loss factor

VT HH

C


107


The capacity is the capacity of the layers

situated at the inside from the insulation layer

(up to a certain thickness, e.g. 0.1 m)

layers

jjji

walls

ii dcCCAC ,


The use factor

108

The use factor as a function of the factor g and

the time constant

Use

facto

r

Gain/Loss ratio

Time constant


Used only for certain parts of the

day (e.g. schools, retail,

restaurants,…)

Always in use

Use factor for thermal gains


g 1 g a

1 g a1

5. The use factor

ΦT

ΦV

ΦS

QHΦI

g 151 338

208 347 0.88

QH T V g S I t

Use factor

a ao

o

Parameter for

Use factor

(thermal inertia)

g S I

T V

Gain/Loss-ratio


111

The energy demand for heating

Determine the net energy demand for heating for every zone of the building, for every month and sum up the values over the year

Use monthly averages

When the monthly average is negative, we assume the energy demand for heating zero


112

The energy demand for heating

Determine the brut energy demand Divide the monthly net energy demand by the monthly average efficiency of the heating

system (distribution, heat release by radiators, convectors, …)

Heizwärmebedarf

Heizenergiebedarf

Erzeugung

Speicherung

Verteilung +

When solar energy systems are present, we

subtract the useful contribution of the solar

system from the total energy use


6. Energy performance number

ΦT

ΦV

ΦS

QHΦI

QH T V g S I t

QH T V g S I t

QH Januar 208 347 0.61 151 338 (31 24 60 60)

QHJanuar 693MJ

g 1 g a

1 g a11 0.881.32

1 0.881.321 0.61


QH Januar

AE693

5 6 23.1MJ / m2

ΦT

ΦV

ΦS

QHΦI

6. Energy performance number

QH T V g S I t

QH

AE

these buildings are examples from austria of very low energy … › content › dam › ethz ›...

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