energy sources for sustainable buildings - cvut.czzmrhavla/ee/ee_esb.pdf · energy sources for...

1/75

Energy Sources

for Sustainable Buildings

with focus on

Solar Thermal & Heat Pumps

Tomáš Matuška

Department of Environmental Engineering

Czech Technical University in Prague

2/75

Content

primary energy as a measure for today buildings

example of primary energy balance for a passive house with

variants of energy source

solar thermal systems

solar collectors & systems, principles, parameters, applications

view on system balance

heat pumps

types, principles, parameters, applications

view on system balance

3/75

Sustainable buildings

what criteria to be met?

thermal comfort

healthy indoor environment

minimized impact on environment (building phase, operation phase,

demolition phase)

safety

economic effectivity

esthetics

social

low energy consumption – most pronounced in last decades

4/75


Mode-Gakuen Spiral

Towers: Nagoya, Japan

Traditional teepee, Taos,

New Mexico

target is: minimized primary energy consumption

5/75


we have many names for „new buildings“

low-energy

passive (clear definition by Passive House Institute)

zero-energy (general definition by EU Directive, no binding values,

member states can define the energy levels)

energy active, clima active

energy plus

self-sufficient

green, eco

energy efficient

autarctic

3-litre

buildings

European legislation:

nearly zero energy buildings from

2020 as energy standard

expressed by primary energy

6/75

Sustainable buildings - differences

zero energy house

is not a house without heating demand

is not a house without external energy demand

is a house with zero annual balance of primary energy (input/output]

annual consumption is compensated by annual production

self-sufficient house

is not a house without heating demand

is a house without external energy demand

is a house with zero actual balance of energy needed (input/output]

actual consumption is covered by actual production

7/75

Primary energy

definition

primary energy = energy from renewable and nonrenewable

sources, which has not undergone any conversion or

transformation process

fossil fuels energy with added energy required for the mining,

transport, treatment (losses)

renewables – most of them derived from solar energy

nonrenewable primary energy should be minimized!

impact to environment, exhausting resources, etc.

term „primary energy“ practicaly associated with „nonrenewable

primary energy“

8/75

Primary energy

conversion factor F

expresses requirement of energy carrier (fuel, electricity, etc) on

primary energy

ratio of primary energy use to energy content delivered to building

statistics: local, global, uncertainties

even renewables could be primary energy intensive!

e.g. wooden pellets – the pellet production in factory consumes energy

9/75

Conversion factor F

Energy carrierF

[kWh/kWh]

Natural gas and other fossil fuels 1,1

Electric energy 3,0

Wood and other biomass 0,1

Wooden pellets 0,2

District heating with RES < 50 % 1,0

District heating with RES between 50 and 80 % 0,3

District heating – with RES > 80 % 0,1

Ambient energy, solar systems 0,0

Electricity export from building -3.0

Heat export from building -1.0

Czech legislation

10/75

Use of primary energy

11/75

Use of primary energy

primary energy ratio PER

express requirements of building technical system on primary energy

ratio between energy supplied to cover the building demands Q

(heating, cooling, DHW, lighting, appliances, pumps, fans, etc.) and

primary energy demand PE and

FPE

QPER

η==

η operational efficiency of the whole system, related to

energy content of fuels

12/75

Examples – PER for heating sources

Heat source / energy carrier F ηηηη PER

[ - ] [ - ] [ - ]

Electric boiler / electricity 3.00 1.00 0.33

Heat pump / electricity 3.00 2.90 0.97

Gas boiler standard / natural gas 1.10 0.75 0.68

Gas boiler condensing / natural gas 1.10 0.95 0.85

Pellet boiler / wooden pellets 0.20 0.80 4.00

Solar thermal system / solar energy 0.00 1.00 ∞

13/75

Primary energy demand (passive FH)

passive family house 150 m2

space heating 3000 kWh/a, DHW 3000 kWh/a, auxiliary 300 kWh/a

electric boiler, efficiency 100 %;

gas boiler standard (cycling), efficiency 75 %;

gas boiler condensing (output control), efficiency 95 %;

pellet boiler (storage), efficiency 80 %;

heat pump with COP = 3,0;

solar combined system with supply of 2000 kWh/m2.a (8 m2 x 250 kWh/m2)

and electric back-up heater (efficiency 100 %);

solar combined system with supply of 2000 kWh/m2.a (8 m2 x 250 kWh/m2)

and condensing boiler (efficiency 95 %).

14/75

0 20 40 60 80 100 120 140

electric boiler

gas boiler standard

gas boiler condensing

pellet boiler

heat pump

solar system + electric boiler

solar system + gas boiler

PE [kWh/(m2.a)]

Primary energy demand (passive FH)

demands: space heating: 3000 kWh/a, DHW: 3000 kWh/a, auxiliary: 300 kWh/a

60 kWh/m2.a

30 kWh/m2.a

68 m2 PV

7 m2 PV

20 m2 PV

46 m2 PV

26 m2 PV

35 m2 PV

28 m2 PV

15/75

Solar Thermal Systems

solar radiation

collectors

system performance

16/75

Solar energy in Europe

zdroj: PVGIS

17/75

Solar energy in Czech republic

zdroj: PVGIS

18/75

Solar energy in Austria

be careful for transfer of experience with solar !

19/75

Optimum slope ?

southeast west

southeast - southwest

15-6

0°

20/75

Solar collectors

Header pipe forheat removal

Risers - pipes

Transparent cover - glazing

Absorber

Thermal insulation

Collector frame

21/75

Solar flat-plate collectors

flat glazing

solar glass, low-iron glass

flat absorber

selective coating

(high absorptance, low emittance)

copper, aluminium

pipe register

serpentine, harp

collector box

insulated

22/75

Solar flat-plate collectors

advantage for integration into building envelope

roof

facade

23/75

Solar tube collectors with flat absorber

tube (cylinder) glazing

vacuum tube

flat absorber

selective coating


copper, aluminium

heat transfer to fluid

U-pipe or concentric pipe

heat pipe (evaporation,

condensation)

24/75

Solar tube collectors with round absorber

tube (cylinder) glazing

evacuated

tube (cylinder) absorber

selective coating on glass tube


heat transfer to fluid

heat transfer fin

U-pipe or concentric pipe

heat pipe (evaporation,

condensation)

25/75

Difference in vacuum tube collectors

tube collector with flat absorber tube collector with tube absorber

26/75

Solar collector principle

Heat loss through

glazingReflection

at absorber

Reflection at glazing

Incident solar

radiation

Heat loss through

side and back wall

Heat removal by fluid

27/75

Determination of heat output

)( k1k2k ttcMQ −⋅⋅= &&

)( k1k2k ttcMQ −⋅⋅= &&

tk1

tk2G

M. kAG

Q

⋅= k

&

η

efficiency [-]

heat output [W]

testing performed according to EN 12975-2 (EN ISO 9806)

stationary conditions defined in standard, at least 4 different points

221 kk

mtt

t+=

mean fluid temperature [-]

te

Ak

28/75

Measured points and regression

0,0

0,2

0,4

0,6

0,8

1,0

0,00 0,05 0,10 0,15 0,20

(t m - t e)/G [m2.K/W]

ηηηη [-]

as close as possible (tm – te) = 0

regression

parabolic function

29/75

Efficiency from testing

η0 „optical“ efficiency [-], better: zero-loss efficiency

a1 linear heat loss coefficient [W/(m2.K)]

a2 quadratic heat loss coefficient [W/(m2.K2)]

values ηηηη0, a1, a2 related to reference collector area Ak (defined in EN standard)

coefficients are given by producer, supplier or testing institute based ontest report in accordance to EN 12975-2

2

210

−⋅⋅−

−⋅−=

G

ttGa

G

tta ememηη

regression parabolic function in form y = a + bx + cx2

30/75

Reference collector area Ak

gross area: AG

aperture area: Aa

absorber area: AA

k

k

AG

Q

⋅=

&

η

31/75


AA AA

AA

Aa Aa Aa

32/75


aperture: comparison of collector quality, construction

gross area: decision on potential for given application (limited space on roof)

Aa = 0,9 AG Aa = 0,75 AG Aa = 0,6 AG Aa = 0,8 AG

33/75

Typical coefficients

Collector typeηηηη0 a1 a2

- W/(m2K) W/(m2K2)

Unglazed 0.85 20 -

Glazed with nonselective absorber 0.75 6.5 0.030

Glazed with selective absorber 0.78 4.2 0.015

Vacuum single tube (flat absorber) 0.75 1.5 0.008

Vacuum tube Sydney 0.65 1.5 0.005

34/75

Heat output (power) of solar collector

GAQ kk 0η=&

solar collector power (normal incidence, clear sky)

installed (nominal) power

for defined conditions (according to ESTIF):

G = 1000 W/m2 te = 20 °C tm = 50 °C

peak power (without heat loss)

])()([ 2210 ememkkk ttattaGAGAQ −⋅−−⋅−=⋅⋅= ηη&

G = 1000 W/m2

35/75

0

400

800

1200

1600

0 50 100 150

Qk

[W]

(tm - te) [K]

G = 1000 W/m2

Heat output (power) of solar collector

installed heat power

peak heat power

36/75

Testing of solar collectors

Reliability tests

internal pressure

high temperature resistance

exposure

external thermal shock

internal thermal shock

rain penetration (glazed)

mechanical load

impact resistance

test report (!)

37/75

Solar collector / applications

0.0

0.2

0.4

0.6

0.8

1.0

0 20 40 60 80 100 120 140 160t m - t e [K]

ηηηη [-]

unglazed flat/plate selective

single vacuum tube Sydney vacuum tube

pools hot water & space heating

process heat high temperature

industrial applications

38/75

Efficiency and power calculation

let’s make an example

39/75


flat-plate vacuum tube

η0,a 0,75 0,65 -

a1,a 3,5 1,5 W/m2K

a2,a 0,015 0,005 W/m2K2

AG 4 m2

Aa 3,6 2,4 m2

calculation of daily efficiency for April,

Prague city, slope 45°, azimuth 45°

GT,m W/m2

te,s °C

tk,m °C

473

10,7

40

40/75



ηk -

Qk,m W

Qk,month kWh/month

( )mT

semk

mT

semkk

G

tta

G

tta

,

2,,

2

,

,,

10

−⋅−

−⋅−= ηη

dayTkkdayk HAQ ,, ⋅⋅= η

mTkkmk GAQ ,, ⋅⋅= η&

0,51 0,55

862 622

220 159

=monTH ,121 kWh/m2.month

41/75

Nominal and peak power


G 1000 W/m2

te,s 20 °C

tm 50 °C

ηk

Qk,nom W

Qk,peak W

GAQ kpeakk 0, η=&

0,63 0,60

2273 1441

2700 1560

42/75

Solar collectors applications

low temperature (< 40 °C)

pool water heating (unglazed collectors)

mid temperature (< 90 °C)

hot water, space heating (single glazed flat-plate collectors, vacuum

tube collectors)

high temperature (> 90 °C)

process heat (vacuum collector, multiple glazing collectors,

concentrating collectors)

43/75

Balance of solar thermal system

solar

collectors

solar

storage

tank

load

storage

collector

lopp

solar storage

loop

load loop

back-up heating

back-up

heaterboun

dary

of s

olar

sys

tem

44/75

Solar system parameters

Annual heat gain, solar yield [kWh/a]

supplied into storage Qk

supplied to load – used solar system gain Qss,u

Annual energy savings Qu [kWh/a]

influenced by operational efficiency of given heat source (boiler) ηhs

consumption of electricity for pumps in solar system

base for primary enegy savings, emission savings

45/75


Specific anual solar heat gain qss,u [kWh/(m2.a)]

referenced to aperture area of solar collectors Aa

specific annual energy savings

economic parameter:

savings / m2 vs. investment / m2

Solar coverage, solar fraction f [%]

f = 100 * used heat gain / heat demand

... percentual coverage of demand

46/75


specific solar heat gain qss,u [kWh/m2.a]

solar fraction [-]duss

uss

p

d

p

uss

QQ

Q

Q

Q

Q

Qf

+=−==

,

,, 1

47/75

qss,u = 400 kWh/m2 f = 60 %

Hot water example - balance

48/75

qss,u = 600 kWh/m2 f = 40 %


49/75

qss,u = 300 kWh/m2 f = 65 %


increase of solar fraction means decrease of specific heat gain

50/75


0

500

1000

1500

2000

2500

3000

3500

1 2 3 4 5 6 7 8 9 10 11 12

měsíc

Q TV , Q k

[kWh] 65 %60 %40 %

month

51/75

How to design a solar system

economic design

maximize usable specific heat gains qss,u [kWh/m2a] = minimize the

collector area

ecologic design

maximize solar fraction f [%] = maximize primary energy savings =

maximize the collector area

limited design

limiting conditions by building structure (roof size, possible slope and

orientation of collectors, architectonic consequences), optimizing size of

collector field

right design meets expectation of investor

52/75

Collector area influences components

flowrate of solar system

pipe dimension

insulation thickness

pressure loss of loops, hydraulics

size of circulation pump

volume of solar system

size of expansion vessel

support constructions

heat exchanger, storage size

53/75

Solar systems for hot water preparation

54/75

Solar systems for hot water preparation

family houses

(3 to 8 m2; 200 to 400 l), solar fraction 50 to 70 %

solar yields 300 to 400 kWh/m2.a

block of flats, hotels, ...

(from 25 to 200 m2; 1 to 8 m3), solar fraction 40 až 50 %


water preheating

solar fraction to 40 %

solsolar yields 500 to 600 kWh/m2.a

55/75

Solar combined systems (HW+SH)

56/75

Solar combined systems (HW+SH)

family houses

(6 to 12 m2; 500 to 2 000 l)

solar fraction: standard houses 10 to 20 %

low energy houses, passive houses 20 to 40 %


block of flats

(40 to 200 m2; 4 to 16 m3)

solar fraction 10 to 20 %


57/75

Passive houses and solar systems

low heat demand for DHW

reduction of HW demand : energy saving shower & facets

heat loss reduction: pipe insulation

low space heating demand

reduced transmission loss

ventilation with heat recovery

use of solar energy gains in interior

need for space heating only in extreme winter period

i.e. period without sufficient solar radiation - problematic use of solar system for space heating in low energy houses

low heat load = low temperature heating systems = advantage for RES

58/75

Heat demand in passive house

0

500

1000

1500

2000

I II III IV V VI VII VIII IX X XI XII

měsíc

po

třeb

a te

pla

[kW

h/m

ěs]

period without heating

energy passive house

space heating 3000 kWh/a

hot water 3000 kWh/a

month

hea

t d

eman

d [

kWh

/mo

nth

]

59/75

How to design a combined system for PH?

0

500

1000

1500

2000

I II III IV V VI VII VIII IX X XI XII

měsíc

po

třeb

a te

pla

[kW

h/m

ěs]

4 m2 of solar collectors = 380 kWh/m2 = 31 %

8 m2 of solar collectors = 240 kWh/m2 = 39 %

with no use in house

month

hea

t d

eman

d [

kWh

/mo

nth

]

60/75

Example – solar DHW for family house

2 or 3 collectors? for water heating

61/75

Example – solar DHW system

monthly heat demand Qd,HW for DHW

daily demand 8.4 kWh/day x number of days

monthly available solar system gain Qk,u

calculation of collector efficiency for given climate condition ηk

calculation of monthly irradiation HT,month

balance of demand x gain

( )[ ]HWd,kmonthT,kmonthu,ss, ;19,0min QpAHQ −⋅⋅⋅⋅= η

62/75

Solar collector efficiency

mean daily fluid temperature in collector tk,m

Applicationtk,m [°C]

Water preheating, solar fraction < 35 % 35

Hot water preparation, 35 % < solar fraction < 70 % 40

Hot water preparation, solar fraction > 70 % 50

How water and space heating, solar fraction < 25 % 50

How water and space heating, solar fraction > 25 % 60

63/75

Heat losses – relative figures

reduction factor ( )pAHQ −⋅⋅⋅⋅= 19,0 kdayT,kuk, η

Application p

Hot water preparation, up to 10 m2 0,20

Hot water preparation, from 10 to 50 m2 0,10

Hot water preparation, from 50 to 200 m2 0,05

Hot water preparation, above 200 m2 0,03

Hot water and space heating, up to 10 m2 0,30

Hot water and space heating, from 10 to 50 m2 0,20

Hot water and space heating, from 50 to 200 m2 0,10

Hot water and space heating, above 200 m2 0,06

64/75

Example – solar collector

solar collector: flat-plate

η0 = 0.75

a1 = 3.5 W/m2K

a2 = 0.015 W/m2K2

Ak1 = 1.8 m2 (aperture)

slope 45°

azimuth 15° to west

65/75


month tes Gm ηηηηk HT,month

°C W/m 2 −−−− kWh/m 2

1

2

3

4

5

6

7

8

9

10

11

12

66/75



°C W/m 2 −−−− kWh/m 2

1 1.8 408

2 2.7 479

3 6.3 526

4 10.7 521

5 16 516

6 18.6 512

7 20.5 508

8 21.1 509

9 17.1 509

10 11.7 479

11 6.4 417

12 3.6 377

67/75



°C W/m 2 −−−− kWh/m 2

1 1.8 408 0.37

2 2.7 479 0.43

3 6.3 526 0.49

4 10.7 521 0.53

5 16 516 0.57

6 18.6 512 0.59

7 20.5 508 0.60

8 21.1 509 0.61

9 17.1 509 0.58

10 11.7 479 0.52

11 6.4 417 0.43

12 3.6 377 0.36

68/75



°C W/m 2 −−−− kWh/m 2

1 1.8 408 0.37 35.0

2 2.7 479 0.43 55.8

3 6.3 526 0.49 92.3

4 10.7 521 0.53 126.0

5 16 516 0.57 146.6

6 18.6 512 0.59 136.8

7 20.5 508 0.60 136.9

8 21.1 509 0.61 147.3

9 17.1 509 0.58 103.7

10 11.7 479 0.52 84.1

11 6.4 417 0.43 44.6

12 3.6 377 0.36 28.3

69/75


měsíc Qku,month Qku,month Qd,HW Qss,u Qss,u

kWh kWh kWh kWh kWh

1

2

3

4

5

6

7

8

9

10

11

12

2 collectors 3 collectors 2 collectors 3 collectors

70/75



kWh kWh kWh kWh kWh

1 33 50

2 63 94

3 118 177

4 173 259

5 217 325

6 209 314

7 214 322

8 233 349

9 155 233

10 113 169

11 49 74

12 26 40


71/75



kWh kWh kWh kWh kWh

1 33 50 260

2 63 94 235

3 118 177 260

4 173 259 252

5 217 325 260

6 209 314 252

7 214 322 260

8 233 349 260

9 155 233 252

10 113 169 260

11 49 74 252

12 26 40 260


72/75



kWh kWh kWh kWh kWh

1 33 50 260 33 50

2 63 94 235 63 94

3 118 177 260 118 177

4 173 259 252 173 252

5 217 325 260 217 260

6 209 314 252 209 252

7 214 322 260 214 260

8 233 349 260 233 260

9 155 233 252 155 233

10 113 169 260 113 169

11 49 74 252 49 74

12 26 40 260 26 40


73/75

Example – results

total heat demand Qd,HW

3066 kWh/a

total solar system usable gain Qss,u

2 collectors

3 collectors

solar fraction specific heat gains

2 collectors

3 collectors

what is better?

economic

ecologic

1604 kWh/a

2122 kWh/a

52 %

69 %

446 kWh/m2.a

393 kWh/m2.a

74/75

Example – results

75/75

Tomáš Matuška

Dept. of Environmental Engineering

Faculty of Mechanical Engineering,

CTU in Prague

Technická 4, 166 07 Prague 6

[email protected]

energy sources for sustainable buildings - cvut.czzmrhavla/ee/ee_esb.pdf · energy sources for...

Documents