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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
Sustainable buildings
Mode-Gakuen Spiral
Towers: Nagoya, Japan
Traditional teepee, Taos,
New Mexico
target is: minimized primary energy consumption
5/75
Sustainable buildings
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
(high absorptance, low emittance)
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
(high absorptance, low emittance)
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
Reference collector area Ak
AA AA
AA
Aa Aa Aa
32/75
Reference collector area Ak
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
Efficiency and power calculation
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
Efficiency and power calculation
flat-plate vacuum tube
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
flat-plate vacuum tube
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
Solar system parameters
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
Solar system parameters
specific solar heat gain qss,u [kWh/m2.a]
solar fraction [-]duss
uss
p
d
p
uss
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 %
Hot water example - balance
49/75
qss,u = 300 kWh/m2 f = 65 %
Hot water example - balance
increase of solar fraction means decrease of specific heat gain
50/75
Hot water example - balance
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 %
solar yields 400 to 500 kWh/m2.a
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 %
solar yields 250 to 350 kWh/m2.a
block of flats
(40 to 200 m2; 4 to 16 m3)
solar fraction 10 to 20 %
solar yields 350 to 450 kWh/m2.a
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
Example – solar DHW system
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
Example – solar DHW system
month tes Gm ηηηηk HT,month
°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
Example – solar DHW system
month tes Gm ηηηηk HT,month
°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
Example – solar DHW system
month tes Gm ηηηηk HT,month
°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
Example – solar DHW system
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
Example – solar DHW system
měsíc Qku,month Qku,month Qd,HW Qss,u Qss,u
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
2 collectors 3 collectors 2 collectors 3 collectors
71/75
Example – solar DHW system
měsíc Qku,month Qku,month Qd,HW Qss,u Qss,u
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
2 collectors 3 collectors 2 collectors 3 collectors
72/75
Example – solar DHW system
měsíc Qku,month Qku,month Qd,HW Qss,u Qss,u
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
2 collectors 3 collectors 2 collectors 3 collectors
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