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EnginEEring AnD inSTALLATiOn 2011 | STiEBEL ELTrOn
SOLAr | rEnEwABLES
A 296003-36390-8670
STIEBEL ELTRON GmbH & Co. KG | Dr.-Stiebel-Straße
37603 Holzminden | www.stiebel-eltron.com
» iSSuE nOvEmBEr 2011
EnginEEring AnD inSTALLATiOn.
SOLAr
DHw rEnEwABLES Air cOnDiTiOning rOOm HEAT ing
296003_Plama_Solar_Umschlag_en.indd 1 02.01.2012 12:10:04
EnginEEring AnD inSTALLATiOn
Issue November 2011
Reprinting or duplication, even partially, only with our express permission.
STIEBEL ELTRON GmbH & Co. KG, D-37603 Holzminden
Legal notice
Although we have tried to make this technical guide as accurate as possible, we are not liable for any inaccuracies
in its content. Information concerning equipment levels and specification are subject to modification. The equipment
features described in this technical guide are not binding properties of our products. Due to our policy of ongoing
improvement, some features may have subsequently been changed or even removed. Our advisors will be happy to
consult with you regarding the currently applicable equipment features. Pictorial illustrations in this technical guide
only represent sample applications. The illustrations also contain installation components, accessories and special
equipment, which is not part of the standard delivery.
Specification
Dimensions in the diagrams are in millimetres unless stated otherwise. Pressure figures may be stated in pascals
(MPa, hPa, kPa) or in bars (bar, mbar). The details of threaded connections are given in accordance with ISO 228. Fuse
types and sizes are stated in accordance with VDE. Output details apply to new appliances with clean heat exchangers.
296003_Plama_Solar_Umschlag_en.indd 2 10.11.2011 15:57:36
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 2 10.11.2011 16:00:45
Introduction 5
Investment for the future 5
Basics 6
Principles of system engineering 8
DHW heating and coverage 9
General function 16
Terminology and descriptions 18
Collector orientation and inclination 19
Efficiency curve 20
System design 22
Climate zones | Europe 23
Small DHW systems | Sizing nomograph 24
Large DHW systems 26
Hygienic DHW heating 28
Central heating backup 29
Private swimming pool water heating 30
Sizing the expansion vessel 32
Sizing heat exchangers 34
Sizing collector arrays 35
Collector array sizing up to 16 collectors 36
Collector array sizing from 16 collectors 38
Pipe friction diagram, copper pipes 39
Pipework | Solders | Ventilation 40
Safety valve | Heat transfer medium | Thermal insulation 41
Lightning protection 42
Transport | Installation height | Snow and ice load 43
Edge and corner areas 44
Types of installation 45
Vertical installation on tiled roofs 45
Horizontal installation on tiled roofs 46
Horizontal installation on tiled roofs above each other 47
Installation on corrugated roofs 48
Wall mounting 49
Flat roof installation 50
Slate roof installation 52
Plain tile roof installation 53
Roof integration 54
Product catalogue for collectors 57
High performance flat-plate rooftop collector | SOL 27 premium 57
High performance flat-plate rooftop collector | SOL 27 premium W 62
High performance flat-plate rooftop collector | SOL 27 basic 68
High performance flat-plate rooftop collector | SOL 27 basic W 73
High performance flat-plate collector for roof integration | SOL 23 premium 94
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 3 10.11.2011 16:00:45
Product catalogue for accessories 102
Control unit | SOM 6 plus 102
Control unit | SOM 7 plus 104
Control unit | SOM 8 plus 106
Heat meter | SOM WMZ SOL 111
Compact installation | SOKI basic 112
Compact installation | SOKI 6/7 plus 114
Compact installation | SOKI E premium 116
Components 118
DHW cylinders 124
Wall mounted cylinder | KS 150 SOL 124
Floorstanding cylinder | SBB plus 128
Floorstanding cylinder | SBB basic 134
Floorstanding cylinder | SBB WP SOL 140
Floorstanding cylinder | SBB SOL 146
Heating water buffer cylinders and instantaneous water heaters 152
Buffer cylinder | SBP E SOL 152
Instantaneous water heater | SBS W SOL 162
Combi cylinders 170
Combi cylinder | SBK 600/150 170
Product catalogue for DHW heating accessories 175
Product range 175
Plate heat exchangers 176
Fresh water modules 177
Electric flanged immersion heaters 178
Indirect coils 180
Solar sets 181
Solar sets for DHW heating 181
Solar ventilation sets for DHW heating and central heating 182
Solar sets for heat pump backup 184
Standard circuits 187
Key 187
Reheating with integral electric flanged immersion heater | Integral solar control unit 189
Reheating with instantaneous water heater 190
Central heating backup | Reheating with heat pump | Instantaneous cylinder 191
Integral ventilation unit with solar DHW heating and central heating backup 193
Central heating backup | Reheating with gas or oil boiler | Combi cylinder 195
Central heating backup | Swimming pool | Reheating with gas/oil | Two-cylinder system 197
Central heating backup | Reheating with heat pump | Two-cylinder system 199
Safety datasheet | H-30 L 201
Safety datasheet | H-30 LS 205
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 4 10.11.2011 16:00:45
Investment for the future
Introduction
The outlook is sunny:
The earth’s energy resources
The sun provides us with an inexhaustible
supply of energy. Every year, it delivers
2850 times more energy than we require
on earth. Even in central European lati-
tudes, we can still utilise solar radiation to
generate useful heat, because solar ener-
gy is available in unlimited amounts, free
of charge. It offers complete independ-
ence and enables decentralised provision
of energy.
In contrast to fossil fuels, solar energy
is straightforward and environmentally
responsible, as the combustion of fos-
sil fuels causes harmful emissions. The
negative effects on the environment can
be proven.
Our demand for energy will only in-
crease with time. Renewables, and solar
energy in particular, will play an in-
creasingly important part in our endeav-
our to reduce emissions for a safer and
cleaner future.
Advantages of solar thermal systems:
l Relative independence from fl uctuat-
ing energy prices
l High DHW convenience in all applica-
tion areas
l In spring and autumn, the central
heating system can be backed up
with water heated by solar energy
l Greater independence from fl uctuat-
ing energy prices
l Value added to your property
l CO
2
emissions are substantially re-
duced
l Conserving fossil fuels
l Environmental awareness is reward-
ed with state subsidies
l Optimum combination options with
our heat pumps and ventilation sys-
tems
l Ideal for modernising central heating
systems and in new builds
Your competent and reliable partner
Solar thermal systems for DHW heating,
central heating backup and swimming
pool water heating are amongst the
most interesting technological develop-
ments to take into account the demand
for renewables.
To make the task of the engineers and
traders easier, we supply matching, eas-
ily installed solar thermal systems.
These
systems combine high quality with an
affordable initial outlay.
In addition, you can rest assured that
all our products work can be combined
with one another.
Solar radiation 2850 3.80
Wind energy 200 0.50
Biomass 20 0.40
Geothermal heat 5 1.00
Ocean energy 2 0.05
Hydropower 1 0.15
Renewables total 3000 5.90
Source: Manfred Fischedick, Ole Langniss, Joachim Nitsch: “Nach dem Ausstieg – Zukunftskurs
Erneuerbare Energien” [After the Exit – Future Course of Renewable Energies], S. Hirzel Verlag, 2000
Jährlicher
Weltener-
giebedarf
Sonnenenergie
Wasserkraft
und Meeres-
energie
Erdwärme Biomasse Windenergie
Quelle: DLR, Dr. Nitsch
26_05_01_0727_
Annual
global
energy
demand
Hydropower
and ocean
energy
Geother-
mal heat
Biomass Wind energy
Solar energy
Source: DLR, Dr Nitsch
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 5 10.11.2011 16:00:46
How much sunshine do we get?
In Germany, the sun shines for be-
tween 1400and1900 hours per annum.
This means that we get between 975
and 1275kWh of free solar energy per
square metre every year.
This solar radiation corresponds to the
energy content of 230–310kg wood
fuel, 180–235kg lignite briquettes,
95–120m
3
natural gas or 95-120l fuel
oil. Solar energy can therefore make a
significant contribution to reducing CO
2
emissions.
How well does a solar thermal system
perform?
This question is best answered using an
example:
A household with four occupants has
an average daily DHW demand of ap-
prox.160 litres at 45°C. This cor-
responds to an energy demand of
6-8kWh. For this DHW demand, a
system with 4-6m² collector area and
a 300 l cylinder would be ideal. Such a
system would cover, on an annual av-
erage, up to 70% of the DHW demand
using solar energy. Of course, this de-
pends on local conditions and the an-
nual hours of sunshine. The adjacent
diagram shows how many hours of sun-
shine there are in different locations.
Basics
71 %
100 %
48 %
22 %
Frühling
März - Mai
Sommer
Juni - August
Herbst
Sept. - Nov.
Winter
Dez. - Feb.
Solaranteil
Zusatzenergie
26_05_01_0645_
600-700 700-800 800-900 900-1000 1000-1100 1100-1200 1200-1300 1300-1400 1400-1500 1500-1600 1600-1700 1700-1800 1800-1900
Valencia
Malaga
Sevilla
Zaragoza
Madrid
Tunis
Algiers
Rabat
Bilbao
Porto
Lisboa
Toulouse
Bordeaux
Nantes
Marseille
Luxembourg
Bern
Paris
Lyon
Lille
Napoli
Venezia
Milano
Roma
Torino
Cagliari
Palermo
Wien
Manchester
Burmingham
München
Stuttgart
Frankfurt
Köln
Hannover
Bremen
Hamburg
Amsterdam
Bruxelles
Belfast
Dublin
Berlin
London
Edinburgh
Genova
Sarajewo
Sofija
Zagreb
Tirane
Belgrad
Izmir
Athenai
Istanbul
Bucuresti
Odessa
Budapest
L´vov
Kijev
Minsk
Warszawa
Krakow
Riga
Moskva
Gdansk
Praha
Brno
Bratislava
Košice
Malmö
Göteborg
Stockholm
Oslo
Kobenhavn
26_05_01_0216_
Global radiation in kWh/m² per annum
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 6 10.11.2011 16:00:48
Solar constants
The average radiation level from the
sun that reaches us on the earth is
1367W/m². The radiation is reduced
through refl ection by the clouds and
absorption in the atmosphere. The ra-
diation that reaches the earth’s surface
is called global radiation. It is composed
of:
Direct radiation
This is the proportion of solar radiation
that hits the earth’s surface without dif-
fusion. Frequency and duration are cru-
cial values for solar technology.
Diffused radiation
This is the result of a proportion of di-
rect radiation hitting various fl oating
particles as it penetrates the atmos-
phere or clouds and being diffused in
different directions. Diffuse radiation
also occurs through refl ection off the
earth’s surface, buildings, etc.
26_05_01_0712_
1
3
2
4
5
The adjacent graphs show the propor-
tions of direct solar radiation and dif-
fuse radiation over the year, subject to
the radiation level and the time of day.
The proportions of types of radiation
and the radiation levels vary during
the day and year. The average annual
proportion of diffuse radiation is ap-
prox.50%. As with the direct radiation,
this radiation is also used by solar ther-
mal systems.
26_05_01_0725_
Jan. Feb.March April May June July Aug Sep. Oct. Nov. Dec.
Diffused radiation
Direct solar radiation
Diffused radiation
Night
Night
Time
08:00
04:00
16:00
12:00
20:00
Radiation (solar climate zone II)
kWh
m² day
26_05_01_0456
Jan. Feb. March Apr. May June July Aug Sep. Oct. Nov. Dec.
0
1
2
3
4
5
6
Global radiation
Direct radiation
Diffused radiation
1 Refl ection
2 Absorption
3 Refl ection
4 Direct radiation
5 Diffused radiation
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 7 10.11.2011 16:00:50
26_05_01_0604
DHW heating
DHW can be heated with solar energy
all year round. For this, coverage of be-
tween 40% and 70% is standard. The
DHW is stored in an SBB DHW cylinder.
The size of the cylinder depends on the
DHW consumption. On days with little
radiation, the solar radiation may be too
low to heat the cylinder to the required
temperature. In this case, the DHW is re-
heated by a heat source. This generally
takes place via the upper indirect coil.
Thermostatic valve
A thermostatic valve enables central
premixing of the DHW downstream of
the cylinder. By mixing cold water into
the hot water from the cylinder, a preset
mixed water temperature of between
30°C and 60°C can be achieved. After
days with intense radiation, the thermo-
static valve offers the advantage of only
allowing the amount of water out of the
cylinder that is required for mixing. If
the household includes children, yet a
cylinder temperature above 60°C is nev-
ertheless required, the central thermo-
static valve provides active anti-scalding
protection. However, in hard water ar-
eas, the cylinder temperature should not
exceed 60°C. In such areas, we recom-
mend regularly checking the cylinder.
If necessary, it must be possible to con-
nect a DHW circulation line to the cold
water inlet of the thermostatic valve.
Reheating
The DHW cylinder reheating facility must
also be able to cover the DHW demand if
there are longer periods of weather with
low radiation. This applies during the
winter months, particularly when the
solar radiation level is lower.
Reheating with fully electronic instan-
taneous water heater
The solar collectors heat the DHW solar
cylinder when there is solar radiation.
In central European latitudes, this stored
energy is often insuffi cient.
The solution is to reheat the DHW. In
most cases, this is achieved using con-
ventional fossil fuels to reheat the top
section of the DHW cylinder. One disad-
vantage of this method is that such sys-
tems fi nd it diffi cult to respond to actual
insolation. A fully electronically control-
led instantaneous water heater can be
used for this. It must be suitable for pre-
heated water.
The instantaneous water heater detects
the temperature of the DHW fl owing
through it and only uses the amount of
energy actually required for reheating.
Electrical energy for reheating is used
here on a demand-dependent basis.
The inlet temperature to one or more in-
stalled fully electronically controlled in-
stantaneous water heaters must be lim-
ited via an upstream thermostatic valve.
Principles of system
engineering
26_05_01_0416_
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 8 10.11.2011 16:00:54
0
20
40
60
80
100
121110090807060504030201
Solar coverage of a standard solar thermal system
Initially, there is a DHW demand of 200
litres per day.
Using a computer program, the annual
operation of the described solar thermal
system has been simulated.
The above graph shows the result for
the possible solar coverage that can be
achieved as part of the total energy de-
mand for DHW heating of 200litres per
day.
Full coverage is impossible during the
winter months. In spring and summer,
the hot water will need hardly any re-
heating.
Around 70% of annual energy costs for
DHW heating have been saved by using
the solar thermal system.
In addition, power savings are also pos-
sible if suitable washing machines or
dishwashers are supplied with water
preheated by solar energy.
The energy required for DHW heating
for a detached house can be signifi -
cantly reduced by using a solar thermal
system.
As can be seen in the following exam-
ple:
- Detached house in climate zone II
- Roof pitch 45°
- The roof faces south and there is no
shading.
- Average household with four
occupants
- The daily DHW demand per person is
50 litres.
- The DHW temperature at the draw-off
points is 45°C.
- The overall absorber area with two
SOL 27 premium collectors is 4.8m².
- The DHW cylinder has a capacity of
300 litres.
- DHW circulation is not installed.
- The single pipe run from the collector
array to the cylinder is 10metres.
- The pipe runs are thermally insulated
to EN12976:2.
DHW heating and coverage
84_05_01_0001
Y Solar coverage in %
X January to December
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 9 10.11.2011 16:00:55
The combination of solar DHW heat-
ing with central heating backup is now
very common. More than 50 % of newly
installed collectors today are intended
for this type of usage. Central heating
backup using solar energy is a particu-
larly attractive option in the transitional
months of March to May and September
to November.
For this, the solar thermal system
should be considered an integral part of
the whole system within the building,
i.e. the solar thermal system can make
varying contributions to the coverage
depending on the heating energy de-
mand and associated standard of insula-
tion. For example, this means that in a
building with insulation to EnEV, 30 %
of the total energy demand (DHW and
central heating) can be covered with a
solar thermal system.
The contribution made by renewables
is increased again if the solar thermal
system is combined with, for example, a
heat pump.
100 %
75 %
50 %
25 %
0 %
84_05_01_0013_
Jan. Feb. March April May June July Aug Sep. Oct. Nov. Dec.
Total energy demand to EnEV 2009
Solar coverage
Solar package with 12 m² collector area, 300 litre DHW cylinder and 700 litre buffer
cylinder | Building heat demand
12
%
15% 30% 60%
Solar coverage of the total energy demand
Building stock be-
fore 1984
EnEV 2009 Passive houseThermal Insulation
Order 1995
26_05_01_0726_
Example:
- 160 m² heated living space
- 4 occupants with a DHW consumption
of 40l/day
- Location Würzburg
- Reheating with heat pump
- 5 SOL 27 premium collectors
(5*2.4m² = 12 m²)
- Orientation SOUTH
- Angle of inclination 45°
- 300 l DHW cylinder
- 750 l buffer cylinder
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 10 10.11.2011 16:00:56
E-074410-0355_
Two-cylinder system
In this version, two different types of
cylinder are used: a DHW cylinder and
a buffer cylinder for central heating
backup. Due to the hydraulic separation
in the DHW and buffer circuits, it is pos-
sible to store larger amounts of thermal
energy. On days with intense radiation,
energy can be stored for days with less
sunshine, and possible system idle times
can be minimised.
When there is a solar yield, the DHW
cylinder is heated as a priority until
the solar control unit indicates that the
specifi ed maximum cylinder tempera-
ture has been reached. If solar thermal
DHW heating is complete and suffi cient
radiation is available, the buffer cylin-
der is heated. This is an extremely ef-
fi cient way to preheat the heating water,
particularly in spring and autumn. The
buffer cylinders are equipped for this
purpose with an integral solar indirect
coil. Due to the layout in the lower cyl-
inder section and the large indirect coil
area, a very effective contribution can
be made to central heating backup.
In this example, the heat pump provides
the reheating, both for DHW heating and
for heating the buffer cylinder. If there
is no solar yield or it is insuffi cient, in
“central heating” operating mode the
fl ow that has been reheated by the heat
pump is transferred via the “buffer heat-
ing” circulation pump into the upper
section of the buffer cylinder. The heat-
ing fl ow, also located in the hot upper
section, supplies the heating circuit via
the heating circuit pump. The tempera-
ture level in the buffer cylinder is delib-
erately high due to the solar connection,
therefore the heating circuit for central
heating is designed to be mixed. 1 Heat pump
2 Buffer cylinder
3 Room heating
4 DHW cylinder
5 Domestic hot water
6 Cold water
7 Solar thermal system
WPLa%20SBP%201
This illustration is to be viewed as a schematic diagram. To keep the illustration simple, some safety assemblies are not shown
and must be installed on site depending on the locally applicable regulations.
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 11 10.11.2011 16:00:58
Instantaneous cylinder system
Wherever space is at a premium, e.g.
mainly in detached houses, but also
in two-family houses and apartment
buildings, this system version can really
show off its strengths. These cylinders
are buffer cylinder and instantaneous
cylinder for DHW heating in one. The
versatility of the instantaneous cylin-
ders stands out due to the fact that vari-
ous heat sources and fuel types can be
combined in this system interface. For
this, a number of connectors for the
heat sources and heat consumers are
arranged on the cylinder, which can be
allocated as required for the specifi c
system. This creates the opportunity to
integrate a solid fuel boiler as well as a
heat pump and a solar thermal system.
With the STIEBEL ELTRON SBS W SOL
instantaneous cylinders, hydraulically
separated heat sources and a solar ther-
mal system for DHW heating and central
heating backup can be combined. The
solar yield is transferred by means of an
oval pipe indirect coil that is arranged
right at the bottom of the cylinder. This
ensures good reheating of the solar sec-
tion and results in an optimum contri-
bution of the solar thermal energy. If the
available solar yield is insuffi cient, e.g.
due to the time of day or at peak DHW
draw-off times, a heat demand is sent to
the heat pump and the amount of heat
required to achieve the set temperature
is provided.
Subject to the type of heat demand –
central heating or DHW heating – the
cylinder will be heated in the upper
(top) or lower (centre) temperature
zone.
Cylinder heating is brought about by
switching the diverter valves. A number
of sensor wells on the cylinder enables
various sensors to be positioned in dif-
ferent places to control the heat source.
This allows the ratio of energy from
solar to energy from the heat pump to
be altered, for example. The fl ow and
return connection for both heating cir-
cuits are located in the central section of
the cylinder, in the central temperature
zone.
E-074410-0381_
If a solar thermal system is integrated, a
higher temperature level than required
for central heating can be assumed in
the instantaneous cylinder. As a result,
both heating circuits are designed to
be mixed and can therefore be control-
led separately as room temperature-
dependent or weather-compensated
circuits. In conjunction with the solar
thermal system, a higher temperature
level can be achieved in the entire in-
stantaneous cylinder. This will cover a
large proportion of the DHW heating
and increase the DHW convenience.
1 Heat pump
2 Instantaneous water heating cylinder
3 Domestic hot water
4 Cold water
5 Room heating
6 3/2-way diverter valve
7 Solar thermal system
WPLa%20SBS%201
This illustration is to be viewed as a schematic diagram. To keep the illustration simple, some safety assemblies are not shown
and must be installed on site depending on the locally applicable regulations.
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 12 10.11.2011 16:01:03
Combi cylinder system
The combi cylinder is ideally suited to
combined DHW heating and central
heating backup in a detached house.
The cylinder is a buffer cylinder with a
smaller, enamelled DHW cylinder inside
it (tank-in-tank cylinder system). The
DHW is heated via the heating water in
the buffer cylinder. The buffer cylinder
is heated via two solar indirect coils.
An advantage of the combi cylinder is
the low space requirement. It requires
only the space to install one cylinder in-
stead of two.
In addition to the function of a buffer
and DHW cylinder, the compact SBK
600/150 system cylinder also enables
combined solar thermal backup for cen-
tral heating and DHW heating.
For both operating modes, the heating
heat pump functions as a reheater in
this type of system. However, many oth-
er heat sources can be used as well, e.g.
solid fuel boilers, stoves with integral
back boilers, or condensing boilers.
DHW heating and central heating occur
at different temperature levels: DHW
heating at a high temperature level;
weather-compensated central heating
at an average temperature level. These
temperature ranges form in the buffer
cylinder subject to the temperature-
related changes in the density of the
water. This is why internal smooth tube
indirect coils are fitted in both the DHW
cylinder section and the heating buffer
section. Subject to demand, they are
heated via the solar thermal system. The
fact that the internal DHW cylinder is
directly surrounded by the smooth tube
indirect coil ensures good heat transfer
from the heat transfer medium to the
water to be heated.
Under the control of the solar control
unit, the heat transfer medium circuit is
hydraulically diverted, primarily to pro-
vide backup for DHW heating and, sub-
ject to demand, to heat the entire cyl-
inder content. When solar DHW heating
is complete, the heating section of the
buffer cylinder is heated to the specified
temperature. This is an extremely ef-
ficient way to preheat the heating water,
particularly in spring and autumn. When
the appropriate signal is issued by the
heat pump control unit, both heating
circuits are heated via a common con-
nector in the centre section of the buffer
cylinder.
As the high solar thermal yield means
a high temperature level is possible in
the entire buffer cylinder, both heating
circuits are designed to be mixed. The
temperatures in the heating circuit flow
are cooled by mixing subject to the out-
side temperature.
The heating circuit return in the lower
section of the buffer cylinder is strati-
fied according to temperature by an
internal inlet device. If the set tempera-
ture is not reached due to insufficient
solar yield, peak DHW draw-off rates
or central heating mode, the required
operating mode is started via the heat
pump control unit. The heat pump flow
is routed into the buffer cylinder at the
specific flow temperature for this oper-
ating mode.
1 Heat pump
2 Instantaneous water heating cylinder
3 Domestic hot water
4 Cold water
5 Room heating
6 3/2-way diverter valve
7 Solar thermal system
WPLa%20SBK%202
This illustration is to be viewed as a schematic diagram. To keep the illustration simple, some safety assemblies are not shown
and must be installed on site depending on the locally applicable regulations.
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 13 10.11.2011 16:01:08
DHW heating with central heating back-
up and swimming pool heating
There are several points in favour of so-
lar swimming pool heating. The highest
demand for public or private outdoor
pools comes in the period from the mid-
dle of May to the middle of September.
This is the time when solar radiation
is at its strongest in Central Europe. In
comparison to DHW heating or central
heating backup, swimming pool heat-
ing requires only low temperatures in
the range of 18°C to 25°C. This enables
the solar energy to be supplied over a
longer period.
In private indoor pools, any excess solar
energy can be supplied to the swimming
pool even in winter. This means the col-
lectors are used effectively and stagna-
tion is largely prevented.
The framework conditions for engineer-
ing solar thermal systems for heating
swimming pool water include the solar
radiation and the heat demand of the
pool. The heat demand depends to a
great extent on the size of the pool, the
depth of the water, the colour of the tiles
in the pool, the required water tempera-
ture and the ambient meteorological
conditions such as air temperature and
wind speed.
E-227756-0000_
Total energy demand to EnEV 2009
Solar coverage
Solar energy that can be used for swimming pool heating
100 %
75 %
50 %
25 %
0 %
Jan. Feb. March April May June July Aug Sep. Oct. Nov. Dec.
84_05_01_0014_
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 14 10.11.2011 16:01:09
WPLa%20SBS%201
Operating mode
From a control point of view, a solar ther-
mal system used for DHW heating, central
heating backup and swimming pool heat-
ing should be seen as a system with an
additional cylinder.
The heating is monitored and controlled
by a solar control unit. Priority logic de-
termines the order in which the cylinder
and swimming pool are heated. DHW
heating usually has the highest priority,
followed by central heating backup and
finally, swimming pool heating.
In the summer months, the excess solar
energy can be used for the swimming
pool.
The hydraulic layout of a solar thermal
system of this kind, as shown in the sys-
tem diagram, can also be designed with
a combi cylinder.
In this case, the solar thermal system
comprises a certain number of solar col-
lectors, a cylinder that simultaneously
provides DHW heating and central heating
backup, and the swimming pool.
Various heat sources can be used for re-
heating, e.g. a gas boiler, oil boiler, pellet
boiler or, as shown, a heat pump. Using a
solar circuit pump, the solar thermal sys-
tem supplies the solar yield to the combi
cylinder and downstream to the swim-
ming pool. Changeover between the con-
sumers takes place with a diverter valve
or pump logic. A heat exchanger sepa-
rates the solar circuit from the swimming
pool circuit to prevent the heat transfer
medium from the solar thermal system
being mixed with the swimming pool
water. The solar control unit ensures op-
timum distribution of the solar energy.
The ideal operating mode of a solar ther-
mal system is one where the solar col-
lectors are able to transfer the solar yield
into the system for as long as possible and
are in a state of stagnation for as little
time as possible.
1 Heat pump
2 Instantaneous water heating cylinder
3 Domestic hot water
4 Cold water
5 Room heating
6 3/2-way diverter valve
7 Solar thermal system
8 Heat exchanger swimming pool
This illustration is to be viewed as a schematic diagram. To keep the illustration simple, some safety assemblies are not shown
and must be installed on site depending on the locally applicable regulations.
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 15 10.11.2011 16:01:14
Layout of a thermal fl at-plate collector
Flat-plate collectors are comprised of a
transparent cover, an absorber, a collec-
tor tray and thermal insulation.
The absorber comprises a coated panel
with a fi tted pipe coil through which the
heat transfer medium circulates.
Absorber
The absorber is the part of the solar col-
lector that absorbs the incident solar
radiation, converts it into thermal en-
ergy, and transfers it to the heat transfer
medium.
General function
Aperture area
The aperture area is the transparent,
visible surface of a collector, through
which the radiation can penetrate. The
aperture area is the reference fi gure
for the conversion factor (effi ciency).
Absorber area
The absorber area is calculated from the di-
mensions of the absorber (lengthxwidth).
Gross area
The gross area is calculated from the
external dimensions of the collector
(length x width). The gross area is im-
portant for both engineering and in-
stallation to calculate the required roof
area. In addition, the gross collector
area is crucial for most state subsidies.
1
2
3
4
26_05_01_0706_
2
4
6
5
7
8
9
1 Safety glass
2 Absorber
3 Harp-shaped pipe
4 Thermal insulation collector back
panel
5 Back panel
6 Manifold
7 Thermal insulation at the side
8 Frame profi le
9 Connections
A
B
C
26_05_01_0705_
A Aperture area
B Absorber area
C Gross area
How a solar thermal system works
The fl at-plate collector absorbs inci-
dent light and converts it into heat.
The thermal energy is transferred to a
liquid heat transfer medium in the collec-
tor. The heat transfer medium transports
the thermal energy from the collector to
a DHW cylinder. The energy from the
heat transfer medium is transferred to
the cylinder content via an indirect coil.
The cooled heat transfer medium is
transported back to the collector via a
circulation pump.
* Properties at 700 W and ∆T
U
= 20 K
8 % refl ection
Heat transfer medium
Aluminium
absorber
100 % insolation
72 % useful heat
5 % radiation (emission)
12 % convection
and thermal con-
ductivity
26_05_01_0451
Copper pipe
Thermal insulation
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 16 10.11.2011 16:01:15
CU panel
α = 0.05
ε = 0.04
Black gloss
α = 0.95
ε = 0.85
Black chrome
α = 0.95
ε = 0.12
PVD layers
α = 0.95
ε = 0.05
Absorption and emission levels
26_05_01_0422
Absorption level α
This specifi es the magnitude to which
the absorber absorbs the irradiated en-
ergy. An absorption level of 0.95 means
that 95% of the radiation that hits the
absorber is converted into heat.
Emissions level ε
The emission level specifi es the magnitude
to which the absorber radiates heat. An
emission level of 0 denotes that the ab-
sorber loses no energy to its surroundings
through radiation.
Transmission level τ
Part of the incident radiation does not
reach the absorber due to refl ection off
the glass cover and absorption as it passes
through the glass material. The level of
transmission describes the transparency
of the glass cover. To achieve a high level
of transmission, special glass is used in
the solar area. This low ferrous safety
glass (SPSG) has a transmission level of
91%. An even higher level of transmission
can be reached with anti-refl ective coat-
ings. Here, refl ections off the glass pane
are reduced. This can be achieved with a
coating or an etching process. It makes a
transmission level of up to 96% possible.
ESG
SPSG is the abbreviation for single pane
safety glass. A special heat treatment
gives the glass increased shock and im-
pact resistance. Furthermore, if damaged,
the glass cover treated in this way breaks
into small pieces of glass that are not
sharp. To achieve a high level of trans-
mission in solar applications, this glass
is manufactured from an extremely pure,
low ferrous glass compound. Only approx.
1% of the solar radiation is absorbed by
the glass cover. 8% of the radiation is
lost through refl ection off the glass sur-
face. This results in a transmission level
of 91%.
Anti-refl ective glass
Losses through refl ection can be substan-
tially reduced if the glass cover is treated.
This can involve a coating or a special
etching process, as with the sunarc®
anti-refl ective glass used by STIEBEL EL-
TRON. In this process, a microstructure
is embedded in the surface of the glass.
This reduces refl ection losses by 5% and
raises the level of transmission from 91%
to 96%. As the coating is part of the glass,
it has the benefi t of greater durability, in
contrast to an applied coating.
26_05_01_0722_
100 %
91 %
100 %
96 %
ESG Anti-refl ec-
tive glass
Transmission level
mirotherm
®
Laser schweißbare
Korrosionsschutzschicht
ALANOD
Grundmaterial
Substrat
PVD-System
IR-Reflexionsschicht
Absorbtionsschicht
Entspiegelungsschicht
26_05_01_0728_
Anti-refl ective layer
Absorption layer
IR refl ection layer
PVD system
ALANOD
Base material
Corrosion protection
layer that can be laser-
welded
Substrate
mirotherm
®
How a solar thermal system works
The fl at-plate collector absorbs inci-
dent light and converts it into heat.
The thermal energy is transferred to a
liquid heat transfer medium in the collec-
tor. The heat transfer medium transports
the thermal energy from the collector to
a DHW cylinder. The energy from the
heat transfer medium is transferred to
the cylinder content via an indirect coil.
The cooled heat transfer medium is
transported back to the collector via a
circulation pump.
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 17 10.11.2011 16:01:19
Standby part
Upper cylinder section or separate
downstream cylinder in which the pre-
heated DHW is heated to the set tem-
perature.
Coatings
Collectors are almost always selectively
coated to ensure that as little of the heat
as possible is lost during the conversion
of the radiation.
Our absorbers are coated with a high
grade mirotherm® material.
The diagram shows that the special prop-
erties of this coating enable it to perform
significantly better than comparable coat-
ings.
Benefits of our absorber coating:
l
High absorption
l Low emissions
l High efficiency
l Ecologically sound materials
l Long service life
Dual mode cylinders
Cylinders divided into two sections
which are heated by different energy
systems. Example: Solar energy is fed
into the lower section; conventional en-
ergy into the upper one.
Heating output of useful heat
The difference between the absorbed
solar radiation and the collector heat
losses.
Solar Keymark
Solar KEYMARK is a protected and regis-
tered European symbol of product quality
issued by the CEN and CENELEC commit-
tees for standardisation. It demonstrates
to the customer that manufacturers have
elected to have their products tested and
monitored by impartial, independent and
competent test institutes in accordance
with standard European quality criteria.
This includes monitoring the manufactur-
ing checks and regular product inspec-
tions of the solar collectors. In the prod-
uct inspections, factors such as usability,
safety, reliability and performance of the
solar collectors are tested.
The Solar KEYMARK test symbol is now a
prerequisite for drawing state subsidies in
many European countries. All STIEBEL EL-
TRON solar collectors are certified accord-
ing to the Solar KEYMARK test procedure.
Idle state (stagnation), idle time (stag-
nation time)
State or period when no heat transfer
medium is circulating in the collector
circuit and the absorbed insolation that
has been converted to heat is not trans-
ferred to a cylinder or consumer.
DHW preheater
The lower cylinder section or separate
cylinder used to directly preheat DHW.
Heat transfer medium
The heat transfer medium is the medium
that absorbs the useful heat in the col-
lector absorber and routes it to a con-
sumer (heat exchanger). It is protected
from frost down to -30 °C and protects
the solar thermal system against corro-
sion through inhibitors.
DHW circulation energy
The thermal energy transferred by the
DHW circulation network to circulate
DHW.
Terminology and descriptions
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 18 10.11.2011 16:01:20
Collector orientation.
The inclination and azimuth angle of
the collector are the crucial factors for
determining the highest possible effi-
ciency.
The best possible collector orientation
must be selected.
If the collector orientation is less than
optimal, this can be compensated for
with a larger collector array.
Angle of inclination.
The angle of inclination specifies the
angle between horizontal and the in-
clined collector. With roof installation, it
is usually determined by the pitch of the
roof. For DHW heating the ideal angle
of inclination is 45°; for central heating
backup it is 60°.
Frame support stands are available for
some fixing systems, which allow the
angle of inclination to be increased.
It is important to try to achieve an ideal
angle of inclination that corresponds to
the required usage period.
Angle of azimuth
The angle of azimuth describes the de-
viation of the collector orientation from
due south (collector oriented towards
south, azimuth = 0°).
In most cases the angle of azimuth is
determined by the orientation of the
building. The highest yield is achieved
when the collector surface faces due
south.
Collector orientation and inclination
Collector inclination
26_05_01_0704_
0° 30°15° 45° 90°60° 75°
60 %
80 %
90 %
100 %
70 %
Collector yield subject to collector inclination
26_05_01_0474
Angle of azimuth
26_05_01_0703_
70 %
80 %
90 %
100 %
90°
W
45°
SW
0°
S
-45°
SO
-90°
O
Collector yield subject to angle of azimuth
26_05_01_0475
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 19 10.11.2011 16:01:21
Effi ciency η
The effi ciency states how much of the
incident radiation the collector converts
into useful heat.
Maximum effi ciency η
0
If the collector loses no heat to the en-
vironment, only the optical losses are
relevant for effi ciency. There is no tem-
perature differential between the aver-
age heat transfer medium temperature
and the ambient temperature. The level
of transmission through the glass pane
and the absorption level of the selective
coating layer determine the effi ciency
η
0
. This is why we also talk about optical
effi ciency. The technical term for optical
effi ciency is the conversion factor.
Temperature differential ∆T [K]
The temperature differential between
the average heat transfer temperature in
the collector and the ambient air around
the collector is called ∆T. The collector
suffers no heat loss if the average heat
transfer medium temperature is equal to
the ambient temperature. At that point,
the collector is at its most effi cient.
The greater the temperature differential,
the higher the heat loss of a collector.
Convection
This is the air circulation that occurs at
a temperature differential between the
collector glass pane and the hot ab-
sorber.
Heat loss factor a
1
[W/m² K]
a
1
describes the linear heat losses of the
collector, relative to the area and the
temperature differential.
Heat loss factor a
2
[W/m² K²]
The heat loss factor a
2
specifi es the cur-
vature of the fi nal effi ciency curve that
takes the non-linear heat losses through
radiation into consideration.
Radiation level G [W/m²]
The radiation level specifi es the power
of the light striking the collector relative
to area.
Effi ciency curve
Formula for calculating the effi ciency
η
= η
0
- -
a
1
ΔT
G
a
2
ΔT
2
G
Example calculation
At an ambient temperature of 25°C
and an average heat transfer medium
temperature of 45°C (∆T=20K), the
effi ciency of the SOL27premium W at
a radiation level of 700 W/m
²
is calcu-
lated as follows:
η = 0.83
- (3.41 W 20 K m
2
/ 700Wm
2
K)
- (0.0161 W (20K)
2
m
2
/ m
2
K 700 W)
= 0.83 - 0.097 - 0.0092
= 0.724
At a temperature differential of 20 K
between the average heat transfer
medium temperature and the ambient
temperature, 72.4% of the radiated
power is converted into useful heat.
1 1
2
3
6
5
7
4
26_05_01_0711_
1 Solar radiation onto the collector
2 Refl ection off the glass pane
3 Absorption by the glass pane
4 Refl ection off the absorber
5 Thermal conductivity of the collector material
6 Heat radiation of the absorber
7 Convection
Display of the collector losses
296003-36390-8670_Plama_Solar_en_mit_Umschlag.indb 20 10.11.2011 16:01:22
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