STIEBEL ELTRON Engineering and solar Technical Guide

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 1400and1900 hours per annum.

This means that we get between 975

and 1275kWh of free solar energy per

square metre every year.

This solar radiation corresponds to the

energy content of 230–310kg wood

fuel, 180–235kg lignite briquettes,

95–120m

3

natural gas or 95-120l 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-8kWh. For this DHW demand, a

system with 4-6m² 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

1367W/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

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 200litres 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 4.8m².

- 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 10metres.

- The pipe runs are thermally insulated

to EN12976:2.

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

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Example:

- 160 m² heated living space

- 4 occupants with a DHW consumption

of 40l/day

- Location Würzburg

- Reheating with heat pump

- 5 SOL 27 premium collectors

(5*2.4m² = 12 m²)

- Orientation SOUTH

- Angle of inclination 45°

- 300 l DHW cylinder

- 750 l buffer cylinder

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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

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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

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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.

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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

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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.

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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.

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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

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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

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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_

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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

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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 (lengthxwidth).

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

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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

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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=20K), the

efﬁ ciency of the SOL27premium 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

/ 700Wm

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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STIEBEL ELTRON Engineering and solar Technical Guide

STIEBEL ELTRON Engineering and solar Technical Guide

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