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                    Guidebook for solar heating systems

  1. Selection of the heat absorber components

All Glass Vacuum tube + Inner Inserted Heat Pipe: Solves the problem of
un-operation of the all glass tube. As the inserted heat pipe is not in a vacuum
but exposed to the air, there is still a problem with freezing and corrosion.
Sometimes water is collected through condensation inside of the tube. The
heat transmission between the surface of the glass tube and the heat
transferring copper plate is not very effective which reduces the efficiency of the
whole system.

Sunda Heat Pipe Vacuum Tube: The high vacuum in the glass tube provides
the collector with a highly efficient heat insulation. Even under adverse
ambient conditions, such as low outdoor temperature and wind, no heat is lost
through heat conduction or convection.

There is no better thermal insulation than the high vacuum of 10-5 bar that
Sunda Solar Technology uses for its collectors (every good Thermos flask
confirms this statement!). This is a great advantage especially during the cold
months of the year.

+ Excellent thermal insulation guarantees high performance year-round.
+ Also, optimally suited for traditional heating system support or back-up

Simultaneously, due to the collector bring located inside the evacuated glass
tube, the high vacuum protects the absorber surface’s selective coating from
moisture, steaming up, soiling, corrosion and degradation during the collector’s
entire life. The glass tube exterior is perfectly smooth and self-cleaning.

   2.   Selection of the Inner Tank

Depending on the material used for the inner tank there are three types of water
tanks to choose from:
Zinc coated steel plate tank:    the thickness of the zinc layer protection is only
0.06mm. This is not sufficient to withstand corrosion permanently, so the
endurance of the inner tank is relatively short.

Stainless steel tank: stainless steel is the right material for the inner tank.
But problems might occur at the welding seam when temperature differences
lead to expansion and contraction of the material. As the welding changes the
characteristics of the stainless steel, there might also be corrosion at the joints,
which can drastically reduce the endurance.

Enameled steel tank: the enameled surface is made of quartz (SiO2). It has
a high chemical stability, prevents corrosion and is even acid-proof. The
durability of this type of tank can well extend 25 years. The thickness of the
steel is 2mm, so the water tank can bear high pressure up to 0.8 MPa. It is
ready to use in the water supply systems of most cities.

   3. Selection of the solar water heater system
There are two different pipe connections: open-circuit and close-circuit

Open-circuit systems work with the atmospheric pressure. The water flows
with the pressure caused by the height difference between water tank and
shower nozzle, so the water pressure is not very high and the whole system is
not working continuously and is inconvenient. When the hot water is used up,
the water tank is empty, then cold water must be filled into the tank.

Close circuit systems work with the pressure of the local water supply network,
so the tank has to be strong enough to withstand this. The rate of flow is high,
the whole system works continuously and is easy to operate. The recharge of
the tank works automatically and so the tank is always full and ready to use.
An overflow or shortages in water are prevented.

   4.   Selection of the sealing types

In recent years, a silica gel ring was the most common solution to seal the
connection between tube and water tank. But ageing of the ring has led to
leakage problems in some cases. The silica gel is not strong enough to
withstand high pressure, so it can only be used for low-pressure systems.
A metal sealing is the better choice, so that the tank can be operated with high
or low pressure. This sealing is maintenance free as there is no ageing of the


Two types of tanks are used in Sunda solar water heater: un-pressurized tank
for open loop solar water heater system and pressurized tank for closed loop
heater system. The inside of the tank is made from stainless steel or
enameled steel. The tanks have been carefully designed to avoid a mixing of
the layers of hot and cold water. High durability of the welded joints is ensured
by employment of gas protection welding.

   1). Outside cover: galvanized steel coated by gray colour coating, 0.5mm

   2). Insulation:    direct-injected polyurethane foam in 50mm thickness.

   3). Seido heat pipe vacuum tube.

   4). Cold water inlet, for un-pressurized tank also hot water outlet

   5). Internal tank: high quality 2.0mm thickness enameled steel or 0.6mm
   thickness 304 stainless steel.

   6). Auxiliary electric heater inside water tank: two types auxiliary electric
   heaters for choice: normal electric heat pipe and water-electrical isolated
   heater, 1.5 KW

   7). Drain plub.

   8). Safety Valve

   9) One-way valve

   10). Hot water to house
   11). Catholic protection: Magnesium anode

   12). Airflow pipe

   13). Overflow pipe

   14). Side cover: ABS engineered Plastic with additive for resistance to
   ultraviolet ray and ageing.

   15). Test pressure: 7 bar

                   Sunda solar water heaters components

Sunda collector: from SEIDO heat pipe vacuum tube, high efficiency and low

Hot water tank:   stainless steel or enameled steel tank with capacity 120 liter
or 160 liter.

Stand profiles: steel with spray plastic coating, well designed, good durability
and easy installation, 45’ tilt stand angle on flat roofs.

Reflector:   aluminum plate.

Fitting and accessories:       all necessary parts for a complete solar water
heater system.


  - The vacuum tube solar collector with heat pipe is a breakthrough in solar
technology. The efficiency of collector has been fundamentally improved.

  - The tubes are made of rigid borosilicate glass with thickness of 2.5mm.
The outside dimensions are 100x2000mm for SEIDO 1 and 70 x 1800 mm for
SEIDO 10. The metal absorber and the heat pipe are inserted in the glass
tube, to achieve the highest efficiency the absorber is sputtered with an
aluminum nitride selective coating, which transforms over 92% of the incoming
solar radiation into heat. The glass tube is evacuated to achieve a perfect
insulation and a long lasting protection against corrosion and other
environmental influences.

  - With its superior heat pipe technology, the collector reacts very fast to solar
radiation. This leads to high efficiency even in cloudy weather and in winter.
No freezing problems occur even at temperature below – 50’ C.

  - The system has a esthetical appearance and is easy to install.

  - Vacuum tubes can bear high stagnation temperature up to 250’C and
whole system provides hot water with temperature from 40 – 80 ‘C

                     Product Sheet – Solar collectors SEIDO

  Technical data

   1. Energy technology with convincing results
   The sun provides us with an inexhaustible potential for energy which today
can be usefully exploited by means of high technology. SEIDO solar collectors
have been specially designed for the supply of hot water. They can obtain up
to 70 per cent of the energy required for this purpose over one year. During the
summer, they can practically cover 100% of the daily requirements and they still
make an important contribution even in the relatively sunless months of winter.
Given a correspondingly intense level of solar radiation, SEIDO solar collectors
can cover a large part of our hot water needs-even at outdoor temperatures of
minus 15 degrees centigrade. The convincing results were accomplished
through the use of tried-and tested technology developed in the aerospace

  2. new type of solar collector

  The heart of the SEIDO solar collector is an aluminium nitride absorber plate.
With its selective coating, the absorber transforms over 92 percent of incoming
solar radiation into heat. A ‘heat pipe’ transfers the heat and feeds this into the
heating circuit via a copper condenser. The collector pipes and the heating
circuit are separated from one another by means of dry connection. This
means that individual pipes can easily be replaced at any time whenever
necessary-without interrupting the operation of the system. In order to prevent
the heat loss which usually occurs in solar collectors due to the circulation of air,
the absorber and heat pipe are mounted in a highly stable vacuum glass tube.
This stops energy from being lost due to air circulation and protects the
absorber plate and heat pipe in the long term against corrosion or other
environmental influences.

  3. A circuit and a system

  A self-contained heating circuit transports the heat from the collector to the in
house hot-water storage tank (approx. 300I). There the heat is passed on to
the in-house hot-water storage tank by a heat exchanger and the water for
domestic use is heated. When the heat supplied by the collector is not
sufficient to attain the desired temperature, a conventional heating system takes
over and completes the heating process. An electronic control unit constantly
checks whether the temperature at the collector opening is greater than the
temperature in the in-house hot-water storage tank. In this case, the control
unit switches on the heating circuit.

  4. A concept to meet your own personal requirements

 SEIDO solar collectors can be installed without difficulty on any kind of roof.
There is enough room for them even on the smallest available area. Around
three square meters are sufficient to cover about 70 percent of the hot water
needs of a household of four persons. For the operation of larger systems too,
such as industrial, hotel or sports facilities, SEIDO solar collectors are
eminently suitable. With their enormous-efficiency, they can provide enough
energy to meet even high demands for hot water. Individual planning is of
decisive importance for the dimensioning and layout of the solar energy
system. That is why factors such as climatic data, energy consumption and
roof orientation and inclination are analyzed and evaluated in specially
developed computer programs. Thus SEIDO solar energy systems always
fulfill specific requirements and guarantee optimal service, comfort and


SEIDO Solar Collectors can efficiently be used anywhere where hot water is
needed and solar radiation is sufficient. There are many utilization in following

Sanitary hot water
Home heating
Pool heating
Industrial process heat

Preparing Hot Water
Seido solar collectors have been specially designed for supplying hot water. In
a typical two circuits system for a private home, a self - contained heating circuit
transports the heat from the collector to the in-house hot water storage tank.
There the heat is transferred to the storage tank by a heat exchanger and the
water for domestic use is heated. When the heat supplied by the collector is not
sufficient to attain the desired temperature, a conventional heating system takes
over automatically and completes the heating process.

An electronic control unit constantly checks whether the temperature at the
collector is higher than the temperature in the in-house hot water storage tank.
If this is the case the control unit starts the heating circuit.

An evacuated tube employing heat pipe technology is a hi-technology product,
requiring more than over 40 processing steps carried out in strict accordance
with our ISO9001 quality insurance system and German industry standard DIN
  4757. Moreover Sunda's strong research and development team, with more
  than 20 engineers and experts from the field of machinery, thermal physical,
  automation, heating and electronic, works closely with many domestic and
  overseas research institutes and manufacturers. Our team is on the cutting
  edge of the newest information and technology developments and can
  seamlessly implement product improvements into production processes.

                                  Collector Module

SUNDA's Seido1/5/10 collectors are suitable for applications where aesthetics as well
as efficiency are important. These collectors allow for easy installation and they are
suitable for single unit installations or large-scale installations for heating or air
conditioning projects. The main features are as follows:

Long service life
Easy integration into buildings
High efficiency
Improved conversion at low solar irradiation levels
Frost free design
Elegant design for aesthetic appearance
Convenient design for easy maintenance without interrupting the system operation

Collector Dimensions
Seido collector modules consist of an array of Sunda evacuated tubes, insulated
manifold header, support frame and standard frame package for shingle roof
installation. Manifold headers have capacities of 8 ,16 and 20 tubes. The dimensions
are as follows:

<Dimension of Seido Collector Module>
                                Evacuated Tube

Seido evacuated tubes were developed in 1986 by Sunda and Daimler-Benz
Aerospace with support from the UNDP. Over ten years of cooperative research and
development by Sino-germane experts resulted in today's proven design. Our
products display a superior performance according to tests of the SPF and TüV.
Download the results of test. Sunda's vacuum tubes are very suitable for OEM solar
collector manufacturers and appropriate for the majority of installations. Seido
evacuated tubes exhibit the following characteristics:

  Highly efficient
  Extremely durable
  Maintenance free
  Easy mounting
  Currently Sunda offers five types of evacuated tubes: SEIDO1, SEIDO 2,
  SEIDO 3, SEIDO 5 and SEIDO 10.

  SEIDO1 SEIDO 5 SEIDO 10: These are heat pipe vacuum tube. Seido1 and
  Seido 5 tubes have large dimensions with an outer diameter 100 mm and length
  2000 mm. The only difference between them is the profile of the absorber plate;
  Seido 1 has a flat absorber, Seido 5 has bent or convex absorber. Seido 10
  heat pipe tubes have smaller dimensions and bigger condensers compared to
  Seido 1 and Seido 5. Its features and advantages are identical to the Seido1,
  but it appears sleeker due to the outer diameter being only 70mm and its
              shorter length of 1800 mm.

SEIDO1 and SEIDO 10 Heat Pipe Vacuum Tube with Flat Absorber

Higher temperature! 60-95 oC
Can be integrated into building architecture
High efficiencies serve in frosty winter environments
No corrosion or scaling problems
Easy to install, durable and reliable
Easy maintenance - system continues to operate even if individual tubes require replacement (no draining of
Capable of high system operating pressure
SEIDO5 Heat Pipe Vacuum Tube with Bend Absorber

10~14% more energy gained from the solar radiation
High efficiencies seven in frosty winter environments
No corrosion or scaling problems
Low heat capacity, starts producing quickly
Dry connection between tubes and heating circuit
Easy installation and maintenance
Capable of high system operating pressure
Domestic Hot Water Heater

To prepare hot water for family (Sanitary Domestic Hot Water- SDHW) Sunda
has developed a water heater, which combines a Seido solar collector and
storage tank into one product.
Because of its environment friendly technology, reliability and low price, it is
widely used throughout the world, especially in China, Italy, Greece, Spain and
also Africa. We offer three types hot water heater with SUNDA brand name.
These products have the following advantages:

Long service life
Provision of hot water all year round
Ease of use and maintenance
Aesthetically pleasing design
Economical to operate and consumer - friendly pricing

System Working Principle

Heat Pipe Hot Water Heater: This product consists of a heat pipe collector, steel
water tank with enamel coating and stainless steel or zinc plated angle steel
support frame. The condenser of heat pipe tube is directly inserted in the non-
corroding copper protection tube within the water tank and boasts the following

Consists of Seido heat pipe vacuum tube. Vacuum tubes are made of
borosilicate glass with thickness of 2.5 mm and have external diameter D=100
mm and length L=2000 mm. The aluminium absorber inserted within is
selectively coated with Al-N-O having an absorption coefficient a>0.92 and
emission coefficient e<0.08. The air pressure (vacuum) inside glass tubes is
<0,001 Pa.

Fast response times because of the heat pipe's high efficiency in transferring
heat even in low solar irradiation and winter weather.
Aluminum reflector integrated with plastic coated angle steel support frame,
aesthetically pleasing result with built-in safety, durability and easy of
The reflective surface is of polished aluminum so that the characteristics of
reflection are not degraded by dust and ageing.
Frost free operation to -50oC
Less installation space required on the roof.
Longer durability, easy maintenance
Series connections for larger projects are made with ease.
Aluminum profile support frame, easy for installation.


   Side cover made of plastic ABS with additive for resistance to ultraviolet

    radiation and ageing.

   Tank cover made of colored aluminum - beautiful and elegant design.

   Thick alloy steel tank (1.5 mm ) with quartz enamel coating inside for

    corrosion resistance

   CO2 welding technology used during tank fabrication

   High strength of tank material, working pressure up to 6 bar

   All-metal, patented sealing technology insures no leakage problems

   Special, non-corroding protection tube between the condenser and water

    with no decrease of heat transfer
   Expanded polyurethane insulation injected in liquid form which expands

    giving perfect insulation, rigidity and tightness

   Anode protection using magnesium bar

   Design insures no mixing of hot and cold water

                               Technical data


<Typical Construction of Heat Pipe Tube>

                              Heat Pipe Technology

A heat pipe acts like a low-resistance thermal conductor. Due to its thermal-
physical properties, its heat transfer rate is thousand's times greater than
that of the best solid heat conductor of the same dimensions. Sunda's Seido
heat pipe is a closed system comprised of two meters of copper tubing, an
evaporator section, a capillary wick structure, a condenser section and a
small amount of vaporizable fluid. The heat pipe employs an evaporating-
condensing cycle.

The evaporator section is tightly bonded to the absorber plate, where it
captures the heat from the absorber and evaporates the liquid to steam,
which moves up to the condenser section. The condenser protrudes out from
the evacuated tube and is inserted into the heat exchanger manifold. There
this steam will be condensed by water flowing through the manifold. Latent
heat energy will be released to the process water through this phase change
of vapor to liquid. In vacuum tube solar collectors, the condensation zone is
at a higher level than the evaporation zone. The transport medium
condenses and returns to the evaporation zone under the influence of
gravity. This process is repeated continuously thereby heating the water in
the solar loop.

Selective Coating
To achieve the highest efficiency of heat transfer the absorber treated with
an aluminium-nitride selective coating, which is applied using a magnetic
sputtering technique. This special optical coating transforms more than 92%
of the incoming solar radiation into heat.

Heat Pressure Sealing and Evacuated
Heat pipes are inserted into the aluminum absorbers forming assemblies,
which in turn are inserted into the glass tubes. The tubes are made of
borosilicate glass, which is strong and has a high transmittance for solar
irradiation. In order to reduce the convection heat lost, glass tubes are
evacuated to vacuum pressure of <10-3 Pa. Sunda uses a patented
technique employing high heat and pressure to insure stable glass-to-metal
vacuum seals. In order to keep the stability of vacuum for a long time, a
barium "getter" is used. Through evacuating air out of the glass tube the
absorber material and selective coating are protected from corrosion and
other environment influences. This ensures a lifetime of at least 15 years
without loss of efficiency.
                            SUNDA COMPANY?

For many years, the name SUNDA has leading technology in the
solarthermal field in the world.

Sunda was originally founded as a joint venture between the German
company DASA and the Chinese company SUNPU. Sunda was formed by
merging outstanding engineering with cost-efficient manufacturing.        The
result has been long-lasting, quality solar thermal products.

Through diligent research and development over decades, the Seido series
was designed. These new vacuum tubes maintain a high performance level
as well as a long life span.
With the addition of a modern production plant near Beijing, China. Sunda
now has an annual capacity of 500,000 tubes and is considered on of the
largest vacuum tube enterprises in the world.

The outstanding efficiency and reliability of the Seido tubes have been
demonstrated thousands of times in private homes and apartment buildings
on all continents. The Seido series has also proved to be an ideal solution
worldwide for the heating and cooling of large scale plants, some of which
well exceed 2000 tubes.

Since the year 2000, Sunda has been led solely by its Chinese partners.
Products and manufacturing are regularly improved in cooperation with
research institutions. In 2001, the factory, built on more than 8000 m2, was
certified according to ISO 9001 standards. All tubes fulfill the requirements
on DIN 4757 and the German TUV.

The German Sunda Solartechnik GmbH, located in Waibingen near Stuttgart,
distributes the products quickly and competently to the European customers.

Sunda Solartechnik is a qualified partner for meeting your needs. In
addition to product distribution, Sunda is available to answer questions
concerning project planning and product installation.
Sunda supplies a whole range of products from specialized vacuum tubes to
the common domestic hot water heaters to satisfy both domestic and
overseas market requirements. Our products are utilized preheating, air
conditioning and preparing hot water for family hotel. Sunda vacuum tubes
undergo more than 40 processing steps in compliance with strict quality
control to produce an extremely efficient, durable product that can be used in
any climate, including subzero temperatures.

We have established a world-wide distribution network capable of providing
pre- and post sales service to our valued customers. Our collectors are
installed around the globe including Europe, North America, Asia and Africa.
No matter where you are - Germany, Austria, England, U.S.A, Thailand,
Japan as well as Africa you can see the utilization of our products. To better
serve the large market for solar collectors in Europe, Sunda Solartechnik
GmbH. in Germany, Sunpu in China.       Now, Sunda Korea in Korea.

Currently we are the number one of solar thermal industry.
Our employees of Sunda are very familiarly with solar energy technology
and business.
We welcome your inquiries and look forward to serving you.

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