NARVA full vacuum tubes

Solar collectors need to be isolated appropriately to prevent that the collected heat is giving off to the environment. Flat collectors are isolated
with special insulation material, which is used when building houses. Mineral wool is used very often because of its good insulating
effect but in comparison to vacuum it is very bad. Vacuum tubes have been developed to improve solar collectors and its heat loss.
There are single-walled and double-walled vacuum tubes on the market. The majority of collector manufacturers uses double-walled vacuum tubes.

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Double-walled vacuum tubes
Single-walled NARVA tubes
Illustration double walled tubes heat-pipe-Function principle


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Double-walled tubes are similarly constructed to a Thermos bottle. The inner components are enclosed by a double-walled vacuumized
glass cylinder. On the basis of construction it is necessary to close the front with a cap. At the same time, an air exchange
between the inner tube and the environment is happening. This can lead to heat loss and condensation, which in turn damages the
glass. Additionally the exchange with the ambient air causes pollution and corrosion to the absorber plate. This reduces the
performance by time.

The absorbing inner part of the single-walled tubes that are used by us are completely separated from the environment. The
construction of the tube is comparable with a bulb. The inner pipe and the absorber are completely in vacuum. Specialists
call them full vacuum tubes. NARVA , which manufactures these tubes, is a traditional company with many years of experience
in manufacturing illuminants. The company manufactures 200.000 fluorescent tubes a day.

The front of NARVA full vacuum tubes is vacuum seal connected to the outer glass cylinder. Therefore there is no exchange
between the inner of the tube and the environment. That is why corrosion and condensing can be totally excluded. The
patented glass-to-metal sealing provides durable protection of the vacuum.

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Tube types

direct flow

heat pipe

direct flow Full-Vacuum tube Functioning Grafic heat pipe vacuum tube
Functioning Functioning
The fluid is directly pumped through the tube by a pump.
Two into each other lying copper pipes are sealed onto the
absorber plate. The absorber is heated by the sun and gives
off heat to the pipe and the containing fluid. The cold
heat transfer fluid flows through the inner pipe up to the
tube peak and back through the outer pipe into the manifold.
At the same time the fluid takes the heat from the absorber
and goes heated back in the manifold and finally to the
consumer. 
Heat pipe tubes have an own circuit, which Transports
heat to the manifold. The heat is taken off there and
further transported to the heating system.
This own circuit works through a special fluid that
condenses in the heat pipe and rises up to the condenser.
There the heat is emitted to the fluid because the vapor
condenses again. Afterwards the medium flows back into
the pipe peak because of the gravity.
To ensure this principle it is necessary to mount the
collectors with an angle of 5°.
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Advantages Advantages
  • due to their flat characteristic applicable to a heat transfer
    medium temperature of 150 ° C in continuous operation
  • complies all requirements according to DIN EN 12975-2
  • flexible mounting options – facade, Balcony, flat roof,
    pitched roof
  • high performance
  • designed for a durability of 20 years
  • stagnation temperature : up to 300 ° C
  • to avoid danger of frost a proper heat transfer must be used
  • variable cut-off at 100 ° C or 160 ° C based on customer
    requirements
  • work in an angle of 5 – 75 ° without any output losses
  • dry connection – tube exchange possible without emptying
    the whole system
  • overheating protected
  • complies all requirements according to DIN EN 12975-2
  • designed for a durability of 20 years
  • frost-proof
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Technical data:
Absorber coating: one side (standard)
Technical data:
Absorber coating: one side (standard)
Nominal length (mm) 2.000
Tube length (mm) 2.010
Diameter glass tube (mm) 56
Length connection pipe (mm) 57
Aperture area glass tube (m²) 0,1010
Nominal capacity tube (W)
at a radiation of 1.000 W/m²
80
Collected heat at 1.000 kWh/a*m²
temperature difference 40 K (kWh/a)
72
Collected heat at 1.000 kWh/a*m²
temperature difference 1.000 K (kWh/a)
61
Heat transition coefficient linear (W/m²*K²) 1,12
Heat transition coefficient quadratic (W/m²*K²) 0,004
Efficiency factor 0,781
Nominal length (mm) 2.000
Tube length (mm) 2.010
Diameter glass tube (mm) 56
Length connection pipe (mm) 30,5
Aperture area glass tube (m²) 0,1010
Nominal capacity tube (W)
at a radiation of 1.000 W/m²
76
Collected heat at 1.000 kWh/a*m²
temperature difference 40 K (kWh/a)
68
Collected heat at 1.000 kWh/a*m²
temperature difference 1.000 K (kWh/a)
57
Heat transition coefficient linear (W/m²*K²) 1,12
Heat transition coefficient quadratic (W/m²*K²) 0,004
Efficiency factor 0,750

NARVA full vacuum tubes

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