Evacuated Solar Tubes

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Evacuated Solar Tubes


Solar Collectors using glass evacuated tubes, called Solar Tubes, are the most efficient Collectors available and are particularly suitable for the UK and other northern European countries. Their efficiency is such that they heat water all year round working even on cloudy days.


The HS-VAC1.8 is the solar absorber. It absorbs solar energy converting it into heat and is a “twin-glass tube”. This type of tube performs reliably and is a component part of tube type solar water heating panel. Fifteen HS-VAC1.8 tubes are mounted on a vertical incline into a heat exchanger to form a solar hot water Collector.


How it works

The process by which solar radiation is converted into heat is as follows.

The HS-VAC1.8 has an excellent selective absorption coating which produces an efficient method of heat generation. This heats the inside skin of the glass tube where the heat is transferred through conduction and radiation to the centreing metal heat fins and the central copper tube. This tube contains pure water with anti corrosion additives. The inside of the tube is at a reduced pressure so that the water boils at around 30°c. The hot water vapour rises to top of heat pipe where the heat is transferred to the circulating water, the vapour condenses and drains back down the tube.

As the HS-VAC1.8 has less parts to absorb heat before any meaningful heat transfer can take place, it starts producing heat more quickly than flat solar panels, even on cloudy days. It can even produce heat on sunny days at -30°c. It also is more resistant to frost damage and scaling. Each HS-VAC1.8 works independently of other tubes in the same racking system. This means that if a tube is damaged, the other tubes are unaffected and the system still produces solar energy.

The HS-VAC1.8 performs better than flat plate solar collectors in cold weather because it minimises heat transfer losses to the water.

Solar water heaters using the HS-VAC1.8 are aligned in parallel; the angle of mounting depends upon the latitude of the particular location. In general, the efficiency of a HS-VAC1.8 system depends upon a number of factors, one important one being the level of solar in the region.

Basic Specifications of the HS-VAC1.8

Structure All-Glass Double-tube co-axial structure
Glass Material High borosilicate 3.3 glass
External pipe diameter/thickness 58mm, +/- 0.6mm; T=1.6mm
Internal pipe diameter/thickness 58mm, +/- 0.6mm; T=1.6mm
Pipe length 1800mm
Coating Structure Cu/SS-ALN(H)/SS-ALN(L)/ALN
Sf*dime»nt method 3 Target magnetron sputtering plating
Specific absorption As=0.93~0.96(AM1.5)
Emission ratio eh=0.04~0.06(80°C+/-5)


 Vacuum tightness  P<=5.0*10~3Pa
 Idle sunning property parameters  Y=260-300m2 7KW
Solar Irradiation for preset water temperature H<=4.7MJ/m2(O58)
H<=3.7~4.2 MJ/m2
Solar irradiation for preset water temperature H<=3.7MJ/m2(047)
H<=2.9~3.2 MJ/m2
 Average Heat Loss coefficient  ULT= 0.4-0.6 w/( m2 °C)