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Haining Hengji Solar water heater Technology Co., Ltd.
Haining Hengji Solar water heater Technology Co., Ltd.  

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Solar Evacuated Tubes;Solar Vacuum Tube 

Price: 1.8~2.0 USD 
Payment Terms: T/T,L/C,WU 
Place of Origin: Zhejiang, China (Mainland) 
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Product Detail

Means of Transport: Ocean,Land
Packing: normal package
Installation: Wall Mounted
Certification: CE
Production Capacity: 5000pcs/day
Delivery Date: 7 days after deposit
Type: Tankless
Use: Bathroom

Solar Evacuated tubes are the absorber of the solar water heater. They absorb solar energy converting it into heat for use in water heating.

Each evacuated tube consists of two glass tubes made from extremely strong borosilicate glass. The outer tube is transparent allowing light rays to pass through with minimal reflection. The inner tube is coated with a special selective coating (Al-N/Al) which features excellent solar radiation absorption and minimal reflection properties. The top of the two tubes are fused together and the air contained in the space between the two layers of glass is pumped out while exposing the tube to high temperatures. This "evacuation" of the gasses forms a vacuum, which is an important factor in the performance of the evacuated tubes.

Why a vacuum? As you would know if you have used a glass lined thermos flask, a vacuum is an excellent insulator. This is important because once the evacuated tube absorbs the radiation from the sun and converts it to heat, we don't want to lose it!! The vacuum helps to achieve this. The insulation properties are so good that while the inside of the tube may be 150oC / 304oF , the outer tube is cold to touch. This means that evacuated tube water heaters can perform well even in cold weather when flat plate collectors perform poorly due to heat loss (during high Delta-T conditions).

In order to maintain the vacuum between the two glass layers, a barium getter is used (the same as in television tubes). During manufacture of the evacuated tube this getter is exposed to high temperatures which causes the bottom of the evacuated tube to be coated with a pure layer of barium. This barium layer actively absorbs any CO, CO2, N2, O2, H2O and H2 out-gassed from the evacuated tube during storage and operation, thus helping to maintaining the vacuum. The barium layer also provides a clear visual indicator of the vacuum status. The silver coloured barium layer will turn white if the vacuum is ever lost. This makes it easy to determine whether or not a tube is in good condition. See picture below.
Solar Evacuated Tubes/Vacuum TubeSolar Evacuated Tubes/Vacuum Tube

Evacuated tubes are aligned in parallel, the angle of mounting depends upon the latitude of your location. In a North South orientation the tubes can passively track heat from the sun all day. In an East West orientation they can track the sun all year round.

The efficiency of a evacuated water heater is dependent upon a number of factors, one important one being the level of evacuated radiation (insolation) in your region.

Evacuated Tube Basic Specifications

Length (nominal)

1500mm /1800mm

Outer tube diameter


Inner tube diameter


Glass thickness


Thermal expansion

3.3x10-6 oC


Borosilicate Glass 3.3

Absorptive Coating

Graded Al-N/Al


>92% (AM1.5)


<8% (80oC)


P<5x10-3 Pa

Stagnation Temperature


Heat Loss

<0.8W/ ( m2oC )

Maximum Strength


skype Mr. Ken Shen

Tel: 86-573-87817725
Fax: 86-573-87816388
Mobile: 86- 158 6831 5412
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Company Info

Haining Hengji Solar water heater Technology Co., Ltd. [China (Mainland)]

Business Type:Manufacturer, Trading Company
City: Jiaxing
Province/State: Zhejiang
Country/Region: China (Mainland)

Ken Shen:   skype
Rita Ying:   skype
Nancy Sun:   skype
Fiona Ding:   skype
Shelly Duan:   skype

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