Evacuated Tube
Evacuated tubes are made up of two layers of borosilicate glass,also called “pyrex”. Borosilicate glass is a strong glass that can withstand high temperature. The outer tube is transparent allowing UV rays to pass through with minimal reflection. The inner tube is coated with a thermal radiation absorbing layer, aluminum nitride (AlN). This layer also reduces reflection in order to increase absorption. The two tubes are sealed at one end and the air in the gap between them is evacuated.
The Vacuum Space
The reason for the vacuum space is because it forms a heat insulating barrier and once the radiation is absorbed through the evacuated tubes the heat that is generated will not escape into the atmosphere. This is similar to a common known “thermos bottle.
Evacuated Tube Layout
With the vacuum space in place the evacuated tubes can work well even in cold weather as its thermal losses are only 3-5%
Heat Pipe
A heat pipe is situated within each evacuated tube engulfed by an aluminum heat fin. The tube is tightly sealed to prevent any water, dust or air from entering and affecting the performance of the heat pipe and the aluminum heat fin.
A heat pipe is an extremely efficient thermal conductor that transfers large quantities of heat via a thermal conducting fluid.
A small amount of this fluid is sealed inside the heat pipe. Once the heat pipe is heated due to the absorbed solar energy the fluid inside it vaporizes and rises to the condensing zone where the heat is transferred to the water flowing through the manifold. The loss of heat causes the vapour to condense and flow back down the heat pipe where the process is once again repeated. The heat pipe is made of copper in order to maximize the heat transfer rate.
A heat pipe can transfer heat 10 000 times more efficient then any other heat conductor.
Evacuated Tube Solar Collector
The evacuated tube solar collector works by absorbing solar energy in the form of UV rays and converting it into thermal energy. An evacuated tube solar collector contains a number of evacuated tubes. Each evacuated tube is responsible for independantly absorbing the sun's radiation that reaches it.
An evacuated tube is made up of 2 layers of strong borosilicate glass that are joined together. There is a vacuum in between the 2 layers of glass. This layer of vacuum allows the tube to retain its heat once it is gathered. The UV rays are absorbed by an absorbing film which lies in between the 2 layers of glass on the inside layer. This special absorbing film absorbs more than 92% of the UV rays that incident the tube and rejects less than 8% back to the atmosphere.
The heat is transferred by conduction to a copper fin inside the inner layer of glass.
A heat pipe that is inserted into the fin absorbs this heat and transfers it to the copper header at the top of the collector. The heat pipe is a thin copper tube which contains a small amount of purified water. Once the heat pipe is subject to a small amount of heat the water vaporizes and turns into steam. It then rises to the top of the heat pipe where it reaches a condenser. Once the heat is removed from the condenser by a heating fluid such as water or a mixture of water and glycol, the vapor condense to a liquid and returns to the bottom of the heat pipe where it repeats its cycle.
The condenser is inserted into a copper manifold where the heat is transferred to the heating fluid passing through the manifold. A manifold is a copper pipe with a set of sleeves distributed along its length. Each sleeve receives the condensing end of a heat pipe. At this intersection the fluid flowing through the manifold absorbs all the heat from the condenser and continues through the manifold.
Solar Heating Collector Manifold
The heat pipe and the copper fin are placed inside the evacuated tube where they are protected from the elements and are not able to emit heat via conduction or convection to the atmosphere, only to the copper header. This gives the evacuated tubes their high efficiency. This also allows the evacuated tube solar collector to out perform any other solar collector on the market.
Frequently Asked Questions
How does a solar domestic hot water system work?
A solar domestic hot water system works in two phases. First, solar energy is captured and converted into heat. This is done by the solar collector. Thermal fluid, which resists freezing, is pumped into the collector where it absorbs the heat. The second phase occurs in the heat exchanger tank where the thermal fluid exchanges its heat to the water in the tank. Thus, the water in the tank is heated and sent to the current heating system.
Is there enough sunshine in Canada to heat water throughout the year?
Yes, there is plenty of sunshine in Canada for an evacuated tube solar collector. Unlike other solar collectors the evacuated tube absorbs over 92% of the UV rays.
Can it withstand elemental forces such as high winds, hail and snow?
Yes, the collectors are designed to withstand high wind speeds and heavy snow fall. The glass tubes can withstand hail stones up to 25mm (1in) in diameter.
Why should I install a solar water heating system?
For Reduce Energy Costs
Whether you are a home owner or a business owner solar energy is free and will have a drastic effect on your energy bills. With the rising cost of energy whether, it is natural gas or electricity, consumers will look for a renewable and free source of energy. Wind and solar energy so far are the easiest to implement.
Reduce Environmental Effects
Reducing greenhouse gasses will slow down global warming as well as air and water pollution. Using solar energy will also reduce the demand for fossil fuels.
Increase Property Value
Property value will increase if a solar hot water system is installed.