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Vacuum Tube Solar Water Heater

How Does a Vacuum (Evacuated) Tube Solar Water Heater Work?


The vacuum tube collector consists of an array of borosilicate (low iron content) glass tubes.  Inside the glass tubes are copper tubes filled with liquid having a low boiling point.  The copper tubes are heated by the sun/UV which vaporizes the liquid and causes a change of state.  The vapor rises to the top of the tube and transfers the heat into a common heat exchanger in the solar collector.  Water is heated as it passes through the heat exchanger.  Vacuum tube collectors achieve excellent results not just year-round, but particularly in cold and windy conditions.  The collector’s absorbers are located inside vacuum tubes, which, much like thermos, have excellent insulating qualities and prevent heat loss.  The absorptive coefficient = 95%.   BTU output/day in southern Idaho/eastern Oregon = 36,000.




The solar water heater system includes a controller and temperature sensors which monitor the fluid temperature in the solar collector and hot water storage tank.  The controller will initiate the pump operation during a hot water demand, and turn the pump off when the desired hot water temperature is achieved in the storage tank.  The pump circulates colder water from the bottom of the water tank through the solar collector and returns the heated water to the tank.  This cycle continues as long as the solar collector is providing hot water.  When there is no heat available the controller turns the pump off.  Very high efficiency system.





The advantages of a vacuum tube solar water heater include:



      The angle of the solar tube array is not critical as the tubes are round and they passively track the sun – more solar radiation is absorbed over more hours of daylight.      There is no water flowing through the evacuated tubes.  The heat generated in the tubes gets a direct copper-to-copper transfer at the solar collector.       The tubes withstand a 1-inch hail stone.      Vacuum tube solar collectors are much more efficient than flat plate solar heaters.      No freezing concern.  The solar collector loop contains non-toxic glycol which is separated from the domestic water by a heat exchanger.      Very little maintenance.  Perfect for home, business, commercial, industrial, agricultural.



Matrix Renewable Energy will provide all of the components and labor necessary to complete the perfect solar water heating system for your application. 



Evacuated Tube Solar Hot Water Systems for

Domestic Hot Water, Radiant Floor Heating, Space Heating, & Swimming Pools



The advantages of evacuated tube technology are truly dramatic when used for solar domestic water heating, radiant floor heating, space heating, and swimming pools.  Evacuated tube heat pipe collectors can attain high temperatures and retain heat even when it is very cold outside.  Due to their superior Incidence Angle Modifier they collect solar energy evenly throughout the day resulting in a lower buffer or thermal storage requirement. There are many other advantages as well.



Evacuated Tubes

The SPP solar thermal collector system installed by Matrix Renewable Energy uses evacuated tubes (glass-glass seal), copper headers, copper heat pipes, aluminum casing, glass wool insulation, and an all-stainless steel frame.  The tubes are made from low emissivity borosilicate glass (glass with a very low iron content that has superior durability and heat resistance) with an all-glass seal and they employ AL/N on AL selective coating, which enables the use of the whole solar energy spectrum to generate heat.  This produces greater thermal efficiency in bright sunshine but also produces high efficiency in overcast or diffuse sunlight conditions. Further, the tubes are evacuated and have a barium getter (vacuum indicator) which changes color from silver to white if a tube’s vacuum has been compromised. 




 Heat Pipes


The SPP evacuated tube system uses a specialized internal heat pipe.  A heat pipe allows for rapid heat transfer. The heat pipe itself is a copper tube that maintains a vacuum and contains a liquid with unique thermo properties.  The low pressure (vacuum) in the copper pipes causes the liquid to boil at a low temperature (86oF), and the resulting high temperature steam heat gets transferred to the heat exchanger within the solar collector.  After the heat is transferred the fluid in the heat pipe condenses and the thermo cycle continues to repeat the process.  The heat pipes are made from very high purity oxygen free copper to ensure the long term longevity of the heat pipe.





Copper Heat Exchanger (Header)


The heat exchanger is made from copper which makes for excellent heat transfer and is corrosion resistant and allows all connections to be brazed rather than soldered. It uses “dry” plug-in heat pipes meaning that the connections are plug-and-play which makes installation or replacement very simple.



  Aluminum Manifold/SS Frame


The manifold uses a powder-coated all-aluminum casing for durability, structural integrity and light weight.  The light weight is important for ease of installation and to reduce total roof loading in larger installations that can in some cases include up to 150 collectors. The manifold is packed with glass wool insulation and is sealed with special UV stabilized silicone rubber that can withstand temperatures of up to 482 degrees F.  The frame for the solar collector is stainless steel and can be adapted to any roof material system.



Incidence Angle Modifier (IAM)

IAM is the variance in output performance of a solar collector as the angle of the sun changes in relation to the surface of the collector.  The graph compares the IAM of evacuated tubes (blue line) to a premium flat-plate collector (green line).  You can see that both systems are about equal in the middle of the day but during the morning or afternoon the evacuated tubes have a much better angle of incidence.





Can a solar water heating system be used in place of a traditional gas or electric water heating system?

In order to ensure proper efficiency of your water heating system, a solar energy system must usually be used in conjunction with a traditional gas or electric heating system, rather than as an alternative to a traditional system.  While it is possible to size a system to provide a 100% solution, the best return on investment occurs when a system is sized to provide most of the hot water, most of the time.