While evacuated tube technology clearly surpasses flat panels for nearly all water heating applications, the advantages are truly dramatic when used for solar air conditioning, heating or commercial process.
That’s because evacuated tube heat pipe collectors can more easily attain the higher temperatures needed, they can collect and retain heat even when it is very cold outside, and due to their superior Incidence Angle Modifier they collect solar energy more evenly throughout the day resulting in a lower buffer or thermal storage requirement. There are many other advantages as well.
Below is information about the SPP collectors and some of the reasons why, after intensive research, we selected this technology as opposed to flat plate collectors or other brands of evacuated tube collectors for our solar air conditioning, solar heating and other commercial and process applications.
The SPP solar thermal collector system 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.
An examination of the tubes shows that the outside is actually 2 layers of glass and a vacuum has been created between them.
A good way to demonstrate this would be to fill an empty tube with very hot water and notice that it does not even get warm as you hold the tube in your hands. That is because of the “thermos effect” created by having a vacuum between the layers of glass.
The header 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.
By comparison, other evacuated tube systems that require the manifold be opened for installation or replacement which is time consuming and can cause burns to the installers hands on a sunny day.
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.
Some evacuated tube systems are what is called a U-Tube, meaning that the glycol solution enters and exist each tube as opposed to flowing across a manifold. The SPP evacuated tube system uses what is called a 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 small amount of liquid.
The low pressure (vacuum) in the copper pipes means that the liquid boils at a low temperature (about 30oC / 86oF), turning to steam and rushing up to the heat of the heat pipe, carrying heat. It dumps the heat (to the glycol solution running through the header), condenses and runs back down to repeat the process.
The SPP heat pipes are made from Oxygen free copper of a very high purity, which is important to ensure the long term longevity of the heat pipe.
Normal water pipe copper (as used for the header) is not suitable for the heat pipe because over time oxygen and other trace element leach out, forming an air pocket in the top of the heat pipe.
A well thought out and durable frame system is imperative for the cost-effective installation of a large thermal collector system. SPP offers an all-stainless steel mounting solution for every situation.