Evacuated tube solar collectors consist of a heat exchanger and a series of heat collector tubes. The tubes have a vacuum between an inner and outer layers of borosilicate, a toughened glass. The solar evacuated tubes absorb and retain heat from the atmosphere. Inside the tubes are sealed copper heat pipes containing a small amount of liquid which vapourises and rises to the top of the heat pipes. The water from the tank flows through the heat exchanger manifold at the top of the collector. It absorbs the heat from condenser at the top of the heat pipe and returns the heated water to the storage tank.
The evacuated tube concept is engineered to perfection. So how does it work and why is it the best performer?
At SolarArk we use a Triple Target Tube (copper, aluminium and titanium) which allows our tube to utilize both ultraviolet (UV) and infrared (IR) energy. The tube is cylindrical and under vacuum, enabling maximum absorption of the sun’s energy to convert to heat for your hot water system.
The top layer or film is engineered to absorb maximum UV and IR radiation through the filter coating, and plays a pivotal role by resisting reflection.
The middle layer or film is the Heat Absorbance Layer. It reacts with the UV and IR radiation to generate the heat which is transferred to the aluminium fin and heat pipe.
The bottom layer or film is the IR reflector layer; this copper layer reflects any remaining IR energy back into the middle film the heat absorbance layer. This layer gives the SolarArk tube its distinctive “red glow” in the interior of the vacuum tube and not forgetting a healthy performance advantage of 12% over our competitors!
How do you know if your tubes are under vacuum as there’s nothing to see? Each tube is manufactured with a vacuum “tell-tale”. The technical term is “Barium Getter”. If the tube is under a vacuum, the tube will have a “metallic” tip at the closed end – it’s that simple! If the tip is milky white, the tube has lost vacuum and needs replaced at the system next service.
As part of our commitment to quality, our collectors pass through our stringent Quality Procedures. All components are tested individually to guarantee the highest quality meeting all Australian and International solar collector standards. Our solar evacuated tubes conform to the hail and high wind loading criteria tests on a worldwide level. Our frames are certified for all Cyclonic Regions.
Our SolarArk heat pipes perform a pivotal role in the operation of our solar hot water systems. There are basically two sections that make a heat pipe; they are the evaporator or “tail”, and the condenser or “bulb”. In basic terms, the operation of the heat pipe is to transfer efficiently the heat from the solar absorber to the collector manifold. As the entire heat pipe is under vacuum conditions, it greatly lowers the boiling point of the working solution to around 25°C, making heat pipes an effective method of solar hot water heating.
The heating action works by a cycle of evaporation and condensation. In the first stage, the working fluid evaporates travelling to the condenser section of the heat pipe which is within the manifold. In the second stage, the working fluid condenses.
The process is gravity driven; after exchanging the heat into the manifold, the condensate flows back into the evaporator section where it evaporates and the cycle continues.
The SolarArk heat pipe is specially designed to deliver high heat transfer rates. The heat transfer occurs via an internal process of evaporation, condensation and convection. In addition, the heat pipe has superior anti-freezing performance.
One of the main characteristics of the SolarArk heat pipe is that it has a lower thermal mass, allowing the collector to have an accelerated start-up time, delivering hot water quicker!
Our heat pipe is constructed using pure oxygen free red copper, the highest grade. The pipe “tail” and heat transfer “bulb” are then vacuumed and injected with a specially formulated solution. The solution is comprised of a water base with a suspension of nano-sized particles. The purpose of the particles is to increase thermal conductivity of the solution. They also help control the freezing point, therefore avoiding damage to the heat pipe.
SolarArk’s heat exchanger, commonly known as the manifold, has been designed by our team of in-house engineers from scratch. Our manifold is unique to SolarArk; we do not use a “generic” design used by the wider evacuated tube industry, and that’s one of the reasons our evacuated tube solar hot water system attracts the highest STC values and is at the top of the performance tables.
The internal of the manifold is constructed from pure red copper which is the highest grade; this type of copper performs under even the toughest operating conditions. The heat pipe “bulb” recess cup is positioned into the main length of the heat exchanger and the cups are automatically brazed in place in our semi-automated production facility.
In accordance with our quality policy the completed heat exchanger (12, 20 or 30 tube) is subjected to the following procedures, ensuring that our collectors are fit to wear our 15 year warranty badge.
The heat exchanger is dynamically designed for optimum performance. This means our unique design ensures minimal thermal resistance, but allows maximum thermal heat exchange output. We exchange the maximum energy with the lowest losses!
This is achieved by reducing the build tolerances between the heat pipe condenser “bulb” and manifold “cup”. Overall, we control the heat pipe fluid and ensure a smooth flow of the heat transfer fluid around the heat pipe condenser. This provides maximum heat transfer from heat pipe condenser to manifold.
As we have taken great care to deliver maximum heat exchange, we have continued with our exacting standards with the insulation and finish of the complete manifold, delivering outstanding heat loss results. Our heat exchanger is thermally encased using high density rock wool insulation, which is then wrapped in powder coated aluminium housing.
At SolarArk our engineers have developed and honed the evacuated tube design to deliver class leading performance. This is independently proven with our government accredited STC points. A simple but effective comparison of a SolarArk system versus our competitors can be made by looking at the industry benchmark system for a solar hot water system (a 30 tube 315 L electric middle-element tank). The SolarArk model achieves more STC certificates than our closest competitor, which means more $$ in your pocket upfront and over the life of the system.
