TRADITIONAL AUXILIARY TANK SYSTEM (ALSO CALLED FEEDER TANK SYSTEM)
The first thing you have to understand is that a Low-Pressure system comes as a complete package. This will include the tank and the tube collector, stand and auxiliary tank. Low-Pressure systems are Closed coupled systems, meaning that the tubes connect directly into the tank.
Heated water is pushed up the pipes filling the tank with the hot water and subsequently pushing the cold water back down into the tubes for re-heating. This process happens continuously throughout the day. When the Low-Pressure solar geyser is installed, the tank is placed at the top and the collector at the bottom. A small section of the tubes leads into the tank, which establishes a direct connection between the two.
Given the way it's assembled, there's no need for a pump to circulate the water. Instead, the natural process of gravity will make sure the hot water inside the tubes move up, while the cold water moves down. This is referred to as a thermosiphon process. Cold water is essentially heavier than hot water, and it will kick-start the convection cycle.
There are three challenges to consider though. The first is that the water pressure is gravity created, therefore the distance above the taps will determine the pressure of the water that comes out of them. The second challenge is when one of the tubes fail. If this happens the entire system needs to be shut down before repairs can be made. But if controlled and installed correctly, there shouldn't be any temperature problems.
As for a single tube breaking, it doesn't happen very often. The third is if you use a low-pressure system in a residence that has municipal water pressure, the mixing of the hot and cold can be a challenge because the cold water overpowers the hot water, for which in winter ends up being either soft hot water of warm medium pressure. So, if you're looking for a basic, efficient and affordable Solar Geyser system, you should definitely consider a low pressure one.
NEW LOW PRESSURE SYSTEM
The new Low Pressure System works on the exact same principles as the traditional Low Pressure system, in that it is a closed coupled system. The New low pressure system’s flow of water is now controlled with a solenoid that is connected to an electric control panel. The electric control panel and solenoid is connected to the geyser with equipment that determine the water level, therefore indicating when to open the solenoid for the inflow of water into the geyser. The natural process of gravity will make sure the hot water inside the tubes move up, while the cold water moves down. This is referred to as a thermosiphon process.
Definite challenges with this system is in the fact that for the system to work, end users should have access to electricity