The sunbeams warm the absorber in the solar collectors installed on the roof. This heat is transferred to a heat transfer fluid via the coil welded onto the absorber. The fluid, heated in this way, is circulated by a pump in a closed circuit of pipes. Gradually, it gives up the heat from the solar collectors to the water contained in the cylinders. This water, heated free of charge by solar energy, will be routed to the collective hot water system's distribution network.
Two types of technology exist: pressurized system and drainback system
The Sunoptimo drainback
A system based on drainback, also called a self-draining or gravity drain system, allows the solar collectors to drain naturally and passively every time the circulation pump stops. The fluid is thus immune to overheating and freezing.
The installation is composed of solar collectors, a hydraulic unit, a drain tank, one or more hot water cylinders, a control system and a network of hermetically sealed pipes.
This system is partially filled with air and solar fluid. The control system switches the pump on as soon as it recognizes that solar energy can be delivered to the domestic hot water cylinders.
Once the cylinders are up to temperature or when the energy supplied by the collectors becomes insufficient, the pump is shut down. The fluid in the collectors drains back down into the drain tank installed in the boiler room.
It takes the place occupied by the air which is naturally displaced up into the collectors. The sensors are then immune to freezing and overheating. Unlike the fluid in a pressurised system, the air can be heated and compressed without deteriorating in an irreversible manner and without damaging the rest of the installation.
Conventional "pressurized" system
Unlike a drainback system, a conventional system does not drain. With the pump stopped, the liquid remains in the collectors, overheats, is vaporized and deteriorates with time.
This overheating represents a technical limit on sizing to approximately 40% to 45% of the solar fraction (percentage savings that can be made). This system requires greater maintenance.