HVAC design engineers have used pressurized glycol systems for decades to transfer heat from boilers to the load. This method is the standard for hydronic heating systems and many industrial heat transfer tasks. Naturally, they applied this design to solar systems, treating the collectors as the boiler and the tank as the receiver. If you walk into most professional engineering firms and ask them to design you a hydronic heating system OR a solar system, they will grab their manuals that show how to assemble a pressurized glycol loop.
Since it is too expensive to fill the solar storage tank with a glycol solution, the heat is transferred from the collector loop into the tank through a heat exchanger. The collector fluid goes through one side of the exchanger and the tank water goes through the other side. There are two pumps, one on each side of the exchanger, and controls to turn the pumps on. Glycol loops are “charged” all the time. This is good. They remain ready to run whenever the pump kicks in. When such a system is installed, coin vents (can turn the screw with a dime) are installed at all the high points where air can accumulate and vapor https://topenergy.com.vn/ lock the system. The startup procedure is to fill and pressurize the lines (maybe 15 psi) and go around to all the coin vents and burp the air out. Over the years, people have invented clever coin vents that when dry will leak air and when wet will seal. That way you don’t have to go to each one to burp it, it will do so by itself. It is like the rope caulking used in boat hulls for thousands of years. As long as the boat stays in the water, all is fine. If you take it out and let the caulking dry out, it will leak until the caulking gets soaked again. There are many other kinds of automatic air vents, some based on the float system seen in toilets. Safety also requires a pop-off valve near the boiler (i.e. collectors) to relieve pressure in case the boiler controls go haywire. A glycol-water mix is a great solvent for shingles and plastics, including tile floors. So the pop-off valves must have a pipe running to a drain to contain the liquid in the event of a failure.