Manifolds and freezer panels are the biggest complaint you’ll hear about solar hot water systems. The simplest solar hot water system with the best frost protection is the closed system with a glycol-filled tank and flat panels on the roof. Glycol acts as a heat transfer fluid, but it also acts as an antifreeze to prevent water from freezing in the panels. However, glycol-filled flat panels have two drawbacks. The glycol is food grade; any leak will seriously affect the taste of the water in the aquarium.
Water-filled flat panel systems are more efficient than similarly sized vacuum tube systems
However, in the colder months, panels of water-filled systems would freeze and crack if they did not have a primary and secondary frost protection system. These systems are based on the principle that moving water freezes at much lower temperatures than standing water. Reece’s solar hot water systems collect thermal energy from sunlight and uses it to heat water as an alternative to electricity or gas. A crucial part of this method is the insulation of heat transfer pipes. Solar water systems use a built-in device to ensure that the water inside the tank does not overheat during intense solar radiation.
In water-filled flat panel systems, an electronic sensor mounted on top of the panels detects when the water temperature in the panels falls below 3 degrees Celsius. When this happens, the sensor turns on an electric, solar energy circulation pump. It forces water to move through the system from the bottom of the storage tank to the panels. It is called the primary frost protection system. An antifreeze valve is installed as an additional antifreeze system on flat panels filled with water. The valve opens automatically when the water temperature in the panels falls below 2 degrees Celsius.
The pressure of cold water entering the storage tank increases the water pressure in the panels. It causes water to constantly flow through the panels and out of the freeze valve. It maintains the flow of water through the panels. Without water pressure, the valve will open, but water will not flow out of the panels, and the water in the panels will remain stationary. Unfortunately, most rural water systems rely on an electric booster pump to provide constant water pressure. Consequently, in a power outage, the primary and secondary frost protection systems will fail.
Conclusion
If efficiency is important to you, balanced with good frost protection, our experience has shown that it is best to install solar vacuum tube hot water systems in rural alpine areas. Vacuum tube systems require a primary frost protection system. However, vacuum tube systems contain very little water, and this water is enclosed in a well-insulated jacket. Therefore, during a power outage, the likelihood of freezing and cracking, as in a water-filled flat panel system, is reduced.