Freeze Protection: Active vs. Passive Active and passive solar water heaters are the two primary types of solar water heaters. A pump circulates a heat transfer fluid between a tank and a collector in active systems. Passive systems, on the other hand, do not utilize a pump, which usually implies that the collector and tank are near to one another. Both types of systems have benefits, and one of the benefits of active systems is freeze protection. To prevent freezing, they can utilize glycol anti-freeze or a drain-back system. This freeze protection, however, comes at a cost: a more expensive system that is difficult to install and maintain. They also necessitate pumps (which use power and have moving components that fail) and/or glycol, which acidifies over time and can ruin the system from the inside. Passive systems, contrary to popular belief, can also be frost protected. We recommend adopting a drain-back type system or utilizing your passive solar water heater seasonally in locations that endure persistent severe freezes, such as Alaska or Minnesota. However, in most other cases, a Sunbank will suffice. Sunbank pioneered a freeze prevention technology that permits passive solar water heaters to be deployed outside of their normally acceptable temperature ranges. 
The first thing to grasp is that the Sunbank itself, including the tanks and collectors, is naturally frost protected. The collectors are good too -35oF, and the tank, which is highly insulated and loaded with 40 or 80 gallons of thermal mass depending on your model, would have to be left in very cold weather for several days with no heat input or flow to approach freezing. The piping between the Sunbank tank and the conditioned room is the section of the system that is prone to freezing. How Do I Use Freeze Protection? Reduce the distance between the tank and the conditioned environment. This run will already be quite short for installations on a sloping roof - on the order of 12′′ - 18′′. Instead of copper, use PEX plumbing. It can also freeze without bursting, in addition to being less costly and more durable. This is not something you should rely on, but it is a useful function if the rest of your system fails. Insulate the PEX with insulation with a suitable R-value for your area. Wrap the insulation in a protective aluminum or PVC sheathing to keep UV rays out and air gaps closed. 
How Do I Use Freeze Protection? Reduce the distance between the tank and the conditioned environment. This run will already be quite short for installations on a sloping roof - on the order of 12′′ - 18′′. Instead of copper, use PEX plumbing. It can also freeze without bursting, in addition to being less costly and more durable. This is not something you should rely on, but it is a useful function if the rest of your system fails. Insulate the PEX with insulation with a suitable R-value for your area. Wrap the insulation in a protective aluminum or PVC sheathing to keep UV rays out and air gaps closed. Install a recirculation system and/or thermal heat tape. When paired with the Sunbank controller, a recirculation pump provides rapid hot water at the tap while simultaneously acting as an active freeze and overheat prevention system. A relay on the Sunbank controller may power the pump. When the controller detects that the Sunbank is becoming too hot, it can activate the heat to disperse the heat. 
Alternatively, to avoid freezing, configure the controller to circulate the water at night throughout the winter. These systems are simple to install in any home and are available for purchase on our website. If the power goes out and you're worried about freezing, simply leave the hot water side of the faucet running gently overnight. Set up a freeze-protection valve. Options 1-4 will satisfy 95% of our consumers. In circumstances when freezing is a constant worry, a freeze prevention valve may be considered. A freeze prevention valve is a mechanical mechanism that opens at 35 degrees Fahrenheit and closes at 40 degrees Fahrenheit, enabling water to flow through the pipe and preventing it from freezing. It is connected to the drain and put on the hot return pipe immediately before it enters the conditions space. It is an SRCC-approved freeze prevention device that operates even when the power is turned off. 
This comprehensive freeze protection system provides the convenience of a passive system as well as the certainty that you have a redundant system that will not leave you vulnerable to freezing in mild temperatures. The liquid used to convey heat from the solar panel to the cylinder in most solar thermal systems is antifreeze. However, there are a few water-only drain back systems. Propylene glycol is a non-toxic antifreeze (as opposed to toxic ethylene glycol). Your solar system may require an antifreeze replacement. This is not always the case; we will first assess the state of your system.
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