If freeze protection is an issue than a closed system with anti freeze is a good idea.
Closed loop solar water heater system.
The direct open loop solar water system freeze recirculation is both the simplest and most efficient type of solar heating system.
Most new solar homes feature a variation of one kind or another.
In this system potable water is drawn directly from the storage tank and circulated through the array to be heated and returned to a recirculation port in the tank.
Closed systems are often used in second homes or primary residences in areas prone to long power outages.
Glycol or some equivalent antifreeze fluid fills.
The heated water then flows into the storage tank before it s channeled into the heat exchanger.
Closed loop active antifreeze systems are the most versatile and failsafe of all the solar supplemental water heating systems.
Propylene glycol and the new bio green are common antifreeze materials we have several options for exchanging the heat to the clean domestic hot water.
A special water heater tank incorporating a heat exchanger works in conjunction with one or more flat plate roof mounted collectors.
Covers closed loop antifreeze systems and drainback systems.
To protect the unit you must consider an open or closed water heater system.
Closed loop solar heating system.
Lots on installation detail.
The down side is two heat sources.
Closed loop solar water heater systems sometimes referred to as anti freeze or glycol systems include the heat collectors insulated piping a circulating pump an expansion tank a hot water storage tank a heat exchanger solar fluid usually a solution of water and nontoxic propylene glycol antifreeze a controller valves and gauges.
In the case of the closed loop solar heating system the htf is typically a mixture of water and propylene glycol.
Heat exchangers in the storage tank eliminate a pump but make eventual tank replacement more.
Closed loop solar water heaters have few limitations with collector placement the collector loop is antifreeze filled and are permanently charged.
When the controller senses that the sun is shining and your tank needs a warm up it signals the pump to send water through the black collector panels.
The process of filling the plumbing system with this antifreeze while purging all the air out must be done systematically and in the right order.
Installation basics for solar domestic water heating systems chuck marken and ken olsen.
Very good articles on selecting the components for a closed loop solar hot water heating system suitable for cold climates.
Instead of relying on glycol for freeze protection this system allows all the water in the array to drain back from the array and into a storage vessel in the solar loop when the pump is turned off.
An open water heater system is when water that increased its volume and pressure due to the heating freely goes from the storage tank into the cold water supply line and eventually into the municipal water system if the pressure is high enough.
Indirect solar water drainback systems are also a indirect design that use a heat exchanger to separate the collector loop from the potable water.
