In an attempt to have their systems reclassified to gain more sales, some manufacturers have incorporated freeze- protection schemes into their “mild climate” systems. The bottom line? Buyer beware if you’re considering installing one of these systems in your “harsh” climate. Only two designs—drainback and antifreeze systems—offer reliable freeze protection in these areas. Here are some freeze-protection devices that have caused collectors to freeze in the past —and consequently have required expensive repairs or replacement.
Direct pump with recirculation. Some differential controls for turning pumps on and off also have a “freeze-protection feature” that can be set to recirculate water from the storage tank to the collector. The logic is that the warmed, stored water can be routed to the collector to prevent it from freezing. But this method has ruined collectors when unusually bad winter storms move in and power outages occur. Without electricity to power the control and pump, water can stagnate in the collector, and a hard freeze can burst the collector riser tubes.
Freeze valves (a.k.a. dribble valves). For freeze protection, some direct-pump, ICS, and thermosyphon systems use a freeze valve, a passive valve that is set to open at a low temperature (either 35°F or 45°F). When the valve opens, water from the municipal or well system enters the collector, and the near-freezing water in the collector dribbles from the valve onto the roof or the ground. Although this strategy is perhaps more reliable than recirculation systems, it is far from fail-safe. Hard (mineral-laden) water can eventually clog the valve, and poof!—the supposed freeze protection is gone.
Draindown valves, which were incorporated into direct-pump systems all over the United States, have been one of the worst hiccups in solar-thermal history. At a preset, low temperature, a controller activated the valves to divert water in the collectors to drain outside. However, like freeze valves, draindown valves were prone to failure due to corrosion, hard-water deposits, and clogging. Typically, the first winter freeze ruined the collector—when the valve failed, the collectors remained full of water and froze.