I was in a parking garage that has sprinklers and i found myself wondering how the water in the pipes is kept from freezing in the winter or it the system is not charged unless needed hence no water is in the pipes to freeze. Someone who knows about such things can clear up this slight mystery for me.
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Sprinklers can be dry pipe and wet pipe, with numerous derivatives. Some dry pipe units are connected directly to a water supply but charged with nitrogen where piping is exposed, others are not pressurized but are connected to water supply through a valve operated by temperature sensors rather than fusible links in the sprinkler heads. Some wet by systems are wrapped with variable output heating tape which supplies just enough heat to keep them just above freezing. This last variety is used in unheated warehouses which provide some shelter.