Say you have an air handling unit equipped with a freeze stat. If a freeze stat fails, normally the dampers will close, the supply fan will shut off, and the pump for the heating coils will turn on at 100% (at least with the units I look after). Now, if the only function that failed to engage was the outside air dampers closing and they ended up stuck open, would the coils still be at risk of freezing and bursting even though a hot medium is circulating through the coils (that is constantly being reheated via heat exchanger/boiler)? Even if a freeze stat fails to trip, wouldn't the heating coils already be circulating fluid at 100% capacity in abnormally cold conditions? Wouldn't this prevent coils from bursting in every instance when a freeze stat fails? Assume it's -30 degree celcius weather outside.
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