How do we optimize the switchover point for steam coil valve modulation to F&B damper modulation? Well if the end goal is to avoid freezing the steam coil, we should switch over when its freezing out of course! Face and Bypass changeover: The Issue This is nothing novel, most hydronic or steam coils use the same controls. ![]() The issue that was resolved with the use of the F&B damper arrangement is to prevent the coil from freezing, so anytime the coil isn’t at risk of freezing the face and bypass dampers will open to allow full airflow through the steam coil and the steam coil control valve will modulate to maintain the discharge air temperature. ![]() Pretty neat, huh? Face and Bypass control The F&B dampers direct a portion of the airflow through the steam coil and another portion bypasses the coil in order to achieve the necessary discharge air temperature and prevent a freezing airstream from damaging the steam coil. One of the neat ways we’ve design around this is to use a Face and Bypass (F&B) damper arrangement to allow the coil to have maximum steam flow to prevent freezing. Due to the low mass of water in a steam coil, it has a higher propensity to freezing when conditions are right. These coils use control valves to modulate the flow of steam to the coil. ![]() Many air handling units in colder climates are equipped with steam heating coils. Basics of steam coil and face and bypass operation
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