Air Handler Water Coil Freeze Stat - Freezing Protection Control
Air Handler Water Coil Freeze Stat - The HVAC Air Handler Freeze Stat is a low-temperature limit control and it is used mainly in commercial systems in the duct work on economizers or in air handlers just before any coil especially water coils. It is a safety and protection control to prevent extremely cold air from reaching the hot water or chilled water coils inside the air handler where the air enters from the economizer.

Under ideal control setup if the freeze stat trips the economizer dampers close and the blower fan stops. This prevents coils from freezing. A frozen coil can bust open and will need to be replaced if it freezes thus the purpose of the freeze stat in HVAC air handler applications which utilize economizers for free cooling.

Air Handler Water Coil Freeze Stat

Coils protect by a temp control installed upstream of the water coilThere are some instances where HVAC maintenance departments have problems with nuisance trips on freeze stats and the HVAC maintenance department decides to jump this device out. This can cause severe damage to the equipment if the economizer feeds freezing air through the air handler. If the HVAC maintenance department experiences nuisance trips which cannot be adjusted through the range settings on the freeze stat device then the freeze stat should be replaced with a new freeze stat rather than jumping out the device. It would be better to disable the economizer than to jump out the freeze if a problem occurs.

Air Handler Water Coil Freeze Stat - Sequence of Operation

The sequence of operation for any freeze stat inside an air handler will include stopping the blower, closing all outside air dampers, opening the return air dampers, and opening all valves serving chilled water or hot water coils inside the air handling unit. When these valves open the appropriate pumps should energize or respond so that the water will flow through the coils preventing a freezing coil which will likely burst open if it freezes. Another spelling for it is freezestat.

Air Handler Water Coil Freeze Stat - Conclusion

One of the biggest problems with freeze stats is nuisance trips. Often, in some cases, this causes the maintenance department to decrease the trip temperature of the freeze stat to try to prevent the nuisance trips. It is important that the freeze stat trips before the coil freezes so other methods should be used rather than lowering the temperature on the freeze to prevent nuisance trips. An adjustment to the economizer system or other methods should be used to other than lowering the trip temperature.

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Air Handler Water Coil Freeze Stat

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