MIL-HDBK-1003/3
7.3.5
Freezing of Steam Coils - General. Care should be taken in both
design and construction of systems with steam heating coils to prevent coil
freeze-up. Two primary causes of coil freeze-up are: (1) stratification of
the air entering the coil due to poor mixing of outside air and return air,
and (2) buildup of condensate in the coil. While it is virtually impossible
to design a system with freeze-proof coils, careful consideration in the
following areas could air in minimizing coil freezing problems.
7.3.5.1
Freezing Due to Air Stratification. See Figure 29. In general,
outside air and return air are mixed in proportions that will provide an
average mixed air temperature above freezing. However, if the outside air and
return air streams are not thoroughly mixed, stratification of air can occur
across the coil. This condition results in localized cold spots where
sub-freezing air contacts the coil and can cause freezing. Care should be
taken when locating the steam coil and designing the
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