12-19. Freeze protection system
There are two features to the T-H2-DV or T-H2-OS freeze protection system: the automatic firing system
and the ceramic heating blocks. The automatic firing system allows the T-H2-DV or T-H2-OS to briefly
fire on for about 3 seconds and the ceramic heating blocks will heat up whatever portion of the heat
exchanger the blocks are strapped to. The firing system mainly focuses on providing freeze protection
around the heat exchanger drum. The five kind of heating blocks focus on protecting the inlet, outlet
and drain piping inside the T-H2-DV or T-H2-OS, as well as the front drum pipe. The conditions to
activate either feature are different from each other. However, the two features are not mutually
exclusive, because they focus on different areas of the T-H2-DV or T-H2-OS. As long as each particular
feature’s activation requirements are met, it is possible for both features to operate at the same time.
Automatic firing system
Gas and electrical power are required for this feature to operate.
After 5 minutes have elapsed since the T-H2-DV or T-H2-OS previous firing operation, the computer will
continually check the temperatures of the inlet and output thermistors (the output thermistor is the one
that checks the temperature of the water immediately leaving the heat exchanger, not the water leaving
the T-H2-DV or T-H2-OS, which is mixed with water from the bypass valve). The automatic firing system
will not activate at all unless these 5 minutes have elapsed.
When the computer checks for these temperatures, the freeze protection firing system will activate if:
T
in
> 46°F and T
out
< 37°F
where T
in
is the temperature of inlet thermistor and T
out
is the temperature of the output thermistor.
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