The capillary device of frost protection thermostats must cover all the surface area of the heating coil.
The FPT can only be installed after the 1st heating coil. We will study the reason for this in the
Explain why the FPT set at approx. + 5 [°C] (41°F) cannot be installed in front of the heating coil.
Explain why, even when installed after the heating coil, it still ensures anti-frost protection.
The FPT cannot be installed in front of the heating coil because, being cooled by the cool air intake, still not heated, it would risk stopping the AHU even though the coil is properly fed with hot water and there is no risk of freezing.
The AHU must be able to operate whatever the outside temperature.
When installed after the heating coil, the FPT simply registers the proper working of the heating coil.
If in extreme cold conditions the temperature of the exhaust air from the coil is higher than 5 [°C] (41 °F), it means it is well supplied with hot water and there is no risk of freezing.
Indicate the usual functions controlled by the FPT in the case of risk of freezing?
As a general rule, in the case of risk of freezing, the frost protection thermostat:
– Stops the fan blower motor
– Stops the air return fan motor
– Closes the fresh air inlets and exhaust air outlets
– Activates the opening of the hot water coil regulation valve
– Sets off an alarm