SystemAir HHFlex C, Operating Instructions Manual, Page: 31 / 47

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5.11 Hot water pre-heating Coil
Parameters for this function are available in Actual/setpoint and Settings.
5.11.1 Heat Recovery Frost Protection
The temperature entering the heat recovery exchanger is controlled as shown in the sketch below.
A PID controller is used. Tuning of the PID controller is possible in the menu Settings (Advanced User).
5.11.2 Water Coil Frost Protection (TA01)
A switching frost thermostat is located downstream the hot water coil in order to prevent it from freezing in case of
insufficient hot water supply. Capillary temperatures over a length of 300mm below the predefined alarm level generate a
frost alarm (TA01) and the unit will go into frost mode. The frost mode will initiate the following actions:
1.
Ventilation is stopped and air dampers are closed (if applicable)
2. All control valves will be forced to 80% open.
3. All pumps are started and heat demand command is on
A frost alarm shall be considered as an urgent alarm and has to be reset in the electrical panel of the air handling unit. The
frost thermostat itself resets automatically if the temperature rises sufficiently above the alarm level.
If the unit is also equipped with a frost coil with frost protection thermostat, the frost thermostat on the heating coil
downstream the heat recovery device is omitted.
The default hardware setting for the frost thermostat alarm is +5°C.
5.11.3 Warm Up at Unit Start Up
This function is not active when indoor unit is selected
To avoid unintentional frost alarm, a startup delay mode for winter operation is programmed.
If the outdoor temperature (TT06) is below a preset value (d5°C), the fans will only be started after a fixed preset
time delay (5 min) in order to pre-heat the heating coil. During this time delay the hot water control valve (CV03) is
opened at a preset value (default 100%). Heat demand (WV01) and pump (CP03) on signal are generated simultaneously.
For this purpose an outdoor temperature (TT06) sensor for wall mounting (not duct sensor) is mandatory!
5.11.4 Unit Frost Protection
This function is not active when indoor unit is selected
To secure outdoor units against unintentional frost alarm during unoccupied mode, a hot water flow across the heating coil
is created if the outdoor temperature (TT06) is below the preset value (d7°C), the hot water control valve (VC03)
is opened at a preset value (default 50%). Heat demand ((WV01) and pump (CP03) on signal are generated
simultaneously.
Valve Opening (VC03)
Measured Value
100%
Setpoint
Pump
(CP03) On
&
Heat Demand
(WV01)
10%
5%