3.2
System extensions for frost protection
Depending on extract air temperature and humidity, a danger of freezing will exist at the heat
exchanger exhaust air side, particularly under frost conditions in winter. The heat exchanger must be
protected against ice formation during low outside air temperatures of ca. -3°C or less, using suitable
measures.
Various strategies may be followed to protect the heat exchanger from freezing:
Frost protection via heat exchanger bypass
Frost protection of the water (Glycol)
Frost protection via pre-heater coils – electric version
A frost protection alarm will trigger if none of these measures produce an effect after 5 minutes, i.e. if exhaust air
temperature remains below minimum level despite fully open bypass damper and PWW pre-heating exchanger or
electrical pre-heater on full power.
3.2.1 Frost protection via heat exchanger bypass
If the ventilation unit has no pre-heating exchanger, a bypass may be used to protect the heat exchanger from
freezing. Cold outside air will in this case bypass the heat exchanger via a duct and the warm extract air will be
used to protect the exchanger from freezing.
With this arrangement, a re-heater exchanger is recommended, in order to maintain a minimum supply air
temperature.
Damper actuators are controlled via a 0-10 V signal.
Description of the control system:
The bypass arrangement will protect the heat exchanger from freezing. The temperature sensor must be
positioned in the exhaust air directly after the heat exchanger.
To protect the heat exchanger from freezing, the frost protection temperature (factory setting -5°C) and frost
protection P-band (factory setting 2°C) parameters must be set. This means that the bypass damper will remain
closed down to a frost protection temperature plus frost protection P-band. Starting from this temperature, the
bypass damper will steadily open and will be fully open when the frost protection temperature is reached.
Heat exchanger with bypass
O P E R A T I N G A N D I N S T A L L A T I O N I N S T R U C T I O N S L G
7 5 0 - L G 6 0 0 0
P A G E
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