O P E R AT I N G A N D I N STA L L AT I O N I N ST R U CT I O N S SYST E M V E N T E C H LG 5 0 0 P
PAG E 1 1
Heat exchanger with bypass
4.2 POSSIBILITIES OF SYSTEM
EXPANSIONS FOR
FROST PROTECTION
Depending on extract air
temperature and humidity, a
danger of freezing will exist at
the heat exchanger exhaust air side, par-
ticularly 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 free-
zing:
• 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 elec-
trical pre-heater on full power.
4.2.1 Frost protection via heat exchanger
bypass
If the ventilation unit has no pre-heating
exchanger, a bypass may be used to pro-
tect 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 or-
der 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 free-
zing, the frost protection temperature
(factory setting -5°C) and frost protec-
tion P-band (factory setting 2°C) para-
meters 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.
Illustration: Primary parameters
