4.5 Defrost function
By measuring the pressure difference over the exchanger the need for defrosting can be detected. The
differential pressure transmitter is auto calibrated by the system to obtain the correct pressure in relation to
the airflow. Manual calibration is possible, e. g. after cleaning of exchanger.
The bypass damper opens to reduce the flow of cold outdoor air through the heat exchanger. When the
bypass defrosting is initiated the supply temperature is allowed to decrease 4K from the setpoint. If the
actual supply air temperature is decreased more then -4K a stop defrost sequence will be initiated. If stop
defrost is not allowed, the unit will stop and the alarm
Analogue deicing
is presented in the display.
Table 1:
Exchanger deicing
Yes
Set if exchanger deicing will be used, Yes/No
Bypass
On
Exchanger deicing allowed with bypass, On/Off.
Stop deicing
On
Exchanger deicing allowed with stop of the supply air fan (SAF),On/Off
Activation temp
0.0
Outdoor temperature limit to allow deicing function
Stop temp SAF
-8
Outdoor temperature limit for forced stop deicing, interlock of bypass
deicing
Setp Press dev
50%
Setpoint in percent of the pressure deviation to start deicing
Stop hyst
60%
Reduction of the pressure deviation in percent to cancel deicing.
Topvex FC
Operation and Maintenance Instructions
125918
25
Systemair Sverige AB
