To prevent the heat exchanger from freezing and
becoming damaged as a consequence, the supply air
temperature is measured immediately after the heat
exchanger (when viewed in airflow direction). If the tem-
perature falls below a set limit, the heating valve opens,
the fans are switched off, and the damper closes. The
control system will not return to its previous configura-
tion until the room temperature has increased to at least
1 K (can be configured) above the temperature limit.
Recommended
Supply air temperature limit: 8 °C
Frost protection
If the outdoor temperature is
≤
-20 °C (can be config-
ured) or if there is no outdoor temperature signal, the
unit is switched off; this is to protect it if operating tem-
peratures are too low.
Heat recovery frost protection
If the outdoor temperature is very low, the airflow
through the heat recovery unit on the extract air side
may become impaired or even impossible due to the
freezing of the condensate; to prevent this from hap-
pening, the control system opens a motorised bypass
damper. The bypass remains open until the outdoor air
temperature has risen to at least 2 K (can be config-
ured) above the limit.
Recommended
Limit value: -6 °C
Frost protection of the heat recovery unit can be sig-
nalled with an alarm relay on DO6/DO7.
As an alternative, the heat recovery unit can be used as
standard. After 180 minutes (configurable) the unit is set
to secondary air operation for 20 minutes (configurable)
such that ice build-up is avoided and the extract air duct
is de-iced if necessary.
After the set time has elapsed, the previous operating
mode is resumed.
This function can be used all year round and helps to
reduce the water heating energy required.
A condensate drain is required when you use this
function.
3.1.2.7.5 Start-up delay
If the outdoor air temperature is below 3 °C (can be con-
figured), the start-up of the fans is delayed if one of the
following is true:
The ventilation unit is restarted
The frost protection function ends
The fan stage is changed from 0 to 1
Start-up delay means that the heating valve opens and
the heating coil is preheated for 300 s (can be config-
ured). After the preheating time has elapsed, the control
system starts the operating mode valid for this time.
3.1.2.7.6 Free cooling
Free cooling means that outdoor air is supplied directly
to the room, without passing through the heat recovery
unit.
Requirements:
Room temperature > comfort temperature range
Outdoor air temperature < comfort range upper limit
∆
t Room temperature to outdoor temperature >5 K
(can be configured) for at least 10 minutes
The supply air temperature for the operating mode
must not fall below the set limit
If the room temperature to outdoor air temperature dif-
ference falls below 1 K (can be configured) or if the
room temperature reaches the comfort temperature
range, free cooling is disabled. The unit resumes the
original operating mode.
Recommended
Select free cooling for the following operating modes:
–
Unoccupied
–
Standby
–
Occupied
3.1.2.7.7 Free heating
Free heating means that outdoor air is supplied directly
to the room, without passing through the heat recovery
unit.
Requirements:
Room temperature < comfort temperature range
Outdoor air temperature > comfort range lower limit
∆
t Room temperature to outdoor temperature >2 K
(can be configured) for at least 10 minutes
The supply air temperature for the operating mode
must not exceed the set temperature limit
If the outdoor air temperature to room air temperature
difference falls below 1 K (can be configured) or if the
room temperature reaches the comfort range, free
heating is disabled.
Control of ventilation units
FSL
‑
CONTROL II > Functional description
Single room control system FSL
‑
CONTROL II
20