VALLOX DIGIT SE / VKL
°
C
°
C
Temperature of supply air going
from the unit to the dwelling
Temperature of outdoor air coming to the unit
-20
22
°
C
-10
0
+10
0
10
20
30
Temperature of outdoor air coming to the unit
1
2
3
4
HR cell anti-freezing starts to function
+20
© VALLOX • We reserve the right to make changes without prior notification.
POST-HEATING
10
EXAMPLE: Outdoor air temperature rise in the heat recoverycell
with an electric and water radiator
Curve 1
Supply air temperature without post-heating = only heat
recovery.
Curve 2
Supply air temperature controlled by the thermostat of the
electric radiator, adjustment setting 23
°
C (air flow less than 75
l/s).
Curve 3
Supply air temperature with water radiator, water +35
°
C and
water flow 0.05 dm
3
/s. Air flow 50 l/s. Valve fully open.
Because heat release of water radiator is dependent on many
factors, the curves are approximate. Glycol decreases radiator
power by circa 10...20% depending on mixture.
Curve 4
A 1000 W post-heating radiator can heat e.g. 100 l/s air by
circa 8
°
C at most.
Post heating radiator
Electric radiator 1000W, or water radiator (VKL model)
Post-heating in DIGIT SE VKL operates in a similar fashion to an electric radiator but the actuator
is an electric thermostat valve, which is open when dead. The water radiator in the VKL model
also has an automatic anti-freezing function, which stops all functions when supply air temperature
is below 7
°
C and outdoor temperature is below 0
°
C. At the same time, the valve remains
open and the self-actuated dampers of the fans close. (The control panel shows the fault message
FREEZING ALERT.) The unit restarts and the dampers open as soon as supply air temperature
exceeds 10
°
C.
In the VKL model it is also possible to bring non-freezing heat transfer fluid into the post-heating
radiator. In addition, the radiator can be provided with a separate non-freezing heating circuit.
It can be built for example with the heat exchanger (V) supplied with the unit. See the mounting
examples in the technical specification in the section describing water-circulating radiator
connections.
Post-heating regulation
There are two ways to control post-heating.
1. Supply air constant temperature control
• In DIGIT SE, post-heating control is proportional: when the chosen temperature exceeds
supply air temperature by more than 2.5
°
C, the radiator is on 100% of the time; when
the temperature differential gets smaller, the on time of the radiator is reduced
automatically in two-minute sequences. The temperature range is 10…30
°
C.
• The heating radiator is on when the ( ) sign is displayed in the main display of the
control panel.
• The main display of the control panel shows the temperature of supply air.
• Temperature control is only active when post-heating has been switched on.
2. Supply air cascade control
• Supply air temperature control can be replaced with cascade control.
• Cascade control changes the mode of regulating the post-heating radiator: the
temperature of air blown to the ventilation zone is controlled on the basis of extract air.
• The program aims at keeping supply air temperature at the value that depends on the
difference between extract air and the setpoint as follows: if extract air is hotter than the
setpoint, the temperature of supply air is lower than the setpoint by the same amount. If
extract air is cooler than the setpoint, supply air is hotter by the same amount. For
instance, if indoor air temperature is 25
°
C and the setpoint is 24
°
C, the aim is to blow
23
°
C air to the ventilation zone. If temperature in the ventilation zone is 24
°
C and the
setpoint is 25
°
C, the aim is to blow 26
°
C air to the ventilation zone.
• The aim is to permanently keep the temperature of air blown to the ventilation zone
within the range +10...+30
°
C.
• Cascade control can be chosen on the control panel, and it is active when post-heating
has been switched on.
• The heating radiator is on when the ( ) sign is displayed in the main display of the
control panel.
Heat exchanger (V)
Water/liquid-
radiator
(VKL model)
Electric
radiator
