14
System operation strategy
Introduction
This section describes the operation strategy in various conditions.
For a user specific running operation see user guide at page 27
Preheat
If preheater is installed, the unit can add electrical heat to the T1 incoming outside air,
in order to reduce defrost situations, and increase the supply air temperature.
Preheater can be enabled/disabled on the HRC3 in installer mode, if preheat
module is set to “present” in the pc tool when installing
Preheat is applied after the T1 sensor.
If outside temperature is <-3°C or supply air is < 16,5°C the preheater will
switch on with 10% power.
The power will increase/decrease 10% for each 60 seconds depending on the
T1 or T2 temperature.
Setpoints cannot be changed
Defrost
In cold conditions where T1 is below -3°C and exhaust T4 is <+2°C the condensed wa-
ter could built up as ice in the heat exchanger, blocking the air path and eventually de-
stroying the heat exchanger.
In order to prevent this sequence is initiated:
Apply additional heat with preheater if mounted
The supply fan speed will decrease with 3 rpm/second until minimum RPM is
reached.
After 10 seconds at this speed the supply fan will stop completely, while the
ongoing exhaust fan is supplying warmer air into the heat exchanger compo-
nent, to remove any potential ice.
When T4 yet again is >+8°C the supply fan will start at minimum RPM, and then
increase speed with 3 rpm/second until the original required speed is regained.
If T4 becomes <+2°C during the speed increase cycle, the supply fan will de-
crease speed again.
If T1<= -13°C for more than 4 minutes and 25 seconds, even with defrost
mode active, the unit will stop all operation for 30 minutes, and reattempt pre-
vious operation condition. If electrical built in preheat is present, this total off
mode is disabled.
The defrost operation will create an underpressure inside the house, so if fireplace
mode is enabled, and defrost is necessary; the unit will stop all operation in 4 hours in-
stead. Setpoints cannot be changed.
When defrost is active a HRC 3 will show
dEF
When defrost has shut all off, the display will flash the T1 temperature
Bypass cooling and
summer mode
See more in the user guide page 27
