Carel k.Air, User Manual, Page: 76 / 192

76
Functions
k.air +030220981 rel. 1.2 - 01.12.2020
9.17 Heat recovery
The heat recovery unit is an additional device that provides free energy. If the conditions are favourable, the heat contained in
the exhaust air is recovered and transferred to the primary air, so as to pre-heat or pre-cool it. The heat recovery unit, if enabled
on Ac01, is always available as a control stage in the main sequential temperature control PID. However, the freecooling/freehe-
ating conditions must not be true at the same time, as these are mutually exclusive.
k.air can manage the following types of heat recovery unit:
Type S ignal/actuator C ontrol
Cross-fl ow On/off bypass The bypass damper is activated when the return/room temperature is below the set point by a set
delta in cooling mode, or when the return/room temperature is above the set point by a set delta in
heating mode
Modulating bypass The bypass damper is managed by the heat recovery function when the freecooling/freeheating
conditions are not present. The modulation signal is set by the main sequential temperature control
PID.
Wheel Rotor modulation
signal The bypass damper is managed by the heat recovery function when the freecooling/freeheating
conditions are not present. The modulation signal is set by the main sequential temperature control
PID.
Double on/off
coil Pump on/off signal The on/off signal is activated when the return/room temperature is below the set point by a set
delta in cooling mode, or when the return/room temperature is above the set point by a set delta in
heating mode
Double modu-
lating coil Modulating pump
signal The modulation signal is set by the main sequential temperature control PID. In the I/O menu, the
digital output used to enable the analogue signal can be set.
Tab. 9.af
When heat recovery is enabled, an input can be selected for signalling if the heat recovery unit is clogged. This is signal-only,
with no eff ect on control.
R if D escription D ev Min Max UoM D ir Modbus BAC net
U N IT
Ac01 Fans type (0: On/Off ; 1: 3 speeds; 2: Modulating; 3: Modbus RTU) 2 0 3 - R/W HR1292 PIV2800
Enable return fan FALSE 0 1 - R/W CS225 BV225
Heating exchanger type 0 0 4 - R/W HR1293 PIV2801
For mask usage - 0 1 - R DI696 BV1154
Return fan confi guration error - 0 1 - R DI697 BV1155
Tab. 9.ag
Note:
also see the chapter on heat recovery unit defrost.
The activation temperature diff erentials are needed to determine how effi cient it is to use freecooling/freeheating, considering
that the greater the diff erence between the outside air temperature and the return temperature, the more effi cient the action
will be.
For units with modulating fresh air dampers, the conditions for activating freecooling/freeheating are the same, however free-
cooling/freeheating is considered as the fi rst stage in cascade control. The controller adjusts the modulating fresh air damper (in
sync with the mixing damper), and the bypass damper, if fi tted, is opened completely.
R if D escription D ev Min Max UoM D ir Modbus BAC net
HE A T R E CO VE RY
E001 Heat recovery delta for bypass damper in cooling mode 4.0 - 99.9 99.9 K R/W HR1458 AV2966
Heat recovery delta for bypass damper in heating mode 4.0 - 99.9 99.9 K R/W HR1459 AV2967
E004 Heat exchanger PID parameters - Proportional gain 8.0 0.0 999.9 - R/W HR1460 AV2968
Heat exchanger PID parameters - Integral time 120 0 999 - R/W HR1461 PIV2969
E008 Heating exchanger type 0 0 4 - R HR1293 PIV2801
Bypass damper: minimum opening threshold -5.0 - 50.0 30.0 °C R/W HR1462 AV2970
Bypass damper: maximum opening threshold - 10.0 - 50.0 30.0 °C R/W HR1463 AV2971
E012 Minimum time between heat exchanger defrost 15 0 999 min R/W HR1464 PIV2972
Maximum defrost heat exchanger duration 15 0 999 min R/W HR1466 PIV2973
E016 Exhaust temperature threshold for defrost 20.0 - 50.0 90.0 °C R/W HR1468 AV2974
E020 Stratifi cation correction factor of the room temperature 0.0 0.0 10.0 K R/W HR1469 AV2975
Tab. 9.ah