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86
Functions
k.air +030220981 rel. 1.2 - 01.12.2020
9.24 Heat recovery unit defrost
During the winter, the outside air reaches low temperatures and this may cause ice to form on the heat recovery unit. The heat
recovery unit is defrosted by modulating the opening of the bypass damper (for a plate heat recovery unit) or by reducing the
speed of the thermal wheel.
Notes:
• in very cold climates, to prevent the formation of ice, a heater can be installed that heats the air entering upstream of the heat
recovery unit, using an auxiliary control function (see the corresponding paragraph).
• the above- mentioned devices act independently, therefore if enabled, they can be activated simultaneously.
Important: the heater used to defrost the heat recovery unit is managed independently of the main control function, using
the auxiliary loops.
Defrost prevention
The selection of the type of heat exchanger aff ects the type of action used to obtain the same eff ect of minimum/maximum
heat exchange. See the following table for the actions corresponding to the same heat exchange eff ect.
HE A T R E CO VE RY T YP E
P late W heel
HE A T E XC H ANG E Min Bypass damper open Thermal wheel at minimum speed
Max Bypass damper closed Thermal wheel at maximum speed
Tab. 9.bd
The controller therefore opens the bypass damper and adjusts the speed of the thermal wheel using the same modulating
output, to prevent defrosting.
R if D escription D ev Min Max UoM D ir Modbus BAC net
HE A T R E CO VE RY
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
Tab. 9.be
9.24.1 P late heat recovery unit
The bypass damper opens according to the outside temperature value so as to reduce the amount of fresh outside air entering
the heat exchanger. It continues to be crossed by the fl ow of warm exhaust air (~20°C), so as to assist defrosting.
30220980_163_R01
OFF
Byp_dmp
thr_min
Byp_dmp
thr_max
ON
Ext_T
Bypass
damper
30220980_162_R01
100%
0%
Ext_T
Bypass_
dmp_op (%)
Byp_dmp
thr_min
Byp_dmp
thr_max
Key
Bypass_
dmp_op Bypass damper opening
Byp_dmp_
thr_max Bypass damper maximum
opening threshold
Byp_dmp_
thr_min Bypass damper minimum
opening threshold
Ext_T Outside temperature
Fig. 9.ap
Fig. 9.aq
9.24.2 Thermal wheel
To prevent activation of frost protection, the thermal wheel, starting from the minimum bypass damper opening threshold,
decreases speed until stopping, reducing heat exchange between exhaust air (warm) and fresh air (cool).
30220980_176_R01
100%
0%
Ext_T
H_wheel_speed
Byp_dmp
thr_min
Byp_dmp
thr_max
Key
H_wheel_speed Thermal wheel speed
Byp_dmp_thr_max Bypass damper maximum opening threshold
Byp_dmp_thr_min Bypass damper minimum opening threshold
Ext_T Outside temperature
Fig. 9.ar