Carel k.Air, User Manual, Page: 87 / 192

87
Functions k.air +030220981 rel. 1.2 - 01.12.2020
Condition for entering defrost mode
The unit starts defrosting when the following condition occurs:
• Outside temperature < Bypass damper maximum opening threshold (default = 5°C);
• Exhaust temperature < Exhaust temperature threshold
End defrost conditions
The unit ends the defrosting procedure if one of these conditions occurs:
• Exhaust temperature > Exhaust temperature threshold, or
• The “Maximum defrost duration” time has elapsed from when defrost mode starts.
Note:
when the outside temperature is very low, and the minimum time has elapsed between successive defrosts, defrosting
starts again.
OFF
ON
Byp_Damp_Max_Op_thr
Ext_T_thr
Rec_exch_def
t
t
t
Ext_T
Ext_T
T_ON T_OFF T_ON
30220980_207_R01
Key
Exh_T Exhaust temperature
Ext_T Outside temperature
Byp_Damp_
Max_Op_thr Start defrost threshold
Exh_T_thr End defrost threshold
Rec_exch_def Heat recovery unit defrost
T_ON Maximum defrost duration
T_OFF Minimum time between defrosts
t time
Fig. 9.as
9.25 Evaporator defrost
30220980_196_R01
EXHAUST AIR
EXTERNAL AIR
RETURN AIR
SUPPLY AIR
CP
R V
S
EE V
REC
E
G
T
2
M
T
1
P
1
P
2
P
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.at
During the winter, the outside air reaches low temperatures and consequently the exhaust air temperature is also lower: this can
cause the formation of ice on the evaporator in the cooling circuit. The evaporator can be defrosted:
1. by opening the bypass damper
2. by stopping the compressor
3. by reversing the cycle
These three actions are performed in sequence, so as to optimise energy savings, and only if the previous action does not obtain
the desired eff ect.
Conditions for entering defrost mode
The unit starts defrosting if these three conditions occur simultaneously:
1. unit in heating mode
2. compressor
on
3. evaporation temperature (conversion from suction pressure) < start defrost threshold During defrosting, the fans operate at the
speed set for “Defrost fan request”.