Carel uChiller UCHBP00000200

74
ENG
µchiller +0300053EN rel. 2.2 - 14.12.2021
Functions
5.17 Defrost
During heat pump operation on air/water units, the outdoor coil works as an evaporator. If the outside temperature is low, frost
may form on the coil, resulting in reduced unit effi ciency. To free the coil from frost and restore maximum effi ciency, Chiller
activates the defrost function. Activation depends on the value read by the reference probe (pressure transducer, low pressure
side -> evaporation temperature in the graph), on the activation threshold being exceeded, and a possible delay.
User Code Description Def Min Max UOM
S S039 Defrost: start temperature -1.0 -99.9 99.0 °C
S S040 Defrost: reset start defrost delay threshold 1.0 S039 99.9 °C
S S041 Defrost: delay at start-up 30 0 999 min
S S042 Defrost: end temperature 52.0 -999.9 999.9 °C
S S046 Defrost: min duration 1 0 99 min
S S047 Defrost: max duration 5 0 99 min
Example of defrost activation:
300053_069_R01
D1
Set Thrs
Res Thrs
End Thrs
Te (°C)
Start
Evap
Cond
End
t (s)
Key
T Temperature
End Thrs End defrost temperature
Res Thrs Reset start defrost delay threshold
Set Thrs Start defrost temperature
D1 Defrost start delay
Start Start defrost
End End defrost
T_Cond Condensing temperature
T_Evap Evaporation temperature
Fig. 5.aa
If the defrost temperature does not exceed the reset threshold during the defrost start delay, then the defrost starts. It ends
when the reference probe (pressure transducer, high pressure side -> condensing temperature in the graph) exceeds the end
defrost temperature or the maximum defrost duration has elapsed.
Note: for optimal defrost management, it is recommended to set the start defrost temperature to the evaporation tempe-
rature value at which ice starts forming on the coil (-1.0°C / -1.5°C); the defrost start delay expresses the time needed to accumu-
late a layer of ice that requires defrosting (30- 60 minutes). Also see the paragraph “Sliding defrost”.
5.17.1 Defrost procedure
Notes: in the following description:
• "case with compressor ON" indicates that the phase is only featured if defrost is set with the compressor On;
• "case with compressor off " indicates that the phase is only featured if defrost is set with the compressor Off ;
End defrost can be managed in two ways:
• with the compressor off : the thermal inertia of the condenser is used to end the defrost;
• with the compressor on: to make the defrost as fast as possible.
User Code Description Def Min Max UOM
M S055 Compressor after defrost 0/1=On/Off 001-
Compressor o at end defrost
Compressor on for the entire defrost
300053_070_R01
EE
V
t (s)
Fan
CP
4WV
Defrost
1 3 5 7 9
1042
300053_071_R01
EE
V
t (s)
Fan
CP
4WV
Defrost
1 3 5 6 7 8
42
Fig. 5.ab Fig. 5.ac
Key
Defrost Defrost request
4WV Cycle reversal (4-way valve)
CP Compressor capacity
Fan Enable fans
EEV Electronic expansion valve