Domestic Hot Water Heat Pump Service Manual
35
7.14 Defrost operation
When the evaporation temperature (BT2) falls below 0°C, the evaporator starts to accumulate ice
on its fins. In order to maintain the unit reliability and performance, an automatic defrosting
operation is activated.
Defrosting can occur between 60 minutes and 120 minutes from the last defrosting or from the
last moment in which the evaporation temperature was above 0°C.
Defrosting can occur with two different strategies according to the conditions of the inlet air.
1) If the air temperature is above 4°C, then the defrosting occurs running both compressor and
fan. The fan runs at speed D3 (Fan max speed).
2)
If the air temperature is below 4°C, then the defrosting occurs running the compressor and
stopping the fan.
Before defrosting is completed the fan stops for a short period to allow the excess water in the
unit to leave the unit from the condensate drain.
Defrosting automatically stops when the temperature of the evaporator (BT2)
becomes higher than the set point (D10).
-5
5
15
25
35
45
55
65
75
85
95
00
:0
0:
00
00
:0
5:
50
00
:1
1:
40
00
:1
7:
30
00
:2
3:
20
00
:2
9:
10
00
:3
5:
00
00
:4
0:
50
00
:4
6:
40
00
:5
2:
30
00
:5
8:
20
01
:0
4:
10
01
:1
0:
00
01
:1
5:
50
01
:2
1:
40
01
:2
7:
30
01
:3
3:
20
01
:3
9:
10
01
:4
5:
00
01
:5
0:
50
01
:5
6:
40
02
:0
2:
30
02
:0
8:
20
02
:1
4:
10
02
:2
0:
00
02
:2
5:
50
02
:3
1:
40
02
:3
7:
30
02
:4
3:
20
02
:4
9:
10
02
:5
5:
00
03
:00
:50
03
:0
6:
40
03
:1
2:
30
03
:1
8:
20
03
:2
4:
10
03
:3
0:
00
03
:3
5:
50
03
:4
1:
40
03
:4
7:
30
03
:53
:20
03
:5
9:
10
04
:0
5:
00
04
:1
0:
50
04
:1
6:
40
04
:2
2:
30
04
:2
8:
20
04
:3
4:
10
04
:4
0:
00
04
:45
:50
04
:5
1:
40
Tem
p
e
ratu
re
(
°C)
T1 T air in
T2 air out
T3 T water top
FanSpeedSet
R2 Defrost
DefrostState
Defrost Valve
ON
Defrost Valve
OFF
Defrost OFF
Defrost Timer
Defrost ON
Fan OFF
Fan Auto
Speed
Fan Max
Speed
