Automatic Defrost Function - Siemens RVS41.813 User Manual

Automatic defrost function

Siemens Switzerland Ltd
HVAC Products
Plant in heating mode
In normal heating mode of an air-to-water heat pump, condensation can occur at low
temperatures, causing the evaporator to ice up. This reduces the heat pump's output
and can lead to low-pressure malfunctions or damage to the evaporator.
K1
B84
Y22
T
B91
T
E17
K19
Plant in defrost mode (process reversal)
The evaporator is defrosted either with the fan or – as shown in the example below –
with process reversing valve Y22. For process reversal, a HP partial diagram with
process reversing valve (Y22) must be used.
Demand-dependent defrost control ensures that the defrost energy drawn from the
heating circuit in the case of process reversal will be kept at a minimum. During the
defrost process with process reversal, the fan remains deactivated.
K1
B84
Y22
T
B91
T
E17
K19
When the compressor is in operation, "Duration defrost lock" (2962) and "Time up to
forced defrost" (2963) elapse. If the source temperature (B91) drops below the defrost
release temperature (2951), the defrost release function will be released. The heat
pump can change to defrost operation mode after "Duration defrost lock" at the earliest,
and on completion of "Time up to forced defrost" (2963) at the latest.
When, due to icing up during this period of time, the temperature difference (8477)
between incoming outside air (B91) and evaporator (B84) exceeds the setpoint (8478),
the defrost function is triggered.
User manual RVS61.843, RVS41.813
6 The settings in detail
Gas low-pressure
Gas high-pressure
Liquid
B21
Q9
T
B71
T
Gas low-pressure
Gas high-pressure
Liquid
B21
Q9
T
B71
T
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CE1U2355en_02
28. September 2009