Toshiba RUAGP Series Original Owner's Manual page 52

2. Defrosting operation control
In the Heating mode, the unit controller predicts frost formation on the air heat exchanger of each circuit and
starts defrosting as necessary.
(1) Control to prohibit simultaneous defrosting
Each module independently performs defrosting. One circuit is defrosted at a time in a given module.
Note: The unit controller provides no control over simultaneous defrosting by multiple modules. Thus, multiple
modules can perform defrost operation at the same time.
For 60HP (Powerful heating type), however, there is an upper limit on the number of modules to be
defrosted at the same time, and it is difficult for the hot water outlet temperature during defrosting to
decrease.
(2) Starting defrosting
The unit controller determines the frost formation on the air heat exchanger, based on the difference between
outdoor air and evaporation temperatures. When the amount of frost on a given circuit has reached a predefined
threshold, it starts defrosting. Once defrosting of a circuit is completed, subsequent defrost operation will not be
performed on that circuit for the programmed minimum defrosting interval (default: 20 minutes).
However, for 60HP (Powerful heating type), its frosted state including the relative humidity is assessed.
(3) Completion of defrosting
The unit controller quits defrosting when the condensing temperature has risen above the programmed
temperature. The defrosting operation will also end if the maximum defrosting operation time (10 minutes) is
exceeded after the start of the defrosting operation.
(4) Defrosting sequence
In a defrosting operation, each control device operates as follows:
1: If none of the circuits of a module is performing defrosting, the unit controller begins
preparation for defrosting for a relevant circuit, which consists of stopping the compressor
and the fan, and switching the four-way valve from a heating cycle to a cooling cycle.
2: Approximately 30 seconds after step 1, the compressor is started.
Although fans are basically stopped during defrosting, they may be operated to prevent
high-pressure cut-out.
3: The compressor is stopped when the predefined defrosting conditions are met.
The four-way valve is switched from a cooling cycle back to a heating cycle.
4: Approximately 50 seconds after step 3, the compressor runs and the heating operation is
resumed.
operation
Compressor
4way valve Excitation
Fan
Heating Defrosting
preparation
30 seconds
Run
Run
①
Defrosting
operation
Run (maximum 10 minutes)
②
- 50 -
Recovery
preparation
50 seconds
Excitation
③
Heating
operation
Run
Run
④