Mitsubishi Electric PQHY-P72ZLMU-A Service Handbook page 156

[ VII Control ]
-6- Compressor Frequency Control
Depending on the capacity required, the frequency of the compressor is controlled to keep constant evaporation temperature
(0°C [32°F] = 0.71 MPa [103 psi]) during cooling operation, and condensing temperature (49°C [120°F] = 2.88 MPa [418 psi])
during heating operation.
The table below summarizes the operating frequency ranges of the inverter compressor during normal operation.
The OS in the multiple-heat source-unit system operates at the actual compressor frequency value that is calculated by the
OS based on the preliminary compressor frequency value that the OC determines.
Model
P72 model
P96 model
P120 model
P144 model
P168 model
P192 model
The maximum frequency during heating operation is affected by the water temperature to a certain extent.
(1) Pressure limit
The upper limit of high pressure (63HS1) is preset, and when it exceeds the upper limit, the frequency is decreased every 15
seconds.
The actuation pressure is when the high-pressure reading on 63HS1 is 3.58MPa[519psi].
(2) Discharge temperature limit
Discharge temperature (TH4) of the compressor in operation is monitored, and when it exceeds the upper limit, the frequency
is decreased every minute.
Operating temperature is 115°C [239°F].
(3) Periodic frequency control
Frequency control other than the ones performed at start-up, upon status change, and for protection is called periodic frequen-
cy control (convergent control) and is performed in the following manner.
Periodic control cycle
Periodic control is performed after the following time has passed
30 seconds after compressor start-up
30 seconds after frequency control based on discharge temperature or pressure limit
The amount of frequency change
The amount of frequency change is controlled to approximate the target value based on the evaporation temperature (Te) and
condensing temperature (Tc).
HWE15150
Frequency/cooling (Hz)
Max Min
40 10
56 10
73 10
86 16
99 16
111 16
- 147 -
Frequency/heating (Hz)
Max Min
42 10
52 10
64 10
72 16
87 16
101 16
GB