Unit Control
minimum operating frequency. Then if it is still detected that the leaving water temperature is lower than
the freeze protection temperature, the main unit will stop as per the shutdown frequency but the water
pump keeps normal operation.
When it is detected that the leaving water temperature of the plate heat exchanger is equal to or larger
than the freeze protection withdrawing temperature, freeze protection will exit. At this point, once the
compressor has stopped for three minutes and conditions for startup have been satisfied, the
compressor will run for cooling.
2.2 Heating
2.2.1 Control to the Compressor
When the unit is controlled by the leaving water temperature, the operating frequency of the
compressor will be adjusted by the temperature difference in the way that it increases as the
temperature difference goes up and it decreases as the temperature difference goes down. When the
compressor reaches the minimum frequency but the temperature frequency is still quite large, the unit
will shut down (temperature difference= actual leaving water temperature-leaving water temperature set
point).
2.2.2 Over-temperature Protection
When the compressor is running and it is detected that the leaving water temperature of the auxiliary
electric heater is higher than the over-temperature protection temperature, the compressor will lower its
frequency to the minimal. Then if it is still detected that the leaving water temperature of the auxiliary
electric heater is higher than the over-temperature protection temperature, all loads except the water
pump of the main unit and the 4-way valve will stop. Over-temperature protection will exit until the
leaving water temperature of the auxiliary electric heater is lower than the over-temperature withdrawing
temperature. After that, the unit will resume normal operation.
2.2.3 Control to the Optional Electric Heater
When the Optional electric heater is deactivated through the wired controller, it will never come into
operation. When it is activated, it will run based on the outdoor temperature.
2.3 Water Heating
Water heating can be achieved by either the solar system or the main unit (heat pump).
2.3.1 Water Heating by the Main Unit
1) When the outdoor temperature is out of the operation range, the compressor will not start, and
water heating will be done by the water tank heater.
2) When the outdoor temperature is within the operation range, water heating will be done by the
main unit. The output frequency of the compressor will be adjusted by the difference between the water
tank temperature set point and the actual water tank temperature.
3) Control to the Water Tank Electric Heater
a. when the water tank temperature set point is lower than the maximum value of the water heating
range of the main unit, the auxiliary electric heater of the main unit will run depending on the temperature
difference, and the water tank keeps shut-down.
b. when the water tank temperature set point is higher than the maximum value of the water heating
range of the main unit but the actual water tank temperature is lower than the maximum value of the
water heating range of the main unit, the auxiliary electric heater of the main unit will run depending on
the temperature difference. If the actual water tank temperature is higher than the maximum value of the
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