SiEBE18-526 BP Unit ControlFunction 79Note: 1. In Sky Air models, the indoor units are equipped with distribution capillary tubes ; therefore,the heat exchangers may superheat even when the condition is met.2. In Sky Air models, the heat exchanger intermediate position is provided on the liquidconnection pipe side; as a result, superheated condition is difficult to detect.6.4 SC Control in Heating OperationPurpose of theFunctionThis function ensures appropriate refrigerant distribution when many room units are operating inthe heating mode.Outline The heat exchanger temperatures and liquid pipe temperatures of operating room units aredetected by the liquid pipe thermistors, and the electronic expansion valves' flow rates arecorrected so as to adjust the difference between heat exchanger temperature and liquid pipetemperature of each room unit (hereafter referred to as SC) close to the target values.When SC is higher than target value → Opens the valve of that room unitWhen SC is lower than target value → Closes the valve of that room unitThe liquid pipe temperature and indoor heat exchanger temperature are detected at the time ofevery sampling time of 20 sec for the heating SC control.6.5 Heat Exchanger Isothermal Control in Heating OperationPurpose of theFunctionThis function ensures appropriate refrigerant distribution when room units are operating in theheating mode.It prevents abnormal increase of the high pressure and operation with gas shortage due touneven refrigerant distribution (Protection function).Outline The indoor unit heat exchanger thermistors (of all connected indoor units to the same BP unitincluding non-operating room units) in heating operation are detected. Then, the highest heatexchanger temperature is compared with the heat exchanger temperature of each room unit. Ifthe temperature difference exceeds the predetermined value, it is judged that that indoor unitheat exchanger thermistor position in subcooled zone, and the electronic expansion valves ofroom units with the temperature difference exceeding the predetermined level is opened toreturn to the saturation zone.Since this is a protection function, it is effective for all connected room units in heating operationexcluding those in defrosting operation. This function is inactive in room units with transmissionproblems.Details The heat exchanger temperature is detected at every sampling time of 20 sec of the heatexchanger isothermal control, and maximum value of each heat exchanger temperature isobtained.If the temperature difference between the heat exchanger temperature and maximum heatexchanger temperature value exceeds 8°C, it is judged that the heat exchanger intermediate isin the subcooled zone, and the electronic expansion valve is opened.
