Liebert Challenger 3000

System Performance with Advanced Microprocessor Controls4.1.4 Heating OperationElectric ReheatThe two heat stages are activated when the temperature control calculates a requirement of 50% and100%, respectively. Each stage is deactivated when the heat requirement is 25% less than the activationpoint.Hot Water ReheatThe solenoid valve opens when the requirement for heating is 100% and closes when the requirementdrops below 50%.SCR Electric Reheat (Requires Special Control Software)The SCR (Silicon Controlled Rectifier) controller shall proportionally control the stainless steelreheats to maintain the selected room temperature. The rapid cycling made possible by the SCR controllerprovides precise temperature control, and the more constant element temperature improvesheater life. During operation of the SCR control, the compressor operates continuously. The heatersare modulated to provide temperature control.On units equipped with SCR Reheats, unit operation can be controlled even further with DIP switch#7 on the control board. With DIP switch #7 in the “OFF” position, or “Tight Control,” the compressoris locked on and the SCR Reheats are modulated for very tight temperature control. In the event of amalfunction of the SCR Reheats, the compressor will be turned off if the temperature drops to theLow Temperature Alarm Setpoint. With DIP switch #7 in the “ON” position or “Standard Control,”the compressor will cycle on and off as required to satisfy the requirements for cooling and dehumidificationin a similar manner as a standard unit without SCR Reheats, i.e., Temperature SetpointPLUS Temperature Sensitivity PLUS 1°F. The SCR Reheats are modulated from 0% to 100% asrequired to satisfy the requirements for heating over a control band from the Temperature SetpointMINUS the Temperature Sensitivity MINUS 1°F.4.2 Humidity Control4.2.1 Dehumidification/Humidification Required, in PercentThe humidity control program for the Advanced Microprocessor is based on a calculated % requirementfor dehumidification/ humidification.4.2.2 Response to Control TypesProportional ControlThe % requirement is determined only by the difference between the return air humidity and thehumidity setpoint. As the return air humidity rises above the humidity setpoint, the % dehumidificationrequired increases proportionally from 0 to 100% over a humidity band equal to the humiditysensitivity setting. The converse is true for % humidification requirement.PID Control (Chilled Water or SCR Reheats only)If PID control is selected, humidity is controlled in the proportional mode with the sensitivity bandbeing determined by the humidity sensitivity setpoint.Intelligent Control (Chilled Water only)If intelligent control is selected, the return air humidity is controlled at or near the humidity setpoint.The % dehumidification/humidification required is calculated based on a set of logical “rules” thatsimulate the actions of an expert human operator (see 4.3.3 - Intelligent Control (Chilled Wateronly)).4.2.3 Dehumidification Operation1-Stage Dehumidification, Compressorized Direct Expansion (DX) SystemsDehumidification with the standard configuration is accomplished by operating the compressor withouthot gas bypass active. If system has part coil, dehumidification is accomplished by using only partcoil. If the installation has a very light sensible load, dehumidification will be inhibited at the point atwhich 125% heating would be required to prevent overcooling. Dehumidification would be enabledwhen the temperature increases to the point where only 50% heating is required.31