Daikin RDT-135c Installation And Maintenance Manual

Contents

Daikin RDT-135c Installation And Maintenance Manual Manual pdf 90 page image

88 IM 738-2Unit Options: Enthalpy ControlUnit OptionsEnthalpy ControlOutside Air Enthalpy Control (OAE)Units with MicroTech II control and an economizer comestandard with an electromechanical enthalpy control device(OAE) that senses both the humidity and temperature of theoutside air entering the unit. This device has an enthalpy scalemarked A through D. Table 23 shows the control points at 50%RH for settings A through D. Figure 88 shows this scale on apsychrometric chart. When the outside air conditions exceedthe setting of the device, the outside air dampers are positionedto the minimum outside air intake position by the MicroTech IIcontroller.Differential Enthalpy Control (OAE/RAE)An optional electric differential enthalpy control arrangement(OAE/RAE) is available on units with MicroTech II control. Inthis configuration a solid-state humidity and temperaturesensing device is located in both the return (RAE) and outsideintake (OAE) airstreams. This OAE device has the same Athrough D scale as the device described above. However, withthe OAE/RAE arrangement the switch on OAE must be set allthe way past the “D” setting. With this done, the MicroTech IIcontroller adjusts the return and outside air dampers to use theairstream with the lowest enthalpy.Ground Fault ProtectionThe ground fault protection is designed to protect motors fromdestructive arcing ground faults. The system consists of aground fault relay and a ground fault current sensor. Theground fault relay employs solid state circuits that willinstantaneously trip and open a set of relay contacts in the 115volt control circuit to shut the unit down whenever a groundfault condition exists. The ground fault relay is self powered.The ground fault sensor is a current transformer type of devicelocated on the load side of the power block through which thepower wires of all phases are run.Figure 88. Enthalpy control settingsPhase Voltage Monitor (see page 120)The phase voltage monitor protects against high voltage, phaseimbalance, and phase loss (single phasing) when any one ofthree line voltages drops to 74% or less of setting. This devicealso protects against phase reversal when improper phasesequence is applied to equipment, and low voltage (brownout)when all three line voltages drop to 90% or less of setting. Anindicator run light is ON when all phase voltages are withinspecified limits. The phase voltage monitor is located on theload side of the power block with a set of contacts wired to the115 volt control circuit to shut the unit down whenever thephase voltages are outside the specified limits.Table 23: Enthalpy control settingsControl curve Control point temperature at 50% RHA 73°F (23°C)B 70°F (21°C)C 67°F (19*C)D 63°F (17°C) ( . )40(4.)4()0(0)60(.)6(8.)0()(4)80(6.)8(9.)90()9()00(8)0(40.)()121416182022242630246384042444628ENTHALPYBTUPERPOUNDDRYAIRBADDBA0.500.400.300.200.100.600.700.800.90RELATIVEHUMIDITY(.)40(4.)4()0(0)()60(.)6(8.)0()(4)80(6.)8(9.)90()9()00(8)0(40.)