Carrier 48HC 04-28 Controls, Start-up, Operation And Troubleshooting

Also see for /50HC 04-28: Manual

Contents

Carrier 48HC 04-28 Controls, Start-up, Operation And Troubleshooting Manual pdf 33 page image

33REHEAT CONTROLThe cooling staging and compressor control routines are re-sponsible for controlling each circuit in one of the three sub-modes (Cool, Reheat1, or Reheat2). When there is only a cool-ing demand, one or more circuits will operate in normal cool-ing mode. When there is only dehumidification demand, allcircuits will operate in Reheat2 mode. When there is both cool-ing demand and dehumidification demand, all circuits will op-erate in either Reheat1 or Reheat2 mode, with the portion ofReheat1 circuits determined from the cooling demand. The Re-quested Reheat2 Stages (Operating ModesCOOLHMZRREQ.R) shows the control’s request for reheat cir-cuits if cooling is not already requesting all stages. AvailableReheat2 Stages (Operating ModesCOOLHMZRAVL.R) displays circuits that are available for reheat use. Actu-al Reheat2 Stages (Operating ModesCOOLHMZRACT.R) displays the current number of circuits running in Re-heat2 mode. These three status points should only be moni-tored when there is only a dehumidification demand, becausetheir values can be forfeited to cooling stages when cooling de-mand is present. Reheat2 Stage Incr. Time (Configura-tionHMZRR.INC) and Reheat2 Stage Decr. Time (Con-figurationHMZRR.DEC) set the time delay when addingor subtracting a compressor for a reheat function. These onlyapply when using adaptive thermostat or space sensor control.There are three relay outputs that show reheat status. Cool Re-heat1 Control (OutputsCOOLCRC) shows when the unithas switch from pure cooling to reheat ready (based on a dehu-midification demand). Reheat2 Valve A (Out-putsCOOLRH2.A) and Reheat2 Valve B (Out-putsCOOLRH2.B) display when the respective circuit’sReheat2 valve is energized.A circuit can be restricted from Reheat2 operation by the out-side temperature and saturated suction temperature. Reheat2OAT Limit A (ConfigurationHMZRRA.LO) and Reheat2OAT Limit B (ConfigurationHMZRRB.LO) set the low-est outside temperature the respected circuit is allowed to runin reheat2 mode. The lockout on/off status is shown as Reheat2OAT Lockout A (Operating ModesCOOLHMZRR.LO.A) and Reheat2 OAT Lockout B (OperatingModesCOOLHMZRR.LO.B) for their respective cir-cuit. If a circuit’s saturated suction pressure falls below the lowlimit configuration during Reheat2 operation, the circuit willswitch to reheat1 (the circuits Reheat2 valve will be turned off)for at least 2 minutes and until its suction rises back above thehigh limit. Reheat2 SSP Lo Limit A (Configura-tionHMZRRA.LP) and Reheat2 SSP Lo Limit B (Config-urationHMZRRB.LP) set the low pressure limit for Re-heat2 mode for individual circuits. Reheat2 SSP Hi Limit A(ConfigurationHMZRRA.HP) and Reheat2 SSP Hi LimitB (ConfigurationHMZRRB.HP) set the high pressurelimit for Reheat2 mode for each circuit.REHEAT MODE DIAGNOSTIC HELPThe status of reheat mode sensor inputs may be viewed withinthe display Inputs menu. The status of reheat mode outputsmay be viewed within the display Outputs or Run Sta-tusCOOL menus. Additional diagnostic help, including sta-tus of circuit reheat temperature limit lockouts may be viewedwithin the Humidi-MiZer sub-menu of the cooling mode diag-nostic table at Operating ModesCOOLHMZR.The Service Test mode may be used to force the system to op-erate in various stages of Reheat1 or Reheat2 mode, or to inde-pendently operate the reheat valve control outputs.The following forced operating states are changed or added tothe available service test operation for a Humidi-MiZerequipped unit:Service TestCOOLCMP.A (Cool A Test)A value of On will turn on circuit A in Normal Cooling mode.Service TestCOOLCMP.B (Cool B Test)A value of On will turn on circuits A and B in Normal Coolingmode.Service TestHMZRRH1.A (Reheat1 A Test)A value of On will turn on circuit A in Reheat1 mode.Service TestHMZRRH1.B (Reheat1 B Test)A value of On will turn on circuits A and B in Reheat1 mode.Service TestHMZRRH2.A (Reheat2 A Test)A value of On will turn on circuit A in Reheat2 mode.Service TestHMZRRH2.B (Reheat2 B Test)A value of On will turn on circuits A and B in Reheat2 mode.Service TestHMZRCRC (Cool-Reheat1 Valve Test)For 48/50HC04-12 units, a value of On will turn on the CRCrelay. This will turn on CLV.x valves and turn off RLV.xvalves.For 48/50HC14-28 units, a value of On will turn on the CRCrelay. This will energize the LDV.x valves.Service TestHMZRRHV.A (Reheat2 Valve A Test)A value of On will turn on the RDV.A valve.Service TestHMZRRHV.B (Reheat2 Valve B Test)A value of On will turn on the RDV.B valve.Temperature Compensated StartThis logic is used when the unit is in the unoccupied state. Thecontrol will calculate early Start Bias time based on SpaceTemperature deviation from the occupied cooling and heatingset points. This will allow the control to start the unit so thatthe space is at conditioned levels when the occupied periodstarts. This is required for ASHRAE 90.1 compliance. A spacesensor is required for non-linkage applications.SETTING UP THE SYSTEMThe settings for temperature compensated start can be found inthe local display under ConfigurationUNIT.Temp Comp Strt Cool Factr (TCS.C)This is the factor for the start time bias equation for cooling.Temp Comp Strt Heat Factr (TCS.H)This is the factor for the start time bias equation for heating.NOTE: Temperature compensated start is disabled when thesefactors are set to 0.TEMPERATURE COMPENSATED START LOGICThe following conditions must be met for the algorithm to run:• Unit is in unoccupied state.• Next occupied time is valid.• Current time of day is valid.• Valid space temperature reading is available (sensor orCCN network).The algorithm will calculate a Start Bias time in minutes usingthe following equations:If (space temperature > occupied cooling set point)Start Bias Time = (space temperature – occupied cooling setpoint)* TCS.CIf (space temperature < occupied heating set point)Start Bias Time = (occupied heating set point – space tempera-ture)*TCS.HWhen the Start Bias Time is greater than zero the algorithmwill subtract it from the next occupied time to calculate theITEM EXPANSION RANGE UNITS CCN POINTTCS.C Temp.Cmp.Strt.Cool Factr 0 - 60 min TCSTCOOLTCS.H Temp.Cmp.Strt.Heat Factr 0 - 60 min TCSTHEAT