Carrier 50HCQA Installation Manual download pdf (Page 29)

Reheat Control

The cooling staging and compressor control routines are

responsible for controlling each circuit in one of the three

sub--modes (Cool, Reheat1, or Reheat2). When there is only a

cooling demand, one or more circuits will operate in normal

cooling mode. When there is only dehumidification demand, all

circuits will operate in Reheat2 mode. When there is both cooling

demand and dehumidification demand, all circuits will operate in

either Reheat1 or Reheat2 mode, with the portion of Reheat1

circuits determined from the cooling demand. The Requested

Reheat2 Stages (Operating ModesCOOLHMZRREQ.R)

shows the control’s request for reheat circuits if cooling is not

already requesting all stages. Available Reheat2 Stages (Operating

ModesCOOLHMZRAVL.R) displays circuits that are

available for reheat use. Actual Reheat2 Stages (Operating

ModesCOOLHMZRACT.R) displays the current number

of circuits running in Reheat2 mode. These three status points

should only be monitored when there is only a dehumidification

demand, because their values can be forfeited to cooling stages

when cooling demand is present. Reheat2 Stage Incr. Time

(ConfigurationHMZR R.INC) and Reheat2 Stage Decr. Time

(ConfigurationHMZRR.DEC) set the time delay when

adding or subtracting a compressor for a reheat function. These

only apply when using adaptive thermostat or space sensor control.

There are three relay outputs that show reheat status. Cool -- >

Reheat1 Control (OutputsCOOLCRC) show when the unit

has switch from pure cooling to reheat ready (based on a

dehumidification demand). Reheat2 Valve A

(OutputsCOOLRH2.A) and Reheat2 Valve B

(OutputsCOOLRH2.B) display when the respective circuit’s

Reheat2 valve is energized.

A circuit can be restricted from Reheat2 operation by the outside

temperature and saturated suction temperature. Reheat2 OAT

Limit A (ConfigurationHMZRRA.LO) and Reheat2 OAT

Limit B (ConfigurationHMZRRB.LO) set the lowest outside

temperature the respected circuit is allowed to run in reheat2 mode.

The lockout on/off status is shown as Reheat2 OAT Lockout A

(Operating ModesCOOLHMZRR.LO.A) and Reheat2

OAT Lockout B (Operating ModesCOOLHMZR R.LO.B)

for their respective circuit. If a circuit’s saturated suction pressure

falls below the low limit configuration during Reheat2 operation,

the circuit will switch to reheat1 (the circuits Reheat2 valve will be

turned off) for at least 2 minutes and until its suction rises back

above the high limit. Reheat2 SSP Lo Limit A

(ConfigurationHMZRRA.LP) and Reheat2 SSP Lo Limit B

(ConfigurationHMZRRB.LP) set the low pressure limit for

Reheat2 mode for individual circuits. Reheat2 SSP Hi Limit A

(ConfigurationHMZRRA.HP) and Reheat2 SSP Hi Limit B

(ConfigurationHMZRRB.HP) set the high pressure limit for

Reheat2 mode for each circuit.

Reheat Mode Diagnostic Help

The status of reheat mode sensor inputs may be viewed within the

display Inputs menu. The status of reheat mode outputs may be

viewed within the display Outputs or Run StatusCOOL menus.

Additional diagnostic help, including status of circuit reheat

temperature limit lockouts may be viewed within the

Humidi-MiZer sub-menu of the cooling mode diagnostic table at

Operating ModesCOOLHMZR.

The Service Test mode may be used to force the system to operate

in various stages of Reheat1 or Reheat2 mode, or to independently

operate the reheat valve control outputs.

The following forced operating states are changed or added to the

available service test operation for a Humidi-MiZer equipped 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 Cooling mode.

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 CRC

relay. This will turn on CLV.x valves and turn off RLV.x valves.

For 48/50HC14--28 units, a value of On will turn on the CRC

relay. 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.

EnergyX

For units equipped with the EnergyX factory installed option, there

will be an EnergyX Supplement Installation Instructions in the

unit’s information packet. Refer to this supplement for details on

how the ERV operates relative to the base unit.

Temperature Compensated Start

This logic is used when the unit is in the unoccupied state. The

control will calculate early Start Bias time based on Space

Temperature deviation from the occupied cooling and heating set

points. This will allow the control to start the unit so that the space

is at conditioned levels when the occupied period starts. This is

required for ASHRAE 90.1 compliance. A space sensor is required

for non-linkage applications.

Setting Up the System

The settings for temperature compensated start can be found in the

local display under ConfigurationUNIT.

ITEM EXPANSI O N RANGE UNI TS CCN POINT

TC S.C Temp.Cmp.Strt.Cool Factr 0-60 min TC STCOOL

TC S.H Temp.Cmp.Strt.Heat Factr 0-60 min TCSTHEAT

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 these

factors are set to 0.

Temperature Compensated Start Logic

The following conditions must be met for the algorithm to run:

S Unit is in unoccupied state.

S Next occupied time is valid.

S Current time of day is valid.

S Valid space temperature reading is available (sensor or CCN

network).

The algorithm will calculate a Start Bias time in minutes using the

following equations:

If (space temperature > occupied cooling set point)

Start Bias Time = (space temperature – occupied cooling set

point)* TCS.C

If (space temperature < occupied heating set point)

Start Bias Time = (occupied heating set point – space

temperature)*TCS.H

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Carrier 50HCQA Installation Manual Page 29

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