Carrier 50HCQA Installation Manual download pdf (Page 18)

Constant Volume (CV) Units (FTYP = 1--Speed)

Single speed fan units are controlled by the Indoor Fan Relay 1

(Outputs FANS IDF.1) on the main base board (MBB),

which then operates the indoor fan contactor (IFC). The fan will be

either on or off depending on the unit control type and the

conditions above.

Thermostat Control

In thermostat mode, the IDF relay will be on in the following

situations: fan request G in ON, cooling request Y1 or Y2 is ON,

or heating request W1 or W2 is ON. If the G call is dropped or was

never on with an Y1, Y2, W1, or W2 call; the IDF relay will turn

off after a configurable time delay with respect to the HVAC mode

that is ending.

Space Sensor Control

In Space Sensor mode, the IDF relay will be on if the unit is in

Occupied mode and the indoor fan is configured to always run while

occupied (Configuration I.FAN OC.FN = YES). If the indoor

fan is configured for intermittent fan (OC.FN = No), the fan will only

be on when there are cooling, heating, or dehumidification stages

running; or if there is an air quality demand. During the unoccupied

period, the fan will operate intermittent. With intermittent fan, the IDF

relay will turn off after a configurable time delay with respect to the

HVAC mode that is ending.

Cooling Operation

The 48/50HC unit’s cooling operation consists of: demand, mode

determination, staging request to satisfy the demand, and handling

a request with the unit’s resources. These resources can include

compressors, an economizer, and a reheat coil. This section covers

mechanical cooling. For economizer and reheat cooling, refer to

the Economizer and Humidi--MiZert sections, respectively. The

unit enters a cooling mode based on a demand, decides how to

satisfy the demand, executes its plan, and then leaves the cooling

mode.

Cooling Mode Control

The cooling HVAC mode (Run StatusMODEHVAC=3)has

six different expandable texts: Cooling, Free Cooling, Unoccupied

Free Cooling, Reheat1, Reheat2, or Reheat1/Reheat2. These are all

part of a general cooling mode and resemble the specific type of

cooling that is being performed at any given time. All types of

cooling are still performed under the general cooling function, and

the expanded text is for user reference only. The control will

display if it is ok to select the cooling mode (Operating Modes

COOLOK.CL= Yes).

Thermostat Control

For the unit to enter cooling mode, three things must be true: the

indoor fan must be ok to use, the mode changeover time guard

must be expired, and there must be a cooling demand (Y1, Y2, or

dehumidification demand). The unit will remain in cooling until

the cooling demand is dropped or if any of the above conditions

turn false. If only a dehumidification demand exists and a heat

demand (W1, W2) occurs, the unit will end cooling. The cooling

mode can not officially end until all compressors are off.

Space Sensor Control

For the unit to enter cooling mode, four things must be true: the

indoor fan must be ok to use, the mode changeover time guard

must be expired, the unit must have a valid space temperature, and

there must be a cooling or dehumidification demand. The unit will

remain in cooling for at least one minute and until the cooling

demand drops below --0.5_F or if any of the above conditions turn

false. If only a dehumidification demand exists and the heat

demand becomes greater than the Reheat Heat Setpoint Deadband

(SetpointsRH.HB), the unit will end cooling. The cooling mode

can not officially end until all compressors are off.

Staging Control

Once the unit is in a cooling mode, it must decide what the demand

is and how to satisfy it. If an economizer is installed and can be

used for cooling (Operating ModesCOOLOK.EC= Yes), the

unit will use it first (see economizer section for its operation). If

the economizer can not be used or additional cooling is needed, a

mechanical cooling check is performed. OK to use Compressors?

(Operating ModesCOOLOK.MC), will be set to yes when

compressors are enabled and not locked out. Based on the unit

control configuration, requested cooling stages (Run Status

COOLREQ.C) will be determined then passed to compressor

control to actually add the cooling stages.

Thermostat Control

There are two ways of requesting stages when thermostat control is

enabled, Traditional Thermostat control or Adaptive control.

Traditional Thermostat control is used if the Thermostat Control

Type (T.CTL) is set to 1, 2, or 3 and the economizer is not

available for free cooling. If Thermostat Control (T.CTL) is set to

0 or any time the economizer is available for free cooling, the unit

will use Adaptive control for staging.

T.CTL = 0 (Adaptive Control)

Stage timers, Supply air trend, and supply air temperature limits

apply when determining the request for stages. The first request

(REQ.C=1) comes immediately when the Y1 input is active. The

CoolStageIncreaseTime(ConfigurationCOOLC.INC)or

the Cool Stage Decrease Time (ConfigurationCOOLC.DEC)

has to expire before another stage can be added or a stage can be

subtracted. The Supply--Air Trend (Operating

ModesCOOLSA.TR) decides if the next stage can be

requested or should be subtracted based on the Y2 input status.

If the Y1 and Y2 inputs are dropped, the supply air trend is not

considered because cooling is no longer needed. If at any time

the Supply--Air Temperature (SAT) falls below the Minimum

Supply Air Temperature Upper Level (Configuration

COOLSATSAT.U), the requested stages will not be

allowed to increase. If at any time the SAT falls below the

Minimum Supply Air Temperature Lower Level (Configuration

COOLSATSAT.L), the requested stages will be reduced by

one without honoring C.DEC. If SAT.L and SAT.U are configured

so that they are close together, the last stage of compressor might

cycle rapidly, slowed only by its minimum on and off--time

requirements.

T.CTL=1(1StageY1)andT.CTL=2(2StageY1)

Stage timers, Supply air trend, and supply air temperature limits do

not apply when determining the request for stages. Request staging

will follow the thermostat inputs directly. Y1 will request one

stage. Y2 will request all stages.

T.CTL = 3 (Digital)

Stage timers, Supply air trend, and supply air temperature limits do

not apply when determining the request for stages. Request staging

will follow the thermostat inputs directly. Y1 will request one stage.

Y2 will request two stages. Y1 and Y2 will request all stages.

Space Sensor Control

Space sensor staging control is an adaptive anticipation control that

weighs the actual space demand against the trend of that demand

and the trend of the supply air. It also honors stage time guards

and supply air limits. The demand for cooling in the space is

displayed as the Cooling Demand (Run StatusCOOL

DMD.C). The control tries to anticipate the change in the space

because of its current stage status. This anticipation is based on the

Supply--Air Trend (Operating ModesCOOLSA.TR)andthe

Cool Demand Trend (Operating ModesCOOLTRD.C).

These trends will show the control how the space is reacting to the

current running conditions and help it decide when to add or

remove one stage from the requested stages. The Cool Stage

Increase Time (ConfigurationCOOLC.INC) or the Cool

Stage Decrease Time (ConfigurationCOOLC.DEC)hasto

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Carrier 50HCQA Installation Manual Page 18

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