Carrier 48HE003---006 48HE,HJ, Routine 3 OAT, DX Cooling Temperature, Control Example

48HE,HJ

SIf SAT > SASP + 5 and economizer position >80%, economizer will go to minimum position for 3 minutes or until SAT > 68_F.

SIf compressor one is on then second stage of mechanical cooling will be energized; otherwise the first stage will be energized.

SIntegrator resets.

SEconomizer opens again and controls to SASP after stage one on for 90 seconds.

Routine 3 (OAT > 68)

SEconomizer is opened 100%.

SCompressors 1 and 2 are cycled based on Y1 and Y2 using minimum on and off times and watching the supply air temperature as compared to SATLO1 and SATLO2 set points.

If optional power exhaust is installed, as the outdoor-air damper opens and closes, the power exhaust fans will be energized and deenergized.

If field-installed accessory CO2 sensors are connected to the PremierLink™ control, a PID-controlled demand ventilation strategy will begin to operate. As the CO2 level in the zone increases above the CO2 set point, the minimum position of the damper will be increased proportionally. As the CO2 level decreases because of the increase in fresh air, the outdoor-air damper will be proportionally closed.

HEATING - UNITS WITH ECONOMI$ER2, PREMIER- LINK CONTROL AND A THERMOSTAT

When the thermostat calls for heating, terminal W1 is energized. The PremierLink control will move the economizer damper to the minimum position if there is a call for G and closed if there is a call for W1 without G. In order to prevent thermostat from short cycling, the unit is locked into the heating mode for at least 10 minutes when W1 is energized. The induced-draft motor is then energized and the burner ignition sequence begins.

On units equipped for two stages of heat, when additional heat is needed, W2 is energized and the high-fire solenoid on the main gas valve (MGV) is energized. When the thermostat is satisfied and W1 is deenergized, the IFM stops after a 45-second time-off delay unless G is still maintained.

COOLING - UNITS WITH ECONOMI$ER2, PREMIER- LINK CONTROL AND A ROOM SENSOR

When free cooling is not available, the compressors will be controlled by the PremierLink controller using a PID Error reduction calculation as indicated by Fig 51.

The PremierLink controller will use the following information to determine if free cooling is available:

SIndoor fan has been on for at least 30 seconds.

SThe SPT, SAT, and OAT inputs must have valid readings.

SOAT must be less than 75_F. S OAT must be less than SPT.

SEnthalpy must be LOW (may be jumpered if an enthalpy sensor is not available).

SEconomizer position is NOT forced.

		TEMPERATURE CONTROL
TEMPERATURE	75
	74
	73
	72	SET POINT
	71	TEMPERATURE
	70
SPACE
	69
	68
		TIME

NOTE: PremierLink control performs smart staging of 2 stages of DX cooling and up to 3 stages of heat.

C06042

Fig. 51 ---DX Cooling Temperature

Control Example

		TEMPERATURE CONTROL
TEMPERATURE	75
	74
	73
	72	COOL SETPOINT
	71	TEMPERATURE
	70	HEAT SETPOINT
SPACE
	69
	68
		TIME
		C06043

Fig. 52 ---Economizer Temperature

Control Example

When free cooling is available, the outdoor-air damper is positioned through the use of a Proportional Integral (PID) control process to provide a calculated supply-air temperature into the zone. The supply air will maintain the space temperature between the heating and cooling set points as indicated in Fig. 52.

The PremierLink control will integrate the compressor stages with the economizer based on similar logic as the three routines listed in the previous section. The SASP will float up and down based on the error reduction calculations that compare space temperature and space set point.

When outside-air temperature conditions require the economizer to close for a compressor stage-up sequence, the economizer control integrator is reset to zero after the stage-up sequence is completed. This prevents the supply-air temperature from dropping too quickly and creating a freeze condition that would make the compressor turn off prematurely.

The high space set point is used for DX (direct expansion) cooling control, while the economizer space set point is a calculated value between the heating and cooling set points. The economizer set point will always be at least one degree below the cooling set point, allowing for a smooth transition from mechanical cooling with economizer assist, back to economizer cooling as the cooling set point is achieved. The compressors may be used for initial cooling then the PremierLink controller will modulate the economizer using an error reduction calculation to hold the space temperature between the heating and cooling set points. (See Fig. 52.)

The controller uses the following conditions to determine economizer cooling:

SEnthalpy is Low

SSAT reading is available S OAT reading is available

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