Carrier 50TFQ008-012 specifications DX Cooling Temperature Control Example

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

•If compressor no. 1 is on then second stage of mechani- cal cooling will be energized. Otherwise the first stage will be energized.

•Integrator resets.

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

Routine 3 — (OAT > 68)

•Economizer is opened 100%.

•Compressors 1 and 2 are cycled based on Y1 and Y2 using minimum on and off times and watching the sup- ply 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 ener- gized 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.

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 (proportional integral) Error reduction calculation as indicated by Fig. 41.

The PremierLink controller will use the following informa- tion to determine if free cooling is available:

•Indoor fan has been on for at least 30 seconds.

•The SPT, SAT, and OAT inputs must have valid readings.

•OAT must be less than 75 F.

•OAT must be less than SPT.

•Enthalpy must be LOW (may be jumpered if and enthalpy sensor is not available).

•Economizer position is NOT forced.

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 tempera- ture between the heating and cooling set points as indicated in Fig. 42.

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 com- pare space temperature and space set point.

When outside-air temperature conditions require the econo- mizer to close for a compressor stage-up sequence, the econo- mizer control integrator is reset to zero after the stage-up se- quence 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. 42.

The controller uses the following conditions to determine economizer cooling:

•Enthalpy is Low

•SAT reading is available

•OAT reading is available

•SPT reading is available

•OAT ≤SPT

•Economizer Position is NOT forced

If any of the above conditions are not met, the economizer submaster reference (ECSR) is set to maximum limit and the damper moves to minimum position. The operating sequence is complete. The ECSR is recalculated every 30 seconds.

If an 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.

		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.

Fig. 41 — DX Cooling Temperature

Control Example

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

Fig. 42 — Economizer Temperature

Control Example

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